Maximum speed -Pro craft
The standard approach for prop-driven aircraft is to assume that engine and propeller together produce a power (as opposed to thrust) output that is independent of speed. Calculations analogous to those carried out above for the jet aircraft, but based on power rather than drag, lead to formulae for maximum speed, absolute ceiling, and so on. The resulting equations do not however lend themselves to simple closed-form solutions, and generally, iterative solutions need to be found. Suppose the maximum engine shaft power output is P_{max}. The propeller will convert this to useful propulsive power with an efficiency η ; the useful available propulsive power is thus given by P_{av} = η P_{max}