Auto conversion ideas

[AlphaPilotFlyer]

I thought I’d chime in reluctantly as the original post was about auto conversions and some mentioned about the Toyota aircraft V8 designed and certified in the 1990s. I spoke with one of the engineers on that project as we were designing the V8 GM conversion for our c172. Toyota shut the project down for a nUmber of reasons, but mostly that the already well proven engine had to be so modified for mechanical redundancies as well as software redundancies it raised the cost and FAA cert cost way too much…and some also felt adding the extra stuff to meet FAA requirements made the design less reliable .also, GA was in decline so market shrunk and ROI was just insignificant compared to the Toyotas titanic car business….and US civil liabilities didn’t help.

As I have wrote on issue prior, auto conversions are more than just bolting a v8 to an airframe. To do it right, and safe,, you need resources to make a matched solution. We had a few set backs on our c172 V8….mostly FAA related rather engineering…. but figured it out. In fact, we just flew it across the country last week without issue and even found some airports with MOGAS, but used AVGAS for most stops. But even with paying more for the AVGAS, we were still way cheaper than with original lycoming engine which made the trip way more enjoyable! We were about $24-26/hour with AVGAS fuel and engine reserves…. found MOGAS just over $3/g which got us down to about 21/hr. Total trip on Hobbs was close to 40 hours without burning a drop of oil, so savings add up compared to original engine. Funny enough, often when we fly in to some airports the fob lets us use the crew car to fill up 2 5gal plastic gas containers (we bring on longer trips) at local gas station because they think the engine is cool….also, many airports have MOGAS on field for airport vehicles and equipment as well. So, conversions can be made to work.

We added some photos on CorsairV8 website filling up from car tank transfers using a gasoline 12v transfer pump which works great if you can circumvent or remove the cars anti siphon valve. So we usually burn regular ethanol car gas mostly because it’s cheaper and cleaner. We removed the valve from a SUV and essentially use it as a fuel truck…. We fill it up just outside the airport fence at a local gas station, pull up to plane, put hose down the filler and pump it into plane. AVGAS at out field is over $7/g, car gas less than half that. Also, you can get rebate on highway taxes as well. We sometimes use ethanol free gas at FBOs if no MOGAS option, but it’s usually close in cost to AVGAS, but still cheaper and cleaner burning.

So there’s always nay sayers with little understanding pontificating on the subject of auto conversions, likely due to troubles early on from home builders mounting junk yard engines to aircraft and the news of crashes back then. But it can be done right and a good alternative to legacy engines for many piston aircraft. The benefits, like healer engine and parts, longer TBO, burning car gas and using synthetic oil, can make a big difference in being able to afford flying more.

 

[MackMooney]

I was thinking, how about using one of the new Turbo Diesels without a reduction drive, seems their sweet spot is right in our usual rpm range

 

[AlphaPilotFlyer]

You are correct….. car spark ignition engines produce their effective power band above 2700 rpm, which with a typical prop diameter would cause tips to accelerate too fast and approach Mach speed, which significantly reduces prop efficiency. Thus, need a reduction gear.

Diesels usually run at lower rpm but prop still has same restriction so larger power diesels still require gear reduction. Diesels also produce torsion forces greater than gas engines that are considerable challenge for the gear boxes as well.

However… car engines were designed to have a transmission, now normally computer controlled transmission, that not only isolates engine from abrupt load changes but other factors as keeping the crank shaft perfectly straight….as such, car engines were not designed to handle forces as crank shaft side loading or bending due to typical prop loading….example would be the asymmetrical loading on different prop blade amplified during takeoff where one side produces more thrust than other, which transmits this side force down the crank shaft and into the engine and against the shaft bearings that are keeping the shaft straight….. aircraft engines have far better bearings for such reasons.

So…. For these such reasons, not to mention pulse loads and other vibration issues, using a car turbo diesel without gear box has significant challenges.

 

[Barrett50]

Preface: I have never built or designed any auto conversion engine in an aircraft. I've flown behind several, including a Corvair powered Sonex, and a Piet with a Ford flathead(model T?), and a few others.

The Porsche PFM engine has not been mentioned. The first blush, Porsche was to design a low cost, light weight, direct drive, air cooled engine for aircraft. The finished product was a high cost, heavy, geared drive, water cooled, POS. It failed miserably in the market. Porsche was the elite designer of high perf air cooled auto engines, and even they couldn't make it work out well.

OTOH - another German was rather successful at conversions. The Limbach engine found in some sailplanes and German 'experimentals' is a special product of a 1700cc or 2400cc auto engine from back in the 50s design. They were air cooled, direct drive, light weight and reasonably reliable when provided with enough air to cool the engine properly. I think Limbach still offers engines, however I doubt they use the VW pancake style anymore, as those engine cases and other bits haven't been made for decades. The last air cooled VW engine was produced in Brazil if I recall right. Or maybe, Mexico?

Gearing auto engines for aircraft can be done, but as others have already covered, the torque coupling is a MAJOR consideration for success. Among the many failed systems one that hasn't been mentioned is the cute little BD-5. The jet engine plane was functional, but I don't think anyone has ever solved the torque demands of the various engine and drive combos for the BD-5.

Another part of the problem that is sort of the nexus for this conversion is there's very little market value for someone to effectively solve all the issues with auto conversions. Rotax has the gear drive pretty much figured out, but it's not an auto engine. Belt reduction is used in multiple helicopters, but again, not an auto engine.

The closest success I would consider are the Corvairs. At GM in the late 50s, the design of the Corvair engine needed to be more robust than typical water cooled 6 or 8s. It became a little race engine with forged components in some cases. The conversions with the 5th bearing seem to be robust, good power to weight, and able to be cooled without the heavy water jacket. Smooth engine, and being 6 and horizontally opposed, it's able to be balanced without an external rotating mass. I hope the V8 crowd finds a way to get them converted with good reliability and economy. Seems to be still in the future.

 

[Agronomist]

I thought I’d chime in reluctantly as the original post was about auto conversions and some mentioned about the Toyota aircraft V8 designed and certified in the 1990s. I spoke with one of the engineers on that project as we were designing the V8 GM conversion for our c172. Toyota shut the project down for a nUmber of reasons, but mostly that the already well proven engine had to be so modified for mechanical redundancies as well as software redundancies it raised the cost and FAA cert cost way too much…and some also felt adding the extra stuff to meet FAA requirements made the design less reliable .also, GA was in decline so market shrunk and ROI was just insignificant compared to the Toyotas titanic car business….and US civil liabilities didn’t help.

As I have wrote on issue prior, auto conversions are more than just bolting a v8 to an airframe. To do it right, and safe,, you need resources to make a matched solution. We had a few set backs on our c172 V8….mostly FAA related rather engineering…. but figured it out. In fact, we just flew it across the country last week without issue and even found some airports with MOGAS, but used AVGAS for most stops. But even with paying more for the AVGAS, we were still way cheaper than with original lycoming engine which made the trip way more enjoyable! We were about $24-26/hour with AVGAS fuel and engine reserves…. found MOGAS just over $3/g which got us down to about 21/hr. Total trip on Hobbs was close to 40 hours without burning a drop of oil, so savings add up compared to original engine. Funny enough, often when we fly in to some airports the fob lets us use the crew car to fill up 2 5gal plastic gas containers (we bring on longer trips) at local gas station because they think the engine is cool….also, many airports have MOGAS on field for airport vehicles and equipment as well. So, conversions can be made to work.

We added some photos on CorsairV8 website filling up from car tank transfers using a gasoline 12v transfer pump which works great if you can circumvent or remove the cars anti siphon valve. So we usually burn regular ethanol car gas mostly because it’s cheaper and cleaner. We removed the valve from a SUV and essentially use it as a fuel truck…. We fill it up just outside the airport fence at a local gas station, pull up to plane, put hose down the filler and pump it into plane. AVGAS at out field is over $7/g, car gas less than half that. Also, you can get rebate on highway taxes as well. We sometimes use ethanol free gas at FBOs if no MOGAS option, but it’s usually close in cost to AVGAS, but still cheaper and cleaner burning.

So there’s always nay sayers with little understanding pontificating on the subject of auto conversions, likely due to troubles early on from home builders mounting junk yard engines to aircraft and the news of crashes back then. But it can be done right and a good alternative to legacy engines for many piston aircraft. The benefits, like healer engine and parts, longer TBO, burning car gas and using synthetic oil, can make a big difference in being able to afford flying more.

Using an SUV as a fuel truck is genius

 

[MackMooney]

Preface: I have never built or designed any auto conversion engine in an aircraft. I've flown behind several, including a Corvair powered Sonex, and a Piet with a Ford flathead(model T?), and a few others.

The Porsche PFM engine has not been mentioned. The first blush, Porsche was to design a low cost, light weight, direct drive, air cooled engine for aircraft. The finished product was a high cost, heavy, geared drive, water cooled, POS. It failed miserably in the market. Porsche was the elite designer of high perf air cooled auto engines, and even they couldn't make it work out well.

OTOH - another German was rather successful at conversions. The Limbach engine found in some sailplanes and German 'experimentals' is a special product of a 1700cc or 2400cc auto engine from back in the 50s design. They were air cooled, direct drive, light weight and reasonably reliable when provided with enough air to cool the engine properly. I think Limbach still offers engines, however I doubt they use the VW pancake style anymore, as those engine cases and other bits haven't been made for decades. The last air cooled VW engine was produced in Brazil if I recall right. Or maybe, Mexico?

Gearing auto engines for aircraft can be done, but as others have already covered, the torque coupling is a MAJOR consideration for success. Among the many failed systems one that hasn't been mentioned is the cute little BD-5. The jet engine plane was functional, but I don't think anyone has ever solved the torque demands of the various engine and drive combos for the BD-5.

Another part of the problem that is sort of the nexus for this conversion is there's very little market value for someone to effectively solve all the issues with auto conversions. Rotax has the gear drive pretty much figured out, but it's not an auto engine. Belt reduction is used in multiple helicopters, but again, not an auto engine.

The closest success I would consider are the Corvairs. At GM in the late 50s, the design of the Corvair engine needed to be more robust than typical water cooled 6 or 8s. It became a little race engine with forged components in some cases. The conversions with the 5th bearing seem to be robust, good power to weight, and able to be cooled without the heavy water jacket. Smooth engine, and being 6 and horizontally opposed, it's able to be balanced without an external rotating mass. I hope the V8 crowd finds a way to get them converted with good reliability and economy. Seems to be still in the future.

I"d expect to have some sort of interface between the crank and the prop, prob will never get around that but I get away from having to run the engine at excessive speeds and i eliminate the need for dual ignition systems. unfortunately you are trading weight, what can you do

 

[Barrett50]

I"d expect to have some sort of interface between the crank and the prop, prob will never get around that but I get away from having to run the engine at excessive speeds and i eliminate the need for dual ignition systems. unfortunately you are trading weight, what can you do

The Corvair in aircraft often use a 'fifth bearing' on the front to support prop and gyroscopic loads. The housing is billet Al, and the bearing is steel of course. The weight increase is worth the extra crank support. See flycorvair <dot> net for further info and supplies.

 

[moparrob66]

I love the diesel idea and I think about it more than i probably should. First concern is horsepower to weight ratio. That might not be as concerning as I think, since the lower peak horsepower is typically accompanied by higher torque numbers. Would that allow a bigger prop to produce more thrust? Enough to offset the lower horsepower? I may have to find out for myself at great time and expense.

 

[Dan Thomas]

I may have to find out for myself at great time and expense.

Remember that SMA found out for themselves at great time and expense. $1 billion dollars by the time they had only 50 or their diesel engines flying worldwide, and they all had problems that cost even more money to fix.

 

[Daleandee]

The Corvair in aircraft often use a 'fifth bearing' on the front to support prop and gyroscopic loads. The housing is billet Al, and the bearing is steel of course. The weight increase is worth the extra crank support. See flycorvair <dot> net for further info and supplies.

I have a Dan Weseman 5th bearing on my 3.0 Corvair conversion. They work ...

 

[AlphaPilotFlyer]

I think you are right RE the real issue with a good EXP auto conversion

Another part of the problem that is sort of the nexus for this conversion is there's very little market value for someone to effectively solve all the issues with auto conversions.

Our intent with the C172 program was to do all the heavy lifting that most experimenters would not likely have the experience, fancy degrees or skill sets to do themselves.... not to mention time. To do it right it also takes more money than its worth for a one-off. RE the Porsche engine.... it ran into many of same issues toyota had developing their certified engine based on a Lexus V8, as well as we experienced ..... modern car engines are very reliable and to add redundancies that are statistically not needed to meet same aero standards adds other potential points of failures and expense. We have a couple of links on our website to articles we wrote on the issue of meeting FAA requirements, but essentially it comes down to difficulties using 1940 cert requirements for modern engines.

 

[Dan Thomas]

but essentially it comes down to difficulties using 1940 cert requirements for modern engines.

Engine failures kill people today just as quickly as they did in 1940. That's why the standards are still there. And since electrical problems are the single biggest source of engine problems, as we use more electronics in the engine's operation we have to be sure they don't quit, or have backups. Even todays airliners, full of expensive and high-quality electronic controls, have to have layers of redundancy.

 

[sansoneservices]

I know its a controversial topic, but inquiring minds like mine want to know.

An obvious problem is the gearbox or psru. Has anyone tried a boat drive like the Casale V drive? They are made in a variety of gear ratios as well as angles and they put up with constant, high power use. Why wouldnt it work in an airplane?

Another thought I have is displacement vs rpms. Since auto engines are designed for peak advertised hp lasting only briefly on an onramp or green light, wouldnt they be fine at 2700 rpm continuously? Most cars like my 327ci suburban do fine at 80mph indefinitely at 2200-2500 rpm depending on overdrive or axle gearing. If an o-360 were tuned for it and not turning a propeller, spinning it faster could make 350-400 horsepower like a 360 cubic inch auto engine, right?

Is there a good reason I couldnt use an alloy auto engine of 350-400 cubic inches direct drive to s propeller with a camshaft and carburetor optimized for 2700rpm and have better parts availability and equal or better reliability?


Talk some sense into me before i start accumulating aluminum blocks and heads for hillbilly R&D....

 

[moparrob66]

You rang?

 

[sansoneservices]

Stick with known auto conversions unless you really want headaches. Corvair, Volkswagen, Subaru, Rotax, Viking has a 195hp conversion. These companies have experience and support for your a/c project

 

[moparrob66]

I have and still may consider the Viking 195. Im still uncomfortable with the idea of running a honda accord at full power for hours over the Sierra Nevadas....

 

[tspear]

Stick with known auto conversions unless you really want headaches. Corvair, Volkswagen, Subaru, Rotax, Viking has a 195hp conversion. These companies have experience and support for your a/c project

I suggest researching Viking before recommending them. The reputation is very mixed, with a lot of "bad blood" in there.

Tim

 

[AlphaPilotFlyer]

Engine failures kill people today just as quickly as they did in 1940. That's why the standards are still there

maybe you are right....let's continue to use 1940 cert standards on equipment that was never even conceived of then....better yet, why not simply use the Wright Brothers standards for modern things as flat panels and EFI systems.... and insist on same methods to test compliance such as destructive testing and pulling max G's in actual plane.... brilliant!

since electrical problems are the single biggest source of engine problems,

Electrical faults are not the primary cause of accidents in any AWC category, not even close, especially since vast majority of engines are magneto ignition...... not sure where you obtained your views or understanding of which you post

 

[Bell206]

maybe you are right....let's continue to use 1940 cert standards on equipment that was never even conceived of then.

What I find interesting is that a so-called modern vehicle engine can't even meet the 1940s CAR 13 engine requirements let alone the newer Part 33 requirements. Not much really to brag on.

Electrical faults are not the primary cause of accidents in any AWC category, not even close,

Except he didn’t state it was the primary cause of accidents. He stated it’s the #1 cause of engine problems which do have an electrical system that includes the magnetos, P-leads, etc. And given the electrical system on any aircraft is the most neglected system, he's pretty darn close on the comment.

However, this doesn’t only pertain to those 1940s aircraft/engines either. Just look at the DA62 incident in Dallas a few years back. Modern airframe, new design Part 33 engines, 5 independent modern electrical sources, yet it still had a complete electrical failure, lost power on both engines and landed on a highway shortly after takeoff. Ironically, with a 1940s type engine system installed it would have kept flying. Go figure.

 

[Dan Thomas]

maybe you are right....let's continue to use 1940 cert standards on equipment that was never even conceived of then....better yet, why not simply use the Wright Brothers standards for modern things as flat panels and EFI systems.... and insist on same methods to test compliance such as destructive testing and pulling max G's in actual plane.... brilliant!

False equivalency. Between the Wrights and the late 1940s, engines developed much more than they have in the 75 years since. The changes since then have been mostly metallurgical and in lubricants.

Electrical faults are not the primary cause of accidents in any AWC category, not even close, especially since vast majority of engines are magneto ignition...... not sure where you obtained your views or understanding of which you post

Magnetos are a perennial source of problems, mostly since the majority of owners ignore the mag manufacturer's inspection recommendations. The Bendix dual mags have ONE impulse spring driving the whole thing, and when it breaks due to undetected corrosion, both mags go to TDC and the engine basically quits.

Alternators regularly quit because their field brushes have worn out, another 500-hour recommended inspection item. And without the alternator, the guy in IMC is often in trouble. Yes, accidents have happened due to that, and to failed vacuum pumps, the third ignored component. No gyro instruments. Even your glass panel system is only good for an hour after alternator failure. With lights on, it's less, a lot less. The engine doesn't have to quit due to electrical failure if the pilot loses control when the instrumentation fails.

 

[moparrob66]

I think the most likely failure for a modern auto conversion would be the fuel pump, assuming the PSRU is properly designed. Thats a pretty common failure that results in a tow to the shop, and one that cant really be prevented with proper maintenance.

The alternator debate makes me think the pulley should be resized for aircraft use to prevent premature wear, but redundant fuel pumps could be a simple solution. I could even modify a donor vehicle to run in comparable rpm and load ranges (freeway trips in lower gears/higher rpms, long grades) to see what problems arise from the higher, constant rpms and make adjustments as necessary, or scrap the idea altogether.

 

[MackMooney]

it's 2024, use a brushless alternator, weighs a bit more but should pretty much never need maintenance.

 

[moparrob66]

I'll read up on brushless alternators. Im sure a lot has improved since my days of swapping them out of my 66 Chrysler in the Kragen parking lot. I think my best time was 5 minutes, hood open to hood closed.

 

[Dan Thomas]

I think the most likely failure for a modern auto conversion would be the fuel pump, assuming the PSRU is properly designed. Thats a pretty common failure that results in a tow to the shop, and one that cant really be prevented with proper maintenance.

That's an automotive problem. Electric fuel pumps fail, and fail suddenly. Aircraft fuel pumps are engine-driven, with an electric backup that seldom runs. Most often it ages out long before it ever wears out.

So if one uses an auto conversion with only electric fuel pumps, expect problems. Newer technology comes with newer problems and failure modes.

The alternator debate makes me think the pulley should be resized for aircraft use to prevent premature wear

That alternator is belted or geared to the engine at a ratio that allows it to develop sufficient power at idle. Gearing it lower defeats that, and we're back to the bad old days of generators that didn't generate anything until you started the takeoff roll. No thanks. A longer taxi at night, with the lights on, could easily result in radio failure before you took off.

Stuff has been engineered the way it is by some really smart people for some really good reasons. When there is a truly dumb problem, either an AD forces change, or some aftermarket outfit creates a good fix with an STC to legalize it.

it's 2024, use a brushless alternator, weighs a bit more but should pretty much never need maintenance.

I haven't encountered such alternators in the automotive world, but my recent auto experience is limited. Got an article or promo on a brushless alternator that would fit inside an airplane cowl? The only brushless alternators I'm familiar with are the big ones built for heavy trucks way back in the 1980s.

 

[Daleandee]

I have a 120 hp Corvair conversion. It uses gravity feed for fuel and a brushless dynamo (20 amp) that requires a voltage regulator. Pretty rock solid set up thus far ...

 

[Dan Thomas]

I have a 120 hp Corvair conversion. It uses gravity feed for fuel and a brushless dynamo (20 amp) that requires a voltage regulator. Pretty rock solid set up thus far ...

Does that regulator control the field? Or is the dynamo a permanent-magnet affair where the regulator controls the output directly?

 

[Daleandee]

Does that regulator control the field? Or is the dynamo a permanent-magnet affair where the regulator controls the output directly?

PM with AC output. The VR controls the output ...

 

[Dan Thomas]

PM with AC output. The VR controls the output ...

View attachment 134357

Ok. That's same principle as the old bicycle headlight generators. The regulator here will introduce resistance to keep system voltage to 13.8 or so. It will get rid of the excess power as heat. And it's why it's only 20 amps. Bigger output means bigger wasted heat anytime the full output isn't being used. Not a true brushless alternator. True brushless alternators have a regulated field feed winding that is on the rotor and fed by a separate stator winding.

 

[AV8R_87]

Some VRs actually are full blown switching power supplies, taking a higer and variable voltage and stepping it down to the proper output. Or at a minimum chopping it down using PWM like the older solar charge controllers.

 

[Daleandee]

I understand it's not a true brushless alternator as referred to these days but it is brushless and it does put out AC ...

Also available in a 35 amp version but many aircraft need higher output than that. The 20 amp version does very well on my experimental and charges my Odyssey battery at 14.7 which is where they say the battery is most happy ...

FWIW