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
Click to expand...
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.
Click to expand...

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!
Click to expand...
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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