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Aircraft certified motor vehicle engines. Is there a niche for them


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I am not even thinking of using automotive engines, but maybe suggesting that someone might think of designing an aircraft engine with the technologies available now. It would revolutionise the aircraft engine business.

 

Isn't that the Rotax 912?

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Ya gotta remember cars have gears to get the full use out of their small cube high HP power plants, planes operate in 'top gear' all the time. Try getting these cars to accelerate (and last) starting in top gear! That's why we have large capacity big bore direct drive engines.

I am not unsympathetic to your position but your logic would seem to be a little shaky:

 

- we do have "geared" aircraft engines the famous RR Merlin, the ubiquitous Rotax, to name just two

- aircraft engines have what is in effect a "slip drive" called a propeller. They do not start in top gear. It takes air/forward speed to get your prop delivering its best thrust - a bit like slipping the clutch or an old style 3 speed automatic.

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There's a reason why the old clunkers are still being produced in their zillions compared to a very small amount of 'alternate' engines......they simply work!

 

And thats why I am not interested in new fandangled cars or anything else that is engine powered. Even my old Kenworth does not have a turbo on it :-)

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I am not unsympathetic to your position but your logic would seem to be a little shaky:

 

- we do have "geared" aircraft engines the famous RR Merlin, the ubiquitous Rotax, to name just two

- aircraft engines have what is in effect a "slip drive" called a propeller. They do not start in top gear. It takes air/forward speed to get your prop delivering its best thrust - a bit like slipping the clutch or an old style 3 speed automatic.

 

Not 'shaky' at all, I'm just backing the clear leader in A/C engines.

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What I am proposing is an engine that puts out twice the specific power of the Rotax 912. No gearbox, one litre displacement and 160bhp. Better fuel efficiency too. It could run on diesel or avgas or mogas or jets1

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It's easy to make an engine with far more power than current aircraft engines.

What's the hard part is making them put out that power reliably.

This bloke seems to know what he is talking about regarding chevy v8's for aircraft use.

Note the part about piston speeds and their effect on reliability.

 

It is interesting to note that every aircraft piston engine designed to operate at sustained mean piston speeds over about 3000 fpm have been short-lived. We have demonstrated with previous engines that mean piston speeds (MPS) of 2900 and 2600 FT/MIN for takeoff and cruise respectively are reasonable for extended life, all other things being correct.

 

 

http://www.epi-eng.com/aircraft_engine_products/ls_crate_engines.htm

 

Here's a calculator for those that want to throw some figures around...

http://www.hotrodmath.com/pistonspeed-calculator.php

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My preference would be for a small gas turbine. However machining costs for a gt that has efficiency around that of a reciprocating engine are huge. I expect that 3D printing will develop to allow a high surface finish in about 10 to 20 years. This would reduce manufacturing costs to allow them to cost around the same as present as aircraft piston engines. In a GT the compressor pressure needs to be about 200psi and first row turbine blades need to have leading edge cooling with small ducts up to the turbine first stage inlet. A PT6 design is by far the best as it removes the need for a gearbox.

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It's easy to make an engine with far more power than current aircraft engines.

What's the hard part is making them put out that power reliably.

This bloke seems to know what he is talking about regarding chevy v8's for aircraft use.

Note the part about piston speeds and their effect on reliability.

 

It is interesting to note that every aircraft piston engine designed to operate at sustained mean piston speeds over about 3000 fpm have been short-lived. We have demonstrated with previous engines that mean piston speeds (MPS) of 2900 and 2600 FT/MIN for takeoff and cruise respectively are reasonable for extended life, all other things being correct.

 

 

http://www.epi-eng.com/aircraft_engine_products/ls_crate_engines.htm

 

Here's a calculator for those that want to throw some figures around...

http://www.hotrodmath.com/pistonspeed-calculator.php

Yes wear increases dramatically with higher speeds and who wants a gearbox? Heavy and another point of unreliability. Ok the Spitfire had one but it's design life was only 200 hours.

What I am suggesting is a 3000rpm max engine producing 160hp per litre. Same technology as many Auto engines produced today. It is NOT an Otto cycle but more closely resembles a diesel cycle.

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Yes wear increases dramatically with higher speeds and who wants a gearbox? Heavy and another point of unreliability. Ok the Spitfire had one but it's design life was only 200 hours.

What I am suggesting is a 3000rpm max engine producing 160hp per litre. Same technology as many Auto engines produced today. It is NOT an Otto cycle but more closely resembles a diesel cycle.

 

Ah! the old rev's = re-bores argument - this old chestnut, complete false, has been around for ever. You just have to look at the dominance of small high revving engines in the auto market, to see that the big bore "donk"s beloved of North Americans ans some Australian, have had their day.

 

Aircraft gearboxes have also been around for ever and are , in the right application, an excellent way of bringing a high revving/speed engine down to more acceptable/efficient prop speeds.

 

As for design life - an engine/ aircraft destined for a combat role can not easily be compared with the same engine/air-frame operated in a civilian environment - lower/conservative speed limits on cruises/manoeuvring, concerns about fuel economic/equipment longevity, etc that are of little relevance to combat.

 

,

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Difference with high speed bike and auto engines and aircraft engines is that bikes and Auto engines only do the high revs for very little time and don't contribute to overall wear to any extent. In the Mooney club we has an American race car engineer. His comment was that above 7000rpm wear accelerates to an unacceptable rate for racing long distances. My Toyota Echo motor would rev to 9000rpm, yes I used it to that speed on acceleration, but it was above 7000rpm for maybe 1%of engine time. I believe that direct drive is much better than a gearbox, obviously not shared by all.

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Yes wear increases dramatically with higher speeds and who wants a gearbox? Heavy and another point of unreliability. Ok the Spitfire had one but it's design life was only 200 hours.

What I am suggesting is a 3000rpm max engine producing 160hp per litre. Same technology as many Auto engines produced today. It is NOT an Otto cycle but more closely resembles a diesel cycle.

 

What modern car engines produces its power at only 3000 rpm?

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There's a reason why the old clunkers are still being produced in their zillions compared to a very small amount of 'alternate' engines......they simply work!

Part of that reason is also that in order to have any sort of market they have to negotiate a truckload of certification processes including STCs if they want people to install them in existing aircraft, not to mention that aviation is full of old shellbacks who are wary of anything new. It's kind of a self fulfilling prophecy when they come out with "it'll never work".

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What modern car engines produces its power at only 3000 rpm?

 

You have just made an argument for a gear box. Rotax 912 ULS max take off Hp 5800 rpm gear box standard reduction ratio is 2.27:1 with 2.43:1 optional. - prop speed 2387 - 2555 - very efficient & quiet range

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Difference with high speed bike and auto engines and aircraft engines is that bikes and Auto engines only do the high revs for very little time and don't contribute to overall wear to any extent. In the Mooney club we has an American race car engineer. His comment was that above 7000rpm wear accelerates to an unacceptable rate for racing long distances. My Toyota Echo motor would rev to 9000rpm, yes I used it to that speed on acceleration, but it was above 7000rpm for maybe 1%of engine time. I believe that direct drive is much better than a gearbox, obviously not shared by all.

It comes down to proper design. Yes you will wear out a Chevy if you rev it at 7000 all day because the bearing sizes and piston speeds are all very high at those revs. engines designed to rev have smaller journals to give less bearing speed and shorter strokes to give less piston speed. I've had motorcycles that rev at 14000 rpm to maintain highway speed and will happily do it for hours.

To make a certain amount of power you need to burn a certain amount of fuel regardless of engine size or revs, and in doing so will generate the same amount of heat. If you can lose 160hp worth of heat from an air cooled Lycoming, you can lose it from a Subaru with liquid cooling.

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I reckon the alloy Chev V8 has real aero potential. There's enough of them around for the right bit's to be known. Too big for our purposes though.

IF I was building a new plane it's not easy to decide on what engine. RV's are well suited to the Lycoming although I don't know just how good the "Superior" is. Nev

I believe the bloke who's building a 1:1 scale Spitfire here in Hobart is planning on using a Chev V8.

Can't remember his name now - I have met him at the Sandfly strip, there was an article on his build in the ABC a year or two back.

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AFAIK USA is awash with aero gearbox designs for LS1 to LS3 blocks. It's not that they are anything special, they are the most common engine to be rebuilt or modified. For example electric water pumps, dry sumps different cams and so-on. EAA has dozens of articles just on this engine series.

 

The other thing to understand is that even the smallest displacement LS1 running a variable pitch prop will limit its output at altitude very quickly so it's only running peak power from sea level to about 4000 feet. That could be as little as five minutes with peak torque typically around 5800 RPM. After that, power will be limited by air density, to the benefit of engine life.

 

Also of note, the typical application is a two seat home built not a skydiving 182 so expect a lot more mechanical sympathy from the operator.

 

I've seen a turbo converted iron block straight six out of a Volvo 166 two door used for aero tows. This is a very early example of electronic fuel injection and not a very pretty installation. When the owner was asked about reliability he said "Pfft, non-existent. We buy the spares in bulk and strip the engine every season, about 250 hours. We have an overhauled engine ready to go, after it's been run in on the dyno and pickled. After inspecting the worn parts, I wouldn't run it past 500 hours without an overhaul".

 

You pays yo' money...

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Reduction drives are a critical component of any aero engine especially a turbine where the ratio is large. Layshaft is inferior to sun and planetary but care has to be taken to get all to load equally with planetary or multi layshaft set ups.. There's power loss so heat is involved and torsional vibration issues COST and weight. Where a particular engine was made in a geared and straight coupled motor the service life and reliability for the motor is invariably worse in the higher revving geared one. This is what one would expect Higher revving engines have more load reversals which all other things being equal. will cause more fatigue. Reduction gears should not be operated on "Float" power, especially turbines but apples to all. Nev

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I used to operate the 'Gitso' Continental engines and they required special handling otherwise two things would happen, you either destroyed the geared engine or you where sacked!

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Flew a C 175? that had the geared 300. Smooth but very busy at the usual revs. Much more performance.. Not many around (says it all). Nev

 

They where a pussycat engine, not popular due cost etc, the GTSIO520's where a brute!

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Reduction drives are a critical component of any aero engine especially a turbine where the ratio is large. Layshaft is inferior to sun and planetary but care has to be taken to get all to load equally with planetary or multi layshaft set ups.. There's power loss so heat is involved and torsional vibration issues COST and weight. Where a particular engine was made in a geared and straight coupled motor the service life and reliability for the motor is invariably worse in the higher revving geared one. This is what one would expect Higher revving engines have more load reversals which all other things being equal. will cause more fatigue. Reduction gears should not be operated on "Float" power, especially turbines but apples to all. Nev

A PT6 has no gearbox. The RB211and all of its derivatives that drive a shaft has no gearbox. The PT6 is a brilliant design.

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A PT6 has no gearbox. The RB211and all of its derivatives that drive a shaft has no gearbox. The PT6 is a brilliant design.

 

Oh brother!?please explain how the power turbine drives the prop at around 2000rpm??

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