Do PSRU's increase engine HP X or so?

[pierre smith]

Me

I'm ready and willing to cut a check for the dyno costs. Anyone? Anyone?

Count me in for the dyno costs.

Oh, I have a 37,500 RPM engine with a PRSU....a double planetary gear setup producing 680 shaft horsepower at 2200 prop RPM ...(no typos).

Regards,

 

[flytoboat]

simple math

Pierre,
So from what I've learned from this thread (if my math is correct), your engine turning at 37500 rpm must produce about 40 HP to get 680 HP at the prop.

JUST KIDDING!

 

[cytoxin]

LOL,
This thread just confirms my thoughts and makes me think of my buddy's 4 cyl Egg RV 7........4800 RPM/7 GPH...34" M.P. and tadaaaah...162 MPH. But, it sounds like an Indy car coming by my hangar.

Lycosaurus yes...

well thanks peirre, youve uncovered the attraction for me. now i see what it is they like about it

 

[rv6ejguy]

not t jump threads here, but who cares at this point.....why would anyone want a timing belt on an airplane? esp turning at max rpm. im sure all of this has been said before but car engines are not built to stand up to max rpm for the duty cycles we demand from them. if so nascar engine builders would have a much easier job. and they use 10 times better parts than factory.
yet they scatter all the time. turning a factory built eng to those rpms really concerns me. especially watching the students in my class get new cars like the WRX, EVO's and SRT4s only to have them huffing smoke at low miles...i say they are dogging them but in reallity they are just driving them like we fly them. WFO if you want to run a car engine wouldnt you build it so you could develop the power at the crank that your application requires with out G/R to each his own i suspect. get a lyc and be done with it. oh yeah i would suspect at the rpms stated the psru eats around 20-40 hp.which depends on the lube used in it.

We're not talking about running an EJ255 (STI) at 7000 rpm and 70 inches in cruise. That would be asking for low life. Dumb kids running 25 psi on pump gas and a chip at the track are going to blow up. We see it all the time. On the other hand, I've been an instructor at drivers schools for many years and never seen a Subaru blow up at the track here if it was stock. I've seen other brands expire and plenty of poorly modded ones frag too.

Timing belts are well proven to be very reliable if proper maintenance schedules are followed. Only been about 100 million engines produced with them.

What is is your factual evidence that auto engines are not designed to run at high rpm for long periods? Do you understand that in Germany for instance, cars are driven in the upper part of their rev ranges for a good part of their lives. This is the same type of use, aviation applications mirror. Do you see smoking wrecks all over the Autobahn?

Nascar engines use 10 times better parts than factory? Nonsense. Statements like this show you don't work on Japanese or modern engines like Subaru, Toyota or GM LS engines. These are designed to operate at high rpms for extended periods by very savvy engineers. The Sube has a forged, heat treated crank, forged rods, the LS a proven nodular iron crank. There are many drag import cars making 1000-1500 hp with stock cranks and blocks- over 500hp/ liter specific output. To put this strength of lousy OE parts in perspective, this is 3000hp on a Lycoming O-360!

The whole idea is to take a good engine design which might have a 7000 rpm factory redline and operate it for takeoff at maybe 5000 and then down at 4000-4500 in cruise. Over a 1000 flying Subes have proven this to be completely viable.

A PRSU eating up 30-40 hp? Again, nonsense. You are talking 20-30,000 watts being dissipated in the box. The thing would be glowing red hot in about 5 minutes if that was the case. A single, straight spur gear is around 98- 98.5% efficient, helical slightly less efficient. Multiple meshes will decrease transfer efficiency. Again, gets some facts on gearbox design. SAE is a good source. I have no cooling air on my gearbox, integral oil (less than 1 quart) and it runs below the coolant temp of the engine all the time. Considering its aluminum case and being directly bolted to the aluminum case, it is pretty obvious that 30-40 hp is not being dissipated within.

I've been doing a poll lately on some other forums about high time Subes, here was a response from a user in Oz-" I depend on my gyro to be ready for work when I want it and when I start work, I might clock up between 50 and 150 hours in a few weeks, sometimes in temps up to 120 F*. The engine runs cool as a cucumber because it has a Nissan Pulsar radiator.
Over 2,000 hours and still strong as ever !! and it came out of a wreck as well."

We've had posts from many people with over 1000 hours, especially from people giving flight training in gyros. High time mentioned so far is 3400 hours. Not too shabby for a piece of junk!

It is amusing to continue to see these posts here. I picture the skeptics, eyes closed, fingers in ears, mouthing ba, ba, ba, ba while another auto powered aircraft takes off and flies away. It's being done every day guys. Sorry, just reality.

 

[Ted Johns]

Optimization

So, now that we have officially stolen this thread:

It seems to me that 150 - 200hp engines are not the best place for a psru. There is probably some heuristic we could come up with that factors in hp, firewall forward weight, and psru weight to predict whether a psru will be a net loss of optimization.

If we look at what factors need to be considered in engine design, we might come up with a list like this:
Performance
Reliability (both short term and long term)
Cost
Weight
Maintainability

It seems to me that the O-360 lycoming is a pretty good effort at maximizing the area under those multiple curves, at this horsepower level.

Now, if we wanted more than say, 500hp, a psru might start to make a lot more sense. It's the obvious choice for a turbo-prop, and the reason is the same as it would be for a piston engine. That is, the turbine needs lots of rpm to make all that hp in a small light package. To make a lot of hp in a small, light piston engine you need the same thing, a lot of rpm.

A psru obviously made sense to the designers of the RR merlin, for example.

 

[Ted Johns]

Forgot about Rotax

Of course there is the Rotax at the low end of the hp scale. Forgot that they used a psru. This engine has done all right for itself.

Perhaps it's just all about the quality and completeness of the engineering.

But for sure, the only substitute for cubic inches is rpm.

 

[SvingenB]

What is is your factual evidence that auto engines are not designed to run at high rpm for long periods? Do you understand that in Germany for instance, cars are driven in the upper part of their rev ranges for a good part of their lives. This is the same type of use, aviation applications mirror. Do you see smoking wrecks all over the Autobahn?

He he. I had a VW K-70 once, long time ago. In the manual it said that the engine was designed to run continuously at full power. The same could be done with my old MB. I don't know about newer cars, I guess it's not politically correct regarding the environment with statements like this in the manuals.

 

[Kevin Horton]

But for sure, the only substitute for cubic inches is rpm.

Or manifold pressure (i.e. turbo-charging or super-charging).

 

[mgomez]

You're all right

Or manifold pressure (i.e. turbo-charging or super-charging).

I guess the phrase "There's no substitute for mass flow" doesn't have the same ring as "There's no replacement for displacement," but you're all correct.

Running more pounds of oxygen (and therefore fuel) through the engine per second is the way to make more power. You can do that with displacement, RPM, supercharging, or (the only remaining choice, I think) changing the fluids that you pour into the engine. Gasoline and air are not the only choices after all...just visit any drag strip.

 

[Scott DellAngelo]

What is is your factual evidence that auto engines are not designed to run at high rpm for long periods? Do you understand that in Germany for instance, cars are driven in the upper part of their rev ranges for a good part of their lives. This is the same type of use, aviation applications mirror. Do you see smoking wrecks all over the Autobahn?

From my personal experience people do not seem to really travel that fast on the Autobahn's in Germany. When I have spent time there for work (and you can bet I was pedal down) I bet the average speed of well over 90% of the cars was 80-85 mph or less. I was shocked at how with no speed limit people really didn't drive much faster than they do with the 65-70 mph speed limits we have.

Scott

 

[Mike S]

Running more pounds of oxygen (and therefore fuel) through the engine per second is the way to make more power. You can do that with displacement, RPM, supercharging, or (the only remaining choice, I think) changing the fluids that you pour into the engine. Gasoline and air are not the only choices after all...just visit any drag strip.

Cam timing, compression, intake tuning, exhaust tuning, port/polish, multi angle valve job, multiple valves, spark timing, spark plug type/gap, friction and drag reduction----knife edging/dry sump/windage tray, synthetic oil, roller/needle bearings, ETC.

 

[cytoxin]

wow didnt intend to get you all wound up

We're not talking about running an EJ255 (STI) at 7000 rpm and 70 inches in cruise. That would be asking for low life. Dumb kids running 25 psi on pump gas and a chip at the track are going to blow up. We see it all the time.

well thats what i said isnt it. thank you for pointing that out.

Timing belts are well proven to be very reliable if proper maintenance schedules are followed. Only been about 100 million engines produced with them.

yes you are correct but i have worked on many japanese cars that under 60 k will shred a timing belt for whatever reason. some fod and more from pulley bearing and the like more than falied lycos? dont know, not counting.

What is is your factual evidence that auto engines are not designed to run at high rpm for long periods? Do you understand that in Germany for instance, cars are driven in the upper part of their rev ranges for a good part of their lives. This is the same type of use, aviation applications mirror. Do you see smoking wrecks all over the Autobahn?

factual eveidence, no ross im not keeping a factual record, just know what
trend ive seen.

Statements like this show you don't work on Japanese or modern engines like Subaru, Toyota or GM LS engines.

uh id have to say your incorrect here

There are many drag import cars making 1000-1500 hp with stock cranks and blocks- over 500hp/ liter specific output. To put this strength of lousy OE parts in perspective, this is 3000hp on a Lycoming O-360!

and yet they tear them down every couple of runs. or they tear tear themselves down

The whole idea is to take a good engine design which might have a 7000 rpm factory redline and operate it for takeoff at maybe 5000 and then down at 4000-4500 in cruise. Over a 1000 flying Subes have proven this to be completely viable. .

is that why they are so slow?

A PRSU eating up 30-40 hp? Again, nonsense.

i said 20 -40 john has the money for the dyno take him up on it, shoot man i'll even pitch in some.

I've been doing a poll lately on some other forums about high time Subes, here was a response from a user in Oz-" I depend on my gyro to be ready for work when I want it and when I start work, I might clock up between 50 and 150 hours in a few weeks, sometimes in temps up to 120 F*. The engine runs cool as a cucumber because it has a Nissan Pulsar radiator.
Over 2,000 hours and still strong as ever !! and it came out of a wreck as well.".

We've had posts from many people with over 1000 hours, especially from people giving flight training in gyros. High time mentioned so far is 3400 hours. Not too shabby for a piece of junk!

isnt that because jan bans people that dont submit to his views

It is amusing to continue to see these posts here. I picture the skeptics, eyes closed, fingers in ears, mouthing ba, ba, ba, ba while another auto powered aircraft takes off and flies away. It's being done every day guys. Sorry, ust reality.

whats the reality? you spend more than i spen for less power, thats the reality.
oh, ok then

 

[Ted Johns]

I guess the phrase "There's no substitute for mass flow" doesn't have the same ring as "There's no replacement for displacement," but you're all correct.

"No substitute for mass flow" has a certain nerdy ring to it. I like it!

 

[rv6ejguy]

The Italian Autostrada might have been a better example of high speed road travel with mainly small displacement cars. Relatives last year there on business rented a 205 hp Ford Focus and were cruising primarily in the 160-180 kmh (100-110 mph) range. They said they were being passed by a constant stream of all types of cars. They put on about 2000 km in about a week at around 5000 rpm for most of it. The car had 150,000 km on it. Worked just fine and they didn't add any oil.

Getting back to the PSRU idea, Rotax has proven that the high rpm, geared engine is light, viable and reliable. Cheap it is not. They spend most of their lives at 5000-5500 rpm. As mentioned by others, proper engineering of the drive is the key to reliability and that is where many of the auto conversions have been weak. Bombardier did it right and got good results (if people keep the idle above 1400 rpm). While PSRUs are not rocket science they should involve science. The other way often used unfortunately is trial and error. It works, it might be cheaper but it takes a while to get issues all worked out. The latter has been the more often used route to date. There has been several pretty poor drive designs which don't have good reliability in the field certainly.

Anyway, I think I'll stop posting about this stuff. Bill Jepson. was right. These guys wore me down. Long live the direct drive Lycoming! I'm selling off all my Subaru stuff and plugging in ECIs to both my projects. Thank goodness I was set straight here by all the knowledgeable people building and flying conversions here and presenting some facts to support their conclusions. These forums are very valuable. To Doug and all VAF members, thanks for putting up with me and sorry for using up all the bandwidth. 1258 posts- I was really trying to top George here! I'll just stick to asking questions from now on.

 

[cytoxin]

coool

The Italian Autostrada might have been a better example of high speed road travel with mainly small displacement cars. Relatives last year there on business rented a 205 hp Ford Focus and were cruising primarily in the 160-180 kmh (100-110 mph) range. They said they were being passed by a constant stream of all types of cars. They put on about 2000 km in about a week at around 5000 rpm for most of it. The car had 150,000 km on it. Worked just fine and they didn't add any oil..

i want to go there sounds like mucho funno

Getting back to the PSRU idea, Rotax has proven that the high rpm, geared engine is light, viable and reliable. Cheap it is not. They spend most of their lives at 5000-5500 rpm. As mentioned by others, proper engineering of the drive is the key to reliability and that is where many of the auto conversions have been weak. Bombardier did it right and got good results (if people keep the idle above 1400 rpm). While PSRUs are not rocket science they should involve science. The other way often used unfortunately is trial and error. It works, it might be cheaper but it takes a while to get issues all worked out. The latter has been the more often used route to date. There has been several pretty poor drive designs which don't have good reliability in the field certainly.

my thought on conversions are that you are trying to find a way to not buy a 25000$ engine. but do /can any of them be done for less with the same reliability? seems the intent to not have a lyc just ends up with a much more complex system. that in and of itself seems to defeat the conversion principle. any who im done here, got to drill holes in my panel.

 

[Yukon]

Jeezz Ross, let's not go off the deep end! The truth was bound to come out eventually. Fact is, Subarus sound good and are marginally smoother than any other composite-proped engine. End of story. If you guys would stop making false claims about equal weight, better fuel consumption and performance, I think we could all get along. Just listen to what young Garth seems to think about "PSRU Power" and tell me that every auto adopter doesn't have some amount of hope in his beliefs.

When are we going to DYNO?

 

[Scott DellAngelo]

It's a $25k, much more complicated, lower performance engine with an almost mandatory $10k prop. My 9A would soundly outperform any non-blown subaru that I have ever seen data on and with a 0SMOH my firewall forward cost could have also bought a new car to drive to the airport for the price of the subaru setup. Somewhere I am missing the benefits of the thing? How many forced landings have Eggenfellner setups had (FWF related)? A fair question to ask. Eggenfellner himself one I remember, Paisley at least 2 (maybe more), and others. I have not followed that well either, but those are definite ones.

Don't get me wrong I would love to see alternatives work, but in my opinion the price has to be better and so should reliability. After all since we're bashing an engine well over half a century old they sure as heck better be more reliable.

 

[RVbySDI]

Exactly, I just talked to my old A&P from Alaska and he thinks I am right. A 300 HP 6000 RPM engine, reduced over 2:1 to standard prop RPM's, would have a lot more torque from this gear reduction, so getting a prop to take advantage of it (3, 4 or 5 blade CS designed for the greater torque), and with pitch adjustments also (on a constant speed, or pitch change on a fixed prop either way) one should be able to tap the greater torque now available off of the shaft from the PSRU unit. I will comm MT on this. And as the torque is the same more or less to start with on the rotery or the Lyconies, this should bring a big improvenment to the proformance of an aircraft using a PSRU on a same HP motor.

Well, Garth, here is my take on all of this. First off, I believe your are confusing the term power with HP. Power and HP are both relative terms. Relative terms mean that these ideas are defined only by relating them to other concepts. Furthermore, all you have to do to alter the meaning of any relative term is to alter any one of the variables that idea relies on for its definition and you have a totally new meaning.

It is my take on your posts that you are attempting to replace one idea of power (torque) with another idea of power (HP). They mean two totally different things and just because we work around machines where we use both of these terms to measure their "power" performance does not mean we can interchange one for the other. These two concepts of power are not interchangeable.

So power has a totally different meaning if we talk about the turning force of an object (torque) compared to the ability over time to produce motion (HP and RPM). Both ideas involve power but each are in reference to totally different concepts. Changing the relationship of what constitutes the given idea of what power is totally changes the meaning of the word.

So, to address your comment about running a low HP engine through a PSRU in order to gain power as measured in terms of torque might be somewhat realistic. Indeed, PSRU's can increase torque to the wheels of a ground based vehicle or to the prop in an airplane. And, you are partially correct in thinking that torque is important in order to produce work in a car or an aircraft. However, the other important factor being left out of the analysis is the issues of movement and time. In order for our aircraft to fly we need it moving through space and it needs to move through that space in a specific amount of time. Without this movement in a specific amount of time (we call this concept speed) we do not have enough power to get the aircraft off of the ground.

This is where your logic becomes flawed and what all of these posters have been attempting to explain to you. You see, if you have all the torque you could ever want (think about that 40 hp tractor pulling that plow through the dirt with incredible amounts of torque being put to its massive big rear tire treads) you are going to sacrifice speed of movement (now think about how fast does that 40 hp tractor pull that plow through the dirt).

As was posted earlier, in our aircraft we need the air movement through that prop to be at a specific speed in order for us to be propelled forward (and upward). Having a large amount of torque at the prop is a good thing. We need a lot of torque to be able to spin that blade through the air and have it "grab" as much of that air as we can. However, we also need the prop to spin at a fast enough speed for the blades to pull forward through the air as they spin. The balance between torque and speed has to be maintained because there is a specific amount of air that has to flow through that prop to allow it to move forward in the air. It has to spin fast enough for it to propel our aircraft forward at the necessary speed for the wings of that aircraft to generate lift. If the speed the prop is turning is not fast enough, it will not move forward through the air fast enough. In turn our flying contraption just becomes another earth bound moving vehicle. Perhaps moving about as fast as that 40 hp tractor but definitely not fast enough to generate lift.

Ok, I hope this can make sense. I feel that sometimes all the numbers and equations can become difficult to follow so stating those equations in other terms can help. Maybe this does help. If it doesn't, well. . . then shall we just move on to MGomez's post below.

Not at all. I will save a fortune when the time comes to buy the engine for my RV-7.

You see, my lawn tractor has a 14.5 HP Briggs & Stratton engine. When I couple that with a 10:1 PSRU, I will have a very low-cost 145 HP engine.

I recognize that this will be a somewhat underpowered RV-7, so I will install a set of bicycle pedals in the right seat. I will put my 8 year-old daughter in the seat -- she can generate an easy 0.1 HP. With a 100:1 gear ratio connected to her pedals , she should add another 10 HP or so.

Oh, I have to first put my daughter on a dyno. Can I run her lean of peak? You know, reduce the number of Cheerios/hour until her temperature peaks, and reduce it by a few more Cheerios?

I recognize, too, that some will object to installing a child, who is meant to power a bicycle, in an airplane. These critics, clearly opposed to the experimental nature of homebuilt airplanes, will insist that on a bicycle, my daughter only occasionally bursts to high power, whereas in an airplane she will be expected to generate high power for hours on end. What do they know?

If I had more children, I might not even need the Briggs & Stratton.

Ok, I have followed this thread with so much laughter the tears in my eyes are making it hard to read. This has got to be one of the funniest posts I have ever read. I cannot contain my laughter and my co-workers are wondering what drug I am on. This is absolutely too much!

 

[gmcjetpilot]

We all are learning all the time (we hope)

Well I just do not understand then. I am told by very knowledgeable people in the past that it is torque HP that does the work. Break HP and torque HP are sometimes widely different on the same engine (Ford diesel with 320 break HP and 640 Torque HP) Which is why big trucks are so powerful, and of course gear reduction will increase power to the wheels of a car or truck, so why not to an aircraft prop? You say the PSRU (through gear reduction like gearing down for a hill in a big truck) increases the torque output, and if torque drives the prop???? Maybe I just need time to see it. Not used to the PSRU thing. All my planes have had direct drive Lycoming in them.

Garth the info you got from our fellow members is right. I would just suggest you Google torque or HP or Horsepower and read some more. Your terminology is a little confused. I understand you are learning. We all where there once.

There is HP and there is Torque, there is no "Torque HP".

The term is Brake HP (not "break HP"). Brake Horsepower (bhp) is kind of an old fashion term. Prior to modern electronic, water, eddi current dyno equipment, HP was measured or quantified as the amount of resistance against a flywheel brake. The method is not really used as much, but the term remains in the auto industry. It is just HP. The BRAKE part is not relevant to anything anymore. However measuring HP consistently does have its challenge. All dynos I can think of measure torque and RPM and derive HP.

There are different HP numbers for cars like flywheel HP or Wheel HP, but it's not relevant to our discussion. We have "shaft HP", Prop HP and Thrust HP. The last, Thrust HP, is the equivalent thrust we get to move us. Props are only 75% to 85% efficient. So for ever 10 HP at the prop flange you get 7.5 to 8.5 hp thrust, so for a 180 HP Lyc the best you can expect is about 153 hp thrust (regardless of PSRU or not).


A PSRU does lose HP from input to output, since no PSRU is 100% efficient.

The direct drive Lyc has this advantage of no PSRU power loss, not to mention lighter and no parts to wear or break. If the engine makes most of its HP well above 2,700 rpm, a reduction is needed or prop losses will be high. Lycoming's and Continentals left the PSRU off by designing engines that turn slow enough to make peak HP/torque below 2,700 rpm so the PROP can be directly driven, saving weight, maintence and efficiency loss through a PSRU. There are trade offs, no better. Alternative guys must usually use PSRU's because all the engines they use where originally designed to be used with a transmission or gear box.


The confusion you are having with PSRU is that they DO NOT make more HP they only allow engines to run at higher RPM's to make more HP.


See the equation below, the higher RPM means more HP. However the design of the engine comes in here. It is true the faster you turn the more HP with in limits of the design. At some point an engine runs out of breath and HP (and torque) drops off. The Lyc is designed to make max power at 2,700 rpm. It will continue to make more power the faster you turn it, but the engine's mechanics are not designed for it and efficiency drops off. Engines designed for HIGH rpm (typically have less displacement per cylinder) only start to make significant power (and torque) above 2,700 rpm. As you know red line on some cars and motorcycles are up in the 6,000 to +9,000 range. Some engine are made to run at 100 RPM max power (large diesel) and some run at +15,000 rpm (two stroke race engines).

The PSRU allows higher engine RPM while gearing down the output, so the prop RPM remains in a normal efficient range. Props on planes like ours start loosing efficiency when turned faster than approx 2,700 rpm. The PSRU itself does not make HP and in fact the mechanics of gear reduction (friction) uses some power. There's no 100% efficient reduction. The only thing it is doing is the "gearing" allows the engine to operate closer to it's peak HP and/or torque rating.

Peak torque and HP don't necessarily occur at the same RPM, but that gets into engine design not PSRU design. The PSRU is just a single gear transmission with no clutch or torque converter if you will. Planes in the end need HP to fly, not torque. HP into a PSRU is slightly less than the output to the prop. However with out a PSRU you could not use small displacement engines that make HP at high RPM's.


The following is the classic HP definition:

Where:

P = Power, hp
N = Rotational shaft speed, rpm
T = Torque, lb-ft

You can solve for Torque from above equation. HP and torque by definition are related. HP is power and Torque is rate of producing HP or torque. In a car TOP SPEED is HP and acceleration or pull is torque. You need both right. For a plane top speed is also HP related not torque, but again the relation of HP and torque are inseparable. You need both and you get both by definition.

No need for me to re-type this info.....here is a LINK with some good basics.

If PSRU's where so great for plane's, they would all have it. Now to be fair many airplanes do have a gear reduction. Turbines engines turn high RPM and need gear reduction to get the Prop to a reasonable speed. Some Lycs and Continentals tried gear reductions. They really are not popular because of the added weight and maintence. It did make more power for a smaller displacement (by running higher engine RPM), but the solution was simply make the cubic inches bigger and turn the engine slow enough to eliminate the gearing. There is not fuel economy by running a smaller engine faster than a big one slower. (Not totally true but to complicated to discuss here and the difference is small.)

Many of the great big piston radials used a modest ratio gear reduction to make a little more HP by turning the engine a little faster, but the main reason was to keep the large diameter prop tips from going supersonic by turning the prop slower. The props of course where designed for the slower RPM. The gear box on those engines where made from magnesium and still weighted more than your whole RV, well may be a whole Lycoming. On the other hand they made several 1000 hp.

There's no doubt you can make more power by turning faster engine RPM's, but the PSRU is not making power the engine is. Also the problem with PSRU's and tractor airplanes with the engine up front, is the aerodynamic drag, trying to fit the device in the nose of the cowl. Also weight-N-balance CG is to be considered. The PSRU must be engineered for harmonics. Another negative is almost always hydraulic prop activation is not an option, leaving only fixed, ground adjustable or electric props, which cost more and just are not as good as hydraulic constant speed props. If you want to believe PSRU you is all goodness with no negatives and makes more efficiency you can, and you would not be totally wrong. However you're ignoring 1/2 of the equation.

 

[David-aviator]

This thread has had 68 salvos of verbal ground fire, no winner just a lot of wasted time and effort. Like some people are protestant and some are catholic, some go with an auto conversion, some don't. It ain't worth loosing any sleep over or worth discussing. I don't give advice anymore, I go out and fly and enjoy it. It really doesn't matter a whole lot to me what anyone thinks or what they fly behind.

This morning I flew some 50 miles to an airport to get the prop balanced one more time. Man, was it rough. Twenty five knot tail wind at 1500' but had not choice to climb staying under some class B airspace. The vibration did not seem that bad after a PSRU upgrade and prop overhaul but my good friend did get it smoothed out some more to .014 ips's. It is smoother than it was even between the bumps.

I had not flown out of a concrete runway for some time so this was nice to notice. No flap take off, 8000 feet long, roll less than half way through the hash marks and the thing is flying. That's ok. So another machine will get off in 1/3 the way through the hash marks - great - in the total scheme of things, that too doesn't matter too much at least not to me.

One comment on the Egg GEN3 PSRU. I've had GEN1 and GEN2 and now this one. It seems to be the best. It runs cool, all the way up to 164F today. No, they do not make more HP, just more torque. The H6 with the MT7 and GEN3 is ok, at least to me. It also is easy to read prop rpm, just half the engine rpm. I cruise mostly at 1700-1900. It is reasonably quiet and efficient.

Bottom line - to each his own. If we all drank the same beer, there'd only be one brewery and that would be sad.

 

[Garth]

All text here deleted by Doug Reeves.

Rules violation (way beyond civility).

 

[szicree]

All text here deleted by Doug Reeves.

Rules violation (way beyond civility).

I think your rules are good and reasonable, but I bet I speak for many when I say that I'm sure curious about what I missed

Maybe there should be a special password protected page that could contain all the inappropriate stuff. Or maybe you could just save it all up and package it for sale on video. Sort of a RV-ators Gone Wild! kinda thing.

 

[Mike S]

Garth---------although your post is now gone, I was able to read it, and think I can shed a bit of light on your question.

Your original post asked the question "Do PSRU's increase engine HP X"

And, the answer of course is no.

After reading the last post, I think I understand your question better. To put it into my own words, can an engine that makes x hp at 5000 rpm, use a PSRU to drive a bigger/faster prop than a x hp at 2500 direct drive engine???

Sure seems logical, both engines make x hp, but one spins twice as fast, so I should just be able to reduce the faster ones output rpm by half, and double its torque with a PSRU.

And, discounting drag losses, you are correct!!!!!

Problem seems to be that you dont realize that the High rpm engine was only making half the torque in the first place.

All the PSRU did was bring the torque back to what the slower engine was already putting out.

End result is that there is no effective difference it the ability to turn a prop between the two engines.

Hope this helps.

 

[Mike S]

I think your rules are good and reasonable, but I bet I speak for many when I say that I'm sure curious about what I missed

Maybe there should be a special password protected page that could contain all the inappropriate stuff. Or maybe you could just save it all up and package it for sale on video. Sort of a RV-ators Gone Wild! kinda thing.

Steve, actually I was in the process of deleting just the last paragraph----which is what I found offensive---- when Doug axed the whole thing---------wasnt too bad, IMHO, but I think Doug is getting a bit tired of the bickering.

 

[Garth]

Getting close now, but again you have to change to playing field to repudiate my observations. The engine of my comparison is the Rotamax at http://rotaryaircraftengines.com/PDF/RotarySpecSheet.pdf which puts out the same torque as HP and is quite flat and constant across the RPM scale, and is more torque than the comparable Lyconey puts out (see graph on the torque/HP curves at http://www.rotamax.net/downloads.html ) Now this is not about accuracy of their claims or some friction loss in the PSRU etc, it is that generally their should be some considerable gain, at whatever rpm one choses, to get this benefit. Just dialing in more pitch probably wont work as if the prop is not so designed it will just over dip and run your MP up with drag instead of thrust and make one think they are maxed out when they may be at a net loss. Anyway it you were correct, then if the torque is same, we are back to my observations. The propeller company's say it is a delicate balance of prop solutions with the many variables involved, and that few even try to do it, but either use a similar used prop for a similar HP engine, even though they use a PSRU (which they say should never be done) or just order one they think is best which it rarely is.

I did not think my comments were so bad and were deserved, but I now give up. I am signing off for good, I too have had enough.

 

[Phyrcooler]

Interesting thread. I hadn't a chance to read it until a few minutes ago. At one point my thought was... "What...?" Then I found posts that were quite interesting...later some that seemed to go a bit sideways (not that that never happens here at VAF!) Then I thought... what we need is a good long post from George to clear things up... oh, wait... there it is!

Hey Garth... relax... we're like family here. You're just a cousin who irritated another. We may argue and get a bit pissy with each other. At the end of the day, you may feel unloved. But, just like family, our ties are stronger than our temporary bicker sessions. What brings us here, and keeps us here... WILL still be here. The love of aircraft and flying.

DJ

 

[DeltaRomeo]

snip....but I think Doug is getting a bit tired of the bickering.

To say the least....

What I look for more than anything in a post is if it is in the tone of a conversation that would be conducted in the 'polite company of strangers'. Anything past that and it's a target by me or (with my complete blessing) any of the moderators.

If a moderator doesn't like it, it's toast.

We run a clean ship here, and that is the price of admission.

b,
dr

 

[Kevin Horton]

Getting close now, but again you have to change to playing field to repudiate my observations. The engine of my comparison is the Rotamax at http://rotaryaircraftengines.com/PDF/RotarySpecSheet.pdf which puts out the same torque as HP and is quite flat and constant across the RPM scale, and is more torque than the comparable Lyconey puts out (see graph on the torque/HP curves at http://www.rotamax.net/downloads.html )

Garth - The Lycomings actually put out a lot more torque than the Rotamax engines. Lycoming doesn't publish torque values, but you can calculate them from the published horsepower and rpm, as there is a fixed mathematical equation that ties those things together.

Torque = power x 5252 / rpm
with torque in units of ft-lb, and power in units of horsepower

So, a 160 hp O-320 will develop this power at 2700 rpm. The torque at this condition = 160 x 5252 / 2700 = 311 ft-lb.

If you are interested in comparing potential performance of different engines, the things of interest are:

• power delivered to the prop (i.e. engine power minus losses in the PSRU),
• prop rpm - too high an rpm will lead to low prop efficiency. Too low an rpm will likely require a large diameter prop, which can cause clearance problems.
• specific fuel consumption - i.e. what is the fuel flow to develop the power,
• weight of engine + PSRU + any required radiators, oil coolers, oil sumps, accessories, etc.

 

[rzbill]

Notes concerning Dyno parts of this thread

In reference to the few comments about dyno testing various aircraft installations, the minimum hardware to get the data would be an accurate tach, two accurate weigh scales for the main landing gear and safe rigging at the tail to resist thrust and level the crank to horizontal.

The difference in the weigh scale readings will allow calculation of torque (after determining moment arm to the crank from the scales) and RPM is from the tach of course.

The prop works wonderfully as a fluid dynamic brake. Measurement of the reaction forces on the main gear will theoretically exactly match the prop torque.

Complex equipment is not necessary if root principles are understood. For instance, I built a dyno 25 years ago that used a sand bucket on a long arm to resist engine torque. Worked great. I even had it set up for static thrust measurement.

 

[David-aviator]

Garth - The Lycomings actually put out a lot more torque than the Rotamax engines. Lycoming doesn't publish torque values, but you can calculate them from the published horsepower and rpm, as there is a fixed mathematical equation that ties those things together.

Torque = power x 5252 / rpm
with torque in units of ft-lb, and power in units of horsepower

So, a 160 hp O-320 will develop this power at 2700 rpm. The torque at this condition = 160 x 5252 / 2700 = 311 ft-lb.

If you are interested in comparing potential performance of different engines, the things of interest are:

• power delivered to the prop (i.e. engine power minus losses in the PSRU),
• prop rpm - too high an rpm will lead to low prop efficiency. Too low an rpm will likely require a large diameter prop, which can cause clearance problems.
• specific fuel consumption - i.e. what is the fuel flow to develop the power,
• weight of engine + PSRU + any required radiators, oil coolers, oil sumps, accessories, etc.

Very good summary. The real proof of the pudding is TAS and fuel burn (performance). It is very difficult to beat a Lycoming engine in an RV. Anyone trying to do so knows it. There are other upsides and downsides but TAS and fuel burn are held by Lycoming. IMHO the PSRU is a down side because it is heavy, another failure mode, and does cost HP and/or fuel burn. The total package has its upside in technology, smoothnes, ease of starting, little maintenance (when the bugs are subdued) and personal satisfaction of getting something different to work. After all, anyone can hang a Lycoming and go fly.

 

[cytoxin]

now thats what im talking about.

After all, anyone can hang a Lycoming and go fly.

amen brother. when i started buuilding, a guy with a turbine on a lancair.(the first one i might add.) told me there are builders and there are pilots. i guess im a pilot because the thought of adding time to my build really does not interest me. the plane has already been invented i just want a good stable platform from which to perform from. for all you builders out there, keep at it, your research will benifit others at some point in time. and i know some of you just like to put it together and take it apart. i got my fill of that with hot rod cars.

 

[gmcjetpilot]

Dyno idea cool but...

In reference to the few comments about dyno testing various aircraft installations, the minimum hardware to get the data would be an accurate tach, two accurate weigh scales for the main landing gear and safe rigging at the tail to resist thrust and level the crank to horizontal.

The difference in the weigh scale readings will allow calculation of torque (after determining moment arm to the crank from the scales) and RPM is from the tach of course.

The prop works wonderfully as a fluid dynamic brake. Measurement of the reaction forces on the main gear will theoretically exactly match the prop torque.

Complex equipment is not necessary if root principles are understood. For instance, I built a dyno 25 years ago that used a sand bucket on a long arm to resist engine torque. Worked great. I even had it set up for static thrust measurement.

Not flaming you but I see some problems with this.

How do you account for PROP efficiency or inefficiency?
What about temp rise of air? (kidding a factor but real small)
What about affect of prop wash over airfoils and "torque" on gear?

It is a cool idea and could calculate the total HP approximately but not accurately, I think? Correct me if I am wrong. I'm not trying to be a spoiler.

I do think pure static thrust is a valid & important measurement all by itself, to compare to static thrust of other engine/props. That is all it will tell you, but includes prop/engine efficiency. To back track that to engine shaft HP is a little hard. There is no sub for true dyno. Frankly dynos and different techniques give different values. That is why SAE has standardized it. Several automakers where sued for claiming dubious HP ratings of cars.

"Power Block" on Spike TV weekends has a show called "Horse Power". They have two dynos: one to measure at rear wheels of cars, the other is a self contained test cell just for engines. I agree a dyno might not be hard to make or design. The engine cell they have utilizes a water pump to measure torque. Auto manufacturers use an electronic "BRAKE" load cell to measure torque. Electromagnets/eddy currents can be used as well. Bottom line is to measure torque (force x arm) and RPM.

 

[rzbill]

Hi George,
I knew quite well that someone would challenge the minimum tools needed to get reasonably accurate HP numbers.

In the case I was trying to represent, it is absolutely immaterial what the prop efficiency is and what the prop actually does to dissipate the absorbed horsepower. The method I was proposing would measure HP at the crank, not any data on thrust. The prop is simply a "brake" to absorb and dissipate power. It would not matter whether it was a pusher, tractor, or some other radial fan, the use would be the same. In our case, our props are already designed to absorb the HP our engines produce at the right RPM, so we do not need a custom adjustable dyno brake.

Since the prop is dissipating the power in a similar fashion to the water or electrodynamic brake, there is torque at the crankshaft. Physics says that the torque must be resisted not just by the prop, but by the structure that holds the engine. Ultimately this translates to the main gear contact with the ground.

You make a reasonable point about prop wash and its effect on the wing and the related lift that would alter the weigh scales. If both wings lift the same, then the effect will cancel since I would be looking for differences between the two scales. Obviously there is a helical aspect to prop wash that will instill some assymetry. If one were to actually use the method, then devices to kill any lift could certainly be duct taped to the wing roots. I think this might be less important than executing the test in a windless environment, simpy due to the winds ability to act on the whole wing area vs the limited area under prop wash.

I wholeheartedly agree that thrust is an important measurement, but the previous thread comments were about Dyno HP only. I wanted readers to understand that it is not necessary to yank their engine(s) and pay big bucks to find out whose "throttle cable is longer"

Admitedly, the dyno I built did not test in the airframe but it still used the prop. I had the engine mounted on a single rail with ball bushings so it would rotate (torque measurement) and slide axially (thrust measurement). My purpose was to confirm some vendor specs (which I did within a few %).

I think an even larger descrepancy than prop wash effect on wing will be the use of a fixed pitch prop. The static RPM will be low by a few hundred RPM, so HP will be lower than delivered at max RPM.

Now for the disclaimer. I myself would think very hard about doing the test this way due to safety concerns. I certainly do not want to be the cause of another video like the wingless engine test that went awry.

Regards

 

[clarkefarm]

NSI Subaru EJ25 on a real dyno

Sort of ancient history because the product is no longer on the market but I put my "215" hp firewall forward package (complete with muffler, 2.12:1 PSRU,basic air filter etc) on a reputable (they tune for Ford and run the State Dyno Challenge) dyno to fuel map new ECU's.

The engine is the 2.5 block with SOHC 2.2 heads (to reduce size and weight) and has NSI induction manifold, modified camshafts, light weight flywheel, sprague clutch etc. etc.

Horsepower at the propellor flange was 162 hp @ 6,000 rpm and 160 at the rated max continuous 5,800 rpm.

It is flying a 9A - heavy at 1130 lbs but carrying lots of extras like tip tanks, fuselage storage box, dual axis A/P, Auto chamelion paint, header tank and lots of redundant engine systems.

It is also a lot slower than an 0-320 with a max IAS of 158 kts at a DA of about 2,000', full power cruise of 155 kts TAS at a DA of 10,000' burning approx 8 gals/hr and economy cruise of 140 kts TAS at a DA of 8,000' burning approx 5.5 gals/hr.

What it does have going for it is fully automatic engine management (running an 02 sensor on the primary ECU) and the ability to do some neat tricks like pulling up to 22º of reverse pitch on the prop which is great for stopping on short or downhill strips - and can, if you are brave enough, be used as a really effective air brake.

Would I do it again ? Probably yes because it has been a real adventure and I have learnt a lot. I am also going to keep modifying to see if I can't reach the magic 163 kts TAS at 8,000 the 9A's should be capable of.

Would post an image but don't know how. [ed. Instructions for posting pics here. dr]

Rupert Clarke
Melbourne Australia

 

[lostpilot28]

Hi Bill,
I've heard of measuring torque this way in a magazine article recently. If I can find it, I'll post which one it was.

An interesting side note about this (sorry to get off-topic again), but Aveo, the company coming out with the new EFIS system in a few months, told me at Oshkosh that one of thier new devices will measure Weight-and-Balance at the gear with micro-sensors installed in the gear.

They didn't give many details, but it sounded like a great way to keep an eye on W&B without doing much work. I'm thinking that you could also use the numbers provided at the wheels to give you the torque from the engine.

 

[mgomez]

Signal/noise issue?

If I did the math right, the method of using the reaction force on the gear to measure engine torque sounds like it might suffer from a low signal/noise ratio.

The torque from a 180 HP 2700 RPM engine is about 350 ft-lbs. The track of the main gear is 6' 8". That means that the force is 52 lbs more on one wheel than on the other...so one is 26 lbs light, and the other is 26 lbs heavy.

The weight of the airplane causes a few hundred lbs on each wheel.

Has anybody calculated how accurately you can measure torque using this method? And what's the effect of the wind?

 

[Yukon]

I can't see how an indisputable, calibrated, torque and horsepower measurement can be made with the engine installed. I therefore limit my offer to pay for a certified test cell run with an atmospheric 4 or 6 cylinder Eggenfellner engine. Anybody?

The NSI engine run is an interesting data point, even though NSI was claiming
215 hp, 160 is close to what Egg is hoping for. 2:12 drive ratio though.

 

[David-aviator]

I can't see how an indisputable, calibrated, torque and horsepower measurement can be made with the engine installed. I therefore limit my offer to pay for a certified test cell run with an atmospheric 4 or 6 cylinder Eggenfellner engine. Anybody?

The NSI engine run is an interesting data point, even though NSI was claiming
215 hp, 160 is close to what Egg is hoping for. 2:12 drive ratio though.

There's an easier way yet and it won't cost more than an hours worth of fuel.

We know the HP of Lycoming engines, just fly the airplane at WOT at 8500' and compare the speed with what Van's has published and do the math. If a 180 HP Lycoming does 180 knots and the alternative engine does 170 knots, it is producing 94.4% of the power of the Lycoming.

At present, based on pure performance, my engine produces about 93% of a 200 HP Lycoming.

 

[Yukon]

There's an easier way yet and it won't cost more than an hours worth of fuel.

We know the HP of Lycoming engines, just fly the airplane at WOT at 8500' and compare the speed with what Van's has published and do the math. If a 180 HP Lycoming does 180 knots and the alternative engine does 170 knots, it is producing 94.4% of the power of the Lycoming.

At present, based on pure performance, my engine produces about 93% of a 200 HP Lycoming.

David,
That's a good start, but I think it's going to be real hard to get two planes with the same props, at the same weight and temperature. Cooling drag will not be compensated for either, and would give the Subaru a hp disadvantage.
Actually, I think a timed climb to 10,000 feet might be a better measure of horsepower, but I haven,t heard of a Subaru that could compete without overheating.

Dyno is the only way to go. With as many of these engines sitting around awaiting installation (or resale) I would think we could put something together.

Anyway, Van's website shows 217 mph top speed for a 7. What are you getting?

 

[David-aviator]

David,
That's a good start, but I think it's going to be real hard to get two planes with the same props, at the same weight and temperature. Cooling drag will not be compensated for either, and would give the Subaru a hp disadvantage.
Actually, I think a timed climb to 10,000 feet might be a better measure of horsepower, but I haven,t heard of a Subaru that could compete without overheating.

Dyno is the only way to go. With as many of these engines sitting around awaiting installation (or resale) I would think we could put something together.

Anyway, Van's website shows 217 mph top speed for a 7. What are you getting?

217 mph where?

Doesn't really matter, I am no where near it. I was looking at 75% power, Vans shows 203 at that power.

The MT-7-C/183-51 prop, which is what was recommended by the EGG factory several years ago, is certified for the 0235 Lycoming (info from MT's web site) and modified for Subaru. I have felt since day one it is not optimized for the H6 at all. It was originally introduced with the 2.5 NA engine. Increasing rpm from 2500 to 2700 with H6 has negative consequences - it simply runs out of steam. The prop is fine for low end performance.

What I should be running with is the new Sensinich prop but I am tired of spending money on this project.

By the way, I can climb to 10,000' easy today without a cooling rest (OAT 60F) but not when it is 90F. If the weather holds, I will time a climb to FL100 tomorrow morning.

 

[DanH]

<< my "215" hp firewall forward package >>

Rupert, did I read you correctly? Your engine package was marketed as 215 HP and your actual dyno runs indicated 162 HP max? Who was the supplier?

In fairness, there are a whole bunch of Lycoming vendors who make similar BS claims.

 

[Yukon]

<< my "215" hp firewall forward package >>

Rupert, did I read you correctly? Your engine package was marketed as 215 HP and your actual dyno runs indicated 162 HP max? Who was the supplier?

In fairness, there are a whole bunch of Lycoming vendors who make similar BS claims.

Dan,
As Rupert stated in his post, NSI, the defunct Subaru converter built and sold the engine. They were well-known for extravegant claims. They closed down several years ago, somewhat prior to Crossflow's failure.

 

[rzbill]

Problems to overcome.

If I did the math right, the method of using the reaction force on the gear to measure engine torque sounds like it might suffer from a low signal/noise ratio.

True. The scales would need to be able to tare out 700 lbs each and still be accurate to .1 lb for a reliable 1 lb reading for instance. If we assume a 1 lb error on each scale, I think that would equate to a roughly 5% HP calculation error. If the scales jump too much, 30 repeated readings would give 95% confidence level in the data.

Neglecting the wind, I contend that the mass of the airframe will damp the torque signal in a manner to make the readings easy. When correctly set, the torque reaction bar on my old dyno would float "stationary" like an analytical balance. Not much variation in signal strength.

With all that said, I think the technique is going to really suffer from actions of the wing. In worst case situations assuming the prop blast or breeze acts at Alphamax, a 6kt breeze could totally wipe out the measurements. If the craft is level, alpha would be generally less and the effect would be less.

Now I'm curious about the article mentioned a few posts ago.

 

[Yukon]

217 mph where?

Doesn't really matter, I am no where near it. I was looking at 75% power, Vans shows 203 at that power.

The MT-7-C/183-51 prop, which is what was recommended by the EGG factory several years ago, is certified for the 0235 Lycoming (info from MT's web site) and modified for Subaru. I have felt since day one it is not optimized for the H6 at all. It was originally introduced with the 2.5 NA engine. Increasing rpm from 2500 to 2700 with H6 has negative consequences - it simply runs out of steam. The prop is fine for low end performance.

What I should be running with is the new Sensinich prop but I am tired of spending money on this project.By the way, I can climb to 10,000' easy today without a cooling rest (OAT 60F) but not when it is 90F. If the weather holds, I will time a climb to FL10 tomorrow morning.

David,
Here's the link for Van's RV-7 performance numbers. http://www.vansaircraft.com/public/rv-7per.htm

I can't believe Jan sold you a prop for a 115 hp engine to install on a 190 hp engine, even if it had modified blades. Surely they are optimized better than that for specific horsepower ranges.

Remember how your engine would barely fly with that fixed-pitch Felix prop? Remember how a Lycoming guy bolted it on his airplane and it flew fine? That is irrefutable evidence that the Egg engine isn't producing the torque and or horsepower that the Lycoming is. A dyno is the only way to confirm these issues, and put this to bed once and for all.

 

[mgomez]

Power goes with speed cubed

If a 180 HP Lycoming does 180 knots and the alternative engine does 170 knots, it is producing 94.4% of the power of the Lycoming.

You know me...type-AR engineer and all that...so forgive me if I point out the error in that statement.

170 is indeed 94.4% of 180. The power, though, is proportional to the cube of the airspeed, so in the above example, the alternative engine is producing 84.2% of the power of the Lycoming. 0.944 * 0.944 * 0.944 = 0.842.

Regards,
Martin

 

[Yukon]

You know me...type-AR engineer and all that...so forgive me if I point out the error in that statement.

170 is indeed 94.4% of 180. The power, though, is proportional to the cube of the airspeed, so in the above example, the alternative engine is producing 84.2% of the power of the Lycoming. 0.944 * 0.944 * 0.944 = 0.842.

Regards,
Martin

Indeed.....Take a look at the incremental speed increases on the Van's website for the RV-7. 160 hp cruises very little slower than a 200 hp.

http://www.vansaircraft.com/public/rv-7per.htm

That's why I think climb rate would be a better measure of hp than speed.

 

[mgomez]

That's why I think climb rate would be a better measure of hp than speed.

A little. The problem with climb rate is that it's proportional to a small difference between two big numbers, i.e. climb rate = (power available - power required)/weight.

That also makes for a poor measurement. It's better in an RV than in a low-performance airplane, granted.

If you want to know power, put the engine on a dyno. One of the best engineers that I know says it simply "If you want to measure something, measure it."

 

[David-aviator]

David,
Here's the link for Van's RV-7 performance numbers. http://www.vansaircraft.com/public/rv-7per.htm
......
I can't believe Jan sold you a prop for a 115 hp engine to install on a 190 hp engine, even if it had modified blades. Surely they are optimized better than that for specific horsepower ranges.
........

The MT-7-C/183-51 was created and certified for the EGG 2.5 engine by MT. It carries a 1500 hour warrantee with that engine. The MTV-7-F/170-09 is certified for the C152. The blade diameter of the Subby version is 183cm, the C152 170cm, about 5 inches less, and the blade designation of 51 verses 09 says something about the blade design but I don't know what it means. There is quite a difference in these props and it is not quite on the mark to conclude they took the Cessna prop and bolted it on the Subaru 2.5.

Beyond all that, MT probably was not consulted about the MT-7 going on the H6. In fact there was no vibration survey with the H6 as the EGG factory ceased being a MT dealer about when I bought the prop and engine. At the time it was the MT-7, the Quinti with Warp Drive blades or the MTV18B/183-59 from Van's for about 2 grand more than the EGG price. There was no Sensinich at that time.

MT has indicated they would do the H6 survey in mid November when they visit their US dealer in Deland, FL. to reinstate the 1500 hour warantee with H6 which is now set at 200 hours. I doubt there is a vibration issue with this engine as it is smoother the 2.5. One of us with the engine will have to show up for the test.

 

[David-aviator]

....
Remember how your engine would barely fly with that fixed-pitch Felix prop? Remember how a Lycoming guy bolted it on his airplane and it flew fine? That is irrefutable evidence that the Egg engine isn't producing the torque and or horsepower that the Lycoming is. A dyno is the only way to confirm these issues, and put this to bed once and for all.

There was more to it, John. Fred Felix cut the prop for a 0360 because we had no other base line. I figured I should have 180 HP (at least) so it ought to be in the ball park. I learned 2 things from that experiment.

First off, the prop was over pitched for the H6. It turned up about 1900 rpm static. I figured if we could get it up to about 2200 or 2300 to give the H6 a chance to wind up, it might work. Fred said he could rework it but not that much. As it was, the engine never had a chance to gather its muscle running at 3450 rpm - it is a 6000 rpm engine. After take off it moved out, but the runway roll was unacceptable for me. I did a similar test with the 2.5 engine running the Quinti system in manual, same thing only worse.

The Lycoming develops good torque and power at moderate rpms, the Subby needs a head of steam in rpm to do the same and if you have that head of steam on the runway, it overspeeds on climb out. Some guys think they can live with a fixed pitch prop and the wide rpm range, I can not. There's too much compromise on the runway.

Second, I could not cool the engine with the fixed pitch. The coolant temp was going over the red line in the pattern and there was nothing I could do about it but land ASAP. It was a new engine and running hotter than it does now, but it was so unacceptable, that issue and the over pitch, something had to give. The RV4 guy next door at the airport was drooling all over that prop so I got my money back but spent a lot more for the MT.

The answer you want probably can only be determined on a dyno. But if we could wind the beast up to 6000 rpm, you might be surprised how much torque and power it has. Jan was headed in that direction with the belt drive and 2.5:1 ratio but that effort failed and he's lucky to have come out of it in one piece. As it is, we are now living with GEN3 and 2.05:1 and crank up a mere 5400 rpm at the prop limit of 2700. The RV-10 speeds he has posted are at 5000 rpm with 4 blades of Sensinich in a Quinti hub.

I believe the power is there if it can be gotten to with an adequate prop and PSRU.

 

[gmcjetpilot]

Van has a good base line set of test.

.... I think climb rate would be a better measure of hp than speed.

Yes, side-by fly-off, including time (and fuel) to climb like Van's team dreamed up.

For the two rotary Power-sport RV-8 v. two Van's RV-8 prototypes, they did a set of "real world" test, which included climb and normal cruise. This put the Power Sport rotaries in a good light performance wise by the way verses the Lycoming, however fuel burn, empty weight and noise where not strong points. Too bad power-sport is not selling engines, which was a highly modified and improved rotary based on the Mazda Wankel.

One test involved all planes taking off and climbing to 8,000 feet at 2,500 rpm and 120 kts. Time to climb was measured. All planes where ballasted to same weight with full fuel. Once at 8,000 feet, they got line-O-breast and still at 2,500 rpm, went full throttle for 5 min. Speeds where compared by GPS. Visually you could see as well which is faster. They throttle back and flew together back to the airport they all departed and landed in order they departed. Fuel was refilled. From this test they go time to climb, max speed at 8,000 ft under identical conditions and total fuel used.

Second test took off from airport 'A" and climbed to 8,500 feet at 130 kts. Once at altitude and over airport 'A' they switched tanks and flew to airport 'B' and back to 'A', about 160 miles total distance. Once over airport 'A' the tanks where switched back and they landed in order again. Landing back at 'A' they refilled the tanks and noted total fuel used and fuel for the tank used for the A-B-A cruise segment at 8,500'. I assume they ballasted to same weight again. They got 'Block' time for a typical cruise segment of a flight and fuel burn.

They also did a noise test for a low fly-by since the Rotaries have a rep for being a little harsh on ears. A dB meter indicated the rotary reputation was deserved.