A propeller engine can be idealised as having constant power available with airspeed.

Question

Why is this the case?

Because the rotational velocity of the propeller can be changed in flight.

Because the engine produces the same power, independent of airspeed.

Because the propulsive efficiency does not change with airspeed.

Because the propeller pitch can be changed in flight

Answer 1

The reason a propeller engine can be idealized as having constant power available with airspeed is primarily because the engine produces the same power, independent of airspeed.

In a properly designed system, the engine has a maximum power output that it can sustain regardless of the aircraft's speed. An important aspect of propeller engines is that while the airspeed may change, the engine's output power remains relatively consistent, allowing for effective thrust generation across different flight conditions.

However, it is also worth noting that factors such as propeller efficiency and the angle of attack can affect actual performance; yet, in an idealized model, the power available remains constant regardless of airspeed.

Adjusting propeller pitch and rotational speed can optimize performance and efficiency under varying conditions, but those factors are considerations for the effective use of the available power rather than reasons for why power remains constant with airspeed.