Engine displacement question

[Dmmoore]

All good answers. Aircraft engines also have a lower compression ratio than automotive engines due to the higher altitudes they run at. Less HP per cubic inch is also less stress in the engine.

Most are at about 1/2 HP per cubic inch. There are some exceptions on the bigger bore engines (IO-550 at 300 hp).

I've never heard of low compression and high altitude being a factor.
A major factor is the distance the flame front has to travel across a combustion chamber. The larger the diameter of a combustion chamber the lower the compression ratio for a given octane.

An example is the 235 HP version of the O-540 Lycoming used in the Piper Cherokee 235 and the 300 HP version of the IO-540 engine used in various high performance aircraft The 235 HP version burns 80/87 octane while the 300 HP version uses 100LL octane. Other than the better fuel metering available using fuel injection (the "I" in IO-540) the major difference in power out put is the 100/130 octane fuel allowing a higher compression ratio.

The same basic engine (GSIO-540) can be boosted to 350 HP by adding a gearbox, a supercharger and increasing the basic engine red line to 3,500 vs 2600 RPM on the non geared engine.

Another reason for the low power output per unit of displacement is the difficulty (read cost) in getting modern engine control systems certified. Where an auto manufacturer may produce a couple million engines during any given year, an aircraft engine manufacturer may only produce about a thousand new engines. Even if the cost of approving the control system of an aircraft engine was the same as the aircraft engine (it isn't, the cost is 8 to 10 times more) the number of units over which the engineering / certification costs are much lower. The development of a modern computer controlled fuel delivery system has only recently started to materialize. The first generation of this system will reduce fuel consumption 10 to 15%. HP increases are also possible but will most likely not be that apparent in the first generation systems.

[3WE]

I think there was a time when an 0-200 was used in racing cars, at a much higher RPM and horsepower.

As we hopefully know: Race car engines blow up a lot and pilots hope that airplane engines blow up rarely.

[JordanD]

I thought you were a pilot.

I just settled for a big watch instead.

[Crunk415balla]

Because it's better to ask and be sure then to always assume you're right.

I thought you were a pilot.

[LRJet Guy]

All good answers. Aircraft engines also have a lower compression ratio than automotive engines due to the higher altitudes they run at. Less HP per cubic inch is also less stress in the engine.

Most are at about 1/2 HP per cubic inch. There are some exceptions on the bigger bore engines (IO-550 at 300 hp).

[JordanD]

Jordan, this is a dumber question then the time you asked me if I wanted to take you in the back of an F-150. Why ask questions you already know the awnser to?

Because it's better to ask and be sure then to always assume you're right.




Biatch.

[Crunk415balla]

Jordan, this is a dumber question then the time you asked me if I wanted to take you in the back of an F-150. Why ask questions you already know the awnser to?

[screaming_emu]

Exactly what he said. You don't want the prop spinning at too high an RPM because as the tips reach the speed of sound they become extremely inefficient. Not to mention that would be loud as hell.

[JordanD]

Ahh, makes sense but I wasn't sure. Thanks!

[Spad13]

Curiosity's got me asking a question that probably won't make much sense.
Why is the displacement for small aircraft engines (the only one I really know of is the Lycoming IO-360) so high? Its displacement is 5.9 liters, but it produces (usually) only 180 horsepower. It seems like in cars most engines that produce that much horsepower have a displacement of around 1.8-2 liters. Most cars with that displacement seem to be V-8's or even V-12's that produce almost three times the amount of horsepower of the Lycoming. My question really is... why so much displacement? Would it have something to do with "low end power" or torque?
That might seem like a bunch of rambling, I don't know a huge amount about engines.

You're exactly right. Recall that car engines produce their peak horsepower at much higher rpm then aircraft engines will ever see. For instance the 122 CID engine in my Focus produces its 140hp at over 5000rpm. Now, imagine what would happen to the prop of your Warrior if it were doing 5000rpm. So, the solution is to either use a small engine and gear the prop or use a big engine and spin it slowly. Most mfr went with the latter, as it's both cheaper and easier to go that route.

[JordanD]

Curiosity's got me asking a question that probably won't make much sense.
Why is the displacement for small aircraft engines (the only one I really know of is the Lycoming IO-360) so high? Its displacement is 5.9 liters, but it produces (usually) only 180 horsepower. It seems like in cars most engines that produce that much horsepower have a displacement of around 1.8-2 liters. Most cars with that displacement seem to be V-8's or even V-12's that produce almost three times the amount of horsepower of the Lycoming. My question really is... why so much displacement? Would it have something to do with "low end power" or torque?
That might seem like a bunch of rambling, I don't know a huge amount about engines.