can't quite grasp the "power available" curve

I understand the "power required" curve as plotted against velocity, but the
concept of "power available" plotted against velocity is escaping me.

How is this curve derived? And why is it "curved"?

Thanks in advance.

"xerj" wrote in message
...
I understand the "power required" curve as plotted against velocity,
but the
concept of "power available" plotted against velocity is escaping me.

How is this curve derived? And why is it "curved"?

Thanks in advance.



You can analyze aircraft steady-state motions using either force or
power relationships. Two of the forces are of course drag D and thrust
T. Power required is Pr = D*V (where V is true airspeed), power
available Pa = T*V. Getting a model of thrust is quite a bit more
difficult than getting a model of drag, but it can be done. The Pa curve
is curved because propeller efficiency, as a function of V, is curved.
For a simple thrust model for fixed-pitch propeller aircraft, see
Performance of Light Aircraft, especially chapters 7 and 8.

John T. Lowry, PhD
Flight Physics