Difference between automotive and aircraft engines

[Cujet]

Originally Posted By: DeepFriar
Some thoughts on this thread:

The Mercedes based Austro AE330's in the Diamond DA-62 look like they represent the state of the auto-engined airplane state of the art. Full, dual FADEC and now with an 1800 hour TBO. Appears to have great payload/range/speed options. And you sure can't argue with how it looks. I don't know how Beech can sell another Baron compared to it.




That 1.3 million dollar, twin diesel DA62 is an amazing performer. One heck of a sexy and comfortable airplane. Just shy of a 200kts on 19GPH total. No question that it's a modern "baron". The only issue is the single engine climb rate at max gross, which in ideal conditions is about 200 FPM. But you can't expect much single engine performance as it's flying on 180HP and it's 5700 pounds.

Quite a capable machine. The engines are expensive. However, only in some situations do the fuel savings offset the HUGE additional mechanical costs.

A good example of this is my little airplane. It burns 10GPH has a 2000 hour TBO, and an overhauled engine is $27K. During that 2000 hours of use, it will burn up $110,000 worth of fuel! Clearly, the fuel use is the major expense in my case. However, if I could get the same performance on 6GPH of Jet A, would it pay for a small diesel? Maybe!

Some of these new generation diesel engines top $250,000 and can't be overhauled. They are simply replaced. At what point does it work out?

The Deltahawk is said to be $70K now. And it burns 9 GPH at 75%. I'm at 10.2GPH for 75%.

 

[DeepFriar]

The Diamond Austros are straight off the MB 6 cyl diesel production line and burn JetA or equivalents. The automotive accessory systems are removed and crushed (Mercedes doesn't want a parts competitor apparently). The aircraft accessories are added and, poof, put it on the wing. No way of knowing a unit cost yet so I suppose it could be $250K but that seems very high given the core here. Too new to know rebuild cost but an MB core diesel is not going to be a throwaway item, this ain't no Rotax or Theilert. Paul Bertorelli at Aviation Consumer said they were the smoothest recips he's ever flown, very low vibration. I think he said something about restarts that you alluded to. And that is that there was a max time limit on shutting an engine down for training but I don't recall that number. Lastly, and it's a shocker to me, a n equipped Baron is also stickered at about $1.4M!

 

[UncleDave]

[/quote]

Amazing numbers! And I don't doubt them. Engine builders can, and do, employ all sorts of methods to increase power and efficiency. However, we only need to look at the marine industry to see the fuel consumption numbers for typical automotive engines under heavy load and higher RPM.
[/quote]

Thanks, that is a marine mill capable of sustaining top RPM for extended periods of time and balanced to a ridiculous degree that it feels like a sewing machine when you step on it.

It worth noting that I got mid .4 BSFC's with a 40 year old carbed small block chevy I set up myself in my garage, and Im just a hick old boy quasi mechanic with a farm background that understands the value of dyno testing and tuning, but we hit it with two jet changes from my baseline.

I have the dyno chart an dBSFC's on both engine one being done at westech, with veteran Steve Brule and a super flow the other being done at Boostpower marine who uses both an in wall and a prop shaft dyno to stimulate in gear changes and idle characteristics so its pretty easy to beat the #'s .55 you laid out in nearly any use scenario if my home made marine engine can beat it with me tuning.

I don't see how we can point to a gear box as being a solid reason not to use auto engines because so many dedicated airplane engines use gearboxes as well there isnt any point in me listing them as everyone has wiki and google, but there are lots of them.

I think we can eliminate BSFC AND gearboxes as a reasons auto engines can't or don't make great plane engines.

To me it comes down to the auto engines evils of a liquid Vs air cooled power plant which itself has compromises like the potential for shock cooling.

Fun thread regardless.

UD

 

[DeepFriar]

Originally Posted By: Cujet
Originally Posted By: DeepFriar
Some thoughts on this thread:

The Mercedes based Austro AE330's in the Diamond DA-62 look like they represent the state of the auto-engined airplane state of the art. Full, dual FADEC and now with an 1800 hour TBO. Appears to have great payload/range/speed options. And you sure can't argue with how it looks. I don't know how Beech can sell another Baron compared to it.




That 1.3 million dollar, twin diesel DA62 is an amazing performer. One heck of a sexy and comfortable airplane. Just shy of a 200kts on 19GPH total. No question that it's a modern "baron". The only issue is the single engine climb rate at max gross, which in ideal conditions is about 200 FPM. But you can't expect much single engine performance as it's flying on 180HP and it's 5700 pounds.



What's the old saying about twins? They have two engines because they NEED two engines. The DA-62 is not much worse than the Baron at about 350 fpm and it's almost exactly the same as a Seneca at 250 fpm (man, the ranks of piston twins has gotten mighty thin). It'd be fun to look through a DA-62 POH for the charts on weight/takeoff distance, etc. If I was thinking about taking off over anything but mostly flat land in any of them I would be taking a hard look at the fuel load and pax against climb rate. Very few missions have passengers 5 and 6 and limiting fuel to say 7-800 miles (easier to slow down in the 62 to achieve
fuel burns of maybe 12-15 gph) would make me breathe a little easier about the one engine inop numbers. I'm sounding like a fanboy but I am just very impressed with the operational flexibilty of that gorgeous airplane. It's never going to be my "problem" but I admire the engineering.

 

[Cujet]

Originally Posted By: UncleDave


I think we can eliminate BSFC AND gearboxes as a reasons auto engines can't or don't make great plane engines.


BSFC on an injected Lyc with an advancing electronic ign, operated 100 degrees lean of peak EGT is amazing! Numbers around 0.33 pounds of fuel per HP hour are common. That old dinosaur can be improved upon. Better thermal efficiency than even the mighty 2017 Toyota Prius.

Those of us in the aviation world just don't see great automotive conversions. We see overweight engines that are less efficient. The gearbox adds to the weight and efficiency problems. The "Mark 9" PSRU reduction gearbox is 71 pounds, without prop governor or associated oil lines. A rough estimate is about 100 pounds added.

http://www.epi-eng.com/gearbox_products/mark-9_gearbox.htm

Many of these designs have been known to fail. Including a well publicized V8 powered Lancair crash in FT Lauderdale, FL. http://www.upi.com/Crashed-experimental-plane-had-car-engine/52911215633618/

One additional factor is the crash rate of automotive engine conversions. The last time I looked it was 5 times the rate of aircraft engine installations on the same airframe.

My 177RG is operated at full throttle at all times except descent. Never an issue.

 

[UncleDave]

I wouldn't expect a 170 series to have any problems with shock cooling, they really arent fast enough.

My friends mooney 201 turbo has that concern however.

Low BSFC's just arent that tough, and lots of dedicated plane engines use gearboxes so they must not think that badly of them

Home built experimental crash far more often that commercially made planes regardless of the engine choices.

Notice the link at bottom of your link with another home built crash story that mentioned nothing about a car engine.

I had a client named Dave riggs (called an aviation criminal by some guy was no doubt one of the biggest jerks around ) whose first lancair crashed because there was no vent installed in the wing tank and it killed the 757 pilot that rented it who ran out of fuel unable to get to the fuel sitting in the wing.

pretty sure this is it https://aviation-safety.net/wikibase/wiki.php?id=45847

His second Lanair 320 crashed when he flew it into a lake in China killing himself and a passenger.

https://fearoflanding.com/accidents/the-incredible-story-of-david-riggs/

I would be interested in seeing your data on the matter if you will share.


UD