Difference between automotive and aircraft engines

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I got to woundering the other day when I was reading about aviation fuel why there is such a radical difference between aircraft engines and automobile engines.

I do understand that their are completely different demands on the engines in each applications and you need far more reliability for something carying people off the ground. Today's engines though seam to have a power to weight ratio and reliability that would make them viable aircraft engines. I can understand the need for more of a modular designe for ease of maintenance and preventative maintenance.

It seems like an alluminum block Ls engine could be a production aircraft engine. I wouldn't want one of these high strung 300hp 1L engines they use in small cars now though.


And now that I go looking I see that their are planes like this. Still and interesting topic of discussion though.
 
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I'm pretty sure I've heard of the GA types putting small block Chevy engines into their planes.
 
IIRC, Volkswagen modified a auto engine to work in a light aircraft.
Did very well, quieter, better fuel economy, etc....
This was same years ago.
Lycoming and Continental engines are basically old designs, with up-dates.
 
Lexus 1UZ V8's were used as aviation engines. Probably due to it's inherent smoothness.
 
There are a lot of differences between airplane engines and automotive/light duty truck applications. Airplane engines experience a lot of run time at a constant speed like maybe a cross country diesel truck. Often the load varies but the engine still runs at the same RPM by using a constant speed prop. The old designs persist because of the cost of certifying a new one. People want reliability, fuel economy and reliability. Airplane engines have not only a different environment but they are attached to a delicate structure that does not suffer or dampen vibration very well. Overall the amount of care taken when rebuilding an airplane engine is fascinating to watch.
 
Average auto engine is running at maybe 20% of its rated power when traveling down the road. Aircraft engines are running maybe closer to 70% of rated power all through the flight. Kind of like marine engines. Lot more stress and thermal stress with the ac engines too. Most auto engines are very lacking in quality of construction as well, you may not think so until you are at 10,000 feet above a huge body of water with no land in sight when it stops.
 
Originally Posted By: dwendt44
IIRC, Volkswagen modified a auto engine to work in a light aircraft.
Did very well, quieter, better fuel economy, etc....
This was same years ago.
Lycoming and Continental engines are basically old designs, with up-dates.



Fornier powered gliders (a bit of an oxymoron, but this is a class of aircraft) used VW flat fours. Mira Slovak flew one of these across the Atlantic.
Porsche did build and certify a flat six. The only application I recall for this Porsche Flug Motor was the Mooney PFM. The engine has long been gone from the scene.
The thing about auto versus aircraft engines is that aircraft piston engines are typically direct drive. The prop is bolted directly to a flange on the crankshaft. Since the prop tips must not reach the speed of sound, which causes a huge loss in efficiency as well as a horrible increase in noise, aircraft engines make their rated power at around 2200 revs. They typically make around 30 bhp/liter and are a few times more costly than auto engines of similar output. Auto engines turn quite a bit faster, so some sort of reduction drive is required.
Also, aircraft engines have dual magneto ignition and can run on left, right or both with the engine's ignition being entirely independent of the aircraft electrical system. Fuel injection is common, but it's a simple and dead reliable mechanical system. Many aircraft still fly with carburetors. Turbocharging is also widely used, but not typically to boost output at sea level. There are some engines that always operate at greater then ambient pressure, but they are usually not long-lived in service. Forced induction is most commonly used to maintain output with altitude in aircraft applications.
All of the above applies to powerplants for type-certified aircraft. For a builder intending to license something in the experimental category, any engine can be used although most of the higher-end kit planes use real (and expensive) aircraft engines.
 
Actually what amazes me is how Rotax can make airplane engines but can't build a half **& decent motorcycle engine...
 
Cessna just got their JT-A 172 approved by the FAA and the European equivalent. It's a 172 that uses 155 HP turbo diesel engine. It almost doubles the range of the 172 and this variant uses less expensive(than AVGAS) JET-A. Hopefully it will sell well and set a new precedent. I can see the big Embry-Riddle and UND types ordering these maybe. We're getting into the half million dollar range...for a 172.
 
Certification costs of new engines are what is killing innovation in aircraft engine design. I've run up against this a couple of times. I used to work at John Deere Rotary Engine Division, back in the late '80's. We were developing a 2-rotor, 3.4L engine for general aviation use. It was turbocharged, direct-injected, stratified-charge and the primary fuel was to be Jet A. Working in conjunction with Avco Lycoming, the engine was designed and prototypes were in progress when management pulled the plug on the project, citing the certification costs and product liability concerns. One engine was completed and run in my test cell for a couple of months, basically to prove it could make rated power.

Then again in the early 90's, I interviewed for a job at Teledyne Continental, where they were working on a 2-stroke diesel, basically using a 53-series Detroit Diesel cylinder design. The chief project engineer took me on a tour of the plant, where he told me that 50% of the volume going through the shop were remanufactured engines. This did not give me a lot of confidence in the future of the business. I stayed where I was at.
 
Originally Posted By: fdcg27
Originally Posted By: dwendt44
IIRC, Volkswagen modified a auto engine to work in a light aircraft.
Did very well, quieter, better fuel economy, etc....
This was same years ago.
Lycoming and Continental engines are basically old designs, with up-dates.



Fornier powered gliders (a bit of an oxymoron, but this is a class of aircraft) used VW flat fours. Mira Slovak flew one of these across the Atlantic.
Porsche did build and certify a flat six. The only application I recall for this Porsche Flug Motor was the Mooney PFM. The engine has long been gone from the scene.
The thing about auto versus aircraft engines is that aircraft piston engines are typically direct drive. The prop is bolted directly to a flange on the crankshaft. Since the prop tips must not reach the speed of sound, which causes a huge loss in efficiency as well as a horrible increase in noise, aircraft engines make their rated power at around 2200 revs. They typically make around 30 bhp/liter and are a few times more costly than auto engines of similar output. Auto engines turn quite a bit faster, so some sort of reduction drive is required.
Also, aircraft engines have dual magneto ignition and can run on left, right or both with the engine's ignition being entirely independent of the aircraft electrical system. Fuel injection is common, but it's a simple and dead reliable mechanical system. Many aircraft still fly with carburetors. Turbocharging is also widely used, but not typically to boost output at sea level. There are some engines that always operate at greater then ambient pressure, but they are usually not long-lived in service. Forced induction is most commonly used to maintain output with altitude in aircraft applications.
All of the above applies to powerplants for type-certified aircraft. For a builder intending to license something in the experimental category, any engine can be used although most of the higher-end kit planes use real (and expensive) aircraft engines.


Then there's the gear box, don't forget that fabulous point for catastrophic failure! You gott have that in there yo hey the rpm down. That adds a whole mother element and maintenance issues. Seriously the only saving grace in those old continental designs were the hugely sloppy tolerances on everything. Built like an AK 47 and the 4 bangers vibrate and shake like a mixmaster.
I recall a 1994 article from avweb telling of a trip through the process by which the turned in core engines were re manufactured back to zero time ( new) by the definition. They take em apart piece by piece tossing the hardware but piling like engine components in bins. Somebody takes all those parts from the bins inspects, x rays as necessary cleans and checks tolerances with a michrometer as needed. Then that same collection of everything that came in with countless hours many decades oldp,accidents, prop strikes and who knows what goes right back into making a new recertified engine. It does get new jugs and pistons, rings ect. All for the princely sum of $15000 at the time. [censored] I could do a better job on my workbench and at least would know how nasty worn and old my parts were.
The one that cinched it for me was the AD to stuff a dowel down on top of a piston to sort of lock it up and wiggle the prop to feel for slop. This was for newly replaced 0200 4 cyl Continentals that power Cessna 150s. If under 25 hours don't bother and all others disregard. If you had one and it wiggled sloppy you had main bearings for an 0300 6 cyl. And had to pull the jugs and switch bearings immediately as a few planes had caged engines at inopportune times. And you want to pay $15 G for that sorta job, not this old boy.
I owned a plane too long to believe everybody puts everything in log books. There's more info in what's not there than what is in most instances and sticking props in the dirt is common. That almost always stops em dead and often requires a tear down. So just remember that engine you're bettin your life on somewhat has connecting rods and a crank shaft that came out of...........a pile .
I will say some of the newer Rotax stuff is pretty nice in spite of there being that little issue of having to send them back to the factory and have the case split every 300 hours. For $1800 ish I'm told. Even then they cost nearly as much as a certified sort with parts nearly the same lofty figures. At least those with more than 85 hp. With all that in mind it's pretty easy to see why light aviation is continuing its death spiral.
 
Originally Posted By: Driz
If you had one and it wiggled sloppy you had main bearings for an 0300 6 cyl. And had to pull the jugs and switch bearings immediately ..



Can't do mains by pulling jugs.... got to split the cases, too.

Originally Posted By: Driz

I will say some of the newer Rotax stuff is pretty nice in spite of there being that little issue of having to send them back to the factory and have the case split every 300 hours. For $1800 ish I'm told.


For which engine, the 2-strokes?

I know of an 80HP Rotax 912 that's got about 1500 hours on it and has never been torn down. Dakota Hawk N73DH
 
I've heard of the old Lexus LS400 1UZ-FE 4.0l V8 engine being used in marine AND aviation applications. It was very well-designed and long lived. But it is watercooled, which is a downside as far as power to weight ratios go.
 
Your use of the term "death spiral" for what's happening to GA in this country is apt.
I drive past one of our county's two public use GA airports on my commute five days a week and I hardly ever see anyone flying even on a nice day. There is a large hanger with its door facing the road and I often see an American (or Grumman) Traveler and a Cessna 337 rolled out and basking in the sun, but I rarely see them fly.
Today is a beautiful CAVU day and the sky should be full of little airplanes.
It isn't.
As GA activity declines, the price of avgas rises, since it is a highly specialized fuel and can only cost more to blend and ship in ever-smaller batches. The number of wrenches qualified to do annuals also shrinks and the cost of having any little thing fixed can only rise as the number of available wrenches declines. The entire parts infrastructure begins to fade away and parts for even a simple aircraft like a 172 or an old Piper Cherokee become less affordable for any individual who seeks to own what should be a very affordable plane.
A number of larger GA airports have but one FBO who basically runs the airport and sets absurd minimum ramp charges for every airplane. The operator can't make any money putting twenty gallons of 100LL in a 172 so they'll price such small craft off the airport.
The list goes on and I don't know what the answer might be. The FAA has tried various things over the years, like allowing STCs for mogas in certain aircraft, more restrictive and less costly to train for pilot licensing and even allowing the sale of low performance factory built aircraft without type certification.
None of this has done much good, so the outlook for all of those old singles that sit at tie-downs and rarely move remains bleak.
It is a pity, but the era of every farmer having an airplane and many ordinary folks owning and flying one appears to have drawn to a close. Organizations like EAA and some of the classic type clubs do what they can to keep the flame alive, but the trend s clear.
 
I think it's just basic economics.

When I sold my plane in '99 or '00, the local regional airport was booming. As far as just the airframe went, I flew it for a decade and sold it for more than twice what I paid for it, because the market was so good and demand was high. The back tie down area was full of light aircraft. Fast forward a few years. The '08 financial crisis hits. An election takes place, and bad times spiral down into a protracted depression.

If you had a good job as a factory manager, or some other position, and all the factories decide now is the right time to up and leave for Mexico as fast as they can lock the factory door, an airplane is probably the first thing you sell to cut your expense. Likewise if you are a small business, and all the business is gone, an airplane is just a money hole. Who would have time to fly, anyway? You're doing the work you used to have employees do.

I also think the private pilot base is aging out. A lot of guys I used to fly with are DEAD. They don't need an airplane.

Now, in fairness, the local airport has built more hangers, and it now looks to be possible to lease a plot of airport land and build your own hanger which was impossible for a long time, so some of these aircraft may be hangered and still at the airport.

But I still think it's just economics. If you have money in your pocket, an airplane looks pretty good. If you are struggling to survive, you don't need it.

I want to get another in a few years when my youngest is a little more grown. And I have a son in law with a couple of boys who is feeling the bug. I hope the economy will be better and I can just buy one, otherwise I would probably have to sell a piece of property. Our local economy has picked up the last few months, so I'm thinking about it again.
 
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