Auto conversion ideas

M

moparrob66

Pre-takeoff checklist
Joined
Mar 31, 2024
Messages
253
Display Name
Display name:
Moparrob
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....
 
Auto engines don’t tend to make anywhere near their peak power at 2700 RPM or below. And besides the PSRU, cooling seems to be very problematic. A potential 3rd issue is having to roll your own FWF package which can involve considerable effort in and of itself. My worthless advice is go down this path with eyes wide open. It can be done successfully but there’s good reasons why auto conversions remain a niche market in the E-AB world.
 
Last edited:
auto conversions are a very complex project. I knew a guy that did harmonic work on clutches for one of the big 3. we had an interesting discussion one day about the harmonics that you have to deal with. also, trying to use an auto engine direct drive, you have to deal with the propeller loads that the crank and bearings were never designed to carry. its a very in-depth problem. a lot of great minds have spent a lot of time working on it and so far nobody has made a unit that was successful.
 
Im intrigued by the apparent success of auto engines in airboats. If i went the direct drive route, I'd want the prop mounted to a shaft with a large bearing support in addition to the crank bearings. Maybe even use the front portion of a continental or lycoming crankshaft. Im leaning towards a zenith 801 and high horsepower will help with climb but its wasted in level flight with all the drag. I think a Chevy LS3 limited to 2700 rpm will make more power than an O-360 for a third the price (or less) and not much more weight.
 
I think you’ll find most airboats use aircraft engines, the 540 in particular. As for getting this done for a third of the price— good luck. You’ve got to look beyond just the purchase price of the motor. That said if you’re really into the journey of adapting any non-aircraft engine and enjoy tackling the challenges then I’m rooting for you. If you’re just looking for a cheap AND reliable alternative to a Lycoming or Continental then I think you’ll end up being disappointed.
 
moparrob66 said:
Im intrigued by the apparent success of auto engines in airboats.
Click to expand...
Emphasis on "apparent." Nobody tracks if an airboat has to get towed/rowed home. Engines that fail in aircraft often result in reportable accidents, and statistics can be extracted from the NTSB reports. No such data for airboats.

I've regularly posted about the reliability statistics for auto engine conversion. If you do go this route, examine the failures of engines/conversions similar to yours so you have an idea of where problems may occur.

Nothing wrong with gear reduction drives, nothing wrong with electronic ignitions, nothing wrong with liquid cooling. The Rotax 9XX series has all three, and has demonstrated an excellent safety record.

Ron Wanttaja
 
wanttaja said:
Nothing wrong with gear reduction drives, nothing wrong with electronic ignitions, nothing wrong with liquid cooling. The Rotax 9XX series has all three, and has demonstrated an excellent safety record.
Click to expand...
The difference is the money and engineering Rotax had at its disposal to make the 9XX series a success plus adoption by airframe manufacturers to implement the installation— you need both to make a successful and reliable airplane.

I think the closest examples from the auto world are VWs and Corvairs but even then they haven’t exactly taken the world by storm even for the airframes for which that are suited.
 
Viking Aircraft Engines have a very successful auto conversion that has become popular in every kind of experimental aircraft. I gladly trade in the Lycoming O-235 in my experimental if I had the money and physical ability to do it.
 
Patey has an airboat prop on Scrappy. It’s being turned by a Lyc 780.
 
I agree that I'll likely spend a lot more than just buying off the shelf components for this endeavor. How soon until one can buy new O-360 crankshafts or new Franklin 220s? I may have the time whether I like it or not.


If its not reliable on the ground, i can sell it to somebody with an airboat?
 
Lndwarrior said:
Viking Aircraft Engines have a very successful auto conversion that has become popular in every kind of experimental aircraft. I gladly trade in the Lycoming O-235 in my experimental if I had the money and physical ability to do it.
Click to expand...
I guess it depends on how you define popular. Not everyone is an Eggenfellner engine fan regardless of the badging. There’s anecdotally as many horror stories as successes with the company and the engines themselves.
 
tsts4 said:
I guess it depends on how you define popular. Not everyone is an Eggenfellner engine fan regardless of the badging. There’s anecdotally as many horror stories as successes with the company and the engines themselves.
Click to expand...
I have a pilot friend that had a fiasco dealing with the egg-man but that's not my story to tell. I've had 12 years of reliable service from a William Wynne designed and Dan Weseman built 3.0 Corvair conversion. It has a 5th bearing mounted to the nose for prop loads on the direct drive six cylinder engine. Cooling has been excellent in my application.

William has spent ~35 years in developement and updating his Corvair conversion process. A list of WW flying corvairs is here (not sure how current this list is):

 
Daleandee said:
I have a pilot friend that had a fiasco dealing with the egg-man but that's not my story to tell. I've had 12 years of reliable service from a William Wynne designed and Dan Weseman built 3.0 Corvair conversion. It has a 5th bearing mounted to the nose for prop loads on the direct drive six cylinder engine. Cooling has been excellent in my application.

William has spent ~35 years in developement and updating his Corvair conversion process. A list of WW flying corvairs is here (not sure how current this list is):

Click to expand...
I’m a big fan of the WW/SPA corvairs. It’s my engine of choice if I ever pull the trigger on a Piet.
 
tsts4 said:
I’m a big fan of the WW/SPA corvairs. It’s my engine of choice if I ever pull the trigger on a Piet.
Click to expand...
I've been pondering the build of a Peit for a few years. I have a buildable Corvair core engine already. I've wanted to build the steel tube fuse but it's been a number of years since I've done much welding. A family member has gifted me an O/A set-up so when I get all of that ready I can take some lessons and do some serious metal melting to get proficient enough to trust my life to my welding.

I see the OP mentioned building an 801 so I trust I'm not too far off the rails with the thread drift ...
 
The much higher rotational mass of an aircraft propeller coupled with less damping makes torsional resonance a major problem in aircraft PSRU design. It's much less of an issue with a much smaller boat prop running in water.
 
Okay good point. Maybe direct drive is a better plan for now...with a big sturdy bearing supporting the prop shaft!
 
Similar proposal just a few days ago here: https://www.pilotsofamerica.com/community/threads/lycoming-engine-replacement.146655/#post-3502093

Scroll down to post #23 to see what I had to say about it.

Conversions are neither easy nor cheap. I've been there and done it. There are so many factors that the builder has to address, or safety is compromised. When your conversion fails over the big city or big lake or big rocky mountains, the money you saved by not using a proven a Lycoming or Continental suddenly looks totally stupid.

90 years this attempt to fly car engines has been going on, and we still don't have any reliable and economical ready-made auto conversion replacements for our legacy engines.
 
tsts4 said:
I guess it depends on how you define popular. Not everyone is an Eggenfellner engine fan regardless of the badging. There’s anecdotally as many horror stories as successes with the company and the engines themselves.
Click to expand...
Jan's earlier conversions were suburu engines, and they did not work out well.

However, Viking Aircraft Engines is a different company and uses Honda engines. With the possible exception of William Wynn I would argue he has more knowledge than anyone when it comes to auto conversions. He has built a solid record, and a solid following, with Viking.

Jan continues to create innovative solutions for the experimental aircraft market.
 
wanttaja said:
I've regularly posted about the reliability statistics for auto engine conversion. If you do go this route, examine the failures of engines/conversions similar to yours so you have an idea of where problems may occur.
Click to expand...
Just to take the thread in a totally different direction…:rolleyes:

I had a neighbor growing up whose first powered airplane had a Henderson motorcycle engine. How did those fare, and are there any currently flying that you’re aware of?
 
I’ll not comment on the Eggenfeller engines, other than “do your homework”. I hope he develops a great engine, as it would highly benefit the home built audience.

That said, auto-conversions are entirely possible and there are quite a few success stories of engines from Subaru to Chevy engines. I have a good friend that flies a Chevy V6 in his RV7 with several hundred hours.

But, and a very big but, the pilot needs to be very aware of what he is flying. @wanttaja @Dan Thomas and @Daleandee are probably some of the best resources you could listen to on this subject. Auto conversions can be very viable, but they are seldom less expensive. The person that wants to research this needs to do a deep dive into Torsional Vibrations and completely understand this phenomenon before they ever even consider flying behind a prop on an engine not designed to spin a prop.

There are forums and threads dedicated to this topic. It’s up to the OP to do his own research… real research, not a 30 minute YouTube vid.
Get a text book.
 
Last edited:
Lndwarrior said:
Viking Aircraft Engines have a very successful auto conversion that has become popular in every kind of experimental aircraft. I gladly trade in the Lycoming O-235 in my experimental if I had the money and physical ability to do it.
Click to expand...

Viking does a great job effectively making it a cult and going after negative press. Viking does have some success, but it is not nearly a rosy picture as many people post.

Tim
 
Fundamentally, auto-conversions can be done. However, you need to be a real problem solver, and likely bring many engineering skills into play.
For avgas VW, Corvair, Lycoming, CMI all have a widely known body of knowledge, which results in significantly less new ground which must be "discovered" and then engineered and designed for.
For Jet-A, you have Austro and CMI solutions, the body of general knowledge is much smaller, but you have large companies that spent millions solving the problems.

When considering airboat PSRUs, be aware they tend to be very heavy for an aviation viewpoint and stiff from a TV perspective. Basically, you can spend millions on design and engineering analysis, or you can over engineer (through material at it) by large margins and accept a higher production cost. Pretty easy to see what choice airboat companies have made.

Tim
 
Lndwarrior said:
Viking Aircraft Engines have a very successful auto conversion that has become popular in every kind of experimental aircraft.
Click to expand...
I'm always curious about where these kinds of claims come from.

I looked at the FAA registry for January of this year, and counted about 150 aircraft that listed a Viking or a Viking Honda engine. There are five times as many Volkswagens, and almost three times as many Subarus. There are roughly the same number of registrations showing Sonex/Aerovee engines.

About 3300 homebuilts don't list an engine type, but there's no reason to believe that a large percentage of those are Vikings. I estimate about 40 or so types with no listed powerplant actually have Viking engines. This also ignores aircraft listed as having a "Honda" engine, but are not specifically listed as Viking.

Now, I have no insight into how many engines Viking has *sold*. Maybe thousands. But all that can be proven is that there's ~150 Viking-powered aircraft in the US. We can extrapolate the "no engine type" data to assume a total ~200 aircraft in the US with active registrations probably have Viking engines.

I'm not sure whether this would constitute a "very successful auto conversion."

Ron Wanttaja
 
Lndwarrior said:
Jan's earlier conversions were suburu engines, and they did not work out well.

However, Viking Aircraft Engines is a different company and uses Honda engines. With the possible exception of William Wynn I would argue he has more knowledge than anyone when it comes to auto conversions. He has built a solid record, and a solid following, with Viking.

Jan continues to create innovative solutions for the experimental aircraft market.
Click to expand...

I think you're overstating their popularity, so I guess we'll just have to agree to disagree. All I can really say is caveat emptor.
 
wanttaja said:
I'm always curious about where these kinds of claims come from.

I looked at the FAA registry for January of this year, and counted about 150 aircraft that listed a Viking or a Viking Honda engine. There are five times as many Volkswagens, and almost three times as many Subarus. There are roughly the same number of registrations showing Sonex/Aerovee engines.

About 3300 homebuilts don't list an engine type, but there's no reason to believe that a large percentage of those are Vikings. I estimate about 40 or so types with no listed powerplant actually have Viking engines. This also ignores aircraft listed as having a "Honda" engine, but are not specifically listed as Viking.

Now, I have no insight into how many engines Viking has *sold*. Maybe thousands. But all that can be proven is that there's ~150 Viking-powered aircraft in the US. We can extrapolate the "no engine type" data to assume a total ~200 aircraft in the US with active registrations probably have Viking engines.

I'm not sure whether this would constitute a "very successful auto conversion."

Ron Wanttaja
Click to expand...
I know of at least one Viking 'deconversion' that made my Rotax decision easier.

Absent any other information than price, Viking seems a no-brainer, when in reality it is a no-brainer.
 
tsts4 said:
I think you're overstating their popularity, so I guess we'll just have to agree to disagree. All I can really say is caveat emptor.
Click to expand...
That’s what happens when all you read are the highly moderated Viking forums that censor anyone who has anything remotely negative to say about their experience with the company or the motor.
 
There seems to be quite a lot of planes doing the STOL competitions with Viking engines.

I'm really struggling with this one as my partner in the plane I'm building is 100% sold on the engine, and I'm lukewarm at best. Yeah, Eggy can be a bit edgy for sure, but that's not really proof it doesn't work.
 
FancyG said:
I know of at least one Viking 'deconversion' that made my Rotax decision easier.
Click to expand...
I get pressed...a lot...to discuss the accident statistics related to Viking engines.

The problem is the small sample size. In my 1998-2022 EAB accident database, there are 416 accidents involving homebuilts with Rotax 912s, there are 1756 accidents involving homebuilts mounting Lycoming engines, but only 19 accidents involving EABs confirmed as having Viking engines installed. A single Lycoming accident affects the statistics by 0.06%, while a single accident affects the Viking results by a full 5%.

The low number of accidents does not imply a highly-reliable engine; homebuilt aircraft are going to crash no matter what engines are installed. The low number of accidents reflects the relatively small number of Viking engines in operational homebuilts...which is the basis for my skepticism whenever I see claims about a large installed base.

The one thing that does stand out is the relatively large number of Viking accidents involving either the engine controller or the electrical system that supplies it...four of the 19 accidents. Curiously, these are all Zenair CH-750s. The NTSB accidents attributes three of these cases to mistakes made by the builder or pilot (you leave the alternator switch off, the battery is going to go dead....). The last case (CEN18LA042) occurred after installation of a replacement Engine Control Unit with updated programming. The NTSB report does not specify the source of the updated programming.

Ron Wanttaja
 
aterry1067 said:
There are forums and threads dedicated to this topic. It’s up to the OP to do his own research… real research, not a 30 minute YouTube vid.
Get a text book.
Click to expand...
There is also https://www.homebuiltairplanes.com/forums/ This is the place to do a search for conversions on various types. One has to remember, though, that there are many posts by people who are "certain that a GM LS engine would be a no-brainer conversion," or who "going to convert" some auto engine, some by those who "are converting" an auto engine, but very few by people who are actively and successfully flying the engines they intended to build or did build. Very few. It reveals both the difficulty of creating a safe conversion, and the shame of a failure. There have been many homebuilts initially powered with an auto engine, with the ongoing bugs and incipient failures resulting in a Lycoming or Continental being installed instead. Like homebuilding the airplane, the old saying holds true for the engine, too: "if you want to fly, buy; if you want to build, build." You really have to want to do a conversion, you have to learn a massive amount of the stuff, likely some of it the hard way, and persistence matters. A lot. It will not be cheap. Or quick.
wanttaja said:
I looked at the FAA registry for January of this year, and counted about 150 aircraft that listed a Viking or a Viking Honda engine. There are five times as many Volkswagens, and almost three times as many Subarus. There are roughly the same number of registrations showing Sonex/Aerovee engines.
Click to expand...
That is the number of registered airplanes. In the US, can a build be registered long before completion and preparation for flight? How many of those "registered" airplanes have actually flown on those engines? It would help the statistics if there was a separate probationary registration category where the registration did not become permanent until the restrictions were flown off.
wanttaja said:
The one thing that does stand out is the relatively large number of Viking accidents involving either the engine controller or the electrical system that supplies it...four of the 19 accidents. Curiously, these are all Zenair CH-750s. The NTSB accidents attributes three of these cases to mistakes made by the builder or pilot (you leave the alternator switch off, the battery is going to go dead....).
Click to expand...
Homebuilders don't take the electrical system seriously enough. Nor do many pilots and owners. It shows up here on POA in the usual alternator-failure stories, or electrical-gremlin stories, and most of it is a lack of proper proactive maintenance and annual inspections. Alternators are run until they quit, ignoring the manufacturers' recommendations that the brushes be inspected every 500 hours. Various circuits fail because their switches and breakers are never closely inspected, and connectors in many places get oily or dirty. Ground connections get corroded.

Stuff needs looking after. Or else. And in many auto conversions, only single ignition is used, and that reliant on the airframe's electrical system. Fuel pumps are electric, too. Everything that engine needs to run is dependent on the electrical system.
 
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....
 
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....
Click to expand...
I had two forced landings, both behind certified engines that were improperly maintained/overhauled.
 
Dan Thomas said:
There is also https://www.homebuiltairplanes.com/forums/ This is the place to do a search for conversions on various types. O
Click to expand...
Just realized that the only way to access those forums as a new member now is by paying $99 a year. They grandfathered many people in but if you didn't already have an account they now charge a yearly fee to post or read anything. It used to be a great site but unfortunately the owner got greedy. Most people on that site don't realize that they changed to be subscription based and wonder why it is always the same people posting or answering questions. I'm not opposed to paying some sort of fee but $100 a year is just too rich for me for what is nothing more than another internet forum.
 
kmacht said:
Just realized that the only way to access those forums as a new member now is by paying $99 a year. They grandfathered many people in but if you didn't already have an account they now charge a yearly fee to post or read anything. It used to be a great site but unfortunately the owner got greedy. Most people on that site don't realize that they changed to be subscription based and wonder why it is always the same people posting or answering questions. I'm not opposed to paying some sort of fee but $100 a year is just too rich for me for what is nothing more than another internet forum.
Click to expand...
Yes, $100 is pretty steep, but you can pay that much for an annual online newspaper subscription. The fee has had the effect of weeding out those who aren't serious, or who are full of "revolutionary" ideas that didn't work 50 years ago and still won't work. Can't argue with people who already have made up their minds that everyone else is wrong.

If you can't afford $100, you can't afford to build an airplane or an engine, or even buy a set of plans.
 
Dan Thomas said:
Yes, $100 is pretty steep, but you can pay that much for an annual online newspaper subscription. The fee has had the effect of weeding out those who aren't serious, or who are full of "revolutionary" ideas that didn't work 50 years ago and still won't work. Can't argue with people who already have made up their minds that everyone else is wrong.
Click to expand...
Yeah but it has also weeded out engineers and pilots like myself who are actively working on new experimental aircraft and auto conversions. At one point it was a great site. Now I have no idea if there are even still enough knowledgeable people on there to make it worth joining and I'm not willing to spend that kind of money just to find out. I guess we will see in a few years how active the forum still is and if the idea of a yearly fee worked out.
 
kmacht said:
Just realized that the only way to access those forums as a new member now is by paying $99 a year.
Click to expand...
The owner is pushing the paid membership but you can still register for free, just go to the "register" page and scroll down for "basic" membership.
 
Last edited:
kmacht said:
Just realized that the only way to access those forums as a new member now is by paying $99 a year. They grandfathered many people in but if you didn't already have an account they now charge a yearly fee to post or read anything. It used to be a great site but unfortunately the owner got greedy. Most people on that site don't realize that they changed to be subscription based and wonder why it is always the same people posting or answering questions. I'm not opposed to paying some sort of fee but $100 a year is just too rich for me for what is nothing more than another internet forum.
Click to expand...

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
 
You must log in or register to reply here.
Back
Top