Auto conversion ideas

In my lifetime, I have known 5 pilot/builders that had auto engine powered experimentals. All spent far more time and money engineering, tinkering, and repairing their one of a kind setup. All experienced multiple small, and sometimes large, failures. All of these aircraft have either been re-engined with Lycomings or have been scrapped out.

I'm not saying it can't be done, but I just can't figure out why it should. It just seems like a square peg, round hole type of solution.
 
hindsight2020 said:
Speaking of small n, the engine that tried to put me in the dirt was a certified Lycoming, not a Viking. What to do... don't answer that I'm being rhetorical....
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"Rhetorical." Then again, rhetorically speaking, how many hours have you flown in aircraft powered by certified Lycomings, vs. hours in Honda-powered aircraft? This is where the statistics get fun....

This plot, to me, shows the fundamental issue with auto-engine conversions. Of the homebuilt powered by traditional engines that suffer an accident due to a mechanical failure of the engine, about 18% of the accidents occur during the initial test period (40 hours). If an auto conversion DOES fail, there's a 30% chance it'll be in that test period.... and about 20% of the accidents occur in the first ten hours!
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During that initial 40-hour test period, the builder of the airplane is supposed to be paying attention to the condition of the airplane...and the engine. Auto engine converters aren't catching incipient problems.

Ron Wanttaja
 
midwestpa24 said:
In my lifetime, I have known 5 pilot/builders that had auto engine powered experimentals. All spent far more time and money engineering, tinkering, and repairing their one of a kind setup. All experienced multiple small, and sometimes large, failures. All of these aircraft have either been re-engined with Lycomings or have been scrapped out.

I'm not saying it can't be done, but I just can't figure out why it should. It just seems like a square peg, round hole type of solution.
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Cost is the major one. A new O-200 costs something like $35,000, a Rotax 912 about the same, but a typical auto engine conversion may go for a third of that. If the C85 in my Fly Baby goes Tango Uniform, it will probably cost me a ton of money. And the engine has been out of production for ~50 years.....

Ron Wanttaja
 
kmacht said:
Yeah but it has also weeded out engineers and pilots like myself who are actively working on new experimental aircraft and auto conversions.
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Engineers and pilots actively working on builds don't generally spend much time on HBA or anything else. They're in the shop, or at work. I'm retired and not building or restoring anything aviation-related at the moment, so I'm here and at HBA. Too much, usually.
 
wanttaja said:
Cost is the major one. A new O-200 costs something like $35,000, a Rotax 912 about the same, but a typical auto engine conversion may go for a third of that. If the C85 in my Fly Baby goes Tango Uniform, it will probably cost me a ton of money. And the engine has been out of production for ~50 years.....

Ron Wanttaja
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Amen. I’m looking at most options for my current build. C-85 or O-200 are candidates, but so are the Rotax 912 series, Aeromomentum, D-motor, Verner, and so on. Maybe, possibly even Corvair, but I dunno. Trying to get a straight answer to a simple question from that cult seems to be an exercise in futility.

There are some pretty interesting options out there.
 
tspear said:
I just tested, you can still register and join for free. Select the basic plan. Note: I used an incognito window to do the testing.

Tim
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Go back in after a few days and you will get a message on every thread you click that says you need to upgrade your account to read replies even after logging in with a basic account.
 
kmacht said:
Go back in after a few days and you will get a message on every thread you click that says you need to upgrade your account to read replies even after logging in with a basic account.
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I'm a moderator over there, I will look into this. The new forum owner has not been transparent about all the changes.
 
wanttaja said:
"Rhetorical." Then again, rhetorically speaking, how many hours have you flown in aircraft powered by certified Lycomings, vs. hours in Honda-powered aircraft? This is where the statistics get fun....

This plot, to me, shows the fundamental issue with auto-engine conversions. Of the homebuilt powered by traditional engines that suffer an accident due to a mechanical failure of the engine, about 18% of the accidents occur during the initial test period (40 hours). If an auto conversion DOES fail, there's a 30% chance it'll be in that test period.... and about 20% of the accidents occur in the first ten hours!
View attachment 127334
During that initial 40-hour test period, the builder of the airplane is supposed to be paying attention to the condition of the airplane...and the engine. Auto engine converters aren't catching incipient problems.

Ron Wanttaja
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but the bigger stat is that what, 18% of 'traditional' (certificated?) engines are also failing in the same timeframe.

trying to deduct reliability numbers when the creators of the item have all, some, or no experience is not a valid reflection on the type of motor.... only the level of effort by the creator.
 
pfarber said:
but the bigger stat is that what, 18% of 'traditional' (certificated?) engines are also failing in the same timeframe.
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So, I have some thoughts on that. I've been in the industry for over 20 years and yes, I've heard of certified engines failing in their infancy, but of the ones I'm aware of, it's generally a situation like a mis-installed oil line, or some other part, a badly-executed break-in, or a specific manufacturing defect that is discovered the hard-way early on. Most of the traditional engine failure modes are very, very predictable and the more data you have from something like a JPI, the more likely you are to catch something and land before it craters on you. The auto-engine guys may also have good instrumentation, and I've seen it, but it's a bit harder to interpret in my experience because it's way less easy to see a correlation or a red-flag due to the smaller data set that the operator likely has.

Aviation engines are also often better designed for the environment. A plane I regularly fly recently had an issue. Either a mechanic forgot a bolt, or a bolt actually worked it's way loose and the unsecured item vibrated it's way into literally cutting an oil return line open sometime during the flight. It was a 4.2 hour flight and we'd lost a third of our oil before landing, but everything was still running well and it was easy to get it returned to service. There was enough "tolerance" in the reserve that we actually didn't know we had a problem until we landed and smelled the oil and then saw it. In contrast, the Glasair that had a turbo failure and put us in a field a few years back had an auto engine and when the turbo failed, it also affected an oil line, and we had a seized engine within 3 minutes of the first indication of a problem.
 
RyanShort1 said:
Aviation engines are also often better designed for the environment. A plane I regularly fly recently had an issue. Either a mechanic forgot a bolt, or a bolt actually worked it's way loose and the unsecured item vibrated it's way into literally cutting an oil return line open sometime during the flight. It was a 4.2 hour flight and we'd lost a third of our oil before landing, but everything was still running well and it was easy to get it returned to service. There was enough "tolerance" in the reserve that we actually didn't know we had a problem until we landed and smelled the oil and then saw it. In contrast, the Glasair that had a turbo failure and put us in a field a few years back had an auto engine and when the turbo failed, it also affected an oil line, and we had a seized engine within 3 minutes of the first indication of a problem.
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I know of a number of cases where turbos failing has shutdown the engines immediately. Or has cratered the engine. Turbo failure killing an engine is not unique to auto-engines.
The problem with auto-engines is not really the engine itself. It is the system installation. Lycoming/CMI have a larger installed base of knowledge to debug system issues.

Tim
 
Auto engines are so retro. Why not be more progressive and go with a nuke or electric of some kind? ;)
 
pfarber said:
but the bigger stat is that what, 18% of 'traditional' (certificated?) engines are also failing in the same timeframe.

trying to deduct reliability numbers when the creators of the item have all, some, or no experience is not a valid reflection on the type of motor.... only the level of effort by the creator.
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So you missed the point of this post?

wanttaja said:
This plot, to me, shows the fundamental issue with auto-engine conversions. Of the homebuilt powered by traditional engines that suffer an accident due to a mechanical failure of the engine, about 18% of the accidents occur during the initial test period (40 hours). If an auto conversion DOES fail, there's a 30% chance it'll be in that test period.... and about 20% of the accidents occur in the first ten hours!
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That 18% of traditional engine failures was in homebuilts, not certified airplanes. It was also 18% of accidents due to failures of traditional engines, not of the total number of traditional engines in homebuilts. Major difference there. Further, homebuilders often rebuild their own engines, and often without following any overhaul manuals. They overtorque hardware and fittings. They use RTV as a sealant, and it extrudes and breaks off and plugs oil galleries and bearings don't get oil and they fail. There are SO many ways to screw up an overhaul.

They also tend to design their own fuel systems, and venting is often badly designed. Inflight airflow causes low pressure in the tanks or header, and the engine starves and quits. (RTV has also been blamed for fuel flow failures in homebuilts.)
Getting fuel tank venting right is not easy; it's similar to getting a good static indication for the airspeed, altimeter and VSI. Trying to get an actual static pressure when you're surrounded by moving air takes a bit of skill and knowledge.

For auto conversions to work efficiently for a propeller, a speed reduction unit is necessary. And that's a major failure point for such conversions. There is a phenomenon known as Torsional Vibration, and it's basically the fight between the engine (which has power and compression strokes that cause the crankshaft to speed up on every power stroke and slow down on every compression stroke) and the propeller (which, due to its mass, wants to turn at a very steady rate of rotation). The reduction unit gets yanked around by this differential, and the loads it suffers from that are larger than the actual HP being transmitted. If it is poorly designed, or just not strong enough, it explodes. The belt or chain or gears fail.
 
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Lots to consider that, apparently, many builders and dreamers don't.
 
Don’t know if they are still in business but try to check out AutoPSRUs.
 
A neighbor at my airstrip bought a Zenith CH750 STOL. The first thing he did was fly directly to Viking headquarters in Edgewood, FL and had them pull the installed O-200 and replace it with a Honda-based Viking engine.

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I’m not an engineer, but superficially the quality of the parts and attention to detail appear first rate. In flight, I don’t think it’s distinguishable from a legacy engine, and engine operation and maintenance appear far more straightforward as well.

Of course, time will tell…
 
Dan Thomas said:
For auto conversions to work efficiently for a propeller, a speed reduction unit is necessary. And that's a major failure point for such conversions
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Rotax has entered the chat. They are snowmobile engines with a reduction gear and are certified for certain aircraft. So it's not that PSRUs fail, or auto engines are bad, but poorly designed PSRUs and engine conversations fail. There is absolutely nothing special about an airplane motor or car motor... they do the exact same thing, and both can be very reliable as long as the installer has the competency to make it work.
 
pfarber said:
Rotax has entered the chat. They are snowmobile engines with a reduction gear and are certified for certain aircraft. So it's not that PSRUs fail, or auto engines are bad, but poorly designed PSRUs and engine conversations fail. There is absolutely nothing special about an airplane motor or car motor... they do the exact same thing, and both can be very reliable as long as the installer has the competency to make it work.
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The Rotax accident record in homebuilts highlights this. From 1998 through 2022, there were 422 homebuilt accidents involving Rotax 912-powered aircraft, vs. 212 accidents involving homebuilts with Subaru conversions.

Even though they had twice as many accidents, only one of the 912 accidents involved the reduction drive, but seven of the Subaru accidents did. Three of the Rotax accidents involved the electronic ignition or engine controller, vs. 14 of the Subarus. One of the Rotax accidents was related to the cooling system, vs. seven of the Subaru ones.

Ron Wanttaja
 
pfarber said:
There is absolutely nothing special about an airplane motor or car motor... they do the exact same thing, and both can be very reliable as long as the installer has the competency to make it work.
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Over on homebuiltairplanes.com there's a retired automotive engineer whose job was analyzing engines and transmissions for torsional vibration, which is the killer of PSRUs. He can quote endless math showing what happens when the thing is not competently designed, and the "successful" PSRUs are more a result of luck than of competent design. Even the RAF redrive I had on the Subaru I installed in a Glastar had its issues, TV among them. There were certain RPMs where you passed through, increasing or decreasing, and did not linger there or bad stuff would happen.

Most people do not understand torsional vibration at all, and that's where the problems start. It is a BIG problem, and it's why most Continentals and Lycomings are direct-drive. They have had geared engines, they had problems with them, sometimes due to pilots ignoring POH instructions on RPM ranges. It is not easy to build one that works safely or for a long time, and so most are overbuilt so as to survive, and that adds weight. Most certified geared engines had splined quill shafts hidden within the crank nose and drive gear to absorb TV. Even the Merlin had that. It's a lot of machining, a lot of calculations, a lot of metallurgy and heat-treatment to get that quill so it will flex forever without snapping. It's a small shaft that takes tremendous torque.

This is an automotive clutch disc:

1717602966409.png

Do you know why those springs are in it? The splined hole in the center is in a plate between the layers of the disc assembly, and it has rectangular slots that those springs fit in. The disc is turned by the engine's flywheel, and transmits the torque via those springs to the splined output plate to the transmission. Other firing-pulse-absorbing parts include the massive, heavy flywheel, the transmission's input shaft, and the wheel driving axles. In a car with an automatic transmission, a fluid clutch called a torque converter does the job of those clutch springs. Transmission fluid between driving and driven turbine discs transmit the torque.

So NO, the airplane and car are different. Thinking simplistically about this stuff is what gets so many builders in trouble. Parts of the RAF redrive hassles were the substitution of a light aluminum flywheel for the original cast iron flywheel, the clutch disc, and the clutch pressure plate. That weight adds up mightily.
 
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Dan Thomas said:
There were certain RPMs where you passed through, increasing or decreasing, and did not linger there or bad stuff would happen.
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It should be remembered that the geared Continentals had rpm range restrictions, too.
Dan Thomas said:
Do you know why those springs are in it? The splined hole in the center is in a plate between the layers of the disc assembly, and it has rectangular slots that those springs fit in. The disc is turned by the engine's flywheel, and transmits the torque via those springs to the splined output plate to the transmission.
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My Fiat had a rubber donut coupling in the driveshaft, too.

Other than the well engineered Rotax redrives, most successful redrives use belts which provide damping via belt slip.
 
Rotax has entered the chat. They are snowmobile engines with a reduction gear and are certified for certain aircraft.
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I don't think I have ever seen a 4 cylinder horizontally opposed engine in a snowmobile before. But then again, I am not a snowmobile expert.
 
Capt. Geoffrey Thorpe said:
I don't think I have ever seen a 4 cylinder horizontally opposed engine in a snowmobile before. But then again, I am not a snowmobile expert.
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Rotax is well-known for their snowmobile engines, but they have also been in aircraft for many decades.

One thing that is interesting to note is that the legacy snowmobile use of 2-stroke power with a CVT operates the engine at a steady RPM over extended periods, similar to the aircraft use case.
 
Dana said:
Other than the well engineered Rotax redrives, most successful redrives use belts which provide damping via belt slip.
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The RAF redrive I was using was a timing-belt affair. No slip, so pretty much no damping.

The moment of inertia of the propeller, combined with the firing frequency of the engine, caused terrific resonance at 1400 RPM, a bit less at 2800, another at 4200, and redline was at 5600. The lower RPMs were the worst, and the engine would shake the whole airplane at those RPMs. The propeller's mass wanted to rotate at a steady speed, and was fighting the engine, which accelerates and decelerates on every firing stroke, decelerating in between those strokes.

pfarber said:
Rotax has entered the chat. They are snowmobile engines with a reduction gear and are certified for certain aircraft.
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Their snowmobile engines are two-strokes, they have a belted or geared PSRU, and none of them are certified for aircraft. Only the horizontally-opposed engines are certified. They are four-strokes and they have a well-engineered geared PSRU. There is no commonality with their snowmobile engines.
 
Dan Thomas said:
Their snowmobile engines are two-strokes, they have a belted or geared PSRU, and none of them are certified for aircraft. Only the horizontally-opposed engines are certified. They are four-strokes and they have a well-engineered geared PSRU. There is no commonality with their snowmobile engines.
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Not entirely true. Rotax has made 4-stroke sled engines for some time.

sledmagazine.com

Rotax 900 ACE Turbo engine: My first impressions

Denis first impressions on the Rotax 900 ACE Turbo engine.
sledmagazine.com sledmagazine.com

That said, they are very different from the aircraft Rotax models.
 
Daleandee said:
Reminds me of this guy (the impossible dream) ... :rolleyes:

SonexBuilders.net View topic - New engine for Sonex??

www.sonexbuilders.net www.sonexbuilders.net
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Sounds interesting - but since the post is from 2019 . . . . . . - did it work??? Would like to hear a follow-up, either way.

There's also the 'Delta Hawk' being currently advertised in the EAA magazine. https://www.deltahawk.com/

And don't forget the 'Corsair' (LS V8 engine) project. https://corsairpower.com/ [It appears those guys don't understand the paperwork process that is required.]
 
40YearDream said:
Sounds interesting - but since the post is from 2019 . . . . . . - did it work??? Would like to hear a follow-up, either way.

There's also the 'Delta Hawk' being currently advertised in the EAA magazine. https://www.deltahawk.com/

And don't forget the 'Corsair' (LS V8 engine) project. https://corsairpower.com/ [It appears those guys don't understand the paperwork process that is required.]
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I'm not the sharpest blade on the mower but my take is that what he was proposing was (let me be kind here) not very well thought out. I was the last one to post in that thread asking for an update about a year ago and I've heard nothing, zip, zilch, nada, zero, no reply ...:dunno:
 
I emailed Corsair power and I was surprised to get a quick reply. By all accounts their design functions well but the hurdles of FAA certification to put it on certified aircraft are too high. I asked if they would offer FWF kits for homebuilts but Jay indicated that the FAA was making that difficult also.

I would have thought that anybody with a lathe and mill could make and sell stuff for experimentals but I guess not.

How about a hydraulic torque converter between the engine and prop? That would probably put a lot of heat into the fluid that youd have to deal with, but it would dampen the vibrations for sure.
 
moparrob66 said:
I asked if they would offer FWF kits for homebuilts but Jay indicated that the FAA was making that difficult also.
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That’s surprising based on that reason. I’d be interested in understanding exactly how the FAA is involved in E-AB FWF packages.
 
moparrob66 said:
How about a hydraulic torque converter between the engine and prop?
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Molt Taylor used the Dodge Flexidyne dry fluid clutch in his Aerocar to allow some slippage without the constant losses from a fluid torque converter.
The company that makes them responded with NFW are we going to sell these for aircraft.
 
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moparrob66 said:
I would have thought that anybody with a lathe and mill could make and sell stuff for experimentals but I guess not.
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They can. There's nothing regulatory that would prevent them from selling such a kit. This had been discussed in previous threads. You can install anything you want on any aircraft provided you follow the appropriate route.

And just to add, to certify an automotive engine for a TC aircraft is next to impossible given how the systems are designed and built. Several PoA posts get into the details of why.
 
I’m having trouble finding regulatory details, but I know there are several Seabees flying under GM V8’s. I can’t imagine there’s an STC, which means they’d have to be Experimental - Exhibition or some such?
 
Yeah I chatted with a guy who stopped in with a corvette-seabee. He said it was worlds better than a stock seabee and that Experimental-Exhibition isnt much of an impediment to his use and enjoyment of the plane.
 
Looks like Toyota started down this path with the 2UZ-FE in the late 1990's. I can't find any sign of it being in a plane. The engine 4.7l V8 seems very reliable. Did result in the starter being in the worst place possible though. My daughter's 4R has 230K miles and still runs so smooth and doesn't burn oil.

www.flightglobal.com

Toyota is cleared to produce piston aero-engine

TOYOTA HAS RECEIVED US Federal Aviation Administration production certification for a piston aero-engine developed jointly with Hamilton Standard. The 270kW (360hp) FV2400-2TC is a twin-turbocharged Vee-8 based on Toyota's Lexus car engine and equipped with a Hamilton Standard full-authority...
www.flightglobal.com www.flightglobal.com
 
Sinistar said:
Looks like Toyota started down this path with the 2UZ-FE in the late 1990's.
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This is/was the aircraft that engine was developed for: Toyota TAA-1. It was built with Rutan's Scaled Composites during the AGATE program which also led to the Cirrus SR20 and Columbia 300. However, due to lack of demand in the general aviation private market Toyota pulled the aircraft and engine along with a number of other companies. But as far as I remember Toyota never surrendered the either TC.
1717873938577.png
 
Thanks for sharing - had no idea. Hard to imagine a Toyota sitting on the ramp!

With a required timing belt (+ water pump) ever 90,000miles (for the vehicke) that would be about every 1,500 hours
 
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