Active and Passive Camber Morphing for Helicopter Rotors towards Performance Improvements in Hover and Vertical Flight

Abstract

Rotor morphing has been investigated in the past for improvement of rotor performance, either for reduction of rotor power demand or for vibratory load alleviation. The present study investigates the application of camber morphing for improvement of rotor performance in hover and vertical flight conditions, with a particular focus on the combination of camber morphing systems and variable RPM rotors. Camber morphing utilizes a smooth flap at the trailing edge of the rotor blade to modify the camber of blade airfoil sections without excessive drag penalties. Two different camber morphing systems will be investigated in this study, namely the active and passive systems. Passive camber morphing, which combines camber morphing with the variable speed rotor concept is the unique aspect of camber morphing which will be the primary focus of this study. The active system can be actuated at frequencies higher than 1/rev of the rotor and requires external power input for functioning. The passive system can be controlled only by varying the RPM of the rotor and requires no additional energy input. Therefore, the passive system is expected to show larger net performance benefits. Variable RPM rotors in themselves show potential towards the reduction of rotor power demand but are largely ineffective for low-speed applications. The combination of camber morphing and the variable speed rotor shows larger performance benefits than those obtained from the two technologies independent of each other. The two technologies, when combined in passive camber morphing, can remedy each other’s deficiencies and improve the overall rotor performance. The use of camber morphing shows more benefit for operating points at or near the edge of the flight envelope since the rotor blade sections encounter high average angles of attack for these operating points. Vertical climb and hover at high altitude are examples of flight conditions investigated. Overall, passive camber morphing shows a larger performance benefit as compared to the active system.