Rotor power savings with active camber actuation varying baseline rotor properties and operating conditions

Abstract

A variation of helicopter main rotor properties was investigated with regard to their effects on active camber induced power savings using a comprehensive analysis model including elastic blade modeling and free vortex wake analysis. A Bo 105 main rotor was used as the baseline rotor in this work. This study was aimed at analyzing the transferability of results on active camber induced power savings to other rotor systems, while also identifying design targets for a rotor designated to be operated with an active camber system. A range of advance ratios from 0 to 0.35 was investigated. Active camber actuation on the modified baseline rotors was examined with regard to the absolute power variation compared to the original baseline rotor, and the relative power variation compared to the modified baseline rotor. The rotor blade torsional stiffness did not prove to be an important design parameter to optimize rotor power at high-speed flight using active camber. Only the relative rotor power savings from active camber notably depended on the blade torsional stiffness. The built-in twist of the baseline Bo 105 rotor was identified to be below the optimum. This lack of efficiency was compensated by active camber. Therefore, active camber yielded a reduced capability to improve rotor power for higher geometric built-in blade twist, especially for low advance ratios. Increased efficiency of the baseline rotor, however, did not necessarily reduce the efficiency gain from active camber. This was shown in case of varying the number of rotor blades and the blade taper ratio, where greater baseline rotor efficiency still resulted in an increase of relative power savings from active camber. A reduction in rotational speed resulted in significant rotor total power savings, but had a negative effect on the power savings from active camber. However, active camber was able to ameliorate detrimental effects from a reduced rotor rotational speed on thrust and stall margins.