In-Flight Thrust Measurements of Propeller-Driven Airplanes

Abstract

The development of a propeller model that will accurately predict airplane engine static and dynamic thrust and torque in a full range of advance ratio has provided a powerful and reliable source for propeller-driven airplane engine simulation that serves as a valuable tool for flight test analysis. A single-element propeller model that reduces the propeller characteristics to a lift and drag coefficient vs angle-of-attack formulation was found to describe accurately the propeller characteristics over a wide operating range. Measurements of airplane indicated airspeed, flight altitude, torque, propeller speed, and throttle setting are the only required parameters for in-flight thrust estimation. A check of the model showed that the predicted and measured values of static thrust, torque, and dynamic thrust were within less than 2% over a wide range of advance ratios. With an accurate model of in-flight thrust measurement, one could add a new gage on propeller-driven airplane to display the amount of available thrust for the pilot or autopilot system, which would have a great impact on both the capability of verifying airplane’s maneuvers and flight safety during recovery procedures. Nomenclature AI = propeller model parameter set C = propeller blade chord CDb = propeller blade drag coefficient CLb = propeller blade lift coefficient C P =p ower coefficient C Q = torque coefficient CT = thrust coefficient J = advance ratio, 101.34 (V/ nD ) N B = number of propeller blades n = speed, rpm Ps = shaft power Q = shaft torque R = propeller radius r = propeller blade element radius s = solidity ratio T = engine thrust x = r/R αb = blade angle of attack θ = blade angle ρ = air density ω = propeller rotational speed, rpm