Calculating Propulsive Efficiency Given Prop Diameter, Velocity, Thrust, and Altitude

HansGruber

An aircraft is flying straight and level at a speed of 150 mph. Its propeller has a diameter of 8 ft and is generating 300 lbf of thrust at an altitude of 3000 ft. What is the propulsive efficiency of the propeller at this operating point?


no equations given, but from searching around Ive found that Propulsive efficiency = (thrust *velocty)/ power


Intuitively, Ive tried several ways to calculate power with the given variables, but all of my answers come out to an efficiency much greater than 1, which, of course, is impossible.

rbeale98

You have thrust and velocity, but you don't have consumed power.

You also need to make sure your units match up. For example, thrust*velocity is a power term, and to get that into (ft-lbs/sec) your thrust needs to be in (lbs) and velocity needs to be in (ft/s). Your power term needs to be in (ft-lbs/sec) as well, then your efficiency formula works. But again, you don't have anything that will give you the power consumed.