Auto Engines Aren't Designed to Take Full Power for More Than a Few Minutes...

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Wanttaja

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I know of an Eggenfeller Subaru equipped HBA that had a new engine fail (the core engine, not the PSRU) within the first three hours of flight, followed by another new engine, not the failed one rebuilt, that failed within its first ten hours of flight. Neither resulted IN damage to the airframe (both occurred over airports) and neither was reported to the FAA.
Yep, and by NTSB 830, none of them WERE reportable:

"Engine failure or damage limited to an engine if only one engine fails or is damaged, [is]... not considered "substantial damage" for the purpose of this part.

I, too, have known several cases where the incident wasn't reported to the FAA. A couple of them DID meet the reporting criteria, but the owner was too feisty/fast and got the residue hidden before the feds got involved.

My philosophy is that these are, probably, generally evenly spread among the aircraft and engines of the homebuilt world. True, a CH-701 is much more likely to be able to set down without damage after an engine failure than a Lancair IV, but I think the generalization will hold. And, of course, it affects homebuilts with production-type engines as well.

Ron Wanttaja
 

rv7charlie

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I know of an Eggenfeller Subaru equipped HBA that had a new engine fail (the core engine, not the PSRU) within the first three hours of flight, followed by another new engine, not the failed one rebuilt, that failed within its first ten hours of flight. Neither resulted IN damage to the airframe (both occurred over airports) and neither was reported to the FAA.

The airplane has had many hours of safe flight with the factory new Lycoming IO-360 that the owner installed after his very expensive and time consuming attempt to use a “modern technology” engine.


BJC
*That* is a perfect example of what Ron referred to as "can't". Given the fact that hundreds, if not thousands, of non-Egg Subarus are flying without failure, the problem is obviously not the engine. It's an engine converter that *can't*. And "can't" is the proper term for the one-off builds that fail, as well. Certainly none of them (at least, not the non-Egg endeavors), intentionally did an improper engine installation. They tried, but didn't get it right.

To the point that the core engine was failing: When the core engine design is statistically reliable, and there are three failures in the same airframe in short order, that's a good indicator of 'operator error'.

Charlie
 

rv7charlie

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To the question about carb ice: One factor that could affect the numbers in a positive way for conversion engines is that many of them are water cooled. This *can* have a significant effect on icing susceptibility. There is even a significant difference in susceptibility between a Lyc, with the carb bolted to the oil pan, and a small Continental, with the carb isolated from hot oil because it's suspended on the intake 'spider'.

Other modes I noticed was 'drive system' and 'cooling system'. Both stats make sense; 'drive systems' are virtually non-existent on piston a/c engines, and so, for all practical purposes, are cooling 'systems'. I'd wager that you'll never find an NTSB report that blames ragged baffling or a clogged oil cooler for cracked cylinders or seized bearings in a traditional a/c engine.
 

TXFlyGuy

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Serious question...how do you tactfully reply to those who tell you, "You want to cruise at 2800-3000 rpm, NOT 4100 rpm. This is for engine longevity and reliability."

There are misconceptions concerning auto engines, how to run them, and reliability, in many (if not all) corners of the aviation world.
 

BJC

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Serious question...how do you tactfully reply to those who tell you, "You want to cruise at 2800-3000 rpm, NOT 4100 rpm. This is for engine longevity and reliability."
Serious answer: “For the performance at 4100 RPM, and the pleasure that I get will from it, I will accept whatever reduction in longevity or reliability it may cause.”

Note that, in two different airplanes, I have operated a Lycoming at 3,200 to 3,350 RPM, including cross-country at 3,000 RPM. You might ask those advising you just how they are operating their engine in their airplane. My experience is that most of them are ready to give advice, but are not flying anything.


BJC
 
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BJC

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When the core engine design is statistically reliable, and there are three failures in the same airframe in short order, that's a good indicator of 'operator error'.
In the case I referenced, of two consecutive new Egg Subes that failed, even Mr. Egg admitted that he had a problem with the ECU (is that the correct term?) programming. No operator error involved, other than dealing with Mr. Egg.


BJC
 

rv7charlie

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That was the reason for the quotes. In the cases the we're discussing, 'operator' would be the guy operating *on* the engine; not simply running it. In other words, circumstances outside the engine's responsibility or control.
 

wsimpso1

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Or the PSRU was doing horrible things to the engine
There are two prominent ways this can happen:

Excess radial and/or angular misalignment between engine crank centerline and PSRU input shaft centerline. Since there are no perfectly machined pieces, the coupler must be executed to accommodate some alignment errors without undue loads on either end or fail the coupler. Design of the PSRU system must keep the misalignment small and well within the crank and bearing capabilities. Exceeding these can quickly trash the weakest of the crank, it's aft main bearing, the PSRU input shaft, and its bearings;

Excess axial load imposed by the PSRU upon the crankshaft. While automotive crankshafts are designed and proven to stand some loads toward the accessory or front end of the engine, this load is clutch throw out and torque converter level. PSRU design must keep axial loads low. Longitudinal misalignment that puts large thrust loads into the crank will quickly fail the weakest of the engine thrust bearings and the PSRU input shaft bearings.

System resonance due to poor torsional vibration management is UNLIKELY to cause issues due to the fact that the major engine pieces and system must have their fundamental frequencies safely above 2x max firing frequency. If their fundamental frequencies were within max 2x firing, the engine would quickly self-destruct... Since we know that modern engines stand going to their original redline rpm for long periods, we know that a system operating resonance from PSRU and prop will not excite damaging resonance in the major engine pieces.

But those first two - yeah, poor alignment can wreck the engine. Eggenfelner systems used a shady alignment scheme including leaving to the builder to select washers to set longitudinal position of the PSRU to the engine. I gotta wonder about how good or bad this was for the engine and rubber isolator.

Billski
 
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BJC

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That was the reason for the quotes. In the cases the we're discussing, 'operator' would be the guy operating *on* the engine; not simply running it. In other words, circumstances outside the engine's responsibility or control.
OK, thanks for that clarification. My friend who had the unfortunate experience with Mr. Egg was a career military pilot and instructor.


BJC
 

BBerson

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If Mr. Egg sold a well proven direct drive auto engine conversion I might be slightly more interested.
 

thjakits

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I assume a prop cruise rpm of 3000 is about the max you would want - a few more for max power...
Consindering turbos and a specific cam grind - what size engine do you need to produce 300 hp at that rpm??
Direct drive V12/10/8/6 or inline 6/4??

I would guess a LS-crate engine could be made to run reliably 300 hp at 3200 rpm if built towards that?
...or a Lexus V8 or certainly a 90s BMW V12...

The question would be how much weight difference do you get for swapping the PSRU for a load-bearing?
That of course could be integated into a forward engine mount...

How would go about inverting the engine (to get the prop line back up)? Specifically the oil that undoubtfully will collect in the cylinder bores and back of the pistons - much of it seeping past the rings and getting into the combustion chambers....

Cheers,

thjakits
 

wsimpso1

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The question would be how much weight difference do you get for swapping the PSRU for a load-bearing?
That of course could be integated into a forward engine mount...
Without running a fairly thorough analysis, I would have a hard time telling you the minimum weight of a prop drive only vs existing PSRU for V8's. I can tell you a few things:

If it is to be a "soft" system, first vibe order will have to below min firing order frequency, the rest of the orders must be managed to be out of operating range:
It will have a "soft" isolator for both torsional vibration and for mis-alignment/deflection between engine and prop shaft.
It will have more flywheel inertia than with a stiff system;
The case will be a big fraction of what it will be for PSRU - at least half;

If it is to be a "stiff" system, If it is to be a "stiff" system, it will need to have all natural frequencies higher than 2x max firing frequency:
It will have an isolator for mis-alignment/deflection between engine and prop shaft that is very stiff in torsion;
Its flywheel will most likely be an automatic transmission type flexplate;
The case will be a big fraction of what it will be for PSRU, and bigger than for the "soft" system;

The only parts eliminated completely by going direct drive are the input shaft, reduction parts and oil. I suspect that the weight save would be less than 1/3 of the all up wieght of the PSRU system, and possibly closer to zero save. Then there is all of the engineering and batch size-of-one parts in a new one. I would buy something that we already know works. YMMV.

How would go about inverting the engine (to get the prop line back up)? Specifically the oil that undoubtfully will collect in the cylinder bores and back of the pistons - much of it seeping past the rings and getting into the combustion chamber?
Inversion is mostly a matter of getting oil flows to go back to your oil tank. Dry sump system design plus remote tank and oil pickup must all be added to the engine. Drains from the heads and crankcase must drain freely by gravity or include scavenge pumps, and your pump pickup will be from the tank. When running, oil going to the pistons is not likely to be much of an issue - modern auto engines cool the pistons with targeted oil spray on the underside of the piston while piston accelerations will toss oil out as each piston approaches BDC . After you shut it down, oil present in the pistons will tend to drain into combustion chambers, so you will need to pull the engine through a few blades prior to start to clear that oil and prevent hydraulic lock.

One other thing that you did not cover was a reliable propellor system is needed. Existing props will cover the power, torque and vibration, but are substantially larger diameter. When you make the needed diameter decrease to stay subsonic at higher rpm, the blade areas will need to be increased. New prop blades then become part of the development too.

Between the engineering, fabrication, and test to make a new direct drive system and to make a reliable oil system for the inverted engine, and a new prop, the existing engine/PSRU/prop systems with good flying histories seem like a pretty good idea.

Billski
 
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