Aero engines vs Auto engines

[danny_galaga]

18 minutes ago, facthunter said:

dg, Your comment Lacked Logic. The rest of what I wrote you completely ignore. .There's plenty of reasons against Car engines & the redrive is  a KNOWN problem. Properly engineered red Gears are Usually LARGE and often Sun and Planetary which is the Best. The Prop is often a significant flywheel and it's not good to Gear a Flywheel to a crankshaft. The Pistons also perform some work as a flywheel but it's cycling where they take energy, stop and give it back. This id at it's worst in flat OR in Line fours. Best is large number of cylinder RADIALS.  Some Motors have tumbling counterweights which dynamically absorb torsional Variations. They give the reduction Gears an easier Life. ALL Gears create some frictional Losses which inevitably creates Heat. even in a small Motor it could be about 2,000 watts  and backlash or play causes Hammering. Put a stethoscope against a Rotax gearbox and Have a listen or even a failed or Loose Harmonic Balancer . These are Large forces we are dealing with. .  Nev

Do the guys designing redrives not know all that you know? I'm being serious. In these discussions, some guys here have concerns about the engine design (for instance, the crank bearings not being built for the types of loads an airplane puts on them), others say it's mostly peripheral things that let them down, like redrives. I seriously feel if that's the case (and I don't know if it is, I haven't looked at failure rates) then that should be something SOMEONE must be capable of engineering properly. Ostensibly, the engine it's connected to is way more complicated.

 

There seem to be some big players saying they've got it sorted. If they have, they should make that a HUGE selling point and offer their design to suit all the most popular conversations. Their GOOD product should crowd out inferior products in the market.

 

What is for sure in my mind, is that along with most of these engines being single ignition only, you have three distinct areas (engine design, redrive design, single ignition ) that aren't 100% 'aero'  that allow for a higher chance of failure than an actual aero engine.

[facthunter]

Aero engines are made as light as is safely Possible. They are also in moving air so why not air cooled even IF that Limits the HP/CU in a bit. It doesn't make specific fuel consumption worse . The higher temps Make it Potentially Better. With Identical Pots cost is reduced and 2 4 & 6 cyl Variants are Possible inline or Flat and Radial configuration. Individual Cylinder replacement is an advantage as the engine doesn't have to be removed and often the Head/ barrel joint is permanent.  Dual ignition is considered essential and there's OFTEN Multiple Variants available of any capacity. Nitrided cranks and Cylinders are the Norm. Crankcases are Heat treated alloy mostly but some Large radials are  high tensile Steel. The biggest Problem in the Aero Market is the LOW total Volume and the Hoo Haa of getting certification. You used to have to start Low for a TBO and earn the right to raise it. NOW people SEEM to be able to CLAIM anything without much substantiation.  The Path to a successful small  Aero engine is littered with Many Failures. Many were Predictable  A lot of engines do not get enough frequent USE and are not Installed well or inhibited when out of use.  An Over-revved Motor is a desk ornament. Over Heated not far Behind.  It's an Aeroplane you are in.  IF you want a Motor that Goes forever Get a Gardiner and put it in a Trawler. Nev

[T510]

2 hours ago, danny_galaga said:

Do the guys designing redrives not know all that you know? I'm being serious. In these discussions, some guys here have concerns about the engine design (for instance, the crank bearings not being built for the types of loads an airplane puts on them), others say it's mostly peripheral things that let them down, like redrives. I seriously feel if that's the case (and I don't know if it is, I haven't looked at failure rates) then that should be something SOMEONE must be capable of engineering properly. Ostensibly, the engine it's connected to is way more complicated.

 

There seem to be some big players saying they've got it sorted. If they have, they should make that a HUGE selling point and offer their design to suit all the most popular conversations. Their GOOD product should crowd out inferior products in the market.

 

What is for sure in my mind, is that along with most of these engines being single ignition only, you have three distinct areas (engine design, redrive design, single ignition ) that aren't 100% 'aero'  that allow for a higher chance of failure than an actual aero engine.

http://www.epi-eng.com/index.html

These guys seem to have their PSRU's sorted, some great information on their website too. They do ag conversions so they would need their reliability sorted, and they do helicopter gearboxes too

 

https://www.aerosportengineering.no/

This company's bought their PSRU design from EPI and have been working on their own BMW V12 based package

 

https://lsaeroengines.com/

LSAero engines have a psru available and seem to be focused on firewall forward packages for Murphy Moose upgrades

 

Haven't been able to find any negative reviews on these companies, not that I have looked that hard.

 

 

[danny_galaga]

I rather like this little engine, designed from the ground up for aircraft. For their own aircraft as it happens. Listen to that cute chug in the last  video clip ☺️

 

Built to rev at 'airplane' revs, it tops out at 3000. Only thing is it seems to not be dual ignition, but I could be wrong.

 

https://spiriteng.com/spirit-v2-engine/

 

 

This is the plane it's designed for. What a lil beauty 😍 

 

https://aopa.org/news-and-media/all-news/2025/july/31/a-neat-little-package

 

[facthunter]

That's the same Plane Skippy went APE over after I gave it the thumbs UP. Nev

[danny_galaga]

9 minutes ago, facthunter said:

That's the same Plane Skippy went APE over after I gave it the thumbs UP. Nev

[T510]

1 hour ago, danny_galaga said:

I rather like this little engine, designed from the ground up for aircraft. For their own aircraft as it happens. Listen to that cute chug in the last  video clip ☺️

 

Built to rev at 'airplane' revs, it tops out at 3000. Only thing is it seems to not be dual ignition, but I could be wrong.

 

https://spiriteng.com/spirit-v2-engine/

 

 

This is the plane it's designed for. What a lil beauty 😍 

 

https://aopa.org/news-and-media/all-news/2025/july/31/a-neat-little-package

 

That's a ripper, I'd have one if the budget allowed

[Thruster88]

Here is an example of an automotive engine conversion with a mode of failure that should have be so obvious. No fault in the core engine, one wreaked aircraft.

 

*** Final Report ***

N15180 Titan T-51D Ashtabula, Ohio 06 JUL 2021

1 No Injury

Pilot Flight Time: 8000 hours (Total, all aircraft), 4000 hours (Total, this make and model)

The intent of the flight was to perform fuel flow and fuel indicator checks on the newly built airplane while taxiing on the ground; however, they were not able to obtain full engine performance on the ground and the pilot elected to take the airplane into the air. After takeoff, while climbing through 200 ft above ground level (agl), the engine lost power. The operator reported that the engine computer circuit breaker had tripped which resulted in the loss of engine power. The pilot attempted to reset the circuit breaker and restart the engine without success. The airplane landed hard on the runway and the left main landing gear collapsed. The left wing sustained substantial damage. A postaccident examination showed that the oxygen sensors used to tune the engine were left on the engine’s cylinder exhaust pipes during the flight. The sensors drew power from the engine’s control computer. During the initial climb, the increased electrical demand to run the oxygen sensors at maximum engine power exceeded the 15-ampere limit on the engine’s control computer, its circuit breaker to tripped, and the engine lost power.

Probable Cause and Findings:
The tripped engine control computer circuit breaker caused by an excessive electrical load on the system, which resulted in a complete loss of engine power during the initial climb.

 

[BrendAn]

2 minutes ago, Thruster88 said:

Here is an example of an automotive engine conversion with a mode of failure that should have be so obvious. No fault in the core engine, one wreaked aircraft.

 

*** Final Report ***

N15180 Titan T-51D Ashtabula, Ohio 06 JUL 2021

1 No Injury

Pilot Flight Time: 8000 hours (Total, all aircraft), 4000 hours (Total, this make and model)

The intent of the flight was to perform fuel flow and fuel indicator checks on the newly built airplane while taxiing on the ground; however, they were not able to obtain full engine performance on the ground and the pilot elected to take the airplane into the air. After takeoff, while climbing through 200 ft above ground level (agl), the engine lost power. The operator reported that the engine computer circuit breaker had tripped which resulted in the loss of engine power. The pilot attempted to reset the circuit breaker and restart the engine without success. The airplane landed hard on the runway and the left main landing gear collapsed. The left wing sustained substantial damage. A postaccident examination showed that the oxygen sensors used to tune the engine were left on the engine’s cylinder exhaust pipes during the flight. The sensors drew power from the engine’s control computer. During the initial climb, the increased electrical demand to run the oxygen sensors at maximum engine power exceeded the 15-ampere limit on the engine’s control computer, its circuit breaker to tripped, and the engine lost power.

Probable Cause and Findings:
The tripped engine control computer circuit breaker caused by an excessive electrical load on the system, which resulted in a complete loss of engine power during the initial climb.

 

What a great idea. Engine won't perform on the ground so let's try it in the air..  Darwin award candidate there.

Lucky he is still around to talk about it..

[T510]

Not to mention leaving tuning O2 sensors in the exhaust, powering them through the ECU and not knowing the required power required through the circuit breaker.

 

Stupidity destroyed that T-51, not the LS engine that powered it