Propeller-Rotor Interaction: a Problem of Helicopter Air-to-Air Refueling

Abstract

During helicopter air-to-air refueling the rotor of the helicopter might enter the slipstream of the tanker aircraft's propeller. Based on blade element momentum theory, the impact of the accelerated air within the propeller slipstream on rotor blade aerodynamics (thrust, rolling and pitching moments) can be solved analytically. The collective and cyclic controls needed for disturbance rejection are computed for a typical air-to-air refueling scenario without or with blade flapping motion. A propeller wake affecting the retreating side of the rotor requires much more pilot controls to retrim than an impingement on the advancing side. Variations of rotor angle of attack, propeller radius, and propeller thrust are performed. The results are verified by application of free-wake for both the propeller and the rotor, taking into account the mutual interactions of the wakes.