Aircraft Performance?

Question

If there are two airplanes with the same engine and prop.
One airplane has 200 horse power and the other has 400 horsepower but same engines and same size prop spinning at the same RPMs.
How does more horse power affect the thrust when both airplanes move the same amount of air?

So in other words you are trying to say that as the two planes climb and lose horsepower the 400 horse power engine would maintain max rpms while the 200 horse power engine would not be able to maintain max rpms as long?

Answer 1

I don't think it makes sense that a 200HP and 400HP engines are the same engine, but I can speak to some propeller function.

Most high performance airplanes have a constant speed propeller which governs its own RPM (within limits) to whatever the pilot has set by adjusting the pitch of the blade. So a 400HP engine powering the same prop will have the ability to spin the prop at the same speed as the 200HP engine, but with more pitch angle, and therefore more air movement and more thrust. You can find some great info on propellers and other aircraft systems in a commercial pilot training handbook.

Answer 2

The amount of thrust delivered by the propellers depends on the size of the prop, the pitch and the rpm. The 400 horsepower engine could drive the prop at a much higher pitch than could the 200 horsepower engine. This lets the prop take bigger bites of the air as it goes around. It would then move more air than smaller engine can.

If you take away the variable pitch prop and hold to your same rpm criteria, the extra horsepower would not be used by the larger engine.

Answer 3

the 400hp engine would only show its true strength when performing. In a climb for example, the rpms would drop, more throttle would be given thus more power would be needed to pull the plane up. the 400hp engine would have more torque and be able to keep the prop spinning faster than the 200hp engine.

Answer 4

An engine rated for 400 HP does not output 400 HP all the time, or even most of the time. The rating simply means that at a certain RPM, the engine is capable of outputting a maximum of 400 HP.

Any engine is certainly capable of outputting less than its maximum rated power, even at its 'best' RPM.

Thrust is determined purely by the amount and velocity of the air being moved by the propellers. It does not matter if a 9-volt battery or a gas turbine is causing it. Thrust is purely a function of the airflow.