Identifying the Propeller Transition to Wing-Like Behavior at High Angles of Incidence

Abstract

The aerodynamic performance of a propeller at high incidence angles, in forward flight, has long been associated with wing-like behaviors. At low to intermediate angles, thrust generally decreases with airspeed, as with the axial propeller, whereas an opposite trend is observed at high angles, resembling wings. However, an explicit determination of the transition from propeller to wing-like behaviors is lacking. Such transition characteristics are investigated, under the scope of the axial and wing-equivalent components of the propeller’s thrust, which have been demonstrated to comprise total thrust, in a previous paper. For this, wind tunnel experiments are conducted at incidence angles up to 90° on four small-scale fixed-pitch propellers, with blade angles up to 23°. At the angle of thrust behavioral inversion , opposite sensitivities to advance ratio are observed for each thrust component, annulling the sensitivity of the thrust coefficient. At angles higher than , as grows, the wing component positive sensitivity is dominant, and the wing component itself largely exceeds the axial term, causing the propeller to behave like a wing. Consequently, is defined as the propeller’s transition angle from axial-dominant to wing-like behavior. The tests showed occurring at lower angles for higher pitch propellers.