24 replies to this topic

[crono33]

sorry for the OT but i am sure some people here have good information on the subject.

i own and fly an advanced microlight aircraft, something with performances comparable to the C150

these airplanes mainly use the rotax 912 or 912S as powerplant. the 100hp version 912ULS costs around 14,000 euro including accessories, a price which is still a fraction of the cost of a lycoming/continental but a price that is considered robbery by many members of the microlight community.

i of course disagree on the "robbery theory". the 912 is built in very small numbers, with high QC standards and so on. i bet they do it for profit and not for charity, and considering the average advanced microlight costs 50k euro, with peaks of 100k for really top of the line stuff, 14k euro is not out of proportion.

now, a lot of folks insist on the theory (with which i disagree) that adapting an automotive engine is a better and cheaper option. this is somewhat refuted by the 30 years of failures in adapting automotive engines to airplanes.

my understanding is that, wieght considerations apart, the operations scenario in airplane use (warm up, then immediate full power for several minutes followed by hours at 70/80% power) is somewhat incompatible with automotive engines, which i suspect are designed for much lower average power usage during their lifetime.

a 912 has a typical time between overhaul of 1500 hours, even though most engines still show to be well within tolerances even after 2000 or more. the supporters of the automotive option however claim that a car engine would be capable of much higher TBO and therefore even using it at high power for extended periods of time is not going to affect reliability or durability. derating engines in this particular scenario is out of question, actually engines have to be "tuned" in order to reach a decent power to weight ratio. like in the case of the 1.2l 8vFIRE, which in the car delivers (if i remember well) 65BHP in the EURO3 version, has to be modified to deliver around 100bhp.

the adaption of automotive engines refers mainly to european-size engines, like for example the 1.2l 8v fiat FIRE engine, or the old EA81 flat four subaru engine. some are daydreaming about the new fiat twin cyl turbo, capable of some 100bhp.

here a snapshot of a 1.2 8V FIRE engine adapted to a CT2K microlight

http://farm2.static....99506307f_o.jpg

a project at which a good friend is working. the engine had to undergo quite extensive (and expensive) mods and still has to be flight tested. its final weight is some 15kg more than the rotax 912, the PSRU alone weights 13kg. the engine has been dyno'ed at 102bhp, thanks to the many mods.

so what do you folks think about the automotive option? would an automotive engine (packaging considerations apart) tuned and modified ensure still decent reliability and durability in the scenario described?

the engine in the picture had to undergo several mods, which required complete dismantling and reassembling of a factory new engine. what do you think about this operation?

and last question. many menbers of the "automotive" option get parts and components from the racing and hi-perf market, claiming that they are superior for both performances and reliability.
personally, i am not so sure these components are the best suited to a high reliability application, considering that i suspect racing parts are rarely tested on large scale for durability like the parts that go into production applciations.

sorry for eventual bad english :-)

[phantom II]

Aren't you a EAAmember? Sport Aviation covers this better than anybody. EAA.org
You may scoff at Lycosaurus engines but with modern technology no auto manufacturer could build an engine like the custom built Thunderbolt found in Red Bull racers and World Aerobatics Championships. www.lycoming.textron.com I have 4 Lycomings in 3 different aircraft. Car engines are not designed for 6 to 13 Gs at full power. The most successful auto engine transplants in aircraft are Suburu, either 4 or 6 cylinder. Tons of material on these engines and easy conversions. Porsche was the biggest disaster of all mainly because of torsional vibrations. Crankshafts broke in auto applications anyway. Plenty Chevy V8s out there especially in 7/8 Mustangs. 350, 502, 575 and the venerable LS1/2 all with great after market support and accessories in mounts and gearboxes,etc. Even SB2 conversions, still cheaper than Lycoming . Corvairs have been used by many builders. Contact EAA for specs. Mazda rotary seems to do well. Don't know about Euro engines.

Aircraft/ Engine Forums

http://groups.yahoo....llnerSubaruSTI/

http://canardaviationforum.dmt.net/

http://groups.yahoo.com/group/FlySoob/

http://groups.yahoo....subaruaircraft/

http://www.vansairforce.net/

http://groups.yahoo....positeaircraft/

http://groups.yahoo....p/titanmustang/

http://groups.yahoo....Geo_uncensored/


http://www.geareddrives.com/ Chevy engines and prop gearbox conversions

http://www.sdsefi.com/aircraft.html Suburu

http://www.kitplanes...nes/155-1.phtml These are important considerations from kitplanes.com


http://www.sdsefi.com/air7.html AutoVs, Certified

http://www.eaa1000.a...emp/engemp1.htm Erbmans Engine Emporium

http://www.ch601.org/engines.htm Various auto and motor cycle engines

http://www.seqair.co...PorschePFM.html Dead on arrival

Converting Auto Engines for Experimental Aircraft (Paperback)
by Richard Finch (Author)

Originally posted by crono33
sorry for the OT but i am sure some people here have good information on the subject.

:-)

[McGuire]

The only problem in adapting automotive engines to aircraft use is they are designed at cross principles. An aircraft engine operates at relatively constant load at low rpm, while an automotive engine operates at widely varying load with max output at considerably greater rpm. An automotive engine is not particularly powerful or efficient when operating at say, a constant 2300 rpm. Piston engines in aircraft are limited in rpm by the tip speed of the propeller (the limit is around .85 mach) so the engines are designed to operate in that range.

So to make an automotive engine effective as an aircraft powerplant, a reduction unit between the engine and propeller (somewhere in the range of 1.3:1 to 2:1) is typically required -- which adds weight, cost and inefficiency, along with a full plate of technical problems, mainly with vibration. The usual experience is that by the time these obstacles are overcome, the apparent advantages in cost, availability etc. have disappeared. And the engine is now operating near constant max output rpm, which shortens its service life and reduces its reliability.

Which leads to the other problem with automotive engines... frankly, that they are designed with the presumption that should a failure occur, the operator can get out and walk home. Traditional aircraft engines are built to much higher standards of reliability and service life. A Lycoming/Continental may be an ancient piece of obsolete junk, but in reality it is an exquisitely constructed ancient piece of obsolete junk. Few if any automotive-based engines have recieved the official FAA okey-dokey for general aviation use.

At one time VW Beetle engines were sort of popular in experimental-rated aircraft. I suppose the idea arose because an air-cooled VW flat four looks much like a traditional light aircraft engine. However, beyond the superficial resemblance the engines are nothing alike. You can spot these VW-powered aircraft from a mile away because the propeller is no longer than a baseball bat, in order to keep the tip speed down.

[phantom II]

I ran a Chevy 350 in my 20' Bertram for years. That's a boat by the way. Ran it all day long at 4200rpm and often at 5400 in salt water for 6 years. Some of those Rotex engines run at 6000rpm all day long for 2000 hours and extensions to 6000 hours. Auto engines in airplanes is a growing world wide business with high tech support. Propellers have smaller diameters now and my Extra had 4 blades.
Car engines in airplanes last longer than Lycomings. They are all geared. You cant run a gearbox in an aerobatic plane. Vibrations are not the problem, it is the Gs. The engineering in some auto engine applications in airplanes will boggle your mind, especially gearboxes. Cooling systems is a science and that is why in modern car racing, you see much transformation of technology from aircraft. The problems you speak of are of the past.
You may want to go to an EAA meet near you and check out some of the venders and their stuff. There's another world out there. Corvairs are a very successful application but Subarus have all but replaced them. They'll run 5 grand all day and last 3 times along as a Lycoming and burn less gas. Chevys generally run at 4500-rpm. A Lycoming 540 CI engine will max at 3000 rpm in some geared and turbo applications but 2700 is usually red line. 25" and 2500RPM (25-25) is what you run in an entire aerobatic sequence except for some maneuvers.

Originally posted by McGuire
The only problem in adapting automotive engines to aircraft use is they are designed at cross principles. An aircraft engine operates at relatively constant load at low rpm, while an automotive engine operates at widely varying load with max output at considerably greater rpm. An automotive engine is not particularly powerful or efficient when operating at say, a constant 2300 rpm. Piston engines in aircraft are limited in rpm by the tip speed of the propeller (the limit is around .85 mach) so the engines are designed to operate in that range.

So to make an automotive engine effective as an aircraft powerplant, a reduction unit between the engine and propeller (somewhere in the range of 1.3:1 to 2:1) is typically required -- which adds weight, cost and inefficiency, along with a full plate of technical problems, mainly with vibration. The usual experience is that by the time these obstacles are overcome, the apparent advantages in cost, availability etc. have disappeared. And the engine is now operating near constant max output rpm, which shortens its service life and reduces its reliability.

Which leads to the other problem with automotive engines... frankly, that they are designed with the presumption that should a failure occur, the operator can get out and walk home. Traditional aircraft engines are built to much higher standards of reliability and service life. A Lycoming/Continental may be an ancient piece of obsolete junk, but in reality it is an exquisitely constructed ancient piece of obsolete junk. Few if any automotive-based engines have recieved the official FAA okey-dokey for general aviation use.

At one time VW Beetle engines were sort of popular in experimental-rated aircraft. I suppose the idea arose because an air-cooled VW flat four looks much like a traditional light aircraft engine. However, beyond the superficial resemblance the engines are nothing alike. You can spot these VW-powered aircraft from a mile away because the propeller is no longer than a baseball bat, in order to keep the tip speed down.

[Greg Locock]

So far as engine life goes that would be the least of my worries. The usual sign off for a prototype engine is 100 hours at full power - when you can survive that you know that you are within 3 years of production. As an example the Mini derived A+ series turbo engine passed first time, whereas the LT5 took a couple of years of further development, including a complete reappraisal of the crankshaft, TV damper and oil pump design. Once the engine is in production it'll be able to withstand much more than 100 hours of constasnt load constant speed high power use, though I'm not sure that 1500 hours is 100% achievable.

Everyone who has a reasonably light powerful engine looks at the aviation market with envy. Very few succeed in breaking in.

[McGuire]

Originally posted by phantom II
You may want to go to an EAA meet near you and check out some of the venders and their stuff. There's another world out there.

Right, the EAA. How many automotive engines are approved by the FAA? Nothing against the EAA at all, but it is a different standard... lower of course.

I am not saying that an automotive engine cannot be successfully -- more or less -- adapted to aircraft use, especially to experimental type rating. The Air Camper flew with a Ford Model A engine 70 years ago. I am only noting that developing a decent aircraft engine of any kind is a much more difficult and complicated task than many imagine. For example it is totally beyond the resources of the home builder, even if he is lucky. And if he is less than perfectly lucky... Rutan tried and failed with the Pond Racer. Those engines were perfectly developed and absolute state of the art in auto racing, and the expert opinion was they were ideally suited and adaptable, but as aircraft powerplants they were proven worthless.

[phantom II]

I have been a member since the 70s, Rutan is a member. There are many people of his ilk in the bussines. It is as advanced as SEMA. You will get your bums but there are the Coddingtons and Fooses also. There are fine prop governors and gearboxes availible but not certified. If you love flying and want bang for the buck instead of paying for some goverment agency or liability fees, The EAA is for you. Even homebuilt planes require inspections and it is a very high standard. My friend who died of cancer recently was a aerodynamicist at NASA, you would hardly call his completely original design low standard. There are many planes that fall into the experimental category but are far superior to aircraft from piper and Cessna. It cost Curtis Pitts $300 000 to certify his S2B in 1977. The Christian Eagle is an experimental version of it same with the Husky which is a modified Cub. I would say that the standard in most cases was higher. Check out some of the kits and the experimental engines and gearbox items sold to the public.

Originally posted by McGuire


Right, the EAA. How many automotive engines are approved by the FAA? Nothing against the EAA at all, but it is a different standard... lower of course.

I am not saying that an automotive engine cannot be successfully -- more or less -- adapted to aircraft use, especially to experimental type rating. The Air Camper flew with a Ford Model A engine 70 years ago. I am only noting that developing a decent aircraft engine of any kind is a much more difficult and complicated task than many imagine. For example it is totally beyond the resources of the home builder, even if he is lucky. And if he is less than perfectly lucky... Rutan tried and failed with the Pond Racer. Those engines were perfectly developed and absolute state of the art in auto racing, and the expert opinion was they were ideally suited and adaptable, but as aircraft powerplants they were proven worthless.

[McGuire]

Originally posted by phantom II
I have been a member since the 70s, Rutan is a member. There are many people of his ilk in the bussines. It is as advanced as SEMA. You will get your bums but there are the Coddingtons and Fooses also. There are fine prop governors and gearboxes availible but not certified. If you love flying and want bang for the buck instead of paying for some goverment agency or liability fees, The EAA is for you. Even homebuilt planes require inspections and it is a very high standard. My friend who died of cancer recently was a aerodynamicist at NASA, you would hardly call his completely original design low standard. There are many planes that fall into the experimental category but are far superior to aircraft from piper and Cessna. It cost Curtis Pitts $300 000 to certify his S2B in 1977. The Christian Eagle is an experimental version of it same with the Husky which is a modified Cub. I would say that the standard in most cases was higher. Check out some of the kits and the experimental engines and gearbox items sold to the public.

We don't really disagree. We are just talking about different levels of development. I was regarding the question as a commercial proposition as that is my thing. If you want to sell some airplane engines, certification is a major consideration.

[phantom II]

The Specialty Equipment Manufacturers Association is a $68 billion industry. Not quite the size of the OEMs. Same with the aircraft industry. It would not survive without profit. The major kit plane manufacturers have produced thousands of airplanes that are sold the world over. I think there are 5000 RVs flying alone let alone Glasairs and Lancairs which are very advanced aircraft designed by the industries leading engineers.
They have to be placarded as experimental, and that simply means that they can't be used for commercial purposes. It does not mean that they are substandard or no capital returns are made. It is shocking what the major aircraft manufacturers churn out but they are up against over whelming odds. Trial lawyers been the most formidable. Just attend an EAA meet and check out the innovation and quality.

Originally posted by McGuire


We don't really disagree. We are just talking about different levels of development. I was regarding the question as a commercial proposition as that is my thing. If you want to sell some airplane engines, certification is a major consideration.

[crono33]

i think there are two sides of the story

as far as homebuilt and experimental goes, using automotive engines is a feasible way, even thought some experimental designers (like rutan) always discouraged homebuilders from using nonstandard powerplant. but if you have the tools, the hands and the right ideas, nobody can stop you from fitting an automotive engine ahead of your firewall. i know folks who have done this with reasonable success.

but making a bolt-on conversion or selling automotive engines adapted to airplane use, i see lots of problems there. developing a working solution will cost a lot of money and time and the numbers dont justify in my view the whole effort.

the rotax engine is a mature product, there are tents of thousands units out with thousands hours. there are dozenz of airplanes designed behind a rotax, specific props and all the other stuff. all things that must be adapted and sorted out for an automotive engine. anyone who can make an automotive conversion won't be able to make a proper validation, like having 10 airplanes doing 1000 hours, or having several engines at the dyno doing realibility and durability tests.
all conversions will be somehow prototypes.

personally, i find hard to believe that an auto engine, modified and fitted with non-factory parts (like valves, pistons and cams), reassembled, tuned up to 40% more of the original power and adapted to airplane use can ensure a reasonable level of durability and reliability.

some italian folk a couple years ago realized a 1.2L 8V FIRE engine conversion and sold some 25. of course most of those are still happily running, but none of them has gone furhter than 800 hours, owners keep a very close eye to the powerplants, and many owners are not willing to admit eventual problems and tend to claim the engines work fine.


last sunday i was crossing the apennines mountains and a colleague flying a VW motorized airplane had to land in the bed of the Taro river. only landing gear damage, but not nice.

[dosco]

Originally posted by phantom II
The engineering in some auto engine applications in airplanes will boggle your mind, especially gearboxes.

Wild-assed-guessing is probably more like it.

When I was at AlliedSignal Engines, I worked with the gearbox engineers that designed the TPE planetary gearbox ... lots of testing, development, and retesting. Not much engineering.

The problems with oil foaming, slinging, and flow through the gearing - at all G loadings - was not trivial. The engineers told me about how the internals were designed, and it was nothing more than guessing and testing.

I hope that the Modeling and Simulation tools in use today result in better designs, but I have my doubts.

[Zoe]

Originally posted by phantom II
Corvairs are a very successful application but Subarus have all but replaced them. They'll run 5 grand all day and last 3 times along as a Lycoming and burn less gas.

I once owned a Subaru and would think very hard before boarding a plane powered by a Subaru engine.....

Zoe

[McGuire]

I think for lighter applications toothed belt would be the way to go. For higher-duty applications I would just as soon not be involved. Keep my name off it. Don't call us, we'll call you. Etc.

[crono33]

even in small engines toothed belts have been more or less abandoned. all rotax engines use very successfully gear reductions. most other manufacturers just use them or copy them.

PSRU's have always been difficult and expensive to build, often being the weak point of powerplants.

the FIAT conversion of the picture i have posted uses a 3 gear reduction (to make the prop turn the same way as rotax, and to get some ground clearance), it weights 13kg against the 3kg of the rotax one.

Originally posted by McGuire
I think for lighter applications toothed belt would be the way to go. For higher-duty applications I would just as soon not be involved. Keep my name off it. Don't call us, we'll call you. Etc.

[crono33]

some subaru conversions have been quite successful, but not on microlights. too heavy

however, the best conversions are not just "conversions" but they are major rebuilds of engine and ancillaries and they dont come cheap

http://ramengines.com/

Originally posted by Zoe


I once owned a Subaru and would think very hard before boarding a plane powered by a Subaru engine.....

Zoe

[miniman]

Crono33, I'm surprised that a 100HP Lycoming or Continental costs so much in Europe, a Lycoming O360 for the amateur market can be purchased here in the US for $20,000 so I imagine a 100HP mill would cost a lot less.

Wouldn't it be better to go that route (aviation engine) and turbocharging (turbonormalizing it really) you'd get full power at most altitudes and all weather conditions while still keeping the full TBO

Just a thought...

[crono33]

where can you get a brand new O360 for that price? i'd buy a dozen :-)

continantal/lycoming are too heavy for advanced microlights, and general light aviation in europe is dead in some countries, and terminal in others; so those engines are not really interesting over here.

in italy, for over 55 million people there are between 300 and 500 small GA private planes. there are in all around 100 airports, and only some 38 of them are controlled.

on the other side, there are more than 500 airstrips for microlights, and around 10,000 registered microlights.

so not many are really interested in GA airplanes any more. the future here in europe is microlights. which are not pipe-and-rag stuff, but machines like this



or this



capable of 130-150 knots cruise burning 4 gallons/hour

Originally posted by miniman
Crono33, I'm surprised that a 100HP Lycoming or Continental costs so much in Europe, a Lycoming O360 for the amateur market can be purchased here in the US for $20,000 so I imagine a 100HP mill would cost a lot less.

Wouldn't it be better to go that route (aviation engine) and turbocharging (turbonormalizing it really) you'd get full power at most altitudes and all weather conditions while still keeping the full TBO

Just a thought...

[miniman]

Chrono33 - http://www.zenithair.../lyc-price.html

General aviation in the US is going the same way with the traditional manufacturers trying to crack the Sport Aviation Market. It is getting tougher in the US with the FAA making noises about implementation of user fees for ATC.

You should attent the EAA convention at Oshkosh WI specially if you are into microlights

[McGuire]

Tough week at Reno this year.

[phantom II]

Tragic.

Originally posted by McGuire
Tough week at Reno this year.

[crono33]

not a good time for aviators. steve fossett still missing, today colin mcrae apparently crashed in his helicopter

many accidents involving warbirds in the last few months.

[crono33]

good morning gentlemen (at least in my TZ)

i have a few more questions about this topic

1 - some of the automotive engines converted for aeronautic use have the over head distributiion driven by toothed belts. what is your opinion about this solution? personally, i still have somewhere 16 bent valves, 8 of which expensive sodium filled ones, result of an almost new slipped belt.

2 - i have learned that the rotax 912 engine use a composite crankshaft with monolitic rods. i thought monolitic crankshafts were superior in reliability; rotax engineers for sure know 10^6 more than me :-) but i was anyway a little surprised. the 912 is FAR certified.


thanks

[McGuire]

Whatever else you can say about them, toothed belts have a very predictable service life. If a timing belt failed shortly after installation, it was either defective (less likely) or installed improperly (more likely). If the belt is misaligned, under/over tensioned, or abraded, it will fail quickly.

[crono33]

i will rephrase it:

would you fly over montaineous terrain, water or at night a single engine aircraft powered by that toothed belted engine? :-)

Originally posted by McGuire
Whatever else you can say about them, toothed belts have a very predictable service life. If a timing belt failed shortly after installation, it was either defective (less likely) or installed improperly (more likely). If the belt is misaligned, under/over tensioned, or abraded, it will fail quickly.

[McGuire]

Yes, I suppose so... as long as the engine were properly engineered and maintained.

That said, timing belts and built-up crankshafts are not features I normally associate with heavy-duty, high-service life, critical-application powerplants. There is nothing wrong with timing belts per se.... they are ubiquitous in NASCAR for example. But when I see a production car with a timing belt, I don't see an engine intended for maximum reliability and service life.

And a built-up crankshaft is fine in a motorcycle, but I don't know about aircraft loadings. That is not to say a composite crankshaft could not be properly engineered for the application, but a one-piece crank has no such issues.