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  #51  
Old 03-21-2012, 08:06 PM
Remag Remag is offline
 
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[quote=CMBAero;642015]Again, we are getting at the same point that were mentioned before in this post...

-Slow Revving... --> You can't turn a propeller too fast or the tip will break the speed of sound and will then destroy your prop... You have to be slow revving but have more torque so you can increase the pitch instead!
No point in using a 10000rpm engine then... Even with a gearbox, you would be adding weight and reducing reliability to get almost the same result!

* Again the Rotax 912 -v- IO-233 debate. Rotax has a gearbox (which is a torque multiplier), is lighter and hugely reliable. Many many aircraft engines run a gearbox. My old M14P radial had a gearbox and was excessively reliable. What about a Merlin?

-Heavy... --> To reduce weight, you would have to use different metals, but then again, it would cost more to produce and add to this all the required test it would need to get the new parts FAA approved...no way a homebuilder or small private plane owner could afford a 40K$ engine fora such a small increase in gas consumption/performance!

* Again the Rotax 912 -v- IO-233 debate. The Rotax is lighter than the Lyco and costs about 25k. You can have a fully certified one if you want. Many RV-12 owners can afford them.

-Noisy --> To cut down on noise, you would need to install mufflers... This means, more weight and performance loss... Who would want that!

* Not me, not to mention muffling the sound of these lovely tractors which I would not want.

As for the dirty engines, we could improve a little on this with better ignition system and fuel injection systems...but again it means more R&D and FAA approved modifications which means you pay more for your engine!

* I have cleaned up my XP-360 considerably by running Mogas. Keeps all of that lead out of my engine and the atmosphere. No gunked up pistons, valves, plugs etc. Only good for some engines though.

Not trying to be rude here, but just trying to explain why it is that we can't really improve on these points when we have something that is already "Reliable" for an already high price!

* I thought is was good post, not rude at all. I just don't think that our engines are all that reliable and the Rotax 912 has proven that it can be done and could be done with higher horsepower engines. We just need to change our mind set.

Regards,

Mark.
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  #52  
Old 03-21-2012, 08:22 PM
CMBAero CMBAero is offline
 
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Quote:
Originally Posted by Bob Kuykendall View Post
A minor quibble: When the prop tips go supersonic, it is not necessarily particularly damaging to the prop itself. There is no magical power to a shock wave that immediately rends asunder anything it touches.

What is bad about pushing the tips transonic is that it is a lot draggier than when they're subsonic. The shock waves pretty much hemorrhage energy by converting it into noise and neighborhood complaints.

In fact, prop tips go transonic and create shock waves pretty regularly. The tip speed doesn't even need to be supersonic; when the tips get to between 60% and 85% (depending on the blade section), the curvature of the airflow around the blade section causes enough local acceleration in the air to get it to go super sonic and rip out some shock waves.

I don't know what happens when the prop is forced solidly into the supersonic realm. I can imagine that a prop runaway caused by a bad governor or something like that would cause some damage. But probably mostly to the engine.
Bob, you are absolutely right, I just didn't want to go into the details since we were talking about engines performance... But thanks to put it all out for the others!

A lot of pilots don't know those information and sometimes thinks that they are getting more performance by pushing their prop speed to the limit by "tweeking" their governor but in fact they are only thinking they are going faster because of the added noise and are in fact creating more stress on the prop and the engine!



[quote=Remag;642040]
Quote:
Originally Posted by CMBAero View Post
Again, we are getting at the same point that were mentioned before in this post...

-Slow Revving... --> You can't turn a propeller too fast or the tip will break the speed of sound and will then destroy your prop... You have to be slow revving but have more torque so you can increase the pitch instead!
No point in using a 10000rpm engine then... Even with a gearbox, you would be adding weight and reducing reliability to get almost the same result!

* Again the Rotax 912 -v- IO-233 debate. Rotax has a gearbox (which is a torque multiplier), is lighter and hugely reliable. Many many aircraft engines run a gearbox. My old M14P radial had a gearbox and was excessively reliable. What about a Merlin?

-Heavy... --> To reduce weight, you would have to use different metals, but then again, it would cost more to produce and add to this all the required test it would need to get the new parts FAA approved...no way a homebuilder or small private plane owner could afford a 40K$ engine fora such a small increase in gas consumption/performance!

* Again the Rotax 912 -v- IO-233 debate. The Rotax is lighter than the Lyco and costs about 25k. You can have a fully certified one if you want. Many RV-12 owners can afford them.

-Noisy --> To cut down on noise, you would need to install mufflers... This means, more weight and performance loss... Who would want that!

* Not me, not to mention muffling the sound of these lovely tractors which I would not want.

As for the dirty engines, we could improve a little on this with better ignition system and fuel injection systems...but again it means more R&D and FAA approved modifications which means you pay more for your engine!

* I have cleaned up my XP-360 considerably by running Mogas. Keeps all of that lead out of my engine and the atmosphere. No gunked up pistons, valves, plugs etc. Only good for some engines though.

Not trying to be rude here, but just trying to explain why it is that we can't really improve on these points when we have something that is already "Reliable" for an already high price!

* I thought is was good post, not rude at all. I just don't think that our engines are all that reliable and the Rotax 912 has proven that it can be done and could be done with higher horsepower engines. We just need to change our mind set.

Regards,

Mark.

You are absolutely right with the information you provided regarding the Rotax 912... For having worked on them in the past, they are nice and powerful small engine, but to compare the weight of the 912 to a io 233 lycoming, you would need to take into consideration also the added weight of the coolant cooler, the coolant tank and the gearbox... I would be curious to know the final weight of an installed 912 vs a io233!?

Problem with the rotax is their size for now, they need to build a Rotax powerful enough for a RV9...
If I would be building a RV12, I think personally I would go toward a Rotax 912!

Change our mind set; yep you are right, problem is, it takes time and money to develop new technologies and get them FAA approved... General Aviation does not generate enough money for this to happen!
In the big guns thought it's different, just take a look at the new P&W that will power the new Bombardier C Series, it is a geared turbofan!
http://en.wikipedia.org/wiki/Pratt_%26_Whitney_PW1000G
http://www.purepowerengine.com/

Sure looks interesting!

Last edited by CMBAero : 03-21-2012 at 08:29 PM.
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  #53  
Old 03-21-2012, 08:43 PM
Remag Remag is offline
 
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You are absolutely right with the information you provided regarding the Rotax 912... For having worked on them in the past, they are nice and powerful small engine, but to compare the weight of the 912 to a io 233 lycoming, you would need to take into consideration also the added weight of the coolant cooler, the coolant tank and the gearbox... I would be curious to know the final weight of an installed 912 vs a io233!?.

* That is a really good point. So I crunched the numbers. The Rotax with EVERYTHING including water (less 3.5 qts of oil) comes in at 150.5 lbs. The Lyco (less 5 qts of oil) comes in at 213 lbs. Rotax less oil is 62.5 lbs lighter.

Problem with the rotax is their size for now, they need to build a Rotax powerful enough for a RV9...
If I would be building a RV12, I think personally I would go toward a Rotax 912!

* Yeah, I wish Rotax would have continued with the 150hp V6 project.

Change our mind set; yep you are right, problem is, it takes time and money to develop new technologies and get them FAA approved... General Aviation does not generate enough money for this to happen!

* True and it is a real shame.

In the big guns thought it's different, just take a look at the new P&W that will power the new Bombardier C Series, it is a geared turbofan!
http://en.wikipedia.org/wiki/Pratt_%26_Whitney_PW1000G
http://www.purepowerengine.com/

Sure looks interesting![/quote]
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  #54  
Old 03-22-2012, 12:02 PM
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frankh frankh is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
Way more variables involved than just these to say that liquid cooling causes more drag- mass of water vs. air, specific heat of water, thermal conductivity, radiator efficiency vs. those of thick cooling fins, duct design, momentum recovery, etc.

There is no evidence to suggest that a well designed liquid cooled installation has more drag than an air cooled one, in fact there are various examples which I've brought up before numerous times showing just the opposite. The fuel burn vs. TAS on the STI RVs is comparable or better than those powered by Lycomings and these don't even have optimized radiator layouts- just stuffed in the cowlings and using the stock Vans inlets.

With regards to new engines, I just don't see anyone being able to design, test and produce a clean sheet design in the small numbers used by this industry and be any cheaper than a Lycoming. While you might, maybe, possibly get 10% better SFCs with a really modern design, would all that trouble, risk and liability exposure be worth it? Doesn't seem like it to me.

The diesel is intriguing but nobody has demonstrated comparable reliability, pricing and longevity in any aero diesel yet and some have been pretty poor. With time, I believe we will see some of these improve and/or prove themselves and if so, these might make more sense in this application of relatively constant rpm/ high power than spark ignition engines.
An interesting experiment would be to measure the the flowrate and temperature of the discharge air temperature from the cowl. Two identical airplanes flying at the same speed, one with water cooling the other with air. The basic question is,,How efficient is each style of engine at heating the cooling air.

The increased surface area of the radiator would in theory provide presumably provide an advantage, the question would be if the if this is enough to compensate for the higher cyl head temps of the air cooled motor.

Actually it would be easier to do the fly off between the Eggenfelner airplane and an identical LYC with an accurate fuel flow meter.

Funny I think we been here before.

I think this comes down to the sense that Van was right..I.e we think there should be something better than the old clunker, but so far we've never seen it.

Anedotally a Lyc running LOP, autofuel with electronic ignition is a pretty darned fuel efficient motor.

Frank
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  #55  
Old 03-22-2012, 03:51 PM
kgood kgood is offline
 
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Default We're getting closer.....

Quote:
Originally Posted by rv6ejguy View Post

The diesel is intriguing but nobody has demonstrated comparable reliability, pricing and longevity in any aero diesel yet and some have been pretty poor. With time, I believe we will see some of these improve and/or prove themselves and if so, these might make more sense in this application of relatively constant rpm/ high power than spark ignition engines.
Myself and 20 or so Wilksch WAM 120 diesel owners might beg to differ.

I now have 320 hours on mine, and there is at least one '9A in the UK with well over 500 hours. I'm not sure what the rest have, but, as far as I know, we're all pretty happy with these engines.

I paid no more for mine than I would have paid for a Lyc O-235, and my '9 performs on par with the O-235-powered '9, while weighing less, and using less fuel. And I can burn diesel or Jet A.

I have had no trouble at all with my engine so far. I fly it regularly, and it requires no "babying" - just get in, heat the glow plugs, start it, and go. No priming, no carb heat, no mixture, no mags, no electricity required to run, hyd CS prop. So far, there has been no downside (unless a little smoke on takeoff bothers you!).

Ross, you are right, there are improvements to be made (namely a higher HP engine), but the WAM is pretty good. I would much rather be flying behind it than any other avgas/mogas engine I've flown behind. As so many have stated, developing a new aircraft engine is a VERY costly and time-consuming effort, with not many rewards, thanks to a small market, liability, and so on.

Kurt Goodfellow
RV9 / WAM 120 diesel, 320 hours.
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  #56  
Old 03-24-2012, 03:02 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by frankh View Post
An interesting experiment would be to measure the the flowrate and temperature of the discharge air temperature from the cowl. Two identical airplanes flying at the same speed, one with water cooling the other with air. The basic question is,,How efficient is each style of engine at heating the cooling air.

The increased surface area of the radiator would in theory provide presumably provide an advantage, the question would be if the if this is enough to compensate for the higher cyl head temps of the air cooled motor.

Actually it would be easier to do the fly off between the Eggenfelner airplane and an identical LYC with an accurate fuel flow meter.

Funny I think we been here before.

I think this comes down to the sense that Van was right..I.e we think there should be something better than the old clunker, but so far we've never seen it.

Anedotally a Lyc running LOP, autofuel with electronic ignition is a pretty darned fuel efficient motor.

Frank
Actually just measuring the cowling exit air temps wouldn't tell us what we really need to know here which is the overall efficiency of the system and to do that we really need two close to identical RVs, same prop and the different engine designs, fly them side by side, switch tanks and fly for 1.5 hours, switch tanks, land and see who burned less fuel on top up.

From all the feedback from customers with atmo Egg conversions, it is clear that fuel flows are higher than a comparable Lycoming at the same TAS. The two modified turbo STIs are noticeably more efficient and repeated tests with calibrated FF meters and the switch tanks/ time/ top up method both show very comparable data to a Lycoming setup. These invariably do not use the same prop though as both STIs use electric MTs and the Lycoming ones don't so this is not totally apples to apples.

As far as the WAM engines go, while I'm VERY impressed with what they have done with a small team, I still reserve judgement until those 20 engines in service all go 2000-2400 hours without major trouble like an O-235 might and I don't see any better performance or fuel flow with the WAM. O-235 RV9s seem to do about the same speeds and fuel flows LOP. The published SFCs for the 2 engines are very similar as well. I've said it before, a few hundred hours on a few engines does not tell us how good an engine design might be long term and for overall operating costs. At the moment, it is encouraging at least and that is a very good start.
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Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 441.0 hrs. on the Hobbs,
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http://sdsefi.com/cpi2.htm



Last edited by rv6ejguy : 04-09-2012 at 12:06 PM.
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  #57  
Old 03-24-2012, 09:23 PM
kgood kgood is offline
 
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Default WAM

Quote:
Originally Posted by rv6ejguy View Post
As far as the WAM engines go, while I'm VERY impressed with what they have done with a small team, I still reserve judgement until those 20 engines in service all go 2000-2400 hours without major trouble like an O-235 might and I don't see any better performance or fuel flow with the WAM. O-235 RV9s seem to do about the same speeds and fuel flows LOP. The published SFCs for the 2 engines are very similar as well. I've said it before, a few hundred hours on a few engines does not tell us how good an engine design might be long term and for overall operating costs. At the moment, it is encouraging at least and that is a very good start.
Point taken. We've got to start somewhere.

With regard to the O-235 being as efficient as the WAM, you may be close once you're in cruise, LOP. But, if you recall when Van's tested the factory RV9A against the WAM, we did a one hour flight, side by side "same day, same way". Actually we (Marc Cook and I), were about 70 lb heavier than Ken K and his brother. Ken and I followed the exact same flight profile, and I burned almost 2 gallons less than he did. The whole purpose of the flight was to compare fuel burn. Ken encouraged me to do everything I could to optimize fuel efficiency, and that he would do the same with the Lyc. It wasn't apples to apples, because the factory '9A had an O-320, but I don't know how many times I've read in this forum (including Ross's posts) that any Lycoming run LOP, throttled back to the lower speeds of the WAM or O-235, would achieve the same efficiency.

I only had 85 hours on the plane at that time, but since then, I've discovered that my efficiency gets better with altitude, thanks to the turbo. If I had that flight to do over again, I think I could have done even better if I flew higher, and made the Lyc burn more fuel in the climb.

As I've said before: when you consider the whole flight profile, the diesel comes out on top, even the less-efficient ones like the WAM.

I agree with what many have said about liquid cooling. If done correctly, it should be more efficient than air cooled. Mine is nowhere near correct yet. It works well, but I know it could be much better. I'm working on it, little by little. But I just can't stop flying long enough to tear it down and make some of the changes that need to be made!
Kurt
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  #58  
Old 03-25-2012, 07:47 AM
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Ron Lee Ron Lee is offline
 
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Originally Posted by kgood View Post
.... but I don't know how many times I've read in this forum (including Ross's posts) that any Lycoming run LOP, throttled back to the lower speeds of the WAM or O-235, would achieve the same efficiency.
This comment has been applied to avgas versus avgas engines.....not avgas to diesel.

A friend has a Golf TDI diesel that gets 50 MPG. Am I to conclude that diesel engines are in general more fuel efficient than gasoline?

If you are using a WAM 120, my gut view is why install a 120 HP powerplant in an aircraft that accepts 160 HP? The Tim Allen principle is solid. Enjoy what you have but that powerplant is not likely to be other than a ultra-minor engine of choice. Plus you will have to accept that an RV so equipped will have close to zero resale value...or only among a rare (very small) number of potential buyers.

Last edited by Ron Lee : 03-25-2012 at 09:59 AM.
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  #59  
Old 03-25-2012, 08:03 PM
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NDrv8r NDrv8r is offline
 
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Originally Posted by bret View Post
I disagree on the 25 MPG, Honda I DTEC 2.2 Diesel is getting 63 MPG, one of their improvments was to inject the fuel at 1,600 BAR, thats 23,000,000 PSI, our comon rail systems are at around 30,000 PSI
23 million psi????? well thats nothin. My RV gets a gazillion miles per gallon.
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  #60  
Old 03-25-2012, 09:40 PM
kgood kgood is offline
 
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Default Avgas vs diesel

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Originally Posted by Ron Lee View Post
This comment has been applied to avgas versus avgas engines.....not avgas to diesel.

A friend has a Golf TDI diesel that gets 50 MPG. Am I to conclude that diesel engines are in general more fuel efficient than gasoline?

If you are using a WAM 120, my gut view is why install a 120 HP powerplant in an aircraft that accepts 160 HP? The Tim Allen principle is solid. Enjoy what you have but that powerplant is not likely to be other than a ultra-minor engine of choice. Plus you will have to accept that an RV so equipped will have close to zero resale value...or only among a rare (very small) number of potential buyers.
Actually, the way I read it, Ross was comparing the economy of the WAM diesel to the avgas O-235, and I just wanted to set the record straight. Diesels are more fuel efficient than gasoline engines. I know of no exceptions, although there may be a few that I'm not aware of. Does that mean that diesels are better than gas engines in airplanes? Ross is right, more development is required to find the answer. But in my case, so far the diesel has been better.

And, yes, your "gut view" is probably right. Why indeed install a 120 hp where a 160 is acceptable? For me, it was because there wasn't a 160 hp diesel available - and the RV9 airframe also accepts a 118 hp engine. Since I understood (and still do) the benefits and inevitability of aerodiesels, I was willing to accept some risks (and this includes financial risk) in order to experiment. There are some of us still out here who are willing to experiment in order to help develop better technologies.

Close to zero resale value? I'm not so sure. I have been amazed at the interest this engine/airframe combination has generated. Most aviators I've spoken with know that avgas as we know it is eventually going to be phased out. They also know Jet A is the most available and preferred aviation fuel worldwide. It's no stretch for most people to understand that diesels will a big part of aviation in the future. In the presentations I have given at forums and EAA chapter meetings, people have been very interested to see what lies ahead. Many are familiar with the amazing progress in automotive diesel technology; they know that it's just a matter of time until this technology is harnessed for GA.

If I offered it for sale today, would it bring what a traditional-powered RV would? Maybe not. Probably not. But I didn't built it to sell. I got what I wanted - and then some.

If you're concerned about resale value, check the "traditional engine" forum, and stick with the tried and proven, same 'ol, same ol. Nothing wrong with that.

Kurt
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