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Yukon
11-29-2007, 07:34 PM
Here is some info on a recent Gen 2 gearbox failure (


See answers below


Steve


--- In subaruaircraft@yahoogroups.com, "Larry" <simpsonl@...> wrote:
>
> Steve,
>
> Could you provide a few more details about your failure? I do not
> recall seeing it mentioned on the group before. Appearance of your
> oil at change?

-------- The oil at the time of failur had 36 hours (mobile 1 75W-90
synthetic)The oil color was light and no observable particles in the
tube.



Any other warning signs before the failure? Noise?

-------- My Gen II Gearbox temps always ran hotter than the engine
and the oil temps. (Normal temps for me were 205 - 210F with climbing
temps for any power above 2100 rpm) In retrospect I have learned
that this was probably a warning sign. After the failure, I used a
loaner gearbox to get the plane home and it ran significanlty cooler
(15-20F)than my original gearbox so I speculate that there was
something amiss with my original gearbox. The day of the failure, it
was very hot in Atlanta and my GB temps were running about 215, this
was probably another warning sign that I did not notice.


> Spiking temps? How catastrophic was the failure? Did it occur in
> flight?

-------- Failure was in flight, After cruising for about 1 1/2 hours
on the day of failure. There was a sudden appearance of loud
squealing noise and the gearbox failed about 3 minutes later. (gears
stripped and engine raced, I shut the engine down in flight) Pure
speculation on my part is that one of the bearings failed and after
the bearing siezed, it lead to a failure of the gears. Again, in
retrospect, I think the high temps were telling me about a problem
that I did not recognize. The dramatic difference in the loaner
Gearbox (much cooler temps) tells me that this was an issue
associated with my gearbox that may or may not be present in other
units. The new Gen III gearbox is much much cooler running in my
plane.



>
> I am also running a Gen 2 (blue front) PSRU and it typically runs
in
> the 200-210F range at full throttle and any prop setting above 2000
> RPM. My engine temps are usually about 30 degrees lower. I have a
2
> inch blast tube and a 1.25 inch blast tube to the bottom and left
> sides of the unit respectively. Aircraft Spruce delivered another
2
> inch tube and some scat today which will be installed next week for
> the right side.
>
> At 25 hours TT and 10 hours since the previous change, the Mobil 1
> 75W-90 oil looked slightly gray but there were no visible metal
> flakes on the fine screen that I strained the oil through. I am
> letting the oil "settle" for 48 hours and then will see if there is
> any sediment and if so, if it is magnetic. Then I will send to for
> analysis.
>
> I am upgrading to the Gen 3 in January, but am concerned that I may
> need to curtail my flying until then.
>
> Thanks for your information.
>
> Larry
>
> --- In subaruaircraft@yahoogroups.com, "n62km" <n62km@> wrote:
> >
> > David, I did have a complete gearbox failure on my H6 normally
> > aspirated Gen II gearbox after about 100 hours. It appears my
> > particular unit was behaving differently than most units (running
> hot)
> > so it might not have be a representative sample of most units in
> the
> > field.
> >
> > I have sinced moved to Gen III and have about ten hours on it.
The
> new
> > unit is running much cooler.
> >
> > Steve RV8 H6
>

Yukon
11-30-2007, 07:47 AM
http://rv-9.com/egg.html

Kahuna
11-30-2007, 08:25 AM
I was sorry to hear abour Steves gear box failure. I did the first flight on that plane. Report here http://www.vansairforce.com/community/showthread.php?t=12643.

Having watched "Subob" (flying friend who used to have a non-egg subaru in his 4) drop 8 Subie engines in his RV-4, there is no chance Id do it. He never failed a gear box, always the lower end of engine. All dead sticks. He had a Ross concentric planetary gear box 2.17:1, Marcotte drive terrain dampener... and through metalergical analysis, concluded that harmonics from the gear box was killing the lower end. He now has a lyco bart 180 in his RV-4. Do not equate Eggs to Subobs, its just one mans experience.

I also went to friend Egg6 RV-10 Dans funeral. Hated that.

gmcjetpilot
11-30-2007, 04:47 PM
What is a Gen II gear box? Is it the latest and greatest from Egg? NEVER MIND I read Yukon's link (http://rv-9.com/egg.html) above, explains it all. The Gen III gearbox was on the tragic RV-10; Kahuna, that must have been very sad indeed, my sincere sympathies.)

Whats a "Subob", a particular brand of engine conversion or just roll your own Subaru?

Ross where are you? What ya think.

Sounds like a TEMP gauge with a real red line temp and and particle sensor for the gearbox would be good idea.

rv6ejguy
11-30-2007, 07:12 PM
Ross where are you? What ya think.



I'm dodging the troll and staying out of these discussions as I said before. I had hoped people would wait for the full NTSB report on Dan's crash before saying anything. The initial report drew no conclusions and there seems to be unusual circumstances involved hence further investigation is merited. We don't know the cause of the power loss in a 7A accident 3 days later either. I don't see the point is speculating about either accident.

Kahuna
12-01-2007, 12:14 AM
Whats a "Subob", a particular brand of engine conversion or just roll your own Subaru?


His name was Bob. After blowing up a few Subaru engines, we now call him "Subob."

gmcjetpilot
12-01-2007, 03:33 AM
His name was Bob. After blowing up a few Subaru engines, we now call him "Subob."ha ha ha ha ha ha :D

rv6ejguy
12-01-2007, 11:04 AM
Of course you are Ross. You are an Egg vendor.

As is often the case, I'm not sure what your point is here? I can only assume you are trying to warn older Egg customers that their gearboxes might fail. This is being discussed out in the open on Jan's site as you have said.

I do think it is counterproductive is to assume that Dan's accident was caused by the Subaru engine any more than the 7A accident 3 days later was caused by the Lycoming engine in it. I know nothing more than anyone else here on either accident. Let's just wait for the facts and maybe we can learn and apply that knowledge to prevent similar circumstances from bringing one of us down.

As many of you know, Dan was an enthusiastic advocate of the Subaru engine and knew full well what he was getting into to I think. He offered his airframe up to Jan for the test program to validate the engine, propeller, gearbox, turbo, cooling and EM systems for several months and they flew the -10 to Oshkosh together earlier. Dan was a friend as well as a customer to Jan.

As David pointed out, there have been several Gen 1 and 2 gearbox failures over the years. They have shown generally good reliability on the atmo EJ25s to date. The Gen 3 is designed to replace those earlier boxes on the higher hp engines and Jan is recommending people upgrade to the stronger box. Seems reasonable with the better pieces now available and he is giving a price break. I view this similarly to the Van's nose gear thing and many other parts upgrades Van's has introduced over the years.

$50K Gearboxes fail on helicopters sometimes and I know that almost every brand of PSRU on the market has had issues or failures. We learn, we improve.

I gave up a month ago posting anything more on the auto vs. Lycoming debates as they are truly never ending and few people seem to care about what I say as someone who has some experience in the field. I can accept that. Let's just fly what interests us.

John, as I look back on your posts on various forums, clearly many of your posts seem directed in anger at Jan's business. You can have any opinion you want about anything you want of course. If this is your crusade so be it I guess.

Jan has made mistakes just as many of us have including Van's, Lycoming, Hartzell, MT, P-mag, IVO etc. The list is endless. Welcome to the human race. I think Jan is trying to make his products better and address known problem areas- nobody will be in business long otherwise. I don't think customers of earlier drives are happy about the new recommendations any more than any of us are when we have to spend money to upgrade something on our aircraft. You don't have to with experimentals of course.

I defend people like Jan because I come from the same field, not because I'm a supplier. To those who design, create, learn and fly their dreams, kudos. To those who hack at them, you'll garner little respect from me. It is so easy to criticize, much harder to do something that few others are doing. If you have a better way of doing something on your RV, share the knowledge here on VAF so that we all may benefit. I know I've learned a lot here.

Jan gives people a second powerplant choice for RVs, warts and all. While you may never buy one, hundreds of others have and like them. Dozens who have bought, don't like them just like many other products available to us. We are all adults here and have to cope with our decisions.

As long as we fly experimental, single engined aircraft there is some risk due to the relatively unproven systems many of us use and there are clearly still risks even using more proven assemblies as we have seen many times as well. The only way to ensure we won't be killed or injured flying is to never fly. I doubt if many of us including Dan would find that an acceptable solution.

allbee
12-01-2007, 11:08 AM
My hats off to you guys.

You give the true meaning to Experiment... al aircraft.

As well as a true test pilot.

same goes for those that want the full glass panel.

David-aviator
12-01-2007, 11:56 AM
ha ha ha ha ha ha :D

George,

I am sure you love your dog but could you find a more flattering picture of it. He/she looks like he/she is spring loaded to bite. Is that item in its mouth a piece of someone's leg or what? :) I suppose it could be a ball.

rodrv6
12-01-2007, 12:11 PM
Ross, thank you for saying what I was having trouble figuring out how to say. (Does that make sense??)
When I made the decision to use an Eggenfellner engine on my RV6, it was after doing a lot of research and talking to people who had been using his engines. Yes, I do know that he is always improving the engine system as things are learned, and that upgrades will always be an ongoing thing. I would be worried if he suddenly stopped trying to improve the product. There are people who are uncomfortable with auto based conversions and would much rather stick to Lycomings. THERE IS NOTHING WRONG WITH THAT! A Lycoming is a fantastic engine and I wouldn't hesitate to use one on a plane. There is also nothing wrong with someone who would like to be a bit "outside the box" and try something different. I happen to be very comfortable with that.
I also take a certain offense to those who would try to criticize Jan's business practices. It's true that he is not a perfect person and has made mistakes and has had some missteps, but after dealing with him for several years I would not hesitate to buy another engine from him in the future. Personally, I think his biggest "flaw" is being a little over-enthusiastic about publicizing new ideas a little early, but at least he's not trying to hide what he's up to!
OK, I'll step down off of the soapbox now :)

szicree
12-01-2007, 12:28 PM
I gave up a month ago posting anything more on the auto vs. Lycoming debates as they are truly never ending and few people seem to care about what I say as someone who has some experience in the field.

Some of us are very interested in what you have to say. First hand experience is what it's all about. This forum is an amazing resource, but the first thing I had to learn was to sift out speculation from actual experience.

It's quite obvious that some of the posts on this topic have a hidden (not so much) agenda. There is no doubt whatsoever in my mind that a Subaru can be adapted to be just as safe as a traditional engine, but I'm not sure we're quite there yet. I hope the guys at the leading edge of this hobby keep pushing.

szicree
12-01-2007, 12:30 PM
George,

I am sure you love your dog but could you find a more flattering picture of it. He/she looks like he/she is spring loaded to bite. Is that item in its mouth a piece of someone's leg or what? :) I suppose it could be a ball.

That's a dog?! I thought it was a lab rat being electrocuted. :D

TSwezey
12-01-2007, 01:22 PM
I think the Sube guys are lucky to have Jan. Jason Day who built my engine, PSRU and prop, didn't do any testing that I can tell. Luckily, there is another customer of his who is the Australian version of Ross doing the engine testing. David, "Australian Ross", almost destroyed his engine using the controller Jason sent out. I didn't run my engine that hard so it was saved. David was able to tell Tracy Crooks, the maker of the controller, how to reprogram it to run the LS2 correctly. Jason also did not do enough, if any, real testing of the PSRU's and props. His customers are the ones testing and finding the problems. The good thing though is Jason is coming up with some of the fixes and correcting them. I had to pay for the controller to be reprogrammed. It was only $82. I am just amazed that people can put stuff to market without thorough testing! I have to send my prop and PSRU back to Jason for some corrections. I am going to Jason's shop with the prop and PSRU to make sure it gets done in a timely and correct fashion. No more trusting of salespeople/manufacturers claims or statements!

Mike S
12-01-2007, 02:03 PM
George,I am sure you love your dog but could you find a more flattering picture of it.


David, you should be careful of what you ask for---------this dog is a real beauty queen compared to his last dog.

rv6ejguy
12-01-2007, 02:14 PM
Ross, thank you for saying what I was having trouble figuring out how to say. (Does that make sense??)
When I made the decision to use an Eggenfellner engine on my RV6, it was after doing a lot of research and talking to people who had been using his engines. Yes, I do know that he is always improving the engine system as things are learned, and that upgrades will always be an ongoing thing. I would be worried if he suddenly stopped trying to improve the product. There are people who are uncomfortable with auto based conversions and would much rather stick to Lycomings. THERE IS NOTHING WRONG WITH THAT! A Lycoming is a fantastic engine and I wouldn't hesitate to use one on a plane. There is also nothing wrong with someone who would like to be a bit "outside the box" and try something different. I happen to be very comfortable with that.
I also take a certain offense to those who would try to criticize Jan's business practices. It's true that he is not a perfect person and has made mistakes and has had some missteps, but after dealing with him for several years I would not hesitate to buy another engine from him in the future. Personally, I think his biggest "flaw" is being a little over-enthusiastic about publicizing new ideas a little early, but at least he's not trying to hide what he's up to!
OK, I'll step down off of the soapbox now :)

I agree with all your points here. That's pretty much how I see this topic as well. I do like to see posts from actual customers here, (yes good or bad).

rv6ejguy
12-01-2007, 02:24 PM
I think the Sube guys are lucky to have Jan. Jason Day who built my engine, PSRU and prop, didn't do any testing that I can tell. Luckily, there is another customer of his who is the Australian version of Ross doing the engine testing. David, "Australian Ross", almost destroyed his engine using the controller Jason sent out. I didn't run my engine that hard so it was saved. David was able to tell Tracy Crooks, the maker of the controller, how to reprogram it to run the LS2 correctly. Jason also did not do enough, if any, real testing of the PSRU's and props. His customers are the ones testing and finding the problems. The good thing though is Jason is coming up with some of the fixes and correcting them. I had to pay for the controller to be reprogrammed. It was only $82. I am just amazed that people can put stuff to market without thorough testing! I have to send my prop and PSRU back to Jason for some corrections. I am going to Jason's shop with the prop and PSRU to make sure it gets done in a timely and correct fashion. No more trusting of salespeople/manufacturers claims or statements!

Todd, this is the reality of new engines, gearboxes, ECUs and props. I considered Jason's props for my RV but as they were essentially unproven, I bit the bullet and wrote the check for an MT instead. I'll find out if that was a good choice or not! Todd's advice should be remembered- if the products have not been flight tested, beware and even if they have, be aware that a few hundred hours may not mean much either. In many instances, you are taking a bigger chance for problems putting an auto conversion on your aircraft in my view.

Yukon
12-01-2007, 05:00 PM
Ross,

My concerns about the Egg engine are not personal in regards to Jan. I have written here many times about other products which I feel are not worthy of installation on our aircraft, with equal fervor.

You mention in one of your posts that you decided against Jason's prop in favor of a tested and proven MT, so I know that you understand the concept of conservative judgement. Listening to Todd Sweeny's recent posts, he too seems to be grasping the seriousness of pairing of an untested airplane, prop,engine and pilot (Think Dan Loyd).

You have been in this business long enough to know that the Feds will spend precious little time investigating the cause of the Loyd accident, due to it's experimental certification. I feel fairly certain that the unfortunate two day 40 hr flyoff on Dan Loyd's RV-10 won't be investigated either, because the Feds just don't have the manning. Our time would be better spent educating our fellow pilots about the dangers they are facing with this equipment, rather than waiting for the FAA.

The pilot of the RV-8 Gen2 failure stated that the GB squealed for three minutes, the teeth stripped off the reduction gear, the engine decoupled and raced. That means I am not speculating, I am stating first-person fact.

rv6ejguy
12-01-2007, 09:42 PM
By all means keep us informed of problems with products but it is more helpful and factual when information comes from first hand experience.

I'd encourage any Egg users to report here what your experiences have been, good or bad. I always appreciate David's well tempered posts on the subject. It seems like he is telling it like it is. The weight, speed, fuel burn and issues do mirror what many people have reported to me.

Most people I know of in the Eggenfellner circle know there have been drive failures. I'm certainly not denying them but Gen 1 and 2 failures have nothing to do with the engine management systems we sell today. If the Gen 3s start exploding in large numbers, we may sell less EMS units to Jan, true, won't be a big deal to us.

The facts don't support any conclusion that there were serious, widespread failures of Gen 1 or 2 boxes on the original atmo EJ25s of which several hundred were sold. It is no secret that these early boxes will probably not last a long time with an EZ30 or supercharged EJ behind them. Jan is publicly stating this! No conspiracy-again. You conveniently ignore David's post about high time units. This is the rule rather than the exception.

This is not being kept secret. Has been discussed on the forums for a 2-3 months or longer. Anyway the Gen 1 and 2 are no longer being sold.

So, this is like the top rudder hinge doubler Van's sent me to install on my RV10 after discovering cracks there on their prototype- I de-rivet the fin and install- not happy in one way but happy in another way that it is better now and may not cause me problems in the future after the plane is painted. We improve and move on.

steve murray
12-01-2007, 09:55 PM
I am the guy who had the gearbox failure. Did I like the Gearbox failure no. Did I know this was an experimental airplane and an experimental engine yes.

This is how me make advances in our hobby, you make some mistakes, you learn, you hopefully get better. If I wanted to fly a more stable, more reliable, less expensive airplane, I would still have my Piper.

I cannot speak highly enough of Jan's support with my gearbox failure. Within days, I had all the spare parts at my house to help me ferry my plane back home. I have called him numerous times on weekends with questions and I get answers. That type of support is very important to me, and speaks to the strong support Jan gives his customers.

I went flying in my Egg RV8 today in Atlanta (beautiful day) and God willining I will be flying more tomorrow morning. (Yes, I will probablly take the cowling off and tinker with something....it's "Experimental Aviation")

Kahuna, I saw your takoff this morning at KLZU, Awesome!! That climb angle looks like 60 degrees from the ground, guess that is why they call it a super-8

Fly safe

Steve

David-aviator
12-01-2007, 11:47 PM
[QUOTE=Yukon;176157]Ross,


In the past 18 months, according to the NTSB, at least 54 RV's have fallen - most of them powered by Lycoming or a clone. How come when you go fishing the hook is baited only for Subaru?

I am not minimizing the problems we have experienced but your messages on the subject are so biased they lack credibility. By omission, you project an image that Lycoming accidents are OK and not worthy of discussion. Of the 54 RV events, there were a number of body bags with Lycoming stamped on them, not Subaru. How come you start threads on Subaru problems so quick but are so slow on Lycoming? Seems to me I read about a huge crank shaft recall recently but no comment from Arizona on that issue.

The start message of this thread had no new news. Most pilots tuned into alternative engines, Subaru in particular, were aware of the PSRU issues before your copy and paste post. It was clearly a fishing expedition and as usual a few of us rose to the bait. This is a lose-lose discusion. Nothing ever is settled. We need solutions to problems not more flush it down the drain thinking - run up the flag and everyone go with Lycoming - man I get tired of that line. Lycomings are OK but that is not an exclusive situation. There's more to life than one brand of beer.

PCHunt
12-02-2007, 12:08 AM
As a newbie on this site, I really appreciate the knowledge and facts and experience that is evident here. OTOH, sometime some emotionalism creeps in.

Has anyone done any kind of proper statistical analysis of crash causes, with respect to engines?

In RV's,

1. How many are powered by Lyc/clones? What percentage of them have crashed due to mechanical engine failure? How many engine failures total, including those ending in a safe/non-damage landing?

2. How many are powered by Subaru variants? What percentage of them have crashed due to mechanical engine failure? How many engine failures total, including those ending in a safe/non-damage landing?

How about a little more science, and a little less heat?

:(Sorry about the rant........ :o

asav8tor
12-02-2007, 01:55 AM
I like my Lyc.

Alt engine guys do the following:

-Work on increasing power plants to provide alternatives

-Keep the price of Lycs somewhat in check by creating the threat of competition.

-Are will to take financial and personal risk I am not willing to take to provide information to the community.

With sincere respect my hat is off to the alt engine guys. You do a service for the Lyc guys. I don't see how the favor is returned so, THANK YOU.

panhandler1956
12-02-2007, 05:20 AM
I like my Lyc.

Alt engine guys do the following:

-Work on increasing power plants to provide alternatives

-Keep the price of Lycs somewhat in check by creating the threat of competition.

-Are will to take financial and personal risk I am not willing to take to provide information to the community.

With sincere respect my hat is off to the alt engine guys. You do a service for the Lyc guys. I don't see how the favor is returned so, THANK YOU.


Amen! In the past I have flown behind Small block Oldsmobile and Chevy engines for hundreds of hours back and forth across the US and I have had failures.

I think it is important to leverage the "experiment" by looking beyond the venerable Lycomings if that is the reason - research and developement. If someone is strapping on an alternative engine with little to no expertise to save a buck, that is a recipe for disaster unless the engine is extremely proven - IMHO (and no I can't quantify "proven").

I worked for a kit manufacturer that used automotive engines as a basis for it's design (FEW 2/3 P-51D) back in the early 90s as their test and demo pilot (not engineering test - someone else did the 1st flights and spins). I had a full time crew chief that was intimately familiar and maintained the aircraft so I am NOT claiming to be any kind of alternate engine expert, more of an end-user with some seat time.

I wish the manufacturers and airplane builders who use these systems all the best.

TSwezey
12-02-2007, 07:36 AM
Amen! In the past I have flown behind Small block Oldsmobile and Chevy engines for hundreds of hours back and forth across the US and I have had failures.



Can you tell us about them and what caused the failure?

N395V
12-02-2007, 07:58 AM
I have deleted 2 posts and edited several others.

Please do not sling mud at each other or vendors.

Geico266
12-02-2007, 08:05 AM
That's a dog?! I thought it was a lab rat being electrocuted. :D

I thought it was a picture of GMC :eek:

roadrunner20
12-02-2007, 08:41 AM
As a newbie on this site, I really appreciate the knowledge and facts and experience that is evident here. OTOH, sometime some emotionalism creeps in.

Has anyone done any kind of proper statistical analysis of crash causes, with respect to engines?

In RV's,

1. How many are powered by Lyc/clones? What percentage of them have crashed due to mechanical engine failure? How many engine failures total, including those ending in a safe/non-damage landing?

2. How many are powered by Subaru variants? What percentage of them have crashed due to mechanical engine failure? How many engine failures total, including those ending in a safe/non-damage landing?

How about a little more science, and a little less heat?

:(Sorry about the rant........ :o

Your point is very well taken.
Dave Dormier stated 54 RV accidents in last 18 months.
Percentage wise of the almost 5500 RV's flying. That is a very small percentage. How many were engine related?

How many RV Subies are flying and have had engine related accidents?
Don't get me wrong here, I almost went with the Sub setup and even had a demo ride ride with Jan. I made the decision to go with Superior as it was still too experimental for me at the time.

rv6ejguy
12-02-2007, 10:30 AM
It is very difficult to compile accurate stats from the NTSB reports due to lacking info and solid conclusions for engine stoppages but if anyone wants to try, it would be interesting.

Having been involved in this field for some time and meeting and talking to many others- yes a fair number who have flown auto engines have had a lot of issues. Some would not repeat the experience, others would.

I've never said that an auto engine with a PSRU is better than a Lyco, just another choice. There are many issues to address when using a PRSU and auto engine in aircraft.

N395V
12-02-2007, 11:48 AM
Yukon

I spent a good deal of time this morning editing your posts to some semblence of civilised communication and yet you continue with criticism of others.

You now have 2 infractions and I will now no longer edit your posts I will just delete them and continue to add infractions until either you are booted from the forum or the moderator buttons no longer show up on my computer. I would consider either option as not unpleasant.

Yukon
12-02-2007, 11:53 AM
Yukon

I spent a good deal of time this morning editing your posts to some semblence of civilised communication and yet you continue with criticism of others.

You now have 2 infractions and I will now no longer edit your posts I will just delete them and continue to add infractions until either you are booted from the forum or the moderator buttons no longer show up on my computer. I would consider either option as not unpleasant.

The choice is yours Milt. However, shooting the messenger isn't going to make our members any safer.

rv8ch
12-02-2007, 01:13 PM
I've got an Eggenfellner engine (not yet flying) and I'm happy to read Yukon's posts. I don't agree with everything he writes, but I very often learn from his comments. Criticism of the Eggenfellner package has prompted me to ensure that my systems are as solid as possible.

The current rash of Gen2 gearbox failures has me very concerned. I have not yet flown, but I'm faced with buying a new gearbox for over $3000. I'm not happy about this. I'm planning to wait until the last moment before I purchase the new gearbox, since as far as I understand there have already been 2 revisions of the Gen3 gearbox. I suspect there will be more before I'm ready for it.

In any case, I'm all for rabble rousing!

Yukon
12-02-2007, 01:20 PM
Thanks Mickey. How's the project coming? How's your back?

Mike S
12-02-2007, 02:32 PM
I've got an Eggenfellner engine (not yet flying) and I'm happy to read Yukon's posts. I don't agree with everything he writes, but I very often learn from his comments.

In any case, I'm all for rabble rousing!

I find it pretty amazing how the usefulness of information can be lost through the delivery.

Yukon does bring up good points, but sometimes his delivery overshadows the message to the point that I, for one, loose sight of the info he is presenting.

And then there was a post -----now deleted----that had no info, only a cheap shot at Ross.

I came very close to doing the same as Milt, but was not quite there----Milt must have a .01% lower tolerance level than I do.

Anyway, Yukon please continue to raise issues as you see fit, but please consider how you present them.

Thanks.

panhandler1956
12-02-2007, 02:35 PM
Can you tell us about them and what caused the failure?

I left that out on purpose, but it was a PSRU failure on the ZZ3 Chevy 350. I don't recall the guy who built it - this was back in 1993. The prop shaft separated in steady-state cruise flight after about 150 hrs (including some acro). The helical gear box we had on the 300 Olds did great, but wasn't dealing with much power or a C/S prop (160-180 hp-IIRC).

The machining was farmed out and they machined the spines on the shaft to end abruptly without a decreasing depth and that caused a stress riser. The shaft was 2" diameter solid steel with a pencil size hole for the C/S prop. The prop wasn't hooked to the engine anymore but stayed on the airplane. I was effectively pushing a 6' foot umbrella through the air. The engine at time of separation went to red line like a governor failure. I throttled back and landed in an open field in North Texas (was on my way to Copperstate). The field was very rough so the airplane didn't fare well.

I ended up moving on as the company was starting to lose interest in this project (costs) and I was looking to build time.

Would I fly another high performance auto conversion - sure I would fly it, not own it. I am fairly handy, but I feel my level of expertise is inadequate, especially if I am loading up my family and flying in the weather at night, etc.

For clarification, I am not talking about a corvair or VW powered low and slow machine like a Pietenpol, I'm talking 200+ HP replacements for IO-360s and IO-540s.

N395V
12-02-2007, 02:52 PM
The choice is yours.


On this point you are 110% correct



However, shooting the messenger isn't going to make our members any safer.

Which is why I didn't delete everythig. I might add, however, that taking cheap shots at Ross does nothing to enhance safety.

rv6ejguy
12-02-2007, 03:15 PM
I left that out on purpose, but it was a PSRU failure on the ZZ3 Chevy 350. I don't recall the guy who built it - this was back in 1993. The prop shaft separated in steady-state cruise flight after about 150 hrs (including some acro). The helical gear box we had on the 300 Olds did great, but wasn't dealing with much power or a C/S prop (160-180 hp-IIRC).

The machining was farmed out and they machined the spines on the shaft to end abruptly without a decreasing depth and that caused a stress riser. The shaft was 2" diameter solid steel with a pencil size hole for the C/S prop. The prop wasn't hooked to the engine anymore but stayed on the airplane. I was effectively pushing a 6' foot umbrella through the air. The engine at time of separation went to red line like a governor failure. I throttled back and landed in an open field in North Texas (was on my way to Copperstate). The field was very rough so the airplane didn't fare well.

I ended up moving on as the company was starting to lose interest in this project (costs) and I was looking to build time.

Would I fly another high performance auto conversion - sure I would fly it, not own it. I am fairly handy, but I feel my level of expertise is inadequate, especially if I am loading up my family and flying in the weather at night, etc.

For clarification, I am not talking about a corvair or VW powered low and slow machine like a Pietenpol, I'm talking 200+ HP replacements for IO-360s and IO-540s.

The fellow I crewed for at Reno this year in Sport Class used to own a Stewart Mustang with a V8 and PSRU. I think he had two drive failures and two forced landings. Not surprisingly, his view of PSRUs is not too positive. After seeing Darryl Greenameyer's PSRU problems across the hangar, he was glad to have a direct drive Conti up front.

I've seen many issues with redrives involve poor machining practices- misalignment of parts and sharp edges creating stress risers and other problems with poor or marginal design practices. These are best tackled by some one experienced in gearbox servicing or design with attention to those machining details which can make or break a good design.

In the auto racing world, small shafts and bearings coupled to flexible casings guarantee a short life. I look for everything to be massively oversized and that is why I like most parts of the Marcotte box. These did have a mod many years back to replace the pilot bushing with a ball bearing. As this was external to the box, it was an easy mod to do myself. No issues to date on the M-300 box that I'm aware of. http://www.sdsefi.com/air14.html

panhandler1956
12-02-2007, 03:32 PM
The fellow I crewed for at Reno this year in Sport Class used to own a Stewart Mustang with a V8 and PSRU. I think he had two drive failures and two forced landings. Not surprisingly, his view of PSRUs is not too positive. After seeing Darryl Greenameyer' PSRU problems across the hangar, he was glad to have a direct drive Conti up front.

I've seen many issues with redrives involve poor machining practices- misalignment of parts and sharp edges creating stress risers and other problems with poor or marginal design practices. These are best tackled by some one experienced in gearbox servicing or design with attention to those machining details which can make or break a good design.

In the auto racing world, small shafts and bearings coupled to flexible casings guarantee a short life. I look for everything to be massively oversized and that is why I like most parts of the Marcotte box. These did have a mod many years back to replace the pilot bushing with a ball bearing. As this was external to the box, it was an easy mod to do myself. No issues to date on the M-300 box that I'm aware of.


Ross,
Sounds like you have a good handle on what it takes and obviously some expertise so you should have good results. There is no doubt that this can and is done successfully. The diesels showing up on the name brand airplanes is especially encouraging for everyone, not just the alternate powerplant community. Best of luck with your airplanes and have fun!

asav8tor
12-02-2007, 04:11 PM
The PSRU does not need to be a weak point. Very mature technology on turboprop aircraft. Nothing that money can't solve. Just dig deeper into the old billfold. :D

gmcjetpilot
12-02-2007, 04:16 PM
I'm glad I stayed out of this. When safety is involved everyone gets worked up. We all friends, no need get the blood pressure up, grab a beer or three.

>Originally Posted by panhandler1956
>Would I fly another high performance auto conversion -
>sure I would fly it, not own it. I am fairly handy, but I feel
>my level of expertise is inadequate, especially if I am loading
>up my family and flying in the weather at night, etc.

I am not trying to pick your words apart but they don't really make sense to me. "Sure I'd fly one, not own it." (PSRU) You feel your level of expertise is inadequate to fly behind a PSRU, especially with the family in weather and at night? What "expertise" and I'm not sure what family, weather and Sun position has to do with it. I don't think there should be two tiers or levels of safety to start with. You just don't trust PSRU's from experience, which is perfectly understandable and reasonable. Personally, if I felt a PSRU was not good enough to fly at night or with passengers, I would not fly it. I do fly a Lyc direct drive. No gear box has ever failed on a direct drive Lycoming. :rolleyes: Bottom line, you don't trust PSRU's from past experience.

As far as two tiers of safety, That's fine for racing, since you accept low level pylon racing is already very risky, somewhat like you accept it with an experimental PSRU's. For everyday flying, the safety level should be as high as possible solo or with passengers, in my opinion. Speaking of racing, remember the Pond Racer and Rick Brickert? :(

Personally I kind of like the belted power guys set-up on V6's from afar; I really do; no gears or oil and easy to inspect, BUT I'm such a boring predictable follower, therefore I'm using a Lycoming, like all sane intelligent people should. (HA, I'M KIDDING LIGHTEN UP FOLKS, A JOKE). :D

Mickey Coggins! Did you get your local engineering paper-work sorted out? Glad to hear from you! ha-ha, RON PAUL? He's my favorite nut. He makes too much sense to win.

rv6ejguy
12-02-2007, 04:29 PM
The PSRU does not need to be a weak point. Very mature technology on turboprop aircraft. Nothing that money can't solve. Just dig deeper into the old billfold. :D

Agreed. I built and modded road racing gearboxes for many years. These were mostly Toyota T50 and W50 production boxes attached to some pretty powerful 4 cylinder turbo engines. The aluminum cased T50 boxes were designed for 100hp and were reliable to about 200. When you put 250+ through them, the bearings turned black and square and all the teeth came off 3rd gear in about 5 minutes. With the cast iron cased W50 and its bigger gears and shafts, 375+hp was no problem with a cooler. I ran the same box for 5 seasons and never touched a bearing or gear- brutalizing it with very fast shifts.

Modern manual longitudinal boxes are super reliable these days.

Aircraft PSRUs are relatively simple by comparison being only 1 speed affairs. Other than the gyroscopic loads which are easily handled by a large diameter shaft and twin tapered roller bearings, the box itself can be straightforward.

We do need to make sure that torsional vibration is not a factor so more flywheel weight and/or a good input damper is a must. I like the designs from Autoflight and EPI best.

panhandler1956
12-02-2007, 05:13 PM
I'm glad I stayed out of this. When safety is involved everyone gets worked up. We all friends, no need get the blood pressure up, grab a beer or three.

>Originally Posted by panhandler1956
>Would I fly another high performance auto conversion -
>sure I would fly it, not own it. I am fairly handy, but I feel
>my level of expertise is inadequate, especially if I am loading
>up my family and flying in the weather at night, etc.

You'd fly one but not own one? You feel your level of expertise is inadequate to fly behind a PSRU, espcially with the faimly in weather and at night? I don't think there should be two tiers or levels of safety. Not sure what family, weather and Sun position has to do with it. You just don't trust them. Personally if I felt it's not good enough to fly with the family, at night or beyond glide of the airport, its not good enough for me to fly, ever. I'm just asking, what skill are you talking about? I assume maintence and not actually designing a gear box. Not sure how hard maintence is or factors into the current issues of PSRU reliability. Bottom line, you don't trust PSRU's from your past experience, at least on higher HP applications. As far as racing, remember the Pond Racer and Rick Brickert? :(



George,
I guess I wasn't clear. If I am flying for hire (test pilot) or doing a favor for a friend, I would strap one of these on - no problem. My point is, it isn't my cup of tea for a "daily driver" and I don't want to "tinker" with it. I trust them to a point, and that point begins and ends with me in the airplane, not my family. This is my level of comfort and it's completely subjective and I won't fault anyone for "experimenting" with alternative powerplants. As mentioned before, it is good for all of us in most instances.
Respectfully,

gmcjetpilot
12-02-2007, 05:19 PM
George,
I guess I wasn't clear. If I am flying for hire (test pilot) or doing a favor for a friend, I would strap one of these on - no problem. My point is, it isn't my cup of tea for a "daily driver" and I don't want to "tinker" with it. I trust them to a point, and that point begins and ends with me in the airplane, not my family. This is my level of comfort and it's completely subjective and I won't fault anyone for "experimenting" with alternative power plants. As mentioned before, it is good for all of us in most instances. Respectfully,Roger that. That makes sense, thank you Sir.

The PSRU does not need to be a weak point. Very mature technology on turboprop aircraft.

Ross: Turbines are smooth and don't pulse out mass "suck-squeeze-bang-blow" pounding harmonics, as you know & said. However gear boxes, even on turbines do fail and big old props go flying, into fuselages, wings and the other engine sometimes. It has happened. Not being mean or throwing stones but those super reliable turboprop gear boxes are often massive and heavy even with exotic steel, magnesium and titanium, or the reduction is integrated into the engines case. My point? I don't have one as usual :rolleyes: (At least I'm honest), but it does point out some differences from what turboprop guys have, verses the add-it-on approach used in our experimental community. To do it right the engine and gear box would be made together, as one unit. The airframe would be designed around that specific engine/gearbox. We kind of "adapt" and compromise with our configurations, to use existing engines in existing airframes.

In cars you can make the gear box long and robust because you have the envelope. Trans weight is not super critical for a car, but even Ferrari's put the gear box in the rear of their front-engined cars for balance. In our little planes you can't really do much (unless you ran a drive shaft and that's another nightmare). We have to make a very flat gear box, that goes on the front of the plane. Aerodynamics is an issue as well. There's no doubt gear boxes can be made to work, but its the limits we have to work with, which challenge us, especially with the R&D budget we or vendors have. The design envelope is small and unforgiving. When a cars trans dies you pull over to the curb.

http://img62.imageshack.us/img62/2569/proploss1nl5.jpg

asav8tor
12-02-2007, 05:55 PM
If you throw enough money at the problem you can solve it. I'm not talking about a couple hundred grand and some guy in a home machine shop. I'm talking big money. As much money as it takes money. Like Government project money. Will the solution be economically viable? Maybe. Maybe not.

The debate is this: Proven mature technology vs new unknown technology

Proven mature:

Lyc
Mags
100LL
Hartzel
2024-T3
Alodine
Zinc Chromate
etc

I'm not going put the other list up. We know what is on it. I don't want to get someone going.

When I have a choice I will pick from the proven mature list. I acknowledge the "proven mature" list would not exist if someone a long time ago did not blaze the trail. The only way we move forward is if someone steps up and puts their money / safety / airplane at a higher level of risk to try something new. Again I thank these individuals. They are willing to lay it all on the line so the rest of us can benefit if they are successful. Many of them have paid with their lives.

nucleus
12-02-2007, 06:02 PM
I'm still trying to get my head around someone selling an engine for aircraft who doesn't dyno them? This makes no sense to me. I don't understand this on the buying or selling side. No insult intended.

Hans

Geico266
12-02-2007, 10:01 PM
I'm still trying to get my head around someone selling an engine for aircraft who doesn't dyno them? This makes no sense to me. I don't understand this on the buying or selling side. No insult intended.

Hans

Not wanting to start a war, my bet is they have been dynoed, who wound't? But my gut tells me the results just wen't what they expected:eek:.

aerial
12-02-2007, 10:20 PM
How about a little more science, and a little less heat?



Several years ago at Sun 'n' Fun I was trying to get a little more information on the Egg conversion for my RV4, I own a Turbocharged Subaru Wagon and like the thought of having a "hi-tech" engine.

But when I asked Jan what his background was with engines, he stated rather sarcastically that he got his experience from working on his Volkswagen. I wasn't sure how to receive the response (funny?), and couldn't get anymore information about his qualifications as an engine builder. I wrote off the Egg conversion after that.

rv6ejguy
12-02-2007, 11:55 PM
Yeah, I already mentioned that turbine gearboxes occasionally fail and in fact turbine engines do as well and more often than some manufacturers let on.

Integral engine/ gearbox designs like the Rotax 912/914 are going to cost what a Rotax does as these involve clean sheet designs. The whole point of auto conversions is the cheap, proven engine core. Of course this is sometimes offset by either an expensive PSRU (way more than that cheap engine) or a crummy, cheap PSRU which blows up, kind of defeating the whole idea- reliability is job 1.

A PSRU is WAY simpler than a 5 speed car transmission though. I've seen and worked on plenty of both. Obviously (to me anyway) bad design and machining are the primary causes of failure with TV coming a close third. Lack of testing, especially with TV seals the fate of many designs. You don't need millions to design a good PSRU. Give me about $40K to deliver a de-bugged sample (if I had time), fully tested and with 1000 flight hours on it.. The real ones out there are $5500-$15,000 for 200-500hp engines.

Some other ones like the Marcotte and Autoflight are strong IMO but lack proper TV testing. This is very difficult as these are installed on different engine types. Jan's Gen 3 is very strong IMO but needs more flight time to be well proven. MT has just completed vibration studies on the Egg EZ30 and their prop. This makes me a lot happier.

The dyno thing has been bandied about before. NSI "dynoed" their engines but their figures were complete nonsense. Because they were "dynoed" however, sales took off. One engineer there argued with me about this for weeks then admitted that there were "some" problems with their data but kept pushing out fabulous stories of 200mph Glastars with NSIs up front. The gullible never bothered to pull out a calculator and run the data, money was already on the way. Never swallow the sales pitch and never be the first in line is my advice.

I couldn't care less how an airplane engine dynos, do a head to head flight test against a known quantity and see how it stacks up. Van's has an open invitation and I like their methodology. No chance for BS here.

gmcjetpilot
12-03-2007, 06:52 AM
Traditionally from what I have seen in the past, HP claims where good faith estimates based on peak HP the automotive manufactures stated in the glossy brochure specs for cars with the same engine. Even some auto HP numbers are suspect, but that was how they did it.

One example is a popular vendor of a do-it-yourself line of Rotary engine components claims 180HP. OK that seems reasonable, but when he races in the sun-N-fun 100, he competed in the Red class or 160HP class? Humm, he does pretty good in the 160 HP class, but in the 180 hp class he would be last. To be fair, alternative engines have shown they can make THRUST (what you really want) equivalent to 180 HP engine or more. However Egg's early stuff that claimed 180HP performed more like 150 or 160 HP.

The problem with using an auto manufactures dyno number is they are based on peak RPM (and sometimes inflated). Many conversions do not run the engine at max or peak HP RPM. Another example is a vendor or PSRU's for LS1's, the new later Gen aluminum small block V8, 350 cu-in Chevy. The max HP is say 6,000 RPM for argument sakes. The PSRUs is geared to turn the prop at an acceptable RPM's with engine RPM's less than 3,000 RPM. The LS1 is rated at 300 HP max @ 6000 rpm. Do the math. You don't have a 300 HP engine at 3,000rpm, may be 200HP at best. The other contraversy is running an engine at max RPM 100% all the time. This is also subject to debate wars, but a Lyc is made to run at 2,700 RPM all day long. Most auto engines in my opinion will not be long lived if ran at high RPM's required to make peak HP all the time. To get max RPM at take-off and get low RPM in cruise would take more than one gear ratio.

The other issue besides RPM is efficiency, loss of HP going thorugh the gear box. Again debate has raged. It's not free to gear or belt down. How much loss? There're ball park numbers you can look up. Bottom line is you don't know until you Dyno the engine set-up in the installed configuration, that is everything, prop, gearbox, exhaust, induction and ignition.

pierre smith
12-03-2007, 08:01 AM
.....on the old Cessna 175, geared Conti's.:

The GO-300 engine
An unusual feature of the 175 is the use of the geared Continental GO-300 engine. Whereas most single-engine airplanes use direct drive, this engine drives the propeller through a reducing gearbox, so that the engine runs at 3200 rpm to turn the propeller at 2400 rpm. The engine was esssentially an O-300 engine with a gearbox mounted on the drive end, and some internal modifications to provide durability at higher engine speeds. The GO-300 engine has a TBO (Time Between Overhaul) of only 1200 hours[1], which compared unfavorably with the ungeared version. The GO-300 engine also suffered reliability problems and helped the 175 develop a poor reputation. Many Skylarks flying today have been converted to larger-displacement direct-drive engines.

The reputation of the GO-300 may not have been deserved, since the problems associated with it were the result of pilots who were familiar with direct-drive engines simply not operating the engine correctly. Pilots unfamiliar with the engine often operated the engine at low RPM settings (2300) appropriate to direct-drive engines, while the 175's Operating Handbook called for 2900 RPM. This prevented the engine's air-cooling system from operating effectively and resulted in a lack of reliability...END.

There are many hours on geared Lyc 0-540's, P-51's and others. As I stated earlier, my PT-6 has over 8000 hours on the original gearbox, absorbing 1200-1300 pounds of torque daily, for 8000 hours and takeoff torque of up to 1600 ft. lbs. during 12-15 takeoffs a day. Gearboxes can definitely be made to live under high power settings. Have any of the smaller boxes on Eggs, 350 Chevies and rotaries been tested to the extent of the aforementioned boxes...? I doubt it. Simply because Lycoming and Pratt and Whitney throw enormous dollars and brains into testing and testing more...often to destruction. IMHO, the smaller vendors are cash-restricted so can't/don't do the full on testing and engineering that the big guys do.

Regards,

Kevin Horton
12-03-2007, 08:43 AM
To be fair, alternative engines have shown they can make THRUST (what you really want) equivalent to 180 HP engine or more.
The only thrust tests I have seen measured static thrust. The thrust of any given engine and prop combination will change significantly as the airspeed changes, and the relationship between thrust and speed will depend on prop blade angle, blade twist, prop rpm, prop diameter, etc, etc. Some of the things that increase static thrust will decrease thrust at normal airspeeds. It is not possible to take thrust results at zero speed and draw any conclusions about performance in a flying aircraft.

Static thrust is a very useful number only if you plan to pull stumps with your aircraft, but it is meaningless for a flying aircraft.

rtry9a
12-03-2007, 08:50 AM
GMC-
Come on, be fair. Tracy ran in the 160hp class because that is what that engine produced with marginally-effective motorcycle carbs early in the development process. Mazda rated that same motor at 140hp in autos. Tracy and others easily get 180 with his current FI system. FWIW, the output in a rotary is dependent on rpm, which is mostly a function of intake system capability. Current systems with the same engine BUT with FI and intakes tuned for ~6000rpm produce 180-200 hp, a bit more ~250 with peripheral porting, up to 300 with turbocharging.

"but a Lyc is made to run at 2,700 RPM all day long" ...BS FLAG, or at least misleading!

2700 is relatively slow rpm; but a Lyc might, or might not, be producing full rated power depending on the situation, prop, etc. Lyc claims peak hp numbers that might be achievable under perfect conditions, everyone knows that a Lyc will not last at full power for extended periods of time in the real world, particularly when leaned- they recommend use around 60% of peak hp most the time, don't they?

The rotaries can hum leaned, at rated power (5000-7000 rpm), as long as you want, with minimal wear and no fear of damage. I agree with your comments as far as most reciprocating engines (ie, Subi and Chev, even Lycs) motors are concerned, the Suzuki is probably an exception- designed for continuous 5000 rpm freeway cruise. The internal stress rises (exponentially?) in a reciprocating engine as rpm increases- think of the mechanical stress involved with the pistons/rods pounding (accelerating and stopping) with each rotation of the crankshaft, particularly with large bore (Lyc) engines.

Update note: Paul Lamar just reported results back from his p-ported intake Renesis (sideport exhaust) test on the Mazdatrix dyno: 264hp, 194ft/lb @ 7200rpm w/Weber carburetor. Sideport exhaust was quiet, stable idle, tested with 87 octane mogas.

captainron
12-03-2007, 08:57 AM
There are many hours on geared Lyc 0-540's, P-51's and others. As I stated earlier, my PT-6 has over 8000 hours on the original gearbox, absorbing 1200-1300 pounds of torque daily, for 8000 hours and takeoff torque of up to 1600 ft. lbs. during 12-15 takeoffs a day.

Regards,

And I'm betting that there is lots of G-loading on the propeller and propeller shaft in your line of work. I think that the Subaru is a good powerplant with proven strong internals, but I think that to be viable in this application, someone is going to have to figure out how to cast an engine block with an integral PSRU housing to really make this work. Such a re-design would have the added benefit of being even more compact and lightweight. There are a lot of aftermarket foundries now that are casting various car blocks and cylinder heads. The pricing is apparently not so high as to keep folks from buying them for their cars, so I think it is within reason to try to get something like this for your planes. This might be beyond Egg's or other would-be Subaru supplier's means, but I think it's high-time to finally do it right, or not at all! Falling airplanes are just not acceptable due to inadequate engineering in today's computer analyzed, and cad-cam world! I think the people who really want Subarus for their planes should demand this and not settle for less. You vote with your pocketbook!

Please deposit $0.02 to hear the next rant.

pierre smith
12-03-2007, 10:10 AM
And I'm betting that there is lots of G-loading on the propeller and propeller shaft in your line of work.

.


....is this. I hit a small residential powerline about 8 years ago, cut it easily while watching a blue ball of fire as the wires were grounded to each other by the prop:eek: I flew home but we decided to dissassemble and check the gears/bearings etc (sudden stoppage and all that)........The repair bill.......$23,000!! The caveat. A great and reliable gearbox but very susceptible to strikes damage....I dunno what a new one would cost.

Regards,

DanH
12-03-2007, 10:28 AM
<<cast an engine block with an integral PSRU housing to really make this work. >>

Are you thinking about shared lubrication, or just alignment and stiffness?

<Falling airplanes are just not acceptable due to inadequate engineering in today's computer analyzed, and cad-cam world! I think the people who really want Subarus for their planes should demand this and not settle for less. You vote with your pocketbook! >>

Hear, hear!

captainron
12-03-2007, 11:06 AM
<<cast an engine block with an integral PSRU housing to really make this work. >>

Are you thinking about shared lubrication, or just alignment and stiffness?

<Falling airplanes are just not acceptable due to inadequate engineering in today's computer analyzed, and cad-cam world! I think the people who really want Subarus for their planes should demand this and not settle for less. You vote with your pocketbook! >>

Hear, hear!
I think that to do it right would require a specialized block and probably a crankshaft that was purpose-designed for this application. A crankshaft that was built to be able to withstand the sustained high RPM and torsional stresses, together with an integral drive gear at the end would be a huge step forward. Could probably share lubrication if the engine was run on the heavy Aeroshells, but then again the standard Subaru car engine was designed with clearances for very light-weight oils in mind. So, another complication to be dealt with.
I'm definitely thinking of of the alignment and stiffness that you mentioned in an integral block-gearbox design. It will demand some engineering and computer time, as well as finding the manufacturing resources to do this right, but you Subaru guys should demand it be done (kinda like your lives depended on it!) or else spend your money elsewhere. You may be thinking by now that the Lyc/clone is exactly what you are looking for, but this IS experimental aviation, and I'm thinking that the Subaru could be a viable powerplant. But not as they are now. Again, J.M.O.

David-aviator
12-03-2007, 11:07 AM
I'm glad I stayed out of this. When safety is involved everyone gets worked up. We all friends, no need get the blood pressure up, grab a beer or three.

.....I don't think there should be two tiers or levels of safety to start with..... therefore I'm using a Lycoming, like all sane intelligent people should. (HA, I'M KIDDING LIGHTEN UP FOLKS, A JOKE). :D

Amen to kicking back and keeping things in perspective.

I don't measure what we do in levels of safety but in levels of risk. Flying an experimental airplane will never be as safe as flying under Part 121. When it comes to IFR, night, or transporting the family, it is the perceived risk that keeps me from doing it. That perceived risk of course is not the same with each pilot, we all look at it through different windows. The amount of risk one will accept gets modified with experience and is directly related to the number of times serious stuff has gone wrong. By modified, I mean "well, I'm glad my wife or a friend was not along on that one" or "sure glad that didn't happen at night".

The reality of engines is, Lycoming is very safe (perceived risk low) and alternate engines somewhat less so (perceived risk a bit higher) although stuff happens most everyday across the board as indicated by the NTSB reports. I had a Lycoming in a previous airplane and liked it a lot. Maybe I got bored and needed something new to mess with. It took months to make the decision to go with Subaru. That was 2 engines, a super charger, and 3 PSRU's ago. A lot of money gone. Would I do it again - some days yes, some days no. The ride has been interesting although at times very frustrating.

I do believe the engine is solid, as tough as Lycoming but in a different more suave way. Provide it with fuel, electricity and air and it perks impressively and without hesitation. We just have to get the rest of this stuff to work better and settle down. I am committed to sticking with it to that end.

Yukon, you're Ok. Just park your sledge hammer in the corner of the hangar for a while. :)

gmcjetpilot
12-03-2007, 11:24 AM
GMC-
Come on, be fair. Tracy ran in the 160hp class because that is what that engine produced with marginally-effective motorcycle carbs early in the development process. Mazda rated that same motor at 140hp in autos. Tracy and others easily get 180 with his current FI system.OK you're a rotary fan. I get it. I think rotaries are COOL, OK. I drove several rotary mazda's in the 70's. I don't want an argument but, come on, be real. When Tracy won in the 160hp class one year, that was something to be proud of, but don't tell me its a 180 or 200hp of equiv Lyc thrust, excuses not withstanding.

No offense but there's always an excuse for rotary performance, high fuel burn & loud exhaust bark. I've heard excuses for 10 yrs (really 20 yrs). There are always breakthrough's that will fix it. First, the Carb excuse, than the Fuel Injection's "mapping is not proper". I've heard it all before. I did not mention Tracy by name. He and his wife are super straight honest (and vary nice) folks. I like his approach & products. However any enthusiast is, well enthusiastic. I reject fuel injection is a panacea of HP or fuel economy on a Rotary (or any engine). Carb or FI on the same LYC does not change HP, at all (well may be 1%). People get confused with the 200HP IO360 angle-valve. Higher compression and different heads makes the extra 20HP, not FI. Yes FI can save fuel on a LYC, about 2% or 3% if you lean carefully, more for LOP ops may be. All I'm saying is Tracy competes in 160HP class and still does, and that was recently, I believe post motorcycle carbs.

FWIW, the output in a rotary is dependent on rpm, which is mostly a function of intake system capability. Current systems with the same engine BUT with FI and intakes tuned for ~6000rpm produce 180-200 hp, a bit more ~250 with peripheral porting, up to 300 with turbocharging.Oh BOY here we go. :D Again I don't want to be disagreeable, but NO. The super custom, expensive defunct Power Sport rotaries (which I admired) where not stock 13B's by any means. They matched a 180hp Lyc's performance (which is great) but at the expense of massive extra fuel flow. Power Sport rated them @ 210HP. Tracy even warns not push HP too far above stock for reliable power. 6,000 rpm! Wow? It's working hard while the Lyc is chugging along to make the same power.

Van's fly-off was between stock factory prototype RV-8's w/ Lycs & two Power Sport RV-8's. The results where published in the RVator, facts meet the fan, real-world-side-by-fly-off data. The RV-8's w/ Power Sports IMHO where the best of the bred, w/ nice aerodynamic cowls & cooling system. The Rotary RV-8's (btw one later crashed due to an electrical problem) are better than a typical roll-your-own stock 13B, in my opinion. Nothing wrong w/ a stock 13B + RWS parts and it's a bargain compared to Power Sport's $40,000? A RWS setup is half or less. Still the Power Sport planes where beauties, but they where heavier & louder (as measured by dB meters). The killer was FF, 13gal/hr verses the Lyc's 9gal/hr, while doing the same thing in the air. OUCH! All factual & no bull. Still the Power Sport 8's turned in impressive & respectful performance. I hope they come back.

Excuses & rationalizations where made about the Power Sport RV-8's fuel burned. The FI was not tuned or something? The fact is rotaries are just fuel hungry, always have & always will be. This is consistent w/ rotary Mazda's on wheels, lousy gas millage, but a Porsche 911 does as well. You can't complain about 18-20 mpg, its a sports car not a Prius. A RV is a sport plane.

"but a Lyc is made to run at 2,700 RPM all day long" ...BS FLAG, or at least misleading! No, it's true not Bee Ess. Let me rephrase, there's no Lyc restriction (time or otherwise) on 100% power or 2,700 RPM (unless the prop's restricted), period, end O-story. Lycs are build like fort knox's.

2700 is relatively slow rpm; but a Lyc might, or might not, be producing full rated power depending on the situation, prop, etc. Lyc claims peak hp numbers that might be achievable under perfect conditions, everyone knows that a Lyc will not last at full power for extended periods of time in the real world, particularly when leaned- they recommend use around 60% of peak hp most the time, don't they?NO NOT PERFECT, NORMAL CONDITIONS!

First, the air-box & pipe's for Lycs in RV's are effiecent, making rated power or more w/ out question @ sea level atmo, std day & 2,700 RPM. YES, you're right 2,700 RPM may not be 100% power, if MAP is less than 29" (such as flying at altitude). Pwr may not be 100% on takeoff with a fixed prop, which does not allow full RPM. This applies to any engines, but auto engines can take a bigger hit with fixed props and poor induction/exhaust pipes.

To be CLEAR: Lycs have NO limits on making 100% HP. Lycs can and do routinely make 100% pwr unless there's weird induction/exhaust restrictions, which is not the case with most RV's. Fact most LYCS in RV's are capable of making more power than stock, not less. They are quasi de-rated, conservatively. Lycs have another advantage, many custom "hot rod" parts for induction, exhaust, ignition, with many vendors. There are three "Lyc" engine vendors as well. Alternative engine guys don't have this.

Flying into less dense air does reduce HP, but that applies to any ATMO engine. However less air density reduces cooling at altitude, which is a problem for turbo/blown engines, which can run hot at altitude. HP does not reduce with altitude but cooling does which is a problem with the supercharged Subie.

I've raced my RV-4 several time, wide open throttle, on the deck, 2750 RPM, all day. Temps where in the green. It's totally fine, ask Lyc engineering, no restrictions on 100% pwr. Lyc does recommend 75% for max engine life. Some Lycs double TBO.

You mention PROPS. Another advantage of Lycs, they have hydraulic constant speed prop capability; most alternative engines have fixed or a less desirable electric wood/glass props, which are not as efficient as a metal props (BA Hartzell or Sensenich-fixed). Prop selection is another reason alternative engines are ham strung, low efficiency props. The LYC is a low RPM torque engine which can even "pull" a fixed prop on takeoff. A fixed prop on a Subie or Mazda will be hurt more on takeoff & climb than on a Lyc. MT blades are not as efficient as a metal BA hartzell.

The rotaries can hum leaned, at rated power (5000-7000 rpm), as long as you want, with minimal wear and no fear of damage.OK that's good, because rotary engines are so fuel inefficient, they need to lean aggressively. Wankel's drink gasoline like a sailor drinks booze on shore leave. A Lyc can be leaned w/ out restriction at 75% pwr and is still more fuel efficient, even at full rich power than a rotary leaned.

I agree with your comments as far as most reciprocating engines (ie, Subi and Chev, even Lycs) motors are concerned, the Suzuki is probably an exception- designed for continuous 5000 rpm freeway cruise. The internal stress rises (exponentially?) in a reciprocating engine as rpm increases- think of the mechanical stress involved with the pistons/rods pounding (accelerating and stopping) with each rotation of the crankshaft, particularly with large bore (Lyc) engines.Lycs are designed for airplanes, to directly drive a prop in the 2,200-2,700 RPM ball park. The 2,700rpm RED LINE is conservative, by design not weakness. A Lyc can turn faster but does not need to. There's no Lyc time or stress limit on making 100% HP. I can fly 100% power all day long or 2,700 RPM. In the winter its easy to make more than 100% w/ dense air. Lycs are not WORKING or breathing hard at rated pwr; they're under-tuned, under-stressed for reliability. They chug along at 75% or 100% rated power, as designed.

rv6ejguy
12-03-2007, 12:24 PM
The high hp Subes have forged steel, nitrided cranks just like a Lycoming except they are way stiffer due to crank pin overlap and much better supported with a bearing on each side of each throw.

Back onto the subject of PSRUs. Integral ones would weigh less but you'll never see that with an affordable auto based engine. Casting a new block with drive casing would make it way more than a Lycoming.

Car gearboxes bolt on just fine thank you and can handle staggering amounts of hp like 1500+HP in the case of a 2JZ Toyota with 4 bolts and two dowel pins. For the sake of a few pounds saved going integral- nobody will be doing this. The bell housing makes a nice space to hold a torsional damper as well and these are really important. On the Sube, the bell housing is integral already so little weight saving would be possible.

A one speed gearbox design is not rocket science at all and does not need a NASA budget to be built. Using pre-existing gears from a OEM heavy duty auto/ truck source reduces costs considerably and ensures good quality and low cost. Alternately, either commercially available quick change spur gears or even custom spur gears are cheap. In fact all the materials right down to a commercially available torsional damper are cheap. The case is far more expensive to either cast in small quantity or CNC out of billet. The torsional testing and long run validation will cost more than building the first box by a long shot especially with fuel prices today but both steps should be done.

captainron
12-03-2007, 12:40 PM
The high hp Subes have forged steel, nitrided cranks just like a Lycoming except they are way stiffer due to crank pin overlap and much better supported with a bearing on each side of each throw.

Back onto the subject of PSRUs. Integral ones would weigh less but you'll never see that with an affordable auto based engine. Casting a new block with drive casing would make it way more than a Lycoming.

Car gearboxes bolt on just fine thank you and can handle staggering amounts of hp like 1500+HP in the case of a 2JZ Toyota with 4 bolts and two dowel pins. For the sake of a few pounds saved going integral- nobody will be doing this. The bell housing makes a nice space to hold a torsional damper as well and these are really important.

A one speed gearbox design is not rocket science at all. Using pre-existing gears from a OEM heavy duty auto/ truck source reduces costs considerably and ensures good quality and low cost. Alternately, either commercially available quick change spur gears or even custom spur gears are cheap. In fact all the materials right down to a commercially available torsional damper are cheap. The case is far more expensive to either cast in small quantity or CNC out of billet. The torsional testing and long run validation will cost more than building the first box by a long shot especially with fuel prices today but both steps should be done.

Well, it sounds like you have the technology down pat and it should all work just fine! I guess that settles it. Maybe Lycoming should take a look at Subaru's crankshaft since it's so superior. They could call the new one Gen II.

rv6ejguy
12-03-2007, 12:54 PM
The only thrust tests I have seen measured static thrust. The thrust of any given engine and prop combination will change significantly as the airspeed changes, and the relationship between thrust and speed will depend on prop blade angle, blade twist, prop rpm, prop diameter, etc, etc. Some of the things that increase static thrust will decrease thrust at normal airspeeds. It is not possible to take thrust results at zero speed and draw any conclusions about performance in a flying aircraft.

Static thrust is a very useful number only if you plan to pull stumps with your aircraft, but it is meaningless for a flying aircraft.

These tests were not trying to establish flight thrust, they were trying to determine relative hp compared to other popular engines. With the same prop this can be a valid way to determine hp. In fact, we use test clubs to determine hp changes based on the hp absorbtion curve supplied by the engine or club manufacturer.

Whether static thrust translates into more flying performance requires flight testing to validate and the side by side test is the easiest way to quantify relative performance in the shortest time with best accuracy. This confirms the whole package performance as well from drive losses, prop efficiency and cooling drag perspectives and in the end this is what we are really concerned about.

Kevin Horton
12-03-2007, 01:09 PM
These tests were not trying to establish flight thrust, they were trying to determine relative hp compared to other popular engines. With the same prop this can be a valid way to determine hp. In, fact we use test clubs to determine hp changes based on the hp absorbtion curve supplied by the engine or club manufacturer.
Ahh. OK. I misunderstood. I agree that if the exact same prop is used on all engines, then static tests would allow comparison.

I must have missed the reported test results of Lycomings vs alternative engines where they all had the same prop. Have those test results been posted anywhere?

Mike S
12-03-2007, 01:18 PM
Well, it sounds like you have the technology down pat and it should all work just fine! I guess that settles it. Maybe Lycoming should take a look at Subaru's crankshaft since it's so superior. They could call the new one Gen II.

Sarcasm aside, the technology used it the Subaru crankshaft wont necessarily work in the Lyc, due to such things as air cooling, bore, stroke, and b/s ratio, just to name a few.

Build a Lyc like a Sube, and the main bearings would end up 4 or 5" in diameter, crank pins same, otherwise pin overlap not possible.

Now, if you will, just imagine what that crank would weigh------and dont forget that there is a couple more of those huge main journals.

Folks, apples and oranges are both fruits, and they are both round, but they are still very different. Much like a car engine, and an aircraft engine.

Anybody out there ever make a pie with oranges???

David-aviator
12-03-2007, 01:27 PM
Sarcasm aside, the technology used it the Subaru crankshaft wont necessarily work in the Lyc, due to such things as air cooling, bore, stroke, and b/s ratio, just to name a few.

Build a Lyc like a Sube, and the main bearings would end up 4 or 5" in diameter, crank pins same, otherwise pin overlap not possible.

Now, if you will, just imagine what that crank would weigh------and dont forget that there is a couple more of those huge main journals.

Folks, apples and oranges are both fruits, and they are both round, but they are still very different. Much like a car engine, and an aircraft engine.

Anybody out there ever make a pie with oranges???

Perhaps the most important reason it wouldn't work is the temp range of Lycoming verses a liquid cooled engine. If Sub ever hit 400F it would be toasted oranges.

gmcjetpilot
12-03-2007, 01:48 PM
The only thrust tests I have seen measured static thrust. The thrust of any given engine and prop combination will change significantly as the airspeed changes, and the relationship between thrust and speed will depend on prop blade angle, blade twist, prop rpm, prop diameter, etc, etc. Some of the things that increase static thrust will decrease thrust at normal airspeeds. It is not possible to take thrust results at zero speed and draw any conclusions about performance in a flying aircraft.

Static thrust is a very useful number only if you plan to pull stumps with your aircraft, but it is meaningless for a flying aircraft.Good point I did not really think about it, but now you mention it, I see that. Thank you Professor Kevin :D. I'm thinking what's more valuable is along the lines of real world in-flight side-by-side performance. That is the PROOF, performance in the air, like the Power Sport v Lycoming fly-off Van did.

Like I always say, my Lyc is for sale, as soon as the subie's and mazda's start winning races and passing me and the gas pump.

gmcjetpilot
12-03-2007, 01:54 PM
Well, it sounds like you have the technology down pat and it should all work just fine! I guess that settles it. Maybe Lycoming should take a look at Subaru's crankshaft since it's so superior. They could call the new one Gen II.ha ha may be so, but seriously Lyc uses the best materials and processes. The difference is the Lyc crank does have to WORK HARD or harder than a car engines crank, thus they're made like a brick outhouse. It's got to take prop loads and pounding from 4 jugs, each with over twice the displacement of a subie.

Not withstanding AD's from a batch of bad poor QC cranks, cranks made in the 50's or 60's are still flying on their 3rd or 4th rebuild. The crank is not life limited and are made to take the abuse. Still there are limits to engineering, but forging and steel alloys to make cranks has not significantly changed (for the better) in 50 years.

NEW forging methods like Electro-Slag Remelting (ESR) (used by Superior) or Vacuum Arc Remelting (VAR) (used by Lycoming ECI) are NOT significantly different or BETTER. ESR is just more environmentally friendly or more automated. VAR requires more work due to the "remelt" part, but this assures a high quality forging, free of inclusion of manganese sulfide and calcium aluminate. Careful inspection can find these inclusions if they do form. Cranks are of course are checked carefully (or should be). New, better steel alloy materials? There's nothing new under the sun with steel alloys, at least for crankshafts.

There are engineering reasons to choose a particular process or alloy (and you stick with it). You don't change the process or materials which have worked for a 1/2 century or more. Frankly the problems with Continental's cranks occurred after a change to new methods of smelting and forging. Lycoming's issues where also in part due to changes in the forging process, to NEW and "modern". The vendor also obviously dropped the QC inspection ball as well. They went back to the original process. Some times old things are good. That is what I tell myself as I get older.

Which one looks more stout, the Subie or Lyc? (The Lyc crank is the manly one on the right :D )


WARNING THIS IS A JOKE; DO NOT TAKE IT SERIOUSLY; THE SUBIE CRANK IS ADEQUATELY ENGINEERED FOR ITS APPLICATION. THERE IS NO WEAKNESS WITH THE BOTTOM END OF A SUBARU ENGINE. LYC CRANKS ARE LARGER TO COPE WITH GREATER DISPLACEMENT AND DIRECT PROP LOADS AND AS WELL IS DESIGNED SO IT HAS AN EXCELLENT 50 YEAR RECORD OF RELIABILITY AND SERVICE.
http://img356.imageshack.us/img356/9494/pumpcrank7jq.jpg

Yukon
12-03-2007, 02:35 PM
My crank is not flaccid! It's manly!

gmcjetpilot
12-03-2007, 02:46 PM
My crank is not flaccid! It's manly!The real question begs to be ask than; are we compensating for something by flying with big manly crankshafts. :rolleyes::D

DanH
12-03-2007, 03:13 PM
I'll take the 5-main crank all day long. I hope you know why.

rv6ejguy
12-03-2007, 04:01 PM
Ahh. OK. I misunderstood. I agree that if the exact same prop is used on all engines, then static tests would allow comparison.

I must have missed the reported test results of Lycomings vs alternative engines where they all had the same prop. Have those test results been posted anywhere?

No you didn't miss anything, if I remember correctly the props were not the same in these tests so the results are not really scientific. These tests only showed that hp was in the ballpark with different props. It was no surprise that a 2.5 running a bunch of boost beat the Lycoming numbers and showed the same performance in the side by side flight test between Robert and Dan or that a turbo EZ30 running a bit of boost also bettered the 360s numbers. Thousands of Subarus are driven every day that put out 50-100% more power than a 360 but this is hardly the point in an airplane. It has to last for 2000 hours putting out 200 for takeoff and 150 for cruise.

Speed vs. fuel burn is the biggie and we'll throw in the weight as well. Only when a good side by side is done can relative performances of the packages be demonstrated. It is doubtful that the Subes in this test were close on fuel burn to Dan's IO.

aerial
12-03-2007, 04:07 PM
http://www.flex.com/~lostsurf/honda.jpg

This would be the end of Subaru conversions and Lycomings would be on the endangered list. I hope they build the factory in my hometown.:rolleyes:

Now if they would just get them to put this aircraft quality engine in a generator (to help avoid liablity), we could buy the reasonably priced generator, use the inverter for solar panels on our house, and put the engine in our experimental. The Japanese would win the war.

I have my flame suit on.;)

Oh, yea, and Captain John could arrange a group buy for us all.

rv6ejguy
12-03-2007, 04:26 PM
There is nothing wrong with a "good" Lycoming crank otherwise they'd be blowing up all the time. Likewise the Sube cranks have real engineering, metallurgy and validation behind them and are very well regarded in racing where specific outputs and rpm (ie stress) far exceed anything seen in the aircraft world by a couple orders of magnitude. Obviously they are not wimpy or weak in any way. One crank is designed for a 6L low rpm 4 banger and the other for a 2.2 or 2.5L high rpm 4 banger. The mechanical requirements are vastly different and looks can be deceiving to the untrained eye.

Both cranks were designed they way they were for many reasons by smart people. That being said, any crank can be broken and if you get enough fatigue cycles, any crank will break eventually. Race cranks and rods have a strict hour limit then they are just tossed. Absolutely the safest way to go. Magnafluxing is a valid way to check for existing cracks but does not ensure that the part will last through the next inspection cycle and indeed, they sometimes don't- both in aircraft and automotive engines.


Let's get this thread back on topic. PSRUs.

David-aviator
12-03-2007, 06:45 PM
....Let's get this thread back on topic. PSRUs.

OK. I flew this afternoon and GEN3 did not make unusual noises or come apart or fail in any way. It registered 116F operating temperarture. The unit seems all right and sure launches the RV quickly. :)

Beyond that, I have nothing to add to this thread.

Flying in 38F weather with 14 gallons of fuel on board sure is fun...the thing really wants to go...but it was a short flight, I need to buy some fuel.

captainron
12-03-2007, 06:46 PM
Let's get this thread back on topic. PSRUs.

OK, lets do that. You say PSRU because you don't think a geared engine, meaning an engine block cast with an integral gearcase, is feasible from a cost standpoint, if I read your previous posts correctly. Nevermind the fact that others like Rotax have gone that route. You also say that a bolt-on transmission attatched to a race engine pushing 1500 horsepower works just fine, thank you!
It's not the driveline, it's what's attached to it and what it's asked to do. Take that race engine and transmission, throttle it back to around 200 horsepower and hang a Hartzell on the output shaft and see how long it lasts. If it doesn't break in a few minutes, add a few gyrations while the prop is running at 2700 RPMs.
Matching components involved in producing power and driving a propeller with it is not the province of the backyard tinkerer, in my opinion, much less so selling said components to the public just because normal regulations on what is deemed airworthy don't apply here. Look at Lycoming's propeller application charts for what prop works with a certain engine, but if you use a different mag or change the compression ratio by the smallest amount, then that prop isn't approved anymore but a different one may be. Who's the controlling and approving engineering authority for these cobbled together drive systems? Don't need anyone overseeing this 'cause it's experimental?
Fine! Just be careful where you fly; Your right to kill yourself should not override my right not to have car engines falling on me.

Geico266
12-03-2007, 07:26 PM
Nevermind the fact that others like Rotax have gone that route.

This what I find "confusing". There are Rotax 912S (100HP) flying with over 4,000 hours on the engines and gear boxes in Europe with little loss of cylinder compression or wear in the gear box. (Except for thrust washer tightening / replacement per Rotax every 100 hours.)

Like has been mentioned in several posts...Why can't we build one that lasts? Can't "they" at least look at the Rotax gear box and say; "Make me one like this to fit the Subie." Use engine oil with a gear additive for lubrication and cooling (like Rotax) and have done with it. Look at what works and learn from it. There are transmissions that bolt right to these engines. Build a 2.43 to 1 gear box that bolts on and call it good. Reinventing the wheel can be costly...in many ways.

rv6ejguy
12-03-2007, 09:37 PM
OK, lets do that. You say PSRU because you don't think a geared engine, meaning an engine block cast with an integral gearcase, is feasible from a cost standpoint, if I read your previous posts correctly. Nevermind the fact that others like Rotax have gone that route. You also say that a bolt-on transmission attatched to a race engine pushing 1500 horsepower works just fine, thank you!
It's not the driveline, it's what's attached to it and what it's asked to do. Take that race engine and transmission, throttle it back to around 200 horsepower and hang a Hartzell on the output shaft and see how long it lasts. If it doesn't break in a few minutes, add a few gyrations while the prop is running at 2700 RPMs.
Matching components involved in producing power and driving a propeller with it is not the province of the backyard tinkerer, in my opinion, much less so selling said components to the public just because normal regulations on what is deemed airworthy don't apply here. Look at Lycoming's propeller application charts for what prop works with a certain engine, but if you use a different mag or change the compression ratio by the smallest amount, then that prop isn't approved anymore but a different one may be. Who's the controlling and approving engineering authority for these cobbled together drive systems? Don't need anyone overseeing this 'cause it's experimental?
Fine! Just be careful where you fly; Your right to kill yourself should not override my right not to have car engines falling on me.

Not sure you are reading this right.

First, a car transmission is not designed to have a prop stuck on the tailshaft. My reference was to another post questioning the stiffness of a bolted on gearbox. Obviously not a problem structurally if we can transmit 1500hp with only a few bolts and 2 dowel pins holding it on.

I'm not advocating sticking a car trans on there for a PSRU. I'm saying that there are 70 pound aluminum 5 speed transmissions that happily transmit 600 hp for a very long time, surely we can design a one speed one to do that job on an airplane for 200hp and 50 lbs. Rotax does it with about 15 lbs. for 100 hp. The Rotax 912/914s are clean sheet aviation engine designs hence the integral gearbox- and the aviation type costs unfortunately.

The idea with car engines is to take a proven $2500 engine, bolt on a proven $5000 gearbox and save the other $10K for fuel. Now the commercial packages are not cheaper than a Lycoming so this cost structure only works for DIYers. I guess the rest just want something different and are willing to pay more. I can only guess why that might be.

Egg has just had the EZ30 tested in flight with the MT prop most clients are using by MT engineers. Same sort of test Hartzell does.

Quite right, you can pretty much do whatever you want in experimental aviation and nobody is looking at gearbox design any more than they look at any engine you want to use including non-certified ones. If you are worried about this so much better hang up the RV and get a Cessna, that way EVERYTHING has been certified and TSO'd for you and you can rest easy that nothing will go wrong.

Also quite right that many PSRUs have been offered by "backyard tinkerers" if you will. Some have been disasters or very short lived, others have proven themselves very reliable. Some designed by P engineers have also failed. Lesson here is anything mechanical can fail even if United Technologies spent $4M developing it.

captainron
12-03-2007, 11:26 PM
Not sure you are reading this right.

First, a car transmission is not designed to have a prop stuck on the tailshaft.

The idea with car engines is to take a proven $2500 engine, bolt on a proven $5000 gearbox and save the other $10K for fuel. Now the commercial packages are not cheaper than a Lycoming so this cost structure only works for DIYers. I guess the rest just don't want something different and are willing to pay more. I can only guess why that might be.

If you are worried about this so much better hang up the RV and get a Cessna, that way EVERYTHING has been certified and TSO'd for you and you can rest easy that nothing will go wrong.



Ross, first let me say that you are a real gentleman on this forum, calmly and lucently explaining your positions. I apologize if I have come across as a wise*** in some of my replies.
I know you weren't advocating hanging a propeller on the tailshaft of a car transmission, I was just making the point of no matter how strong the unit was it would not work in this application.

I'm not so worried about this because I'm building a recognized, proven design, and that I get to determine the build quality of the plane. I'll be hanging a Mattituck experimental on it; not certified but I'm satisfied that it is another proven unit. I believe that trying to adapt a car engine, even a great one like the Subaru to aircraft use by using bolt-on drives just isn't strong or reliable enough. Can you advise of the highest time Subaru now flying (or has flown) that has remained in an "as installed" configuration? How many hours with no parts or assemblies replaced? How many have delivered on the dream you outlined where the extra $10,000 has been used for gas?

As to the folks who you don't think want anything different or willing to pay more-peace of mind ranks way up there, I believe. I know the the Lycoming sounds pretty rough compared to the silky-smoothness of a precision built, modern auto engine, but when you are flying over unknown terrain at night, and when the only thing you can see are the lights in your cockpit, that sound is really soothing. The fact that you really don't worry too much about that sound suddenly changing or stopping altogether is why they are perceived as bargains, even at their "aircraft" prices.
Regards, Ron

captainron
12-03-2007, 11:47 PM
I'll take the 5-main crank all day long. I hope you know why.

I'm hoping the answer is NOT that there is room for each finger!

David-aviator
12-04-2007, 08:01 AM
Egg has just had the EZ30 tested in flight with the MT prop most clients are using by MT engineers. Same sort of test Hartzell does.



Correction, Ross. The EGG factory had nothing to do with the MT vibration survey and the H6 engine. I set it up with MT Germany and Andy Parish flew his airplane to Deland for the test. It had to be done to get the overhaul time reset to 1500 hours from 200 hours.

The survey was not done at the EGG factory because Jan never had the H6/MT combination on his airplane. They were focused on the Quinti/Sensenich system after the batch of MT's were sold. The prop was surveyed with the 2.5 engine and we knew it was OK with the H6 as it is smoother, but the overhaul time was stuck at 200 hours without the formal survey. That survey was done with the GEN3 PSRU and came in quite well, but the official word has not yet been published by MT as far as I know.

rv6ejguy
12-04-2007, 10:24 AM
Correction, Ross. The EGG factory had nothing to do with the MT vibration survey and the H6 engine. I set it up with MT Germany and Andy Parish flew his airplane to Deland for the test. It had to be done to get the overhaul time reset to 1500 hours from 200 hours.

The survey was not done at the EGG factory because Jan never had the H6/MT combination on his airplane. They were focused on the Quinti/Sensenich system after the batch of MT's were sold. The prop was surveyed with the 2.5 engine and we knew it was OK with the H6 as it is smoother, but the overhaul time was stuck at 200 hours without the formal survey. That survey was done with the GEN3 PSRU and came in quite well, but the official word has not yet been published by MT as far as I know.


Thanks for the clarification David. I'm just glad the study has been done.

I'm a bit of a chicken but I don't fly at night cross country or over mountains single engine- any single engine. It's interesting that many people find what I do risky but they are ok flying over the rocks at night because they have a certified engine. We had 3 more people killed last month over the rocks- rod failure on a certified engine. You have no chance at night in this terrain and very little even over less demanding, unlit terrain at night with an engine stoppage.

I have flat prairie and daylight on my side. Who is taking the bigger risk?

Something some people may not have thought of. We've had 6 people killed in the last year here with certified engine stoppages and a few non-fatal forced landings. It can happen to anyone. Fly safe my friends.

Rotary10-RV
12-04-2007, 11:09 AM
OK, lets do that. You say PSRU because you don't think a geared engine, meaning an engine block cast with an integral gearcase, is feasible from a cost standpoint, if I read your previous posts correctly. Nevermind the fact that others like Rotax have gone that route. You also say that a bolt-on transmission attatched to a race engine pushing 1500 horsepower works just fine, thank you!
It's not the driveline, it's what's attached to it and what it's asked to do. Take that race engine and transmission, throttle it back to around 200 horsepower and hang a Hartzell on the output shaft and see how long it lasts. If it doesn't break in a few minutes, add a few gyrations while the prop is running at 2700 RPMs.
Matching components involved in producing power and driving a propeller with it is not the province of the backyard tinkerer, in my opinion, much less so selling said components to the public just because normal regulations on what is deemed airworthy don't apply here. Look at Lycoming's propeller application charts for what prop works with a certain engine, but if you use a different mag or change the compression ratio by the smallest amount, then that prop isn't approved anymore but a different one may be. Who's the controlling and approving engineering authority for these cobbled together drive systems? Don't need anyone overseeing this 'cause it's experimental?
Fine! Just be careful where you fly; Your right to kill yourself should not override my right not to have car engines falling on me.

Ron, I'm not being snide here, but I'm asking, are you a ME? PEME? You are simply incorrect about non-unit gearboxes being strong enough to handle the load. Virtually every Indy car, and F1 car uses the engine as a stressed member of the the chassis. The gearbox has the entire rear suspension load and the load of the wing on it for 500 miles at 200 mph. Please don't think those loads are less than a prop would be. These are cars yes but in reality they are inverted aircraft being forced to the pavement by their flying surfaces. I cannot remember the last time an indy car split in half by having the gearbox break off. A non-unit bolted system will work fine if properly engineered. I am certainly concerned about failure. Any one SELLING a unit to the public should do stress testing, and torsional vibration testing as well. But everybody here should show some perspective, The origin of this thread was about a gearbox failure. The pilot landed safely and the prop DIDN'T fall off. Problems, sure. An epidemic, hardly. Ross always offers a reasoned logical comment, this forum illogically offers scorn. GMC your posts of the two cranks is an equally illogical jibe. ANY good engineer would tell you that the Subaru crank is BETTER and designed with more margin than the Lycoming. The Lyc crank is perfectly fine and has years of refinement behind it, but if you look at the two units rationally you have to say the Subaru is a superior CRANKSHAFT. If you want to bolt a prop directly to the end, no. But due to the higher RPM design you wouldn't do so and you know it George. The comparison was offered in jest, I know. The sad part is that there are tons of people that view these forums that DON'T. Most participants are here to try to learn something or be entertained. I've restricted my posting because I can tell everyone the absolute truth and recieve nothing but ridicule. Ross handles it well, I do not. This section of the forum doesn't deserve as decent a guy as Ross. I limit my postings to times when for the sake of accuracy I fear the non-engineering types will be tainted by conjecture. GMC for your anti-rotary bias, (and don't think you don't have one because you had an RX-7 in '82), you should look on the Aircraft Rotary Engine Site mentioned by the rotary fan. There is a DYNO test of the renesis with p-port mods producing 265 HP. at 7500. The rotary will run at 6000 RPM until you shut it off. Loads at 7500 only marginally more. Remember that the much vaunted turbines run at continously high RPMs 10K and more so a good PSRU can be designed for those RPM's as well. The entire forum is ill-served if we speak opinion and don't lable it as just that, opinion. I also don't want to treat any alternate-engine post with footnotes. I have stopped because posting here is no longer any FUN.
Bill Jepson

Yukon
12-04-2007, 01:16 PM
Bill,
GMC's crankshaft post was a lame attempt at humor! Ha ha ha! Subaru crank is a great CAR crank, and I am sure he meant no disrespect to Subaru automobile owners.

N62XS
12-04-2007, 01:52 PM
And I'm betting that there is lots of G-loading on the propeller and propeller shaft in your line of work. I think that the Subaru is a good powerplant with proven strong internals, but I think that to be viable in this application, someone is going to have to figure out how to cast an engine block with an integral PSRU housing to really make this work. Such a re-design would have the added benefit of being even more compact and lightweight. There are a lot of aftermarket foundries now that are casting various car blocks and cylinder heads. The pricing is apparently not so high as to keep folks from buying them for their cars, so I think it is within reason to try to get something like this for your planes. This might be beyond Egg's or other would-be Subaru supplier's means, but I think it's high-time to finally do it right, or not at all! Falling airplanes are just not acceptable due to inadequate engineering in today's computer analyzed, and cad-cam world! I think the people who really want Subarus for their planes should demand this and not settle for less. You vote with your pocketbook!

AMEN RON!!!!! Car engines are engineered for CARS! Did anyone think about the safety of the people on ground that are possible victims of falling parts from one of these contraptions?

BTW: I hope someone's lawyer is learning how to spell Eggenfellner.

BTW2: THATS NOT GEORGE'S DAWG, THATS GEORGE. Bad hair day?

captainron
12-04-2007, 02:17 PM
Car engines are engineered for CARS! Did anyone think about the safety of the people on ground that are possible victims of falling parts from one of these contraptions?

BTW: I hope someone's lawyer is learning how to spell Eggenfellner.

BTW2: THATS NOT GEORGE'S DAWG, THATS GEORGE. Bad hair day?

Eeeasy there, big fellow! I'm not a big fan of lawyering-up every time I've not had things work out as I expected them to. I think it's kinda your own dang fault if you pass on the tried, tested, and recommended powerplant in favor of Pie-in-the-Sky Engines, Inc.,L.L.C.
Lawyers haven't had much success in making aviation better for us, no matter how much they've been "involved".

DanH
12-04-2007, 03:10 PM
<<I've restricted my posting because I can tell everyone the absolute truth and recieve nothing but ridicule......The entire forum is ill-served if we speak opinion and don't lable it as just that, opinion......I have stopped because posting here is no longer any FUN. >>

I've repeated Bill's comments here because I hope everyone will think about them. Far too many professional engineers have abandoned the forums....and we all lose a great deal because of it.

Bill, I really appreciate it when you post. I'm not a PE, but I'm absolutely convinced airplanes fly based on science and engineering, not opinion. If I write something and you want to polish the pins, please jump in or send me a PM.

Mike S
12-04-2007, 03:21 PM
<<I've restricted my posting because I can tell everyone the absolute truth and recieve nothing but ridicule......The entire forum is ill-served if we speak opinion and don't lable it as just that, opinion......I have stopped because posting here is no longer any FUN. >>

Far too many professional engineers have abandoned the forums....and we all lose a great deal because of it.

Boy aint that the truth.

Bickering doesnt help any of us.

Thanks for the post, Dan.

Ted Johns
12-04-2007, 03:27 PM
... but I'm absolutely convinced airplanes fly based on science and engineering, not opinion.

Amen!!!

Back to the subject of PSRU's, I haven't been able to find any failure reports on Tracy Crook's RD-1B or RD-1C gearboxes. Looks like the engineering may be good in this case. Anyone have any data otherwise?

gmcjetpilot
12-04-2007, 04:08 PM
GMC your posts of the two cranks is an equally illogical jibe. ANY good engineer would tell you that the Subaru crank is BETTER and designed with more margin than the Lycoming. GMC for your anti-rotary bias, (and don't think you don't have one because you had an RX-7 in '82), you should look on the Aircraft Rotary Engine Site mentioned by the rotary fan. Bill JepsonBill first it was a joke lighten up. The Subie crank was ENGINEERED BY ENGINEERS. I put a big placard on the picture that shoud do it.

There is no problem with the Subie crank, OK. Your comments are about personality not facts. You say the Subie crank has "More Margin" but you don't know that; it's probably true, because the crank in a little car engine that has LESS loads. The Lyc is what over 5 liters and has a prop hanging off it. A Subaru is 1.8 liters and connected to a trans through a flex plate? You would expect the crank would be lighter in a small displacement car engine. No offense intended, but I have to laugh at how Subie lovers wax poetic about their CRANK and 5 bearing supports, albeit 5 small journals but adequate. I never said the bottom end of a Subie was weak EVER. I love Subies and drove a '82 4-door GL Subie for 11 years and I'm sad I sold it with 130 K on it. I loved that 1.8L push rod Subie engine (not OHC), 5 speed manual and front wheel drive.

As far as anti-rotary, you no not what you speak of. I have convinced people to use rotary engines for their plane and there are web sites to prove it. If I was going "alternative" it would be a rotary, a turbo rotary. :eek: I know a turbocharged rotary at altitude can do nicely on speed, fuel econ and noise is moot a +12,000 feet. That's not the kind of flying I do, so the normal aspirated Lyc is better for me. Acro, Formation, local X-C, airport hopping, with a once or twice big X-C.

I owned a RX2 and RX3, OK. My friend today owns a RX8 (with the RENESIS engine) and she has to put oil in it between changes (expensive synthetic oil only) and it gets lousy milage, fact. But she gets a big smile on her face (wait for it) when she punches the throttle, winding the Wankel out and it comes on the pipes (like my 2-stroke dirt bike, weeeee). No put down, just facts. You can't pretend there's no down side to the Wankel. With gas prices I suspect the Wankel days are numbered even for Mazda. Racing of all kinds, the rotary is great. However you can't debate me on my personality because I have none, but FACTS you should stick to. Where am I wrong?

PS I read the Aircraft Rotary Engine Site, top to bottom to bottom and love it. I have talked to Tracy at length and read his book. I know all the good, bad and the ugly of wankels. Now if you want to put down Lycs OK, but it really doesn't matter. When the prop meets the air, all the talk stops. Again the Power Sport RV-8's did very well and performed flawlessly, matching the 180HP lyc. Again to be the negative jerk I'm, I have to say they fuel flow was terrible, noise brought out the airport manager, plus they weighed more. Other than that they are very cool engines.

rv6ejguy
12-04-2007, 04:16 PM
Amen!!!

Back to the subject of PSRU's, I haven't been able to find any failure reports on Tracy Crook's RD-1B or RD-1C gearboxes. Looks like the engineering may be good in this case. Anyone have any data otherwise?

Tracy had some bearing issues on his test drive long ago but came up with a fix and warned the few customers who had his drives before anything bad happened. I have not heard of any other problems with his current drives either.

Tracy is a really smart guy and he has put a lot of thought and flight testing into his drives including unique ways of solving TV problems. Note his drives are based on Ford automotive gear sets and are very reasonably priced. His new 6 pinion design should be able to handle quite a bit more power.

Ted Johns
12-04-2007, 04:33 PM
Tracy had some bearing issues on his test drive long ago but came up with a fix and warned the few customers who had his drives before anything bad happened. I have not heard of any other problems with his current drives either.

Tracy is a really smart guy and he has put a lot of thought and flight testing into his drives including unique ways of solving TV problems. Note his drives are based on Ford automotive gear sets and are very reasonably priced. His new 6 pinion design should be able to handle quite a bit more power.

Yeah, I think the bearing issues were with the RD-1A. From what I read, he took good care of the people with the older drives.

Ted Johns
12-04-2007, 04:47 PM
You say the Subie crank has "More Margin" but you don't know that; it's probably true, because the crank in in a little car engine that has LESS loads. The Lyc is what over 5 liters and has a prop hanging off it. A Subaru is 1.8 liters and connected to a trans through a flex plate?

Fact #1) Less loads? A car engine crankshaft needs a higher torsional load margin because you can "pop" the clutch on the engine. Kind of hard to do that on a Lycoming, even with a CS prop. The prop hanging off the crankshaft results in side and thrust loading of the bearings, something the car engine crank is (rightly) not designed for.

Fact #2) 1.8 Liters? GMC, you just guessing here? Is guessing useful to anyone in this business? :rolleyes:

Ted Johns
12-04-2007, 04:51 PM
Again the Power Sport RV-8's did very well and performed flawlessly, matching the 180HP lyc.

Again the Power Sport RV-8's did very well and performed flawlessly, beating the 180HP lyc.

There, fixed that for you. No charge.

The faster of the two Power Sport RV-8's beat the 200HP lyc. :rolleyes:

gmcjetpilot
12-04-2007, 05:30 PM
Yeah, I think the bearing issues were with the RD-1A. From what I read, he took good care of the people with the older drives.The whole story was Tracy was flying his own drive and putting on more hours than anyone. He did periodic inspections and found the issue. I recall something was coming lose. Service history or time in service is important. Tracy flies what he sells and puts more hours on his drives than his customers, so he's ahead of the curve. That is all goodness.

Again the Power Sport RV-8's did very well and performed flawlessly, beating the 180HP lyc. There, fixed that for you. No charge. The faster of the two Power Sport RV-8's beat the 200HP lyc. :rolleyes:You got me. Yea the 200HP was a dog and 9.5 mph slower than the 180HP (what?). Don't know why, probably too many demo flights and a tired engine? Here's the article, read and weep. The power sport did go faster by 1 or 4 mph. I was positive about the performance. You are right 4 mph faster and it only cost 4 gal/hr more fuel to do that. That's 1 gal for every MPH. If Van's planes had a SJ cowl they would have gone 5-8 mph faster. Still no lie I really liked the Power Sport and I'm impressed, but they also cost $40,000 and a Lyc 360 cost almost half that, plus it does not need an $9,000 electric MT prop.

http://img282.imageshack.us/img282/4323/rotary14wv.th.jpg (http://img282.imageshack.us/my.php?image=rotary14wv.jpg) http://img325.imageshack.us/img325/3117/rotary22ms.th.jpg (http://img325.imageshack.us/my.php?image=rotary22ms.jpg)

Fact #1) Less loads? A car engine crankshaft needs a higher torsional load margin because you can "pop" the clutch on the engine. Kind of hard to do that on a Lycoming, even with a CS prop. The prop hanging off the crankshaft results in side and thrust loading of the bearings, something the car engine crank is (rightly) not designed for.

Fact #2) 1.8 Liters? GMC, you just guessing here? Is guessing useful to anyone in this business? :rolleyes:Ted I like your style, you are keeping me honest. Does popping the clutch really cause more torsion? The issue really is not ultimate strength but fatigue, twisting harmonics going on several times a revolution (many thousands of load reversals per minute). That's the worry, harmonics and fatigue. It's just a matter of designing for it. That's why some Lyc cranks have counter weights (harmonic dampers), some don't. Its all by design as needed.

1.8 liters? OK, you got me, I was thinking of my old Subie, which was 1.8L. The Subaru EJ (4 cyl) engines go from 1.5L to 2.5L, I googled/wikipedia'ed (http://en.wikipedia.org/wiki/Subaru_EJ_engine) it. Now I'm an expert. :) None of the Subie 4-bangers are 360 cu-in or 5.899 LITERS! Even Lyc 320 has over twice the displacement of the biggest Subie 4-cyl. People wounder why Lycs make more power at low RPM, they have over twice the displacement! That's why the Lycoming does not work hard to make its rated power. The Subie 3.0 Liter 6cyl Boxer is just over 1/2 the displacement of a Lyc 360 (I know they went to 3.6L in '07). Again mine is still bigger than yours. :rolleyes:

"There ain't no replacement for displacement" (unknown wise man)

Even more amazing is a MAZDA 13B is around 1.3 liters! The later RENESIS is considered a 2.6L engine. (Hard to calculate apples and apples displacement to a reciprocating engine.)

SvingenB
12-04-2007, 06:15 PM
Interesting, but looong read :) But I'm not sure I get the real issue. Rotax 912 is the most numerous aircraft engine in the world, 200k units or something sold up till now. It has been using a gear unit all from the start. It is not fool proof by any means, if you mount a too heavy or slightly unbalanced propeller the gear or crank will break sooner or later. And if you descend with a "wrong" throttle setting above idle but where there is minimal or no load/torque on the propeller axle, you can also ruin the gear unit very fast. I don't think a constant speed propeller with varying aerodynamic damping will make things better.

I don't know (I could be totally lost here), but wouldn't a planetary gear fix all problems?

captainron
12-04-2007, 08:16 PM
I don't know (I could be totally lost here), but wouldn't a planetary gear fix all problems?

I think it would be a great improvement if done properly. Much more gear contact area, shafts aligned in the same plane- which should be good for the flat Subaru motor, strong, bell-housing type enclosure. Lots of advantages in a planetary system.

DanH
12-04-2007, 09:22 PM
The subject is an Egg gearbox failure. Does anyone have a dimensioned drawing of the actual components? Same for the flywheel assembly, with whatever sort of "damper" it might have? Third, mass moment of inertia for the propeller?

Without these things at minimum, (1) serious failure analysis is impossible, and (2) neither fans nor critics know the truth.

lucky333
12-04-2007, 10:45 PM
Without these things at minimum, (1) serious failure analysis is impossible, and (2) neither fans nor critics know the truth.

Bingo!
Dan, you rock.

John

szicree
12-05-2007, 12:35 AM
I've looked over Eggenfellner's website pretty thoroughly and one thing I can't find is where the actual engines come from. I mean, are they brand-new, in-the-crate motors straight from Subaru? Rebuilt from cars? Used?! :eek:

Also, the site says that there have been 500 sold. Dang, that's a whole lotta money!

rodrv6
12-05-2007, 02:23 AM
The engines have been brand new from Subaru for the last several years. Before that, he was using some from low mileage cars that had unfortunate accidents.

rtry9a
12-05-2007, 09:19 AM
To answer the q's about Tracy Crooks redrive- no problems reported. The issue mentioned earlier was from Tracy's original Ross drive. It developed noise and Tracy measured backlash at the Prop, later found to be caused movement related to the lack of a thrust bearing in the Ross design- it caused wear between the planet gear and housing flutes.

Tracy added a thrust bearing and fixed that problem in his design. He epoxied the planet race into the housing to further reduce play, now uses a drilled pin arrangement.

I believe Tracy once also marketed his redrives for the Subaru, but no longer mentions that fact on his website (probably because the demand from Mazda users has tested supply)

FWIW, the original drive, RD-1A used a 4 planet carrier- was designed to replace the Ross redrive. It was designed for 200hp apps. A needle bearing was upgraded to a ball bearing to increase TBO, then eventually replaced with a roller bearing. That redrive is no longer made; it was replaced with the RD-1B.

The RD-1B is a 2.176:1 reverse rotation drive that uses the 6-planet carrier from Fords' HD truck tranny.

RD-1C is a 2.85:1 normal rotation drive that also uses the 6-planet carrier, rated to 300hp. This redrive is recommended for high speed (higher power) engines (Renesis).

David-aviator
12-05-2007, 10:21 AM
The subject is an Egg gearbox failure. Does anyone have a dimensioned drawing of the actual components? Same for the flywheel assembly, with whatever sort of "damper" it might have? Third, mass moment of inertia for the propeller?

Without these things at minimum, (1) serious failure analysis is impossible, and (2) neither fans nor critics know the truth.

First off, I am no engineer, but I can make these observations about the EGG design.

Starting with the engine with the PSRU removed - the original fly wheel has been replaced with a spring loaded devise that weighs about 20 pounds. It is a fly wheel but not connected directed to the crank shaft but rather the load is carried by a series of springs in compression. If you move the prop, you can feel the springs compressing before the crankshaft moves. Its purpose is to dampen the load transferred forward to the PSRU.

The engine is mounted to a half inch aluminum plate, aproximately 30"x18" in size. The PSRU is bolted to the forward side of the plate and connected to the engine with a splined shaft about 8 inches long which slides into a splined plate bolted to the forward side of the fly wheel devise. Fore and aft movement is controlled by 2 large snap rings. Alignment is controlled by plugs in the aluminum plate and in the engine similar to the arrangment with auto transmissions except the plate is aligned to the engine with one set of plugs and the PSRU is aligned to the plate with another. An alignment tool was created to check the total alignment before the PRSU is installed. The aluminum plate is attached to the engine mount structure with bolts through bushings.

The torsion load of the prop is absorbed by the PSRU and the aluminum plate but not the engine crankshaft. The PSRU is a straight through gear reduction (planetary?) resulting in the prop being aligned with the crank shaft and turning in the same direction.

The PSRU failures to date IMHO have been caused by misalignment with the engine resulting in side loads on the aft bearing or torsion loads beyond the design limit of the bearings within the unit. Thats why GEN1 has been quite successful with the original 2.5 engine but not so with later, more powerful engines. GEN2 is simply an upgraded GEN1 with different gears and bearings. It too did not meet the load requirements or was misaligned in the process of field installation. The alignment tool may have come too late as some were installed without it. The tool is necessary to install GEN3.

As previously stated, GEN3 is a totally new beast. The gears and bearings are stronger, it has a different ratio (2.02:1 vrs 1.87:1) and has a machined case instead of cast. It is considerably more expensive to manufacture and to date has been available to upgrading customers at cost or less. The EGG factory is trying to be fair and not go broke in the process.

rv6ejguy
12-05-2007, 10:50 AM
Actually, no. Tracy's first few production drives had a bearing problem which he uncovered and corrected before any customers had accumulated any flight time. This is from Tracy's extensive article in Contact #87, page 23.

I'd consider his boxes to be among the most successful to date.
He has many units flying now successfully and has captured a large majority of the Wankel market. Tracy is the man here.:)

I've seen the Egg drives being assembled. The gears/shafts are off the shelf components from one of the big OEMs and sizes are in the 5 ton truck range. The gears will never break in this application IMO. There have already been at least one bearing revision on the Gen 3. The case looks well designed and machined and very strong. It is a layshaft setup using helical gears. There are some welded assemblies inside which should be fine if proper stress relief and heat treatment is done afterwards. (We'd do a welded mod to the W50 boxes for racing to retain 5th gear at high hp. This worked fine for us).

I am not aware of any rubber TV damper being used but a very heavy dual mass flywheel is always fitted. There seems to be a TV period at about 250 rpm and perhaps another more minor one at around 900 rpm by seat of the pants feel. Engine idle is generally kept just above 1200 where it is very, very smooth.

It is interesting to me that the 3 very different engine/ drive/ prop combos I've been associated with all have a TV period right around 600-950 rpm. Certainly my Sube and the Rotax 912 are a blur down there. Coincidence? Any comment on that Dan?

rtry9a
12-05-2007, 01:20 PM
Ross-
You are probably correct regarding bearing failure- Tracy's original Ross drive did not fail catastrophically, but it was a bad design that drove his desire for something better.

Tracy's "bearing problem" that you refer to involved the ball bearing upgrade I mentioned in my 4th paragraph, which Tracy implemented to improve the 300-hr TBO inherent with the original needle bearing (from Tracy's historical evolution articles in his website). That failed bearing turned out to be a poor quality, cheap Chinese bearing- he fixed that problem with a better quality ball bearing, but eventually upgraded to the German roller bearing now used which has a TBO>2500 hrs. Like you said, no defective units were ever released to the public.

Tracy also mentioned an early bolt failure at the attachment between his drive and flywheel on one early RD-1C. He also fixed that problem with a minor alteration and recall at his own expense (unlike others in the certified aircraft world who will remain nameless). Tracy is definitely a class act.

I agree with you that the RWS RD-1B and 1C are the best affordable redrives available at this time. It is hard to beat a good quality planetary gearset for hard-use durability, compact size, and light weight.

The 2.85 ratio works great within the rotaries' 5000-8000 rpm peak torque/power band (1700-2800 prop rpm). The 2.18 ratio has been effective for fixed pitch economy in cruise, but it has also been reported that it is too tall to deliver peak rpm/power.

As for Subaru applications, it is questionable whether the two available planetary gear ratios with the Ford 4/6-gear carrier present an acceptable fit to deliver peak hp to the propeller. Not knowing the Subi's torque/hp graph, Id have to guess a desire to keep the engine in the 3500-5500 rpm range, which implies approx 2:1 gearing given RV props. Didn't Jan try the 2.178 planetary setup early on? It proved to be less than ideal in delivering peak hp to a fixed prop and finding a better ratio has been nothing but grief to users since. The only solutions I anticipate would involve the use of a lightweight adjustable prop (like the IVO) to work within the heavier-than-Lyc engine weight balance envelope, or possibly a simple 2-speed transmission.

It looks to me like an engine and redrive mismatch problem is in play here: the Subi engines cannot reliably rev high enough for the 2.85 ratio, and the engines cannot produce enough rpm (to deliver peak horsepower) with the 2.18 ratio.

rv6ejguy
12-05-2007, 01:53 PM
I Think Tracy has been so successful in the field because he is smart, tests a lot, gives the straight goods and makes things right if something isn't. All things that any business should be doing.

Ratios of 1.9 to about 2.2 are suitable for most Subaru applications allowing these engines to reach close to power peak rpm at 2700 prop rpm. You are right, The EZ30s would perform better with about a 2.4 ratio due to their higher power peak rpm. Prop blade angle may not be well optimized at lower rpm cruise settings unfortunately and frictional losses at high engine rpm conspire to raise SFCs. It is a careful balancing act.

Forced induction can change torque curves considerably so in all cases, drive ratios should be selected according to each engine's torque and power curves. This was one reason I chose the EG33 over the more modern EZ30. The power and torque peak rpms are only 1000 rpm apart and power peak rpm is 1100 rpm lower as well.

With turbos, there is far less worry about whether you can turn the prop at low engine revs and make any power- usually you can and the engine is far more efficient at low revs, high manifold pressure. Unfortunately then you have the added weight and complexity and cost of the turbo system.

Jan has never used planetary gear sets to my knowledge.

gmcjetpilot
12-05-2007, 02:33 PM
I Think Tracy has been so successful in the field because he is smart, tests a lot, gives the straight goods and makes things right if something isn't. All things that any business should be doing.

With turbos, there is far less worry about whether you can turn the prop at low engine revs and make any power- usually you can and the engine is far more efficient at low revs, high manifold pressure. Unfortunately then you have the added weight and complexity and cost of the turbo system.I agree if going Alternative I would go Rotary and RWS stuff, not as a vote against a Subaru, just that the Rotary is a true alternative engine, it's nothing like a Lyc. A big plus is a true roll-your own deal with RWS parts, so you can make a FWF package for less than a new Lycoming. Rebuild a 13B core yourself, you can come in cheaper than a new Lyc, no doubt by many thousands. The FWF Eggs and Power Sports kits are more expensive than a Lyc. The negatives I mentioned before like higher fuel burn fuel, noise and mixing fuel/gas come with the package, however there are ways to mitigate these, TURBO CHARGER, which is particularly effective on Wankel's.

With a rotary, a turbo is almost a MUST in my opinion. The Rotary wastes or expends some wonderfully high temp, high velocity exhaust gases, which is wasted energy (thus fuel and noise issues). This is why it's perfect for turbocharging, to recover all that energy. It also tones down the exhaust bark, while increasing efficiency, particularly at altitude. When you get a rotary up high into the teens, it comes into its own and MPG is actually good. Also a rotary can be lighter than a Subie package but still not as light as a Lyc.

My flying preference does not included a lot of high altitude long rang cruising, sucking 02. It's just not that fun for me or something I do much of anymore. If I go X-C, 8k to 12k feet or lower is plenty high. Turbo's in general are a pain, at least on Lycs. Lyc powered RV's don't need them because the engines are powerful enough as an ATMO engine. Also I don't want to fly at rarefied altitudes sucking on an Oh-2 mask. There are also Vne issues. Still a turboed Wankel and flying high is a cool deal. To be fair Jets suck gas like crazy down low and only come into their own above FL250.

rtry9a
12-05-2007, 06:23 PM
This is probably not the best place to discuss this, hijacking a Subi thread, but since you started it...

"When you get a rotary up high into the teens, it comes into its own and MPG is actually good. Also a rotary can be lighter than a Subie package but still not as light as a Lyc."

Simply not true, let us see your biased data George!;) Let's put some relevant facts on the table and compare. Not dissing btw, I believe the Lyc is a very worth opponent here, the standard for comparisons.

A rotary does run very well with a turbo, but turbos are certainly is NOT required to meet or outperform a 360 class Lyc power to weight with the correct intake. The 13B class rotary fwf is very close to the o-320/360 in weight with more power potential, closer to O-540 output, assumed range 200-250hp.

We've already mentioned the recent p-port Renesis, naturally aspirated test using 87-octane gas produced 265hp @ 7200rpm ON A DYNOMETER. Ive never seen Lyc output measured on a dyno..., guessing posted numbers are adhoc or estimated. P-porting is not particularly difficult- drill a 2" hole and glue or weld in a pipe; it greatly simplifies the intake system, with only 2 intake runners vs 6.

The basic RENESIS engine weighs about 180 lbs, a little less than older 13B engines- I can lift my engine off the ground (w/o mount, exhaust manifold, cooling system, or redrive). The Lyc 360 weighs close to 300 lbs., the IO360 a bit more. Add to that the weight for mount, exhaust system, ducting, etc. If you have more exact numbers, Id like to see and compare them.

I can show you similar carburetted dynographs of the OEM Renesis and p-ported 13B's = 200-240hp depending on engine configuration. FWIW, you can add an IVO composite magnum adjustable 3 blade prop and add only another 27 lbs complete (and 1/3 the cost), a bit lighter than the Lyc c/s choices I believe.

Kevin Horton
12-05-2007, 07:37 PM
Ive never seen Lyc output measured on a dyno..., guessing posted numbers are adhoc or estimated.
Barrett Precision Engines has ran a lot of unmodified, and modified Lycomings on their dynamometer. Rhonda Barrett-Bewley reports (http://www.vansairforce.com/community/showpost.php?p=145356&postcount=23) that O-360s typically produce 180 hp, but the nominally 200 hp IO-360-A series engines typically only produce 196 hp.

DanH
12-05-2007, 08:41 PM
<<It is interesting to me that the 3 very different engine/ drive/ prop combos I've been associated with all have a TV period right around 600-950 rpm. Certainly my Sube and the Rotax 912 are a blur down there. Coincidence? Any comment on that Dan?>>

Your 4-cyl w/ Marcotte hammers hard at an RPM a little further up the scale...a peak at about 1350, which you push through as quickly as possible, yes? The 912 rattles the ramp and dog system somewhere not far below 2000 if I remember correctly from the last time I did a carb sync. Neither has a soft element suitable for lowering the natural frequency of the system. Yeah, I know, your Marcotte has urethane bushings in the flywheel. Trust me, they are near useless for the above (full disclosure; my opinion, but based on measured spring rates plugged into TV prediction software runs).

David described soft springs in the flywheel of the Egg system. Springs are a reasonable way to lower system frequencies, if they allow enough angular displacement without coil bind. At this time we do not know the Egg's F1 and F2 frequencies, but if your observation is correct, it matches what I would expect for a system with a very soft torsional soft element.

BTW David, springs are not dampers. I've explained the difference before, but I'll try another tack. It may seem hard to believe, but any shaft is also a torsional spring, as all materials are elastic. If the shaft is short and has a large diameter, the spring rate will be very high. If it is long and has a small diameter, the torsional spring rate will be low. The springs in your Egg system have exactly the same effect as a very long, very thin shaft. Now, would you consider a shaft to be a damper?

Ross, back to your question. Concerning outselves only with the system's F1 frequency, the prop drive systems I've observed seem to be between 20 and 50 hertz. The difference is due to design variations, specifically variations in the torsional stiffness of connecting members, and variations in inertias. You'll recall the Powersport design example also, which was to shoot for a very stiff system and thus an F1 above the operating range. The three subjects of your experience merely happen to be at the soft end of the scale.

Let's assume we have a system (you do) with an F1 (fundemental natural frequency) of 45hz. If we bolt it to a 4-cyl 4-stroke, it will resonate at 1350 RPM because that is where natural frequency is matched by the major exciting frequency, firing events. If we bolt it to a 6-cyl 4-stroke (assume the same crank-flywheel stiffness and inertia for this example), it will resonate at 900 RPM. The equation for exciting frequency due to firing events with a 4-stroke is (RPM x # of cyls)/120 = hertz, or turn it around if you know the hertz, ie, (hertz x 120)/ # of cyls = RPM. Point is, just bolting the same drive on a different engine configuration will give you a new resonant RPM.

rv6ejguy
12-05-2007, 09:12 PM
I ran a 912 on a test stand a lot last year and it is very unhappy from about 600 (min idle) to almost 1200 rpm. The frame was very flexible so you could see (and hear) the effects of TV quite graphically. Pretty darn scary actually. Super smooth at 1400.

On my EJ22 setup it is pretty bad from 600 to 950, ok at 1000-1050 (idle) and really bad from 1100 to about 1600 so the 1350 figure is right in the middle of that second point all right.

On the EG33, I'm now installing an 8 pound steel ring on the outer part of the aluminum flywheel to see what effect it will have with and without.

Marcotte has changed the bushing style in my later drive to a stiffer, smaller diameter. Both are neoprene.

It will be interesting to see how bad the EG33 shakes at 900 rpm and how wide that bad range is.

David, do you notice a vibration in your EZ30 around 900 or do you ever idle it that low?

I'm guessing that that death shake some Lycomings do as they are shut down just before the prop stops is TV as well?

gmcjetpilot
12-05-2007, 10:05 PM
"When you get a rotary up high into the teens, it comes into its own and MPG is actually good. Also a rotary can be lighter than a Subie package but still not as light as a Lyc." The 13B class rotary fwf is very close to the o-320/360 in weight with more power potential, closer to O-540 output, assumed range 200-250hp.Of all the alternates the rotary does the best weight wise, but show me some W&B's. I've never seen "light" but some respeciable empty weights. If you push a 13B to 250hp, I think it will die soon and not be advised for a daily flyer, going on what I recall Tracy told me, conservative wise. It physically can make HP for sure, just how long is the question. Radical racing Wankel's do blow up spectacularly.
We've already mentioned the recent p-port Renesis, naturally aspirated test using 87-octane gas produced 265hp @ 7200rpm ON A DYNOMETER. Ive never seen Lyc output measured on a dyno..., guessing posted numbers are adhoc or estimated.Displacement is twice as much as a 13B right, so that is expected. I am guessing they are not laying around cheap? Nope Lyc and Superior Dyno there engines. What Keven said, the 180's are getting about 185. Don't know about the IO360angle valve being/under or over nominally on the Dyno. From the fact the 200HP was 9.5 mph shower than the 180HP Factory prototype in the PowerSport fly off baffles me. I still can't figure out what that was about. I can only assume the 180HP was making 185HP and the 200HP was tired.
The basic RENESIS engine weighs about 180 lbs, a little less than older 13B engines- I can lift my engine off the ground (w/o mount, exhaust manifold, cooling system, or redrive). The Lyc 360 weighs close to 300 lbs., the IO360 a bit more. Add to that the weight for mount, exhaust system, ducting, etc. If you have more exact numbers, Id like to see and compare them.I would love to see that. Are RENESIS engines laying around cheap? I think that single lower scoop like Sam James cowl is probably as good as it gets, verses trying to make a stock Vans cowl with to cheek inlets work. Just saw DOG Fights on the History channel with the P51. That lower belly scoop seems to be the ticket? (Like what Ross is doing on the RV10)
I can show you similar carburetted dynographs of the OEM Renesis and p-ported 13B's = 200-240hp depending on engine configuration. FWIW, you can add an IVO composite magnum adjustable 3 blade prop and add only another 27 lbs complete (and 1/3 the cost), a bit lighter than the Lyc c/s choices I believe.Lighter weight, cool, whats the empty weight? I watch finished RV weights and find water cooled engines are at least 50-100lbs more. Clearly some weight savings can be had with prop and being smart about outfitting the plane. The belted power guys have a reasonably light V6 RV demo plane (not as light as a Lyc plane), but its bare bone, which is fine. That is what you have to do, keep it light. Add weight FWF you better look to save it aft of the FW. Save weight you must. Cost wise, OK I'll quit arguing but 1/3rd? I have seen the math and you're looking at mid-high teens for a RWS Rotary setup. With a NEW Lyc & prop mid-high 20k something. I'm sceptical, may be 33% less but not 66% less. It all depends on what you buy and make with sweat equity. Now being a cheap skate I got my O360A1A for $2,500 and overhauled it for a total of $12,500. I have to admit the used Lyc engine market has dried up, but it's still not impossible to find a used deal. Frankly apples and apples you are talking about a used rotary engine. Still you can beat the Lyc price, I'll grant you. You probably can do it with a Subie but you have to make it all up yourself.

DanH
12-05-2007, 10:52 PM
<<I ran a 912 on a test stand a lot last year and it is very unhappy from about 600 (min idle) to almost 1200 rpm>>

Whoops. It's been a while since I fooled with a 912. I must be thinking of a 582.

<<the 1350 figure is right in the middle of that second point all right.>>

We talked about that in a previous thread.

<<I'm now installing an 8 pound steel ring on the outer part of the aluminum flywheel to see what effect it will have with and without.>>

It will help. How much would require modeling.

<<Marcotte has changed the bushing style in my later drive to a stiffer, smaller diameter. >>

That will worsen shake at the F1 intersection, but may help ensure the F2 intersection is above the operating range, a real concern with the switch from four to six cylinders. To illustrate, consider an F2 of 200 hz and play with the equations from my previous note.

<<It will be interesting to see how bad the EG33 shakes at 900 rpm and how wide that bad range is.>>

It will shake less than it does on the 4-cyl because exciting frequency amplitude is reduced. Expect the range to be the usual 0.8 to 1.2 times peak RPM, give or take a bit.

clarkefarm
12-05-2007, 11:58 PM
FWIW Maxwell Propulsion Systems have taken over the NSI baton and are producing Subaru EJ25 FWF packages which are a pretty complete option.
The sprague clutch in their 2.12:1 gearbox seems to overcome the torsional vibration problem but there have been failures, apparently associated with the former ECU related backfires. (At least the failures involve the clutch locking up so the a/c is still flyable.)
Their Wirlwind fabricated electric adjustable pitch propellor allows the engine to develop its full power at 5700 RPM or cruise at 4000 - 4800 RPM WOT giving reasonable performance and very good fuel burn.
I have an NSI package in a 9A and without having addressed the cooling drag issue can achieve 155 KTAS at a DA of 8,500' or coming back to 4500 RPM, 145 KTAS at a fuel burn of 4.6 gal/hr.

Rupert Clarke
Melbourne Australia

Geico266
12-06-2007, 05:21 AM
I ran a 912 on a test stand a lot last year and it is very unhappy from about 600 (min idle) to almost 1200 rpm. The frame was very flexible so you could see (and hear) the effects of TV quite graphically. Pretty darn scary actually. Super smooth at 1400.

The factory minimum idle RPM for a Rotax 912 / 912S is just under 1400 RPM. If you are really good at adjusting them you can get them to run smooth around 1,000 RPM. They aren't meant to idle below that. If I remember right they have to be turning at least 6-700 RPM just to make the dual Ducati ignitions fire. If you had a rough engine below 1,200 RPM you needed to balance the carbs. Idling a Rotax 912 lower than 1,000 sets up pulses & harmonics from the prop through the gear box that can damage the gear box. If you "ran it alot on a test stand" trying to get it to idle at 600 RPM I suggest you rebuilt the gear box and replace the "spring" washers / spacers. You may have damaged them.

They love to run 5K RPM all day long. Some have over 4,000 hour on the original engine & gear box (properly maintained) and are still in specs.

The Rotax 912 series engines are about as bullet proof an aircraft engine as you can get. There are more Rotax engines flying than ANY other engine.

DanH
12-06-2007, 05:56 AM
<<The sprague clutch in their 2.12:1 gearbox seems to overcome the torsional vibration problem but there have been failures, apparently associated with the former ECU related backfires.>>

I think not (an opinion <g>).

Torsional theory says a sprague will be great. Unfortunately, the engineers at the sprague company recoil in horror at the idea (I called, oh, six years ago). As previously noted, most of our systems are resonant in the 25 to 50 hz range. I suppose there is a special sprague out there somewhere, but spragues sourced from automatic transmissions were never intended to lock and unlock at 25 to 50 times per second.

So, an example. Temporarily lock the clutch by some means, run the system, and assume you observe an obvious evident F1 intersection at 1000 RPM. It starts making noise and shaking the airplane at about 800 RPM, rises to a peak at 1000, and tapers off by 1200. Unlock the clutch, and presto, everything is smooth as glass. Wonderful result, but to do it the clutch is cycling at 33 hz.

Customer A has a light airframe and keeps his tires inflated, so he tends to taxi at 1000 RPM. Customer B has a heavier airframe and his tires are always a little flat, so he tends to taxi at 1300 RPM. Both report excellent system "feel", but poor Customer A will suffer a sprague failure, while customer B will be happy as a clam. "A" racks up a very great number of lock-unlock cycles in not many total operating hours, while "B" may not reach the same number of cycles until he has flown the classic "1000's of hours of testing!".

The catch for sprague flyers should be evident; they have no idea what RPM to avoid.

clarkefarm
12-06-2007, 06:37 AM
Thanks Dan. Good info.
The conventional NSI wisdom (probably an oxymoron) is to keep the idle speed at 2000 RPM or better but I think that the last line of your post suggests that the problem resonance could be anywhere ?
I know that you were only offering an example but if heavy aircraft were an answer the Subaru drivers might be OK because the package is not light. Including header tank with 1.3 gal of gas, coolant, oil, battery, engine mounts (but not front gear), dual coils, pumps, radiator, oil/water heat exchanger, exhaust pipes and muffler, cowls and prop, plus a heap of wiring my little lot weigh in at more than 450 lbs.

Rupert

David-aviator
12-06-2007, 08:13 AM
David, do you notice a vibration in your EZ30 around 900 or do you ever idle it that low?



Idle is set at 800-900 but I never leave it there except for starting. I have not reset it to the factory recommended 1400 because the engine does not like a partially open throttle for start. It starts better the way it is which usually is without hesitation. As soon as the ECU has found its brain, I move the rpm up to 1200-1400. At 800-900 there is what sounds like gear back lash and general vibration throughout. When the engine is warm, it will idle at 700 with quite a bit of gear noise. Is that a separate issue from the low end vibration you and Dan are discussing?

I have run the engine without the PSRU and prop and it appears to be quite smooth at idle but there may be stuff going on I can not detect without vibration gages.

It would be good to know if there are any rpm ranges above 1400 where these plots are converging or whatever happens with vibration. It would be easy to avoid those areas with the CS prop.

rtry9a
12-06-2007, 09:49 AM
Re: rotory discussion- GMCjetpilot

If you push a 13B to 250hp, I think it will die soon

No evidence of that- the power levels depend on the rpm selected- the power curves are linear up to 8000 rpm. Rotaries do not break and they seldom show measurable wear in hard service (up to 3000 hrs so far in a gyrocopter, Tracy has also nearly reached that point in his RV).

That said, most rotary drivers keep rpms in the 5000-6000 range for cruise (abt 160-180hp) where the rotary operates at its best efficiency. Because the envelope is so wide, there are no problems expected by adding more power if wanted for whatever purpose, and, that extra margin is available at higher altitudes as power drops. The only concern is burning more fuel. There is no reason to ever exceed 8000 rpm- that is where the peaks reside and represent the OEM's design red line. The auto racers see rpms in excess of 12K and often under big boost levels where detonation is a primary concern- that is where things get dicy.

Displacement is twice as much as a 13B right, so that is expected. I am guessing they are not laying around cheap

No way- the Renesis is a 13B motor; the rotors and housings are the same size and interchangeable, the 1300cc displacement is identical. The only real differences in the Renesis vs older designs (quite a few iterations involving port size and orientation) is the exclusive use of large side intake and exhaust ports on the Renesis that improve breathing and eliminate cross contamination of the intake charge over the other stock engines. The rotors are slightly higher compression and lighter. The Renesis is ~10 lbs lighter than older motors. The internal gears are hardened (allow higher speeds- a common racing upgrade).

Mazda is talking about bringing out a new higher displacement motor in the next year or two, the 16B (or 1600cc displacement vs 1300cc). IMHO, the biggest plus of the new motor resides in its aluminum end housings that will drop another 50 lbs off of the 13B family in addition to added power/torque.
Powerwise, the Renesis and any of the older p-ported 13B's are close, with a slight edge to the p-ports because of better charge flow, but, they tend to idle rough because of exhaust contamination of the intake air. In addition, there are 3 rotor (20B) engines and a smaller older design (12B) occasionally seen.

FWIW, I bought a nearly new 4-port Renesis for $1800 + 200 shipping. A big lot of motors were sold at the time in Australia (Mazda used these for emission testing, I think). Used 13B typically costs anywhere from $200 up depending on accessories (attached to a sports car...;)) A complete rotary overhaul costs less than $1000. The 3 moving parts and housings seldom show wear unless they are grossly dirty inside, and even then, generally usable after a good cleanup.

I think that single lower scoop like Sam James cowl is probably as good as it gets

The rotaries are quite compact- the radiators and oil cooler can be mounted horizontally under the motor, where the James "P-40" cowl works well. Another possibility is to use an offset shertz beam mount that allows a vertical radiator to be mounted on the side, parallel to the motor- the Vans cowl works fine for that arrangement.

Cost wise, OK I'll quit arguing but 1/3rd? I have seen the math and you're looking at mid-high teens for a RWS Rotary setup. With a NEW Lyc & prop mid-high 20k something.

It all depends on the specific installation, and level of sweat equity, as you said. On the low end, figure approx $2000 for motor+ 3500 for redrive + 1000 for engine controls + 1500 more for cooling, exhaust, intake, and motor mount materials- nothing particularly exotic, mostly welding and assembly. The motor could be less, the incidental materials a little more depending on what you select.

Premanufactured fwf's have been quite expensive, like the Eggs- Im guessing their pricing has been based more on the prices of the competetion (Lyc motors and clones) than on actual costs and labor.

rv6ejguy
12-06-2007, 10:16 AM
The factory minimum idle RPM for a Rotax 912 / 912S is just under 1400 RPM. If you are really good at adjusting them you can get them to run smooth around 1,000 RPM. They aren't meant to idle below that. If I remember right they have to be turning at least 6-700 RPM just to make the dual Ducati ignitions fire. If you had a rough engine below 1,200 RPM you needed to balance the carbs. Idling a Rotax 912 lower than 1,000 sets up pulses & harmonics from the prop through the gear box that can damage the gear box. If you "ran it alot on a test stand" trying to get it to idle at 600 RPM I suggest you rebuilt the gear box and replace the thrust washers / spacers. You may have damaged them.

They love to run 5K RPM all day long. Some have over 4,000 hour on the original engine & gear box (properly maintained) and are still in specs.

The Rotax 912 series engines are about as bullet proof an aircraft engine as you can get. There are more Rotax engines flying than ANY other engine.

We were running with EFI and both OE and our ignition systems on a test stand. The OE ignition requires around 300 rpm to fire, not 600-700 or the engine would never start. The EFI negates any carb synching and improves mixture distribution.

We'd generally establish an idle of 1400 but during R&D would have temporary dips well below 900 while adjusting things. The engine did go back to Rotax after we were done with it.

Having the engine on the stand really allows you to see the severity of low frequency TV. You could feel how hard these points were on the engine and drive.

Yes, these engines are very light and tough and show what a good geared engine can do if operated as per manufacturers guidelines. I think Van made a good choice here to use it on the RV12.

I enjoyed working with the 912. Cool little engine. BTW we will be offering an EFI setup for the 912UL and 912ULS engines in early 2008 after flight testing is complete.

SvingenB
12-06-2007, 03:17 PM
I enjoyed working with the 912. Cool little engine. BTW we will be offering an EFI setup for the 912UL and 912ULS engines in early 2008 after flight testing is complete.
Cool. The market for FI for Rotax is probably huge. If you can make it cheaper than these folks:
http://www.silent-hektik.com/UL_912_1.htm

They also make gears, but max 150 HP and probably wrong ratio for Subaru?:
http://www.silent-hektik.com/UL_R1200_1.htm

DanH
12-06-2007, 03:51 PM
David,
<<At 800-900 there is what sounds like gear back lash and general vibration throughout. When the engine is warm, it will idle at 700 with quite a bit of gear noise. Is that a separate issue from the low end vibration you and Dan are discussing? >>

It is exactly the issue we are discussing, and don't do that!

<<I have run the engine without the PSRU and prop and it appears to be quite smooth at idle but there may be stuff going on I can not detect without vibration gages.>>

Engine without psru and prop is an engineered-by-Subaru system. In that configuration you get no torsional resonance, guaranteed.

Rupert,
<<The conventional NSI wisdom (probably an oxymoron) is to keep the idle speed at 2000 RPM or better but I think that the last line of your post suggests that the problem resonance could be anywhere ?>>

I do not know for sure, but I think the F1 is below 2000, for two reasons. First, the overall system is conventional (for our application) and likely falls in the 25 to 50 hz group I mentioned in a previous post. 50 hz in this case would be 1500 RPM. Two, I'm pretty sure NSI knew where the F1 was located, because they hired a Phd to review the system. Only part of the good doctor's report got released, that being the math proving a sprague would eliminate resonance. I have a copy somewhere in my files; all the mechanical review is missing.

In fairness, I have no idea what brand or type of sprague is currently installed in a Maxwell drive. That takes us back to a previous statement; without engineering data, neither fans nor critics know the truth.

gmcjetpilot
12-07-2007, 02:11 AM
Re: rotory discussion- GMCjetpilot

No evidence of that-

No way-

The rotaries are quite compact-

It all depends on the specific installationI have been schooled. :D Thanks for taking the time to educate my rusty brain. Very interesting. Even though I don't have plans to build or fly a plane with out a Lyc, I enjoy following the progress. Who knows someday I'll come to the dark side. ha ha.

DanH
12-07-2007, 04:22 PM
Egg gearbox failures seem to be entirely random, but perhaps there is a connection. I was scrubbing in the shower this AM (a great place to think), and a detail came to mind. It is just a suspicion, a theory without proof, but maybe worth investigating.

Most of them are bearing failures, yes? The only one I've seen personally seemed to be so; the propshaft had worked it's way forward in the case.

I've previously explained how pilots can run a PSRU system, by luck or on purpose, in operating ranges that don't have torsional issues and thus get very good life. Others may operate in less happy ranges, by ignoring warnings, by lack of warning, by circumstance, or just plain bad luck. Based on observations reported here by Ross and David, let's assume some percentage of operators are cranking and idling less than 1000 RPM. The system seems to be resonant around 800 RPM, meaning it sees high gear loading and likely gear load reversal....which is why it makes noise.

So how does it translate into a bearing failure?

I had a private note mentioning helical gears in the Egg box. A plain helical gear on a shaft generates axial thrust under load, not a problem under normal circumstances; bearings, even plain ball bearings, are rated for some axial thrust. However, a gearbox with load reversal would axially drive the shaft first one way and then the other (fore and aft in this case), as gear tooth contact moved from the front to the back of each tooth. There is some freeplay in the gear mesh, thus during the torque reversal there is some degree of impact when the teeth swap contact faces. The gears are probably as described in some other posts, quite heavy duty for the application, and the tooth impact is no bother to them. However, the impact would drive the gear and shaft axially against the bearing, with impact. The principle would be identical to that of an impact screwdriver, a tool well known to guys who worked on motorcycles in the days of phillips case screws.

Bearings do not survive a lot of impact. Microscopic dents in the balls and races shorten life a lot. In this case, assuming an 800 RPM gear clatter, the axial impact would be happening at 26 times per second.

The degree of impact would be hard to quantify, but it is safe to say axial shaft freeplay would make it worse. I have no idea if any effort is made to precisely control axial shaft freeplay, or even axially preload the bearings at assembly. It should be noted that there isn't any great reason for the designer to worry about precise control of axial freeplay if he doesn't expect load reversal.

Ross, you've seen the components (and you've worked with geaboxes). Are these plain helical gears, and do you think there a possibility of axial impact as installed?

Everyone remember the above is a theory, not a fact.

Yukon
12-07-2007, 04:46 PM
Dan,

Is that why Rotax uses the Sprague clutch?

gmcjetpilot
12-07-2007, 06:31 PM
Dan,

Is that why Rotax uses the Sprague clutch?I did not know what Sprague clutch was exactly so I Googled, coming up with this interesting technical artical on PSRU's. (May be old news but new to me.)

http://www.prime-mover.org/Engines/Torsional/sport_av92/sport_av92.html

Yes its longer than my post and detailed. Lots of good info for those who want to plow through it. He discusses different couplings, belt, torsional, flex, sprague and fluid. Here's the excerpt on the sprague clutch:

"The fifth option, a sprague (or overrunning) clutch, is not necessarily a coupling for the reduction drive; the few applications of this I'm familiar with use the clutch on the output shaft as a preventative measure. The configuration of this clutch is something similar to a ball bearing in that it has an inner race and an outer race, separated by the inner members(spragues). When the input shaft rotates one way, the spragues (which look something like out-of-round cylinders) jam between the inner and outer race, rigidly connecting the input and output shafts together.

In the case of torsional feedback, when the output shaft wants to turn ahead of the input shaft, the spragues unlock and allow the motion. Since the clutch lets go, the vibration isn't allowed to build past the first cycle. Since no energy is generated, none has to be dissipated, allowing the system to operate in a continuous relatively benign environment. I know of at least two manufacturers that are using this system with good success, although both applications are below 100 hp. (Rotax?)

Will any sprague clutch work? No. The system has to be designed for the load and for the frequency at which the system is expected to vibrate. Surprisingly enough though, some off-the-shelf clutches are applicable to a wide range of variables. The best positioning of the clutch seems to be on the output shaft, the slower rate of rotation resulting in lower hoop and locking stresses and allowing the separation of the prop flight loads from the gear train.

The sprague clutch, however, adds complexity to the reduction drive, driving up parts count and cost. Furthermore, since the mechanism depends on metal-to-metal friction contact, the potential exists for wear and contamination of the gear-train by small metal particles.

Operationally, there is also concern since the propeller freewheels when the throttle is pulled back, causing a significant increase in drag and reduction of the glide ratio. If you're on final and take this drag increase into consideration the consequences are minimal, however, in the case where the engine fails enroute, the reduced glide performance can be the difference between a safe landing and one not quite so. One manufacturer has an option for a disk brake but this, of course, adds weight and further complexity to the system."

Yukon
12-07-2007, 06:46 PM
Excellent article, George. I love the last sentence.

DanH
12-07-2007, 06:59 PM
John,
<<Is that why Rotax uses the Sprague clutch? >>

Friction clutch with limited rotation. Nice design, a true damper.

David-aviator
12-07-2007, 08:12 PM
The Cessna 150 0200 starter had a clutch with a zillion little grabbers that jammed on a flat shaft surface when engaged and then they slid over that surface when the engine started and exceeded the speed of the starter.

Was that a sprauge clutch? I remember rebuilding that little sucker every 50 hours or so.

DanH
12-07-2007, 08:18 PM
<<The Cessna 150 0200 starter....Was that a sprauge clutch?>>

Yep.

rv6ejguy
12-07-2007, 08:59 PM
Egg gearbox failures seem to be entirely random, but perhaps there is a connection. I was scrubbing in the shower this AM (a great place to think), and a detail came to mind. It is just a suspicion, a theory without proof, but maybe worth investigating.

Most of them are bearing failures, yes? The only one I've seen personally seemed to be so; the propshaft had worked it's way forward in the case.

I've previously explained how pilots can run a PSRU system, by luck or on purpose, in operating ranges that don't have torsional issues and thus get very good life. Others may operate in less happy ranges, by ignoring warnings, by lack of warning, by circumstance, or just plain bad luck. Based on observations reported here by Ross and David, let's assume some percentage of operators are cranking and idling less than 1000 RPM. The system seems to be resonant around 800 RPM, meaning it sees high gear loading and likely gear load reversal....which is why it makes noise.

So how does it translate into a bearing failure?

I had a private note mentioning helical gears in the Egg box. A plain helical gear on a shaft generates axial thrust under load, not a problem under normal circumstances; bearings, even plain ball bearings, are rated for some axial thrust. However, a gearbox with load reversal would axially drive the shaft first one way and then the other (fore and aft in this case), as gear tooth contact moved from the front to the back of each tooth. There is some freeplay in the gear mesh, thus during the torque reversal there is some degree of impact when the teeth swap contact faces. The gears are probably as described in some other posts, quite heavy duty for the application, and the tooth impact is no bother to them. However, the impact would drive the gear and shaft axially against the bearing, with impact. The principle would be identical to that of an impact screwdriver, a tool well known to guys who worked on motorcycles in the days of phillips case screws.

Bearings do not survive a lot of impact. Microscopic dents in the balls and races shorten life a lot. In this case, assuming an 800 RPM gear clatter, the axial impact would be happening at 26 times per second.

The degree of impact would be hard to quantify, but it is safe to say axial shaft freeplay would make it worse. I have no idea if any effort is made to precisely control axial shaft freeplay, or even axially preload the bearings at assembly. It should be noted that there isn't any great reason for the designer to worry about precise control of axial freeplay if he doesn't expect load reversal.

Ross, you've seen the components (and you've worked with geaboxes). Are these plain helical gears, and do you think there a possibility of axial impact as installed?

Everyone remember the above is a theory, not a fact.

Yes, these are plain helical gears and as usual Dan you bring up good points. Most automotive manual gearboxes do not use ball bearings to take up thrust loads on these gears, they run the gears on glass hard shafts with flanges. Only radial loads are imposed on ball and roller bearings in most designs unless angular contact bearings are fitted. High frequency impact loadings is very bad for bearings in my experience but sustained TV is rarely encountered in automotives because real engineering and testing has been done by the OEM in most cases. However we can do stupid things like trying to pull from 500 rpm in top gear and experience TV outside the normal operating range.

Most problems that I've read about do involve bearing issues. If left uncorrected of course, bearing problems quickly cause gear and case problems leading to disintegration.

The one thing I don't like about the Marcotte box is that they have one ball and one roller bearing bearing supporting the drive gear- a bit short on thrust load capability possibly. Twin tapered roller bearings support the cantilevered driven gear so that part is fine. Maybe the fact that everything is so massive in these boxes makes this a non-issue. We shall see.

The thrust loading on helical gears is fairly substantial. If you try to grab neutral at WOT in your car without depressing the clutch, it is very hard to move the shifter. Try it with your foot off the throttle and it glides right out of gear. (Use your beater for this experiment).

Interestingly EPI discusses plain bearings in certain places being superior to ball or roller bearings. I tend to agree. I don't agree with their views that high pressure engine oil is superior to lubricate PSRU gearsets. While this is proven and makes sense in engines like the Merlin with integrated gearboxes, bath lubrication is lighter, simpler and less expensive and extremely well proven in automotive gearboxes and differentials using proper high pressure gear lubricants. Separate lube also separates potential contamination of the two devices so if one fails, it won't cause the other to by circulating metal bits.

Again, TV rears its ugly head. Rotax 912 gearbox failures are common when operators don't keep the idle above 1200 rpm. Egg has now recommended that the H6s idle at 1400 or so. I don't know if this is due to bad experiences in the case of the Subaru package but I don't see any other reason for the recommendation. I did see a TV problem on these right above the starter cranking rpm which manifested itself in some odd kickbacks during some start cycles. Quite surprisingly, this was solved by advancing ignition timing on the ECU. H6s/ Gen 3 with the factory ECU apparently don't have this issue- do they David? The prop MOI may have a small influence here as well compared to the MT. Our tests were with the really light Sensenich hollow carbon fiber blades.

IMO gears don't need to be very big to reliably transmit a mere 200hp but shafts and bearings do need to be stiff and handle the loads especially with large spans between support. Shaft deflection and overloaded bearings were the primary causes of high hp transmission failures. TV is another thing to add to that list with PSRUs.

Sometimes the flying part is less interesting to me than what's driving my RV up front. It is amazing that all that stuff works up there- so far.

BTW, I too do some of my best thinking in the shower or at the gym doing weights- not sure what that might mean?:confused::)

gmcjetpilot
12-07-2007, 09:32 PM
Interestingly EPI discusses plain bearings in certain places being superior to ball or roller bearings.Isn't plain bearings (babbitt bearings) used on the crankshaft and connecting rod big end bearings in a "modern" engine? :D However it takes pressure lubrication and careful design.

Wikipidia:
"In some applications rolling-element bearings such as ball, or roller bearings have replaced Babbitt bearings. Though such bearings can offer a lower coefficient of friction than plain bearings, their key advantage is that they can operate reliably without a continuous pressurised supply of lubricant. Ball and roller bearings can also be used in designs and configurations which are required to carry radial as well as axial thrusts. However, rolling element bearings lack beneficial damping and shock load capability provided by fluid film bearings."

In engineering school there are course's just on machine elements like bearings and gears. 20lb text and design books are written on the subject. Its not new technology (invented in 1839 by Isaac Babbitt). The science of how the lubrication film or hydrodynamics works in a bearing is interesting. How would you supply pressurized oil to the gear box? independent pump or from the engine. Either way could work. Its understandable why designers want to use splash lubrication and roller bearings.

rv6ejguy
12-07-2007, 09:52 PM
It is possible to use a separate pump like some gearboxes have in order to use plain bearings however this is another complication IMO. You could also just tap oil pressure externally off the engine like the Ross drives used to.

I like bath lubrication for existing auto engine PSRUs which already have a crank seal anyway. Dead simple, nothing to go wrong and the lube has EP additives already. In auto transmissions no soft shell is often used. Hardened steel gear with oil slots rides on hardened steel shaft. Lasts forever. Don need no stinkin' 90 psi oil supply.

The big thing with using engine oil for the gearbox is to have easy access to oil for a hydraulic prop. If you must have one of those, this is the easier way to go.

David-aviator
12-07-2007, 10:00 PM
Quite surprisingly, this was solved by advancing ignition timing on the ECU. H6s/ Gen 3 with the factory ECU apparently don't have this issue- do they David? )

No kick backs - about 80 hours with 2.5 engine and some 225 with H6, both with Subaru ECU's.

Idle was moved up to 1400 with GEN3 out of concern of the gear lash noise or whatever it is. Curious, when the spring loaded fly wheel was installed with GEN2, idle was OK at 700-800 with no gear noise which was present with GEN1 and a solid fly wheel. Then GEN3 enters the picture and gear noise returns and does not go away until 1200-1300. Seems like the ratio and prop speed are factors along with the spring loaded fly wheel.

This stuff is really complicated. I wish we had an inflight survey of hamonic vibration. Maybe that's what MT did with Andy's airplane. Would be good to know if there are any rpm ranges we should avoid other than less than 1400. I will contact him about it.

SvingenB
12-08-2007, 06:06 AM
John,
<<Is that why Rotax uses the Sprague clutch? >>

Friction clutch with limited rotation. Nice design, a true damper.

It has two "operational modes" actually. It is a spring loaded dog gear with a friction clutch. When the dog gear climbs on the ramps, the spring is compressed so it will soften all hard torque impulses. The dog gear has a free play of 30 deg or something and within that free play the friction clutch is in operation. I guess this will be approximately analogue to a spring and chock absorber of a car suspension.

Earlier non certified versions (at least 912UL) only had the dog gear, but I think the clutch is now standard on all 912/912S/914, it can also be retrofitted on older ones. I havn't given this much consideration before (none :) ), so I don't know if the Atec I fly have the clutch or not. Maybe it doesn't, and this is the reason for not flying with zero load on the propeller shaft, since this could probably cause the dog gear to oscillate within its free play.

Anyway, according to Rotax, the clutch/dog gear assembly including correct tension of the spring is the key element regarding reliability of the entire gear train including the crank shaft. If this is important on 100 HP, it surely must be important on 150+ HP with CS prop.

DanH
12-08-2007, 08:07 AM
<<It has two "operational modes" actually. It is a spring loaded dog gear with a friction clutch. When the dog gear climbs on the ramps, the spring is compressed so it will soften all hard torque impulses. The dog gear has a free play of 30 deg or something and within that free play the friction clutch is in operation.>>

I looked up drawings this AM for details. I think both of us were wrong <g>

Previously I said the clutch was rotation limited, thinking as you do above that the clutch slips within the constraints of the 30 degree dog freeplay. No so. The dog on the front side of the big gear drives the clutch dog (4) which is free to rotate on (2), limited only by clutch plate friction. The clutch plates drive outer case (1), which in turn drives (2), which drives the propshaft. Clutch plate preload is provided by spring washers (8). The clutch will slip without limitation if shaft torque rises high enough, or if the spring washers lose their ability to provide the axial clamp force on the clutch plates.

http://img208.imageshack.us/img208/1796/rotax912clutchvx5.jpg (http://imageshack.us)

The axial force holding the dogs in contact is provided by an entirely different set of much larger spring washers positioned forward of the clutch assembly (and not shown in this drawing). These are the subject of a Rotax service bulletin. It states you can monitor the condition of the springs by examining the propeller torque necessary to slide the dogs through their 30 degree freeplay range.

Engines without the clutch get a different set of dogs. If they provide less than 30 degrees of freeplay, you should be able to tell if a particular engine does or does not have a clutch merely by moving the prop and noting the degree of rotation between dog contact. Can someone confirm?

DanH
12-08-2007, 08:34 AM
Ahhh, we're off track again...enough about a Rotax clutch.

Ross, a straight question. Are you subject to a confidentiality agreement with Jan? I understand if you are (I am honoring a few CA's myself), and I'll not bother you further about the gearbox guts.

New thought. Let's suppose you wanted to be sure operators couldn't idle their engine package at a speed low enough to clatter gears at the F1 intersection. However, as David mentioned you might need to allow a low throttle setting for initial starting. Given that the EFI/IGN is software controlled, might one consider a simple idle-up dashpot or solenoid at the throttle body butterfly, with the purpose of bumping idle speed up after, oh, say, 5 seconds of steady state engine operation?

Torsional resonance control via software.

SvingenB
12-08-2007, 08:43 AM
:) I think you are correct (this time). I was looking at some of the drawing in the service bulletings, but they are not drawn accurately enough so one can figure out what is rotating in relation to what. They are more like sketches, and they clearly state that in a note as well :)

But this means that it is a "pure" clutch, a torque restrictor, and the original dog gear doesn't really do anything when the clutch is installed ?

Geico266
12-08-2007, 08:45 AM
The OE ignition requires around 300 rpm to fire, not 600-700 or the engine would never start.
I knew if I went by memory I'd be in trouble.:cool: You are correct 300RPM min. to fire the dual Ducati ignitions.

I read in a post, in this thread, something (can't find it now) about Rotax 912 / 912S gearbox failures. I'm no expert, but I do have 400+ hours flying them. I know of NO Rotax gear box failures. News like that travels pretty fast, but I have never even heard of a gear box failure on a Rotax 912 / 912S. I'm sure there have been failures, but by the time the Rotax engine made in here to the US the bugs were pretty well worked out is my guess. Good reason why we should look at it closely, it works. If anyone knows of any please post.

Great info by all in this thread. Almost 10K views WOW!

David-aviator
12-08-2007, 09:13 AM
New thought. Let's suppose you wanted to be sure operators couldn't idle their engine package at a speed low enough to clatter gears at the F1 intersection. However, as David mentioned you might need to allow a low throttle setting for initial starting. Given that the EFI/IGN is software controlled, might one consider a simple idle-up dashpot or solenoid at the throttle body butterfly, with the purpose of bumping idle speed up after, oh, say, 5 seconds of steady state engine operation?

Torsional resonance control via software.

Such a device is installed in the auto intake but was removed for aircraft use, I don't know why. Some of the engines surge at low speed, even in flight. This is caused by the absense of that idle device. A cure for it is the 1400 idle setting. It does not do it at that setting. It is annoying in flight on final at idle power. The engine won't quit, but it sounds like it may. I had it with the 2.5, but not the H6.

ccrawford
12-08-2007, 10:48 AM
Such a device is installed in the auto intake but was removed for aircraft use, I don't know why. Some of the engines surge at low speed, even in flight. This is caused by the absense of that idle device. A cure for it is the 1400 idle setting. It does not do it at that setting. It is annoying in flight on final at idle power. The engine won't quit, but it sounds like it may. I had it with the 2.5, but not the H6.

I may have missed this before, but is that 1400 idle set on prop or engine rpm?

airguy
12-08-2007, 11:22 AM
Gotta be engine - 1400 is way fast for idle power on the prop:eek:

DanH
12-08-2007, 12:17 PM
<<But this means that it is a "pure" clutch, a torque restrictor, and the original dog gear doesn't really do anything when the clutch is installed ?>>

It is indeed a torque restrictor. Above a set level, it slips. I'm sure the Rotax engineers already had a pretty good idea what shaft torque would break the box or bend the crank nose, so they probably set spring pressure for slip somewhere between that level and, oh, 3 times max mean torque.

The dogs work just like the dogs in the non-clutch gearbox. Apparently the driven dogs on the clutch are a slightly different shape as compared to the non-clutched driven dogs. That is what I would like to confirm, merely as a means of determining if a clutch is installed in any particular box. Anybody know if a non-clutched box has 30 degrees of prop rotation before it turns the crank? I don't think it does.

David-aviator
12-08-2007, 01:00 PM
Gotta be engine - 1400 is way fast for idle power on the prop:eek:

It is engine rpm. The prop is turning at 700.

gmcjetpilot
12-08-2007, 02:08 PM
All the rotary guys may know this by heart but it might be interesting to dissect the RD-1 drive.

Real World Solutions has articles and detailed pics of his successful drive on his site. It shows how it was developed and the philosophy behind it. The features are: stock Mazda flywheel/flex plate, rubber isolator plate, planetary gear set (I believe from Ford transmission) and pressurized bearing lubrication and spray gear lubrication. It utilizes roller bearing (fwd), plain bearing (aft) and even a flat tapered needle thrust bearing.

Here is a three part article discribing philosophy & design development of the RD-1, including mistakes (which is interesting):
http://www.rotaryaviation.com/PSRU%20Zen%20Part%201.htm
http://www.rotaryaviation.com/PSRU%20Zen%20Part%202.html
http://www.rotaryaviation.com/PSRU%20Zen%20Part%203.html

Now at the risk of making rotary guys heads expand with bragging fodder :D, may be, just may be, rotary engines are better suited or easier on a PSRU due to their "smoother" output? Also from the pics below, you can see the engine is more compact, thus it allows a longer PSRU. The compact in-line nature of the RD-1B drive looks desirable or elegant in simplicity. The Wankel having the pressurized oil port is also pretty handy. Clearly Tracy made this drive to fit the rotary and learned from others. The off the shelf planetary gear set (Ford Transmission) is a plus. Gear design seems easy but really needs experts with technical backgrounds. Of course having a engineering degree I may be prejudice, but I'm no gear man. Gear designing is a specialty with subtle "tribal knowledge". It's not super human but with computers today, a dude who knows only enough to put numbers in the computer gets, POOF, a CAD drawing and pretty CNC part. It may look nice but an off the self proven Ford gear set is better than a custom unknown one.

Make no mistake, there are real harmonics going on, destructive ones. If not properly designed (and tested) even a Wankel's PSRU can fail, I'm sure, even if a "Mazda goes Hmmmm".

Pics: Output Shaft (http://www.rotaryaviation.com/images/newpshaft.jpg); Parts disassembled (http://www.rotaryaviation.com/images/psru/RD1Parts2.jpg); Plantary Gear Reduction assembled (http://www.rotaryaviation.com/images/mvc-019s.jpg); RD-1 installed in plane (http://www.rotaryaviation.com/images/mvc-007s.jpg)

http://www.rotaryaviation.com/images/Bruce_RD1_photos/sidelores.jpg

The open flywheel / damper was done for production reasons. I always thought it looked unfinished and crude, but it does give a view of what's going on in there. A solid bell housing casting would look better, but is not cost effective for low production runs as Tracy explains. Clearly he's gone through the Dash 1 through A, B and C. That is good. The longer it stays in service the better. I gather TBO/Major Inspection are in the hundreds of hours? That is probably a must with any PSRU, frequent inspections. Also limits on metal props and acro should put in perspective. PSRU's are not for everyone.

Tracy was fairly inexperienced when he started with his design but seems to have hit a sweet spot after several iterations. I attribute that to: Using off the shelf parts, analysing existing drives (Ross), copying ideas that worked, testing and tear down inspections, willingness to make changes (even painful ones) and making the right design choices, either by talent or luck or may be both. I say luck because he drove a BMW and decided to use elastomer dampers which he carved out shock strut bushings. All kind of on the fly stuff. However going back to my theory, may be the nature of a Wankel is just less critical or harsh on a PSRU? So either he's a natural born designer, got lucky or the Wankel is easier to put a PSRU on? May be a little of all of the above.

The only thing I doubt is he is selling the RD-1 design for other engines? Hmmmm now that does not seem kosher. Every engine needs its own unique PSRU in my opinion. Also in my opinion, every gear box driver should have an OIL TEMP and CHIP detector in their box or oil return line, with idiot light warning. Helicopter guys have temp/chip warning on their gearboxes. When the light comes on they do an immediate emergency landing while praying and sweating.

Mike S
12-08-2007, 02:10 PM
It is engine rpm. The prop is turning at 700.

Been wondering about that myself, a couple of posts that seem to be in conflict with each other way back at the start of this thread, only made sense if one person was talking prop RPM, and the other engine RPM.

For the sake of all of us following this wonderful exchange, please indicate weather you guys are talking prop or engine when you use RPM numbers.

Thanks.

As was stated earlier, it sure is nice to see this kind of exchange without the personal **** drifting in.

rtry9a
12-08-2007, 02:21 PM
George-
Absolutely correct comments regarding harmonic resonance. As interesting as RWS stuff is, you might also check out the website at http://www.rotaryeng.net/ A lot more technical history and information regarding rotary engines: more theoretical than Crook's decidedly practical approach.

rv6ejguy
12-08-2007, 02:34 PM
Regarding 912 gearbox failures. Poor choice of words on my part. In my dealing with Rotech (major Canadian Rotax distributor and overhaul facility), they said they had only seen a couple "fail" but dozens completely trashed inside when they get them and making bad noises. So, inflight failures, almost never. These trashed gearboxes showed the classic signs of low rpm operation, contrary to Rotax's recommendations. Apparently some pilots coming from the direct drive world have trouble coming to grips with an engine idle of 1400 and takeoff rpm of 5800.

Rotary engines and PSRUs are still subject to TV concerns. Tracy Crook has applied more engineering than many of the other drive makers and has therefore had better success than many others. No surprise there to me.

There can be endless combinations of gear types, bearings and TV dampers that will work successfully. Proper analysis and testing will doubtless save money and time in the end over eyeball engineering and crossed fingers.

SvingenB
12-08-2007, 05:41 PM
I knew if I went by memory I'd be in trouble.:cool: You are correct 300RPM min. to fire the dual Ducati ignitions.

I read in a post, in this thread, something (can't find it now) about Rotax 912 / 912S gearbox failures. I'm no expert, but I do have 400+ hours flying them. I know of NO Rotax gear box failures. News like that travels pretty fast, but I have never even heard of a gear box failure on a Rotax 912 / 912S. I'm sure there have been failures, but by the time the Rotax engine made in here to the US the bugs were pretty well worked out is my guess. Good reason why we should look at it closely, it works. If anyone knows of any please post.

Great info by all in this thread. Almost 10K views WOW!
There was one here that desintegrated in the air some half a year ago. The pilot was cruising along normally, then suddenly with no warning whatsoever he heard a big bang, lots of oil on the canopy and no power. The main gear wheel in the gear box broke and one of the parts left like a projectile through the gear box wall then through the cowling. This was a 912 ULS. You can read it here (if you can read Norwegian :) I just put it here as a ref), it's on the bottom of the page. http://www.nak.no/mikro/html/flytrygg/Rapporter/rapporter2007.html
The gear box has been sent to Rotax for examination, but so far no news of what might have been the cause.

This was on a Flight Design CTSW, which now also is marketed in the US under the LSA rules. Most of the 912s are used in Europe under the UL rules, like the CTSW. This means the owner are free to do anything he wants with the engine, sometimes (or maybe often??) against the manufacturers recommendations. I have never heard of a certified 912 having had any problems. If this is due to low number of certified engines, or if the certified engines are maintained much more in accordance with the manufacturers recommendations, I don't know. In general though most 912 makes it to 1500 TBO, and they routinely go 2 and 3 times past that when used as trainers.

gmcjetpilot
12-09-2007, 03:42 PM
This was a 912 ULS. You can read it here (if you can read Norwegian :) I just put it here as a ref), it's on the bottom of the page. http://www.nak.no/mikro/html/flytrygg/Rapporter/rapporter2007.html
The gear box has been sent to Rotax for examination, but so far no news of what might have been the cause.I can't read Norwegian and Google translator can either. Can you translate?

Look there are gear boxes that have not failed and there are gear boxes that will fail, sooner or later. This idea of a mechanical device never, ever failing is a dream, yet to be discovered. That's the prime argument against the gear box PSRU's, if its there, it can fail. The corollary: Direct drive engines don't have a gear box to fail, so failure is eliminated. That is with out debate.

Now you can argue Lyc cranks fail. True, but see above, all mechanical things made by man are subject to failure. The crank however is "solid state". It's a moving part but has no internal moving parts itself (unless it has damper weights). Prop is bolted to the crank, done. The simpler you make it the better for reliability. Lyc and Continental figured out if they make the displacement large enough they don't need higher engine RPM, while still being powerful and efficient. Of course nothing is 100% efficient and compromises are always made.

This does not take away from the fact gear boxes can be made to be safe and reliable. The above is just philosophical; if its not there to fail, it can't fail. Many a Continental, Lyc, Pratt, Wright where produced with integral gear boxes. They worked fine, but you had to be careful back driving the prop. Most radials have a gear reduction. They all work fine. On the other hand they where integral, pressure lubricated and had tight tolerances, which adds cost and weight. They used magnesium where they could**. During overhaul its another thing to do and expense. Even finding someone to work on geared engines can be a challenge.

**BMW makes a in-line 6 cyl magnesium/aluminum composite engine; the core is aluminum (with steel sleeves) and the outer engine case is of magnesium, fused together. It saves 24% weight. Magnesium has pros and cons but they put the materials to best effect. The way the make and fuse/bond/marry the alum and mag parts is interesting. Some Cessna twins have magnesium rims. If they ever catch fire, you RUN. Magnesium burns like the sun (and almost impossible to extinguish).

SvingenB
12-09-2007, 06:02 PM
I can't read Norwegian and Google translator can either. Can you translate?
I did. The rest in there is just more elaborate things about what happened during the emergency landing etc + comments from the pilot and the technical comettee. There are no conclusions (nor any speculations about the cause of the cathastrophic-like failure) since no feedback from Rotax has been received yet. If it's of interest I can post it in this forum when it is received.

Philosophies can be tricky. Another philosophy say that no system is better than its weakest link. The weakest link is the engine itself, and a good designed gear box will improve the reliability of the engine because the gear box unloads and filters out the largest and most destructive forces on the crank shaft like bending, axial oscillations, propeller vibrations, gyroscopic forces etc leaving only torque. This is not unsimilar to the suspension of a car. A good suspension is very complicated with lots of parts that takes very hard loads, but I don't think anyone will agree to the notion that the car will become more reliable if the suspension was removed. A car with the wheels bolted directly on to the chassis would desintegrate very fast.

More complicated technology does not automatically equal less reliability. Comparing the Rotax 912/914 and Jabiru 2200/3300 clearly shows that the most complicated of the two also is the most reliable, by huge margins. I don't believe that reason for the reliability of Lycomings is simplicity, I believe that the truth is that the Lycomings are extremely well designed engines.

rv6ejguy
12-09-2007, 06:20 PM
In all my reading on the popular V12 WW2 engines, the engine itself was far more likely to fail than the reduction gear. The key is to design a reliable box which most of these were. The reduction gear is a very simple device compared to a 48 valve, 12 cylinder, ohc, supercharged engine. The same thing applies today. We just need some science and engineering applied along with some long term testing and the reduction gear is likely to exceed the reliability of any engine bolted to it.

If they could do it 65 years ago, we can certainly do it today. How many manual gearboxes have I have to repair in the last 20 years on my street cars (some with triple the stock hp)? Zero. I used to beat the **** out of them too.

I agree with Dan, buyers should lobby PSRU makers to perform more testing on their drives. Seems to me, this would help sales a fair bit if the manufacturers took this step themselves.

LifeofReiley
12-09-2007, 07:06 PM
What's the use talking here... this Egg guy will be out of business very soon. I feel sorry for anyone who has invested in this.

gasman
12-10-2007, 02:09 AM
Just my post to help it over 10,000

Geico266
12-10-2007, 05:31 AM
In general though most 912 makes it to 1500 TBO, and they routinely go 2 and 3 times past that when used as trainers.

My Norwegian is a tad rusty. ;)

It would be interesting to know more about the history of that engine, and how it was maintained. Was there any follow up investigation? On the other hand, one gear box failure certainly is not a trend with as many Rotax 912 / 912S's that are flying. What this tells me is gear boxes can be made reliable for aircraft applications. The reason I even bring Rotax up is to use it as an example so the VAF engineers can look at it and learn.

David-aviator
12-10-2007, 09:25 AM
I can't read Norwegian and Google translator can either. Can you translate?

Look there are gear boxes that have not failed and there are gear boxes that will fail, sooner or later. This idea of a mechanical device never, ever failing is a dream, yet to be discovered. That's the prime argument against the gear box PSRU's, if its there, it can fail. The corollary: Direct drive engines don't have a gear box to fail, so failure is eliminated. That is with out debate.

Now you can argue Lyc cranks fail. True, but see above, all mechanical things made by man are subject to failure. The crank however is "solid state". It's a moving part but has no internal moving parts itself (unless it has damper weights). Prop is bolted to the crank, done. The simpler you make it the better for reliability. Lyc and Continental figured out if they make the displacement large enough they don't need higher engine RPM, while still being powerful and efficient. Of course nothing is 100% efficient and compromises are always made.

This does not take away from the fact gear boxes can be made to be safe and reliable. The above is just philosophical; if its not there to fail, it can't fail. Many a Continental, Lyc, Pratt, Wright where produced with integral gear boxes. They worked fine, but you had to be careful back driving the prop. Most radials have a gear reduction. They all work fine. On the other hand they where integral, pressure lubricated and had tight tolerances, which adds cost and weight. They used magnesium where they could**. During overhaul its another thing to do and expense. Even finding someone to work on geared engines can be a challenge.

**BMW makes a in-line 6 cyl magnesium/aluminum composite engine; the core is aluminum (with steel sleeves) and the outer engine case is of magnesium, fused together. It saves 24% weight. Magnesium has pros and cons but they put the materials to best effect. The way the make and fuse/bond/marry the alum and mag parts is interesting. Some Cessna twins have magnesium rims. If they ever catch fire, you RUN. Magnesium burns like the sun (and almost impossible to extinguish).

Nothing is perfect, not even an analogy.

Some early versions of EGG PSRU's have failed, but generally there is some warning before the failure. If the temperature is running 200+, watch out. I have not been able to get GEN3 near 200 so far. (Last time I flew before this darn ice storm, it ran at 145.)

There have been no Subaru crank shaft failures. If one compares engine crank shafts, this is a non issue with Subaru.

If a Lycoming crank shaft fails there is no warning. It's running fine and a second later it is not running at all except for some noise. It is not a huge problem in than most Lycoming cranks do not fail, but even after some 80 years of development, they have not been able to make them all bullet proof. They change this or that, find a cheaper vendor, and invariably come out with a version that fails and the recall follows. This can not give anyone a warm and fuzzy feeling.

DanH
12-10-2007, 10:19 AM
Hey, the first thing that would make this forum more productive is to skip Lycoming/alternative engine comparisons. Lycoming is the standard. Serious work, not BS and not random experimentation, will allow the alternative engines to catch up. Yeah, they both break from time to time, so enough already.

Now, who has even so much as a photograph of Egg Gen III internals? Am I to believe that all Egg owners trade a box full of money for a box full of gears and have never looked in the box?

Operating data: David admits to running his system at an RPM that generates noise from the box. What we don't know is how often, and if it is likely to be common among other operators.

How about it? Can we set aside the flag waving and discuss reality?

rv6ejguy
12-10-2007, 10:54 AM
Jan had a photo of the gearbox guts on his site a few months back but I can no longer find it. Maybe someone has this on their HD somewhere?

Like Rotax, Jan is recommending a 1400 rpm idle now. If you own either package, it's a good idea to follow the recommendation probably.

flytoboat
12-10-2007, 11:00 AM
About a third of the way down this page are more pictures:
http://www.eggenfellneraircraft.com/News%20-%20Earlier.htm

TSwezey
12-10-2007, 11:02 AM
Dan or Ross,
Do you have any experience or knowledge of using a Hyvo chain in the PSRU? That's what is inside mine.

DanH
12-10-2007, 02:41 PM
<<knowledge of using a Hyvo chain in the PSRU?>>

Sorry, nothing more than what I've read. Never worked with one. The only noteworthy article I recall was in Contact a few years back, some data supplied by Rousch Racing (?), measurements done driving camshafts I think.

SvingenB
12-10-2007, 03:30 PM
My Norwegian is a tad rusty. ;)

It would be interesting to know more about the history of that engine, and how it was maintained. Was there any follow up investigation? On the other hand, one gear box failure certainly is not a trend with as many Rotax 912 / 912S's that are flying. What this tells me is gear boxes can be made reliable for aircraft applications. The reason I even bring Rotax up is to use it as an example so the VAF engineers can look at it and learn.
The gearbox was sent to Rotax for examination, but no news as of yet. The report doesn't say anything about maintainance and history of the engine, not at this time.

DanH
12-10-2007, 05:01 PM
Thank you Don.

Pictures have limitations of course, but they're a whole lot better than guessing.

http://img91.imageshack.us/img91/5992/egggeniiigearsetaxialnq9.jpg (http://imageshack.us)

Gear A drives gear B, which drives C, which drives D. The D gear is attached to the propshaft. The tail of the propshaft runs in a bearing inside A.

The arrangement of the helical gear angles means torque reversal at a resonant RPM would indeed drive the shafts fore and aft axially (the arrows) at a rate in the hertz range. This would beat the snot out of the bearings. The beating would be much reduced if axial freeplay is carefully shimmed or otherwise kept to a minimum, but offhand I don't think there is any way to eliminate all of it. I can't tell what Jan does to minimize freeplay from just a photo. In this design it needs to be minimized. You can tell the operators absolutely, positively do not run in a resonant range (apparently below 1400 in this case), but that only reduces the total number of hits in a given period of operation. You still must pass through that range at startup, so minimizing axial freeplay to keep the hits small would increase bearing life.

All bets are off if operators routinely ignore the prohibition against low idle speed. I gather there is no mechanical stop or device to prevent low idle, so I'll bet it happens all the time.

Anyway, it's a theory. I could be wrong. Comments?

gmcjetpilot
12-10-2007, 05:10 PM
This would beat the snot out of the bearings.Cars have detonation sensors, which are little microphones. May be a "resonance sensor" on the gear box could warn of gear box rattling? May be the noise is so high it would be impossible to differentiate the noise. May be a vibration sensor. Jet engines have a vibration sensors that displays in the cockpit and recorded by the aircraft. Its used for maintenance.

If low idle is a no-no, than the idle should be set high. Right?

I've got generic engineering knowledge of gears. My knowledge of PSRU's is from the few I've seen around the airport and what's on the web. Why helical gears? They develop thrust loads to start with; on the plus side they're stronger than spur gear due to more tooth contact area continuously in contact, making it more suited for high speed.

Still involute spur gears (straight cut gears) are stout and work well. Big plus is no thrust loads. The Lyc accessory case GEAR BOX is an example of spur gears. Spur gears are louder, but so what, they are not weak if designed properly. It's a designer choice I suppose. Spur gears do have impact loads (which is why they are louder). Even if they rattle (which you will hear) they should be overbuilt to take it. At least the bearings will not get the heck kicked out of them.

Double helical is better still, as thrust loads cancel and you get double the shear area. I think the planetary is the way to go, keeping crank and drive all in one axis.

SvingenB
12-10-2007, 06:21 PM
Trivia: The logo on Citro?n cars, http://www.citroen.com/CWW/fr-FR , comes from double helical gears invented by Andre Citro?n. Citro?n used to produce gears before they started with cars in the early 19 hundreds. The idea was to have a silent gear without the axial thrust forces :D

Mike S
12-10-2007, 06:35 PM
George asked, "why helical gears?"

Simple answer, I suspect, is that they are using off the shelf parts, from an automotive transmission.

And the typical gear used in auto transmissions is helical for the reasons given above------quiet, and continuously engaged teeth.

lucky333
12-10-2007, 08:17 PM
The arrangement of the helical gear angles means torque reversal at a resonant RPM would indeed drive the shafts fore and aft axially (the arrows) at a rate in the hertz range. This would beat the snot out of the bearings. The beating would be much reduced if axial freeplay is carefully shimmed or otherwise kept to a minimum, but offhand I don't think there is any way to eliminate all of it. I can't tell what Jan does to minimize freeplay from just a photo. In this design it needs to be minimized. You can tell the operators absolutely, positively do not run in a resonant range (apparently below 1400 in this case), but that only reduces the total number of hits in a given period of operation. You still must pass through that range at startup, so minimizing axial freeplay to keep the hits small would increase bearing life.

So, Dan, would tapered roller bearings be a better choice? The axial forces you have indicated would not be absorbed by regular ball bearings, yes? If not tapered rollers, what would be a good choice to absorb the axial/radial loads generated by the helical gears? I'm thinking shims would not be a long term choice in an AL housing..

Thanks for your input on this thread. All kool-aid aside, I'm learning a lot!

John

PS for George: the Commander 680 I flew way back when (Lyc IGSO-480s) had geared supercharged (not turbo) engines. The gearing was a planetary affair if I remember right. It had some different operating considerations but when you wound it up to 3300/45" on takeoff, it ran like a scalded cat. Shorter wings than the 500B. A little hot-rod. Don't remember if it had any RPM range limitations. We pretty much shoved the throttles forward and hung on. There were several 680 models, most with bigger (Lyc xxx540) engines.

rv6ejguy
12-10-2007, 08:46 PM
Dan or Ross,
Do you have any experience or knowledge of using a Hyvo chain in the PSRU? That's what is inside mine.

I have no experience with these. EPI has some discussion on their site. Robinson uses this on their PSRUs which seems to work fine but beware of TV again if they have not done analysis.

http://www.v8seabee.com/description.asp

http://www.epi-eng.com/GBX-ChainDrv.htm

I think many people believe that TV can't affect chain or belt drives.

As for the Egg drive, yes, off the shelf gears and shafts to reduce costs and lead times and have reliable stress relief and heat treatment. Can't tell if any of the bearings are angular contact ones or not, I hope the twinned up ones on the prop shaft are. The ones I can see just look like standard ball bearings. Transmission countershafts often just use bronze bushings for thrust and they last forever. I guess time will tell if the bearings stand up well.

Idle speed can be just set with throttle or stop as with Rotax as long as pilot understands. Could be ECU controlled too to take dumb pilot out of the loop.

Spur gears have many advantages. The big disadvantage is noise, this can be very high in some designs but like George says, solves a lot of other problems.

Hard to beat tapered rollers bearings to handle all loads. Look at a lathe or an older car front wb setup. With proper lube, these last a lifetime with high thrust and radial loadings.

I built a chip detector for my Marcotte. Gives me a bit of piece of mind to a slow failure at least.

captainron
12-10-2007, 10:00 PM
Hard to beat tapered rollers bearings to handle all loads. Look at a lathe or an older car front wb setup. With proper lube, these last a lifetime with high thrust and radial loadings.



Quite right, tapered roller bearings can indeed handle large loads. The concern here is, what holds those bearings? Cases that can flex and move under load cannot support a driveshaft that may otherwise be designed correctly.

The auto transmission components shown in the drive photos look beefy, but keep in mind that these components are expected to deliver final drive torque to the propeller, whereas in a car, these components merely deliver torque to the final drive gearing where the real torque is generated.

On a separate note, the previously mentioned Hyvo chain was used on the early GM front wheel drive cars like the Toronado. If I recall correctly, it was used between the engine and transmission, a low torque environment, rather than after the transmission where torque is multiplied. They also commonly drive engine timing components.

David-aviator
12-10-2007, 11:04 PM
Operating data: David admits to running his system at an RPM that generates noise from the box. What we don't know is how often, and if it is likely to be common among other operators.

How about it? Can we set aside the flag waving and discuss reality?

The engine has to start from zero rpm and there is no way it can idle at 1400 without going through the range that produces some noise. That's reality. I don't sit there at 700 rpm for any reason, I don't like the noise and know it is not good. The fine pitch stop blade angle was recently increased about 4 degrees to have better rpm control on take off. That increased blade angle also loaded the PSRU at lower rpm's which I believe goes a long way toward eliminating gear lash. The original noise has been reduced substantially, in fact I have not heard it all since it has gotten cold. As previously stated, idle has not been adjusted to 1400 because I believe the engine starts easier with the throttle fully closed. As soon as the ECU finds its brain, the throttle is moved up to get out of the undesirable range.

Forward and aft load on the shaft bearings can not be avoided. Eggenfellner even advocates a high rate descent procedure with the prop in fine pitch - the load (a load much higher than with the engine at idle) is all in reverse when doing this. It also occurs when landing, the prop acts as huge speed brake. If the unit can not withstand such loads, we are in deep do-do with it.

I find it difficult to image that the slight gear lash after start can be SO harmful. The loads in flight are much higher both ways. Sure, it is good technique to avoid the noisy range if it exists, but we don't have to go nuts over it. Just don't do it.

To date, I have about 310 hours behind these units. None have failed for me so far.

DanH
12-10-2007, 11:56 PM
<<So, Dan, would tapered roller bearings be a better choice?>>

A great many factors go into bearing selection. Those who are really interested in bearing selection and calculation should beg an SKF catalog somewhere. The technical pages are excellent.

Axial thrust, or even reversing axial thrust, is not necessarily a problem. The issue is a possible high-cycle axial impact. The shafts may or may not have some axial freeplay; we don't know enough about the details of this gearbox to be sure. When axial freeplay exists, even if just the internal clearance in the bearings themselves, impact becomes a factor. As freeplay becomes greater, so does the impact. Bearings don't like impact.

Many common applications deal with reversing axial thrust due to helical or hypoid gears. Bearings can be axially preloaded so there is no axial freeplay. You can preload a deep groove ball bearing, an angular contact ball bearing, or an angular contact roller bearing. All will cheerfully accept axial load combined with radial load.

When preload is not possible, the best bearing for dealing with axial impact is an oil lubricated plane bearing. A common example is a crankshaft driving a balance shaft via helical gears. Some Japanese parallel twins privide a nice example; the crank can't be preloaded axially. The axial thrust from the helical gears is limited with half-moon plane bearing inserts at a case web. At idle, such an engine with too much clearance at the thrust bearing inserts sounds like it has a bad rod knock; the crank is clacking back and forth axially with each torque reversal. Get the clearance down to .004" or so with the correct insert and the oil film makes a nice hydraulic shock absorber; it gets quiet. Good way to buy a nice bike cheap if you know what to look for <g>

DanH
12-11-2007, 12:28 AM
<<Forward and aft load on the shaft bearings can not be avoided. Eggenfellner even advocates a high rate descent procedure with the prop in fine pitch ..>>

Correct, but the issue is the number of cycles and the velocity of impact when it changes direction. Going from full throttle to idle and back to full throttle would be one cycle of axial propshaft force. It looks like the
propshaft may be axially fixated anyway; I'm guessing those might be mirror-paired angular contact bearings behind the prop flange, hopefully with preload. If so, there is no bearing impact at all.

Now consider the layshaft. Assume the bearings are not preloaded. If you're at 800 RPM and hearing gearbox clatter, the layshaft is banging fore and aft about 27 times per second.

DanH
12-11-2007, 07:39 AM
Question:
http://img262.imageshack.us/img262/4156/egggeniiigearboxcq0.jpg (http://imageshack.us)

There is a hex head on the front of the case, at about 2 o'clock from the oil level window in this photo. It appears to be centered on the layshaft axis. What is it and what does it do?

David-aviator
12-11-2007, 08:06 AM
Now consider the layshaft. Assume the bearings are not preloaded. If you're at 800 RPM and hearing gearbox clatter, the layshaft is banging fore and aft about 27 times per second.

The frequency is not that high. I can't find the words to describe it, but the frequency is not that high.

The hex head screw you ask about, I believe it is an alternate port for a temp probe. There is another one like it on top.

rv6ejguy
12-11-2007, 10:02 AM
I'm guessing those might be mirror-paired angular contact bearings behind the prop flange, hopefully with preload. If so, there is no bearing impact at all.

.

This would be my guess as well.

David is right. I start my engine at a low idle and wait about 1 second for oil pressure to come up, then advance to 1000 rpm which is out of my noticeable TV range. You always have to pass through the evil range. Same on the Rotax we tested.

DanH
12-11-2007, 10:27 AM
<<The frequency is not that high.>>

Hmmm, that's interesting. Actually 27 hz is based on a wrong input; I was thinking you had a 4-cyl but you have a 6. (800 RPM x 6)/120 is the 3rd order exciting frequency (firing events), or 40 hz. The 6th order (piston inertias) is even higher. Right offhand I can't recall if the 1-1/2 is a major order with a flat 6. Even if it were, it would be 20 hz and still too high by your estimation. One of these has to be matched by some natural frequency to resonate. Lemme think about it.

Can you take a guess? Trivia tip; the average fellow can't verbally count faster than about 4 hz.

David-aviator
12-11-2007, 09:43 PM
<<The frequency is not that high.>>

Hmmm, that's interesting. Actually 27 hz is based on a wrong input; I was thinking you had a 4-cyl but you have a 6. (800 RPM x 6)/120 is the 3rd order exciting frequency (firing events), or 40 hz. The 6th order (piston inertias) is even higher. Right offhand I can't recall if the 1-1/2 is a major order with a flat 6. Even if it were, it would be 20 hz and still too high by your estimation. One of these has to be matched by some natural frequency to resonate. Lemme think about it.

Can you take a guess? Trivia tip; the average fellow can't verbally count faster than about 4 hz.

This is the best I can do with a limited vocabulary.

The engine turns the gear box. The prop, with little or no load, turns easily and gets ahead of the gear box. The gears are momentarily unloaded until the prop slows down and the noise occurs when the gear box catches the prop coming down in rpm. The cycle keeps repeating itself if nothing changes. Some of the noise may be the springs in the fly wheel loading and unloading. If rpm is increased until the gear box is under a constant heavier prop load, the prop does not scoot ahead of the gear box and the cycle is broken. The noise stops.

I believe that when the fine pitch stop blade angle is increased, there is an earlier load on the prop in the rpm curve and the "gear lash" (noise) is lessoned because of it.

It just does not seem to me to be a vibration issue or related to engine piston speed.

DanH
12-11-2007, 10:00 PM
<<The cycle keeps repeating itself....>>

The frequency of this cycle is....?

David-aviator
12-11-2007, 11:09 PM
Can you take a guess? Trivia tip; the average fellow can't verbally count faster than about 4 hz.

It is higher than 4 hz based on counting to 4. :)

But it probably isn't 10 times 4. Your estimate may be correct.

SvingenB
12-12-2007, 11:25 AM
Looking at Eggs web site it seems that the box does not use engine oil from the engine, but use transmission oil. With all the wheels and bearings in there, this would mean about 2-3 % efficiency loss. 200 HP is 150 kW, and 2-3% of that is 3-4 kW that is going to heat up the gearbox. How does it get rid of all that heat? 3 kW is a lot of heat for that little box.

Yukon
12-12-2007, 12:09 PM
Until just recently, they used 90 wt gear oil.

AllanC
12-12-2007, 12:45 PM
John,

not quite. Jan has recommended everyone to change their gearbox oil to Mobil One 75W-90 synthetic gear oil, and I believe this was some months ago. For additional cooling, the factory also recommend that cooling air be taken from the 2/3 radiator shrouds and scat-tubed to the gearbox case. From David's experience, I believe that his gearbox temps are a lot lower than the G2 he had.

The efficiency losses and heat generation calculation by SvingenB may be correct for an engine operated at its continuous max rating, but H-6 users normally cruise at 2100 prop rpm, which is a lot lower (and smoother, quieter) than the 200hp shown. I think (hope) the factory has resolved the gearbox issue. Time will tell.

Allan

Mike S
12-12-2007, 01:01 PM
I think (hope) the factory has resolved the gearbox issue. Time will tell. Allan

Agreed.

No mater if you like traditional, or alt engines, we all benefit when a company in our hobby/sport/obsession succeeds.

For all the perseverance and dogged determination that Egg has shown in the face of development issues, and other impediments to progress, I salute him.

DanH
12-12-2007, 01:06 PM
<<It is higher than 4 hz based on counting to 4. But it probably isn't 10 times 4. Your estimate may be correct.>>

Some dynamic event has to drive the cycle. The list of drivers is finite, and being cyclical, frequency will identify the particular driver. My estimates are based on the common drivers, recip and gas pressure forces, 6th and 3rd order events in this case. And frankly, they are not estimates. Given a specific RPM, number of cylinders, and engine type (4 stroke w/ even crankthrow spacing), the frequency is quite precise.

Other drivers are possible. A good example would be a cyclical variation in load. Some twin-engine airplanes have this problem when props tips are place too close to the fuselage side. With a two-blade prop you can get a twice per rev "bump" when the tips pass through disturbed airflow.

Another possibility is a beat frequency. You hear the beat rather than the two underlying frequencies. The twin engine airplane again provides an example. When you run the two engines at slightly different RPMs you get a very annoying wa-wa-wa beat. The beat may be at only 1 or 2 hz, but that's just the frequency at which the two underlying, much higher frequencies go in and out of sync.

Can you think of a driver (an exciting frequency) for your cycle, whatever hz it may be? For sure the prop doesn't just randomly "get ahead of" the engine.

Please don't think I'm picking on you; not my intent at all. I'm really very pleased to see you thinking about system mechanics.

Yukon
12-12-2007, 06:22 PM
Dan,
This recent discussion centers around idling TV's . Can you address the possibility of cruise power TV's doing the same damage, but at less noticable
intensity, over a longer period of time.

rv6ejguy
12-12-2007, 07:04 PM
I think Dan has some personal experience with that and higher rpm stuff is potentially more dangerous as we humans can't feel these higher frequencies so nothing warns us until something bad happens.

lucky333
12-12-2007, 09:53 PM
And frankly, they are not estimates. Given a specific RPM, number of cylinders, and engine type (4 stroke w/ even crankthrow spacing), the frequency is quite precise.


I'm guessing multiples of the power pulse rate for the number of cyls, 2 or 4 stroke, at the RPM but crankthrow spacing-- eh? That and my general ignorance would scotch any real calcs.. So.. what is/are the general formula(e). That is if its, well..., simple. I'm mainly curious.. Not designing a redrive..

Thanx
John

DanH
12-12-2007, 11:48 PM
<<This recent discussion centers around idling TV's . Can you address the possibility of cruise power TV's doing the same damage, but at less noticable
intensity, over a longer period of time.>>

It is possible, if F2 falls within the operating range. F3 is probably above the operating range for the typical systems of interest here. We went over most of the theory in the Belted Air Power thread. Have another read there, and look at the sample Campbell diagrams. Basic concept: If a natural frequency is intersected by an exciting frequency, the system resonates.

<<I'm guessing multiples of the power pulse rate for the number of cyls, 2 or 4 stroke..So.. what is/are the general formula(e). That is if its, well., simple>>

Hand calculating the natural frequencies of a system with two or three inertias isn't bad. Penciling four or more inertias is quite complicated (for me anyway), but there is software. Before you get to that stage you also do a lot of calculating or measuring to determine the inertia of all the rotating masses and the stiffness of connecting shafts. You need inertia and stiffness values for the frequency calculations.

In contrast, calculating exciting frequencies is dead easy, and you've already seen the basic equation a few posts back. It is (RPM x #cyls)/120 = gas pressure events per second (hz) for a 4-stroke. The "120" is merely a division by 2 (since each piston fires every other rev) and by 60 (to convert events per minute to events per second). Every other exciting frequency due to engine events is a variation on the same equation.

BillL
12-13-2007, 06:51 AM
Dan, It may not be all the normal engine driving variations. The Sube has fuel injection and A/F control. If it still has the O2 sensor and operates on the original maps, it can pertubate the A/F to the point that it also cycles on engine rpm. (Note: this perturbation done to facilitate NOx removal with the catalytic converter.) This can the in the 3-10hz range. Someone else who is more familiar with automotive may can give more exact numbers. Just another potential variable to consider. If the OBDII is operational it could be tracked.

BTW - On two of my larger projects (at work) with over $1M/yr going into them, both had torsional failures and we looked hard at the beginning. Analytically, the freq analysis was a sorting tool, but we had to do dynamic analysis to get actual stresses on both to solve the problem. It is just not that unusual. Yes, gear boxes are problematic, but issues can be resolved. Good luck to Egg.

Bill

David-aviator
12-13-2007, 06:58 AM
Can you think of a driver (an exciting frequency) for your cycle, whatever hz it may be? For sure the prop doesn't just randomly "get ahead of" the engine.

Please don't think I'm picking on you; not my intent at all. I'm really very pleased to see you thinking about system mechanics.

I know what you mean by an exciting frequency, a prop failure on a previous airplane caused major vibration with the control surface. But I am out of ideas as to what could be causing this event at low rpm's. If it isn't a gear lash I don't know what it is or what is causing it.

You say you are sure the prop is not getting ahead of the drive unit and coming back into the gear train, if that is so, why is the phenomenon lessened with a greater blade angle?

pierre smith
12-13-2007, 06:59 AM
To newcomer BillL,
For bringing your expertise to these forums....an incredible amount of talent here! Welcome, and BTW, you can't go wrong with either the -7 or -7A

Regards

DanH
12-13-2007, 08:35 AM
Hi Bill,
Thanks for joining in.

<<pertubate the A/F to the point that it also cycles on engine rpm...This can the in the 3-10hz range.>>

Ah ha, an unusual driver! Ross, you're our FI guy, know anything about it?

<<Analytically, the freq analysis was a sorting tool, but we had to do dynamic analysis to get actual stresses on both to solve the problem.>>

Bless you. I keep preaching about the need for live measurement among PSRU suppliers, but sometimes feel like a mad voice in the wilderness. Can you tell us a little about the methods and tools used for the dynamic analysis?

David-aviator
12-13-2007, 09:02 AM
Hi Bill,
Thanks for joining in.

<<pertubate the A/F to the point that it also cycles on engine rpm...This can the in the 3-10hz range.>>

Ah ha, an unusual driver! Ross, you're our FI guy, know anything about it?

<<Analytically, the freq analysis was a sorting tool, but we had to do dynamic analysis to get actual stresses on both to solve the problem.>>

Bless you. I keep preaching about the need for live measurement among PSRU suppliers, but sometimes feel like a mad voice in the wilderness. Can you tell us a little about the methods and tools used for the dynamic analysis?

We seem to be getting into the "peer-review process" as emphasized on another forum re climate change data. Some peer-review of the EGG PSRU is a very good idea. This technical discussion is way over my head but clearly we need it.

rv6ejguy
12-13-2007, 10:38 AM
Dan, It may not be all the normal engine driving variations. The Sube has fuel injection and A/F control. If it still has the O2 sensor and operates on the original maps, it can pertubate the A/F to the point that it also cycles on engine rpm. (Note: this perturbation done to facilitate NOx removal with the catalytic converter.) This can the in the 3-10hz range. Someone else who is more familiar with automotive may can give more exact numbers. Just another potential variable to consider. If the OBDII is operational it could be tracked.

Bill

In aviation use with the OE ECU, the ECU is almost never in closed loop due to the high load and rpm so this would not be a factor on the H6. The non-OE ECU used in the newer Egg engines does not use an O2 sensor at all.

In closed loop, you are correct, the ECU tries to maintain around 14.7 AFR using a narrow band O2. Since this is a feedback control, there is a delay time between sensing and correction so the AFR is rarely dead on 14.7. This delay is dependent on rpm and proximity of the sensor to the port plus software concerns. HP falls if leaner than 14.7 and increases if richer than 14.7.

Usually torque variations in closed loop are quite small but it is true, that this could be a factor in these applications using closed loop AFR control.

This brings up a good point about other factors causing an unknown excitation. Prop resonance, engine mount resonance etc. could be factors as well. My composite prop has some areas of pitch airspeed and rpm that do set up a resonance for instance.

Good discussion and this shows how important actual testing is and flight testing in particular. Theory may uncover something bad before we even run the engine so that can be highly useful as well.

Yukon
12-13-2007, 11:53 AM
We seem to be getting into the "peer-review process" as emphasized on another forum re climate change data. Some peer-review of the EGG PSRU is a very good idea. This technical discussion is way over my head but clearly we need it.

Amazing transformation happening here from "Shoot the Messenger" to "Peer Review Process". No thanks necessary!

lucky333
12-13-2007, 12:22 PM
No thanks necessary!

John, you know better than that. :p

But I can't help but think that this would be a great time for Egg to chime in and address the engineering issues raised here and how they have been handled in his PSRU.

John

David-aviator
12-13-2007, 01:23 PM
Amazing transformation happening here from "Shoot the Messenger" to "Peer Review Process". No thanks necessary!

Originally you arrived on the scene with a large John Deere backhoe intent on digging a grave for the EGG PSRU. But some 190 messages later that has not happened so it is ok to pat yourself on the back. None of the information going back and forth would have happened without your first post. Thanks (I think). :)

Yukon
12-13-2007, 02:47 PM
David,

I arrived on the scene with a verbatim, first person posting about an Eggenfellner gearbox failure. The messenger is alive and well, but is still recovering from his wounds.

DanH
12-13-2007, 06:18 PM
Hello David,
<<You say you are sure the prop is not getting ahead of the drive unit and coming back into the gear train, if that is so, why is the phenomenon lessened with a greater blade angle?>>

Actually I said "the prop doesn't just randomly get ahead of the engine." The key word is "randomly"; I was trying to emphasize the concept of a forcing frequency and the need to quantify it in order to know the source.

That aside, let's focus on the "getting ahead" part. You're not right and you're not wrong, but a small conceptual shift would be good.

First, forget that the prop and gearbox shafts are spinning at all. Visualize them as stationary. Torsional vibration is a periodic oscillation in shaft torque. As you know, you can have torque without shaft rotation.

The prop is the largest inertia (by far) in a system of inertias connected by shafts. To illustrate the concept, think of a great big flywheel connected to a little flywheel.

http://img156.imageshack.us/img156/9889/simplemodelpo5.jpg (http://imageshack.us)

Grab them with your giant imaginary hands and twist the shaft, then release everything and observe the opposing oscillation. You'll see a lot of angular displacement in each oscillation of the small wheel, and very little angular displacement of the big wheel. The big inertia is the anchor against which the smaller inertia oscillates.

Your prop isn't getting ahead. There may be significant resonant torque applied to it's hub, but at most it is mildly oscillating in it's rotation speed. The rest of the system is oscillating against it. The gears (they're somewhere in the shaft in the simple model) clatter with each torque reversal.

There are several possible explanations for the calming effect of prop blade pitch increase. One might be a change in blade bending mode with a change in axis. Another might be an increase of damping in the form of increased aerodynamic drag. If I remember right, it damps the oscillation of the entire system. If the oscillation wasn't very powerful to begin with, some additional damping could be enough to drop the oscillation below the point of torque reversal. I'll see what denHartog has to say when I get home <g>.

DanH
12-13-2007, 06:30 PM
<<This brings up a good point about other factors causing an unknown excitation. Prop resonance, engine mount resonance etc. could be factors as well.>>

Whoa bubba, don't get confused. Props and engine mounts have natural frequencies, but have little capacity to bring an exciting frequency to the party. They are usually the victim, excited by something else.

Rare exceptions would be things like the "prop tip too close to the fuselage" example in a previous post. The prop would resonate if it had a natural frequency matched by the frequency at which the tips pass the fuselage. If not matched, it wouldn't resonate but would pass the cyclical variation in load onward to the powertrain.

BTW, "bubba" is a term of endearment here in the Deep South <g>

rv6ejguy
12-14-2007, 10:15 AM
Well maybe. I sometimes get a quite noticeable vibration on the ground with a gusting tailwind or in flight in turbulence which I attribute to the composite prop blades flexing. This "feels" exactly like my second TV period around 1400 rpm and is worse on descent with lower manifold pressure. Could be just the prop but don't forget those lovely rubber bushings I have on the flywheel/drive plate.

Seems logical to me that any major loading changes in the prop can set up TV on the other end of the system. No? We see this in automotive drivetrains sometimes.

DanH
12-14-2007, 10:51 AM
Took a quick look at what DenHartog's "Mechanical Vibrations" has to say about propeller damping. Most of his work in the area involved vibration in ship propulsion (his contribution to the WWII effort), which is a bit different from our case (the arrangement of inertias is swapped, prop inertia being small). Only one paragraph regarding aerodynamic damping of aircraft propellers. In short, there is apparently some aerodynamic damping at low frequencies, but not high frequencies. Given that we're talking about low frequencies in David's case, well, the answer is "maybe". Sorry, best I can do for now. Quantifying the damping would require some data gathering.

Ran across a nice diagram while reading, and thought I'd post it here because it illustrates much from this and other threads. Yukon asked about the dangers of an F2 second mode intersection in the upper RPM range. Kahuna told us about his buddy Subob breaking several crankshafts. In another thread there was discussion of second mode and how to measure or detect it, and I pointed out that the second mode wasn't at all like the first. And yesterday I was discussing relative motion of different sized inertias.

http://img209.imageshack.us/img209/6228/f1f2modeshapesto2.jpg (http://imageshack.us)

This is a mode shape diagram for a 4-cyl diesel generator set. The inertias are represented by disks. From left to right, they are the generator rotor, the engine flywheel, four crank assemblies, and a damper. A previous illustration listed the inertia values. In this case the generator has 3.28 times the inertia of the entire rotating engine assembly, much like our prop/engine combinations (for which 5x to 10X is ballpark, best I can tell). Our systems may not be exactly like this plot, but they will be similar.

The straight horizontal line is zero angular displacement. Everything above the line is angular displacement (rotation of the inertia) in one direction (call it positive) and everything below the line is angular displacement in the other direction (call it negative). The little circles at the intersection of the zero line and the ordinates are the vibratory nodes (not modes, don't get confused).

The upper plot is F1. It describes system dynamics typical for the idling case David and I are discussing. Note the relative amplitude of the opposing oscillation for various inertias. The dominant inertia doesn't oscillate much compared to the other inertias, as I described in the previous post. First mode so only one node; the big inertia rotates negative and everything else rotates positive.

The lower plot is F2. Note that now the big inertia and the inertias at far right displace positive while inertias near the center displace in the negative direction. Second mode vibration, so you now have two nodes. Notice the node located in the center of the crankshaft, and in particular, the steep slope of the ordinate (do you now understand Subob's broken crankshafts?). Also note the very low angular displacement of the big inertia. Prop telemetry (or vibration perceived in the cockpit) might not tell you much about what is happening with the poor 'ole crank.

This particular example included a true damper at the free end of the crank. DenHartog notes this system would fail without the damper, as resonant torque is "only" about 5 times mean torque, but would be about 50x without the damper.

BTW, this particular little book costs about $15. Given the amount of torsional heartache we see in the alt engine world, it has the potential for a very good return on investment. Perhaps everyone should ask Santa Claus for a copy? <g>

DanH
12-14-2007, 11:27 AM
<<I sometimes get a quite noticeable vibration on the ground with a gusting tailwind or in flight in turbulence which I attribute to the composite prop blades flexing.>>

Naaa. Come on now, why not fundamentals? Assume a wind from any quarter during runup. The result is a cyclical variation in AOA for each blade as the prop rotates, a well known issue and the reason we are taught to face directly into the wind for runups. I think the frequency of the cycle is (RPM x #blades)/60 = hz, but I reserve the right to think about it some more <g>

Anyway (and similar to the previous prop tip-fuselage example), the prop would resonate if it had a natural frequency matched by the frequency of AOA variation. It is a victim of the variation, not the cause. If not matched, it would not itself resonate but would pass the cyclical variation in load onward to the powertrain. If a powertrain natural frequency is matched, the shaft system resonates. And so on.

rv6ejguy
12-14-2007, 12:31 PM
Dampers on the free end of the crank are often replaced with lightweight, solid aluminum pulleys when used in race cars and aircraft. Bad idea in most cases and I've seen a number of crankshaft breakages over the years shortly after these were installed.

My advice is don't. What kind of damper was Subob using? This could be an alternative cause for failure. Again, we usually can't feel these high frequencies at the rpms these failures usually occur at. More things to worry about. That Lycoming is starting to look pretty good right now.:rolleyes:

SvingenB
12-14-2007, 12:35 PM
Ressonance is not needed for destructive vibrations. Ressonance in a loaded structure, like a shaft, will in most cases lead to destruction very fast, usually within seconds. When designing machines involving rotation, you allways set stiffness and inertia so that the RPM during normal operation is far away from ressonance.

There are two methods doing this, running overcritical or subcritical. This means running above the ressonance frequency or below. My experience is in measuremens and analysis of hydropower turbines. They run sub-critical, meaning they never experience ressonance - ever (at least not mechanical torsional vibrations, but sometimes experience electrical torsional vibration caused by the synchronous generator). A washing machine typically operates over-critical when centrifuging, meaning it accelerates fast to an RPM far above the ressonance RPM. I also believe the rotor on a helicopter operates far above ressonance RPM.

The general rule is (not to be confused with cause-effect):
high RPM and/or large inertia and low torque = over-critical.
Low RPM and/or low inertia and high torque = sub-critical

Anyway, bad destructive vibrations are usually vibrations that occur outside ressonance, since problems with ressonance are solved during design.

With aero engines I am not sure. I would think that a lycoming runs sub-critical? I also think that a Rotax 912 operates sub-critical, and that is one of the reasons for very limited propeller weight (torsional vibrations). But I really don't know. How about the subaru with complex gear involving several shafts and a heavy propeller?

rv6ejguy
12-14-2007, 01:28 PM
Anyway, bad destructive vibrations are usually vibrations that occur outside ressonance, since problems with ressonance are solved during design.

With aero engines I am not sure. I would think that a lycoming runs sub-critical? I also think that a Rotax 912 operates sub-critical, and that is one of the reasons for very limited propeller weight (torsional vibrations). But I really don't know. How about the subaru with complex gear involving several shafts and a heavy propeller?

The problem with many PSRU/ engine / prop combos is that no "design" work in the engineering sense was ever done.

Many rotating systems like car drive trains or our propeller drive trains have a TV period somewhere in the possible operating rpm range. We try (or hope!:eek:) that this rpm is somewhere below the idle range and above the maximum rpm range.

The three systems we have mainly discussed all have some bad periods around the 1200 rpm range perhaps coincidentally. By idling above this rpm, we avoid long term operation here and passage through here is only transient and hopefully not destructive.

Dan's earlier calcs showed that prop MOIs had only a small affect.

SvingenB
12-14-2007, 01:52 PM
The three systems we have mainly discussed all have some bad periods around the 1200 rpm range perhaps coincidentally. By idling above this rpm, we avoid long term operation here and passage through here is only transient and hopefully not destructive.

Yes, but are you sure this is ressonance problems? It could equally well be too low rotational momentum in the propeller at RPM below 1200-1400 so the end result is torque reversal due to the (relatively more pronounced) pulses from the engine. It could also be engine mounts being calibrated for 5000 rpm causing the engine to oscillate around the propellor axis below 1200 rpm or a combination of both.

DanH
12-14-2007, 02:14 PM
<<Dampers on the free end of the crank are often replaced with lightweight, solid aluminum pulleys when used in race cars and aircraft. Bad idea in most cases and I've seen a number of crankshaft breakages over the years shortly after these were installed.>>

The wrong damper can be pretty useless too. Take the classic Lanchester or Houde dampers for example. If the damping rate is too high, all you have is a flywheel. Too low and it does nothing useful.

FWIW, you can also place damping in parallel with a torsional soft element. System damping doesn't have to be at the end of the system.

<<Anyway, bad destructive vibrations are usually vibrations that occur outside ressonance, since problems with ressonance are solved during design.>>

.......among professionals. Love your washing machine example. Is anyone shocked to hear washing machine engineers pay more attention to torsional issues than the average PSRU vendor?

<<I would think that a lycoming runs sub-critical?>>

Great question next time I pass the Lycoming booth at Sun'nFun.

<<I also think that a Rotax 912 operates sub-critical>>

Our typical system (Rotax, Subaru, etc) is mid-critical. For a well-designed system we pass through a resonant RPM or two during startup (and idle above them if we're smart), with the next critical above redline. The M14 radial (short, stif crank) is sub-critical for the 4.5 order, but mildly critical for the 9th.

<<Ressonance in a loaded structure, like a shaft, will in most cases lead to destruction very fast, usually within seconds.>>

Disagree, more or less. It will lead to rapid destruction if the designer was really dumb, but there are lots of systems operating with resonant periods in the operating range. You just need to limit amplitude by design. Heck, even I designed one that worked fine, and I am very near dumb <g>.

Our alt-engine systems operate over a wide speed range and must be lightweight; we don't have the luxury of designing around a narrow speed range, or using huge shafts (high torsional stiffness) to push the criticals up above the speed range.

DanH
12-14-2007, 05:16 PM
<<Yes, but are you sure this is ressonance problems? It could equally well be too low rotational momentum in the propeller at RPM below 1200-1400 so the end result is torque reversal due to the (relatively more pronounced) pulses from the engine. >>

I think the 1200 RPM range is a resonant period. The 912 is a 4-cyl 4-stroke, so 180 degree firing intervals (meaning it has crankshaft torque reversal), plus it has no flywheel on the crank. The lack of flywheel inertia and the crankshaft torque reversal just means the forcing frequency is quite powerful. And I judge the shafts to be too small (admittedly without hard numbers) to push the 2nd order critical above the operating range.

Here's a story from my own experience. It involves an example worse than the 912, a 3-cyl (270 firing interval) 4-stroke with pumped-up compression. The application (a WW1 replica) required a very low idle speed because it had little tiny brakes and high pressure tires on 21" wheels. It was impossible to drop the first critical below a 500 RPM engine idle speed, so the drive system had to be designed to pass through the first major critical without harm. After much engineering, I had a system that only reached about 90 ft-lbs of resonant torque running steady state at the worst-case 1-1/2 order critical around 800 engine RPM.

Here's why I think low rotational momentum and torque reversal mean little by themselves. The above system would cheerfully idle like a clock at 500 engine RPM, meaning less than 250 prop RPM. It did so without significant noise or complaint, at relatively low oscillating shaft torque, even though you could darn near see the prop stop and start. It also sounded like a Model A Ford, much to the delight of onlookers <g>

The same system with Rotax dogs would be noisy, but I don't think it would shake around more than the 3-cyl.

BTW, I'm not guessing about the low oscillating shaft torque at idle, or the 90 ft-lbs when resonant. I had telemetry and a strain gauge on the propshaft, and I can look up the actual values if anybody cares.

Grandy
12-15-2007, 03:10 PM
I read on the Glastar site a note that indicates Eggenfellner is grounding all the non P3 PSRU units. I can't find anything to verify this, so I consider it rumor now, but does anyone know if there is any truth to it?

David-aviator
12-15-2007, 03:40 PM
I read on the Glastar site a note that indicates Eggenfellner is grounding all the non P3 PSRU units. I can't find anything to verify this, so I consider it rumor now, but does anyone know if there is any truth to it?

It is a fact.

DanH
12-15-2007, 04:04 PM
If you bought a Gen II (now grounded), do you pay for the new Gen III gearbox? How much do they cost?

David-aviator
12-15-2007, 05:30 PM
If you bought a Gen II (now grounded), do you pay for the new Gen III gearbox? How much do they cost?

Yes on the first question.

I do not know the answer to the second. Mine cost $2495 but it was below cost to manufacture for sure. The company in CT doing the machine work to create the case is not cheap.

gmcjetpilot
12-15-2007, 06:29 PM
To Eggs credit he is taking action, tough action. I went on the Egg web site and read all the service bulletins and at least he addresses it and is proactive. It's still ugly, but it has to be done. Some companies deny or do nothing in hope the issue will go away and save face (say for example Ford, Chevy....). I find hope in that he has upgraded the box and grounded the Gen II. However it sucks for those that have to shell out the cash.

flyeyes
12-15-2007, 07:35 PM
For Ross, Dan, and others who understand this better than I do...

I've been following this thread from a distance with some interest.

It seems to me that one of the problems is identifying the areas where you might have destructive resonance/vibration, and "seat of the pants" us an unreliable method.

Given that solid state accelerometers and their supporting electronics have become so cheap, would it be possible to instrument the drivetrain and just watch it in real time?

Maybe make it another engine limit--keep the CHT below a certain number, and keep drivetrain vibration below a conservative limit.

David-aviator
12-15-2007, 08:00 PM
For Ross, Dan, and others who understand this better than I do...

I've been following this thread from a distance with some interest.

It seems to me that one of the problems is identifying the areas where you might have destructive resonance/vibration, and "seat of the pants" us an unreliable method.

Given that solid state accelerometers and their supporting electronics have become so cheap, would it be possible to instrument the drivetrain and just watch it in real time?

Maybe make it another engine limit--keep the CHT below a certain number, and keep drivetrain vibration below a conservative limit.

The EGG H6 GEN3 with a MT7 prop was recently flight tested with considerable vibration detection equipment. This was accomplished on a private airplane with MT equipment and a MT engineer recording the numbers.

I e-mailed the pilot to ask if MT had released the data, to date they have not. But the verbal conclusion after the flight was "it is very smooth". :)

DanH
12-15-2007, 09:47 PM
<<I e-mailed the pilot to ask if MT had released the data, to date they have not. >>

Has MT ever released raw prop telemetry data? I got $5 here for you David. You collect by sending me the data. I collect if all they release is "We approve our prop on this engine". Is it a bet? <g>

David-aviator
12-15-2007, 10:52 PM
<<I e-mailed the pilot to ask if MT had released the data, to date they have not. >>

Has MT ever released raw prop telemetry data? I got $5 here for you David. You collect by sending me the data. I collect if all they release is "We approve our prop on this engine". Is it a bet? <g>

:) I think not. But a certificate indicating the combination is OK by them is better than no certificate.

rv6ejguy
12-16-2007, 10:01 AM
For Ross, Dan, and others who understand this better than I do...

I've been following this thread from a distance with some interest.

It seems to me that one of the problems is identifying the areas where you might have destructive resonance/vibration, and "seat of the pants" us an unreliable method.

Given that solid state accelerometers and their supporting electronics have become so cheap, would it be possible to instrument the drivetrain and just watch it in real time?

Maybe make it another engine limit--keep the CHT below a certain number, and keep drivetrain vibration below a conservative limit.

I've looked at doing TV testing with accelerometers and have some components and an idea picked out. Once the -10 is done, I might have time to pursue this so I can use it when I'm ready to run the engine. Not sure if it will work but looks feasible in theory.

DanH
12-24-2007, 08:46 AM
<<Given that solid state accelerometers and their supporting electronics have become so cheap, would it be possible to instrument the drivetrain and just watch it in real time?>>

I'm on record as saying "no", for two reasons. One, I'd like to encourage the conventional method (measuring oscillating shaft torque directly with a strain gauge set). You net a vital piece of info, actual shaft stress, and for the most part the signal contains nothing but shaft torque. The drawback is the requirement to somehow get the signal off the rotating shaft. My own fantasy in this regard involves an electronics wizard lurking here, reading this post, and responding with "Ah, heck, I can make a single channel digital telemetry radio with a hatpin and some junk PC parts" <g>

The other reason is practical; It might be difficult to sort out the indirect indication of torsional oscillation (accelerometer signals due to block rotation around the crank axis) from all the other block motions. The signal from any particular accelerometer will be the sum of all motions. Best I can tell (no serious study here) the signal can be broken down into discrete frequency components with FFT software and other vibration analysis software tools. That's fine, but then you have to identify the source of each discrete frequency. When you get done, you still don't know what you really want to know; amplitude, or "How bad is it?"

Having said all that, I would be delighted to see someone try the accelerometer method, and will cheerfully help if I can. I'd love to be wrong, if the result encourages others toward real test and measurement.

All my best Christmas wishes to you and your families.