A method for flight-test determination of propulsive efficiency and drag

Abstract

A flight-test method is described from which propulsive efficiency as well as parasite and induced drag coefficients can be directly determined using relatively simple instrumentation and analysis techniques. The method uses information contained in the transient response in airspeed for a small power change in level flight in addition to the usual measurement of power required for level flight. Measurements of pitch angle and longitudinal and normal acceleration are eliminated. The theoretical basis for the method, the analytical techniques used, and the results of application of the method to flight-test data are presented. Flight-test data showed performance parameters measured with a standard deviation of about 0.8% for propulsive efficiency, 0.3% for parasite drag coefficient, and 8% for the airplane efficiency factor, e.