piston aero engines

[simonhk]

Hi all,
general question about engine design...
I note that the Lycoming 360 cubic inch engines produce 180 to 210 hp.
As a european, that equates to nearly 6 litres.
360 x .01639 = 5.89 litres.

On the face of it, 180 hp from a 6 litre engine seems really low!

So my question is - what are the design considerations that determine and restrict an piston aero engines power output?

Or, where can I read up on the subject?

SHK

[mini]

Put simply,

High specific power output engines are stressed, often needing exotic materials, complex systems, narrow fuel parameters, lengthy design & test, etc and as a result are expensive. They also tend to be less reliable and more tempermental.

Basically, torque is what you're primarily interested in, it expresses the ability of an engine to turn a prop against resistance. High torque outputs are achieved by using a long stroke, which mitigates against a high reving engine due to reciprocating mass. Best examples are large diesels, huge torque but low power to cc ratio.

Torque, btw, is the only "measured" output of an engine. Power (work done) is calculated by measuring the force moved over a distance (torque) by the time involved.

There are many texts on the subject of engine output, key issues are things like mechanical and thermal efficiency, mean effective pressure etc etc.

Apologies if I've over simplified the issue, not sure what level you're coming from

[noisy]

Bill Gunston writes some excellent books. There is one which deals with the development of piston aero engines. I'm halfway through his gas turbine book and it's excellent.

[avoman]

propellers are basically low rev devices, about 3000 rpm max.
So most piston aero engines are usually the same to avoid a reduction gearbox. So a slow revving device is required. Nevertheless the standard light aircraft piston engines are in my opinion wretchedly primitive and obsolete. Light and powerful by the standards of fifty years ago when they were designed they are not now. Additionally they are very expensive inefficient polluting and noisy. Reliability is achieved with the help of ample maintenance at short intervals.
The huge leaps in car engine technology whereby todays engines produce one percent of the pollution of twenty years ago, with power and reliability and so on have completely passed by GA.
There will never be change until it is forced upon the industry. Economics don't do it so it must be legislation. I love light aircraft but this is overdue!

[pigboat]

Check out the Aircraft Engine Historical Society (www.enginehistory.org/). There's a lot of ground covered there. The problems that Pratt had developing the R2800 crankshaft makes for fascinating reading.

[avoman]

A fascinating book, superbly written, about the development of the piston aero engine: The Power to Fly by LJK Setright, pub Allen and Unwin 1971. Doubtless long out of print but maybe procurable at the library

[rotornut]

While I can't disagree with the fact that piston aero engines are somewhat primitive, there's one great advantage in their design, at least in the case of horizontally opposed engines and, in particular, the O 360. Sometime ago we had to pull a bad cylinder in an HIO 360 pistonbanger in a Hughes 300. It was absolutely a snap to remove and reinstal after the engine shop rebuilt it - all in about a day.

[simonhk]

right on, Avoman!

But surely, nowadays, someone could do better than 200 hp from a six liter engine? It's not dificult to get 70hp per liter out of a car engine and still be reliable...

GA piston engines do seem rather behind the times...

Do the advances made in racing aero engines find their way onto production engines?

I would think that there would be significant crossover between the car and aero engine industries...

Am I being a bit naive?

:rolleyes:

[rotornut]

Don't forget that aero engines operate at much higher sustained power levels than do automotive engines. In spite of this, many piston engines have very good TBOs such as the Lycoming O-320 in the 172 - 2000 hours and more in many cases. If the average airspeed of the 172 is 100 mph plus or minus, then the engine is good for 200,000 miles.