Dynamic Effects on Propeller Blade Section Lift, Drag, and Pitching Moment Coefficients

Abstract : The Propeller Force Module (PFM) uses the blade element/momentum theory to predict propeller forces during maneuvers. A typical inflow angle distribution is studied. The blade sections will encounter spatial and temporal variations in angles of attack. Theories to calculate unsteady effects on section lift, drag, and pitching moment coefficients are formulated and presented in this report. Using the classic approach developed in aerodynamics, the section lift and pitching moment are expressed in circulatory and non-circulatory solutions. The non-circulatory solution is found to be a universal function independent of the type of motion. The circulatory solution depends heavily on the type of motion. In the case of ramp-up and ramp-down motions simulating blade sections experiencing angle of attack variations when maneuvering, an analytical solution is obtained for the circulatory lift. Empirical formula are developed to calculate the delay in stall angle due to unsteady motion. The classic aerodynamic theories assume the flow to be potential which give zero drag. Instead, Leishman's mathematical model assuming a loss of full suction pressure recovery at the leading edge due to viscous effect is adopted in this report to calculate the dynamic drag. The theories are compared with experimental measurements by Francis and Keesee, and by Ham and Garelick with encouraging results.