Enhanced Efficiency and Flight Envelope by Variable Main Rotor Speed For Different Helicopter Configurations
Today, most rotorcraft are operated at constant rotor speeds. Recent studies show that a variable rotor speed increases the efficiency and extends the flight envelope of rotorcraft [1] [3] With a variable rotor speed, rotorcraft can be developed and optimized for a whole operational design range rather than a specific design point. Funded by the German Aviation Research Program (LuFo V 2) and the Austrian Research Program TAKE OFF, the project VARI SPEED intends to give answers about the applicability and the determination of decision factors of such a technology. In this study the effects of a variable speed rotor design on power savings and flight envelope are discussed for various existing helicopter configurations. Calculations were performed using NDARC (NASA Design and Analysis of Rotorcraft) The aircraft chosen for the study are the UH 60A single main rotor and tail rotor helicopter, the CH 47D tandem helicopter, the XH 59A coaxial lift offset helicopter and the XV 15 tiltrotor. Areas of possible power savings, ranges of rotational speed and main rotor torque effects are presented. The effects of additional transmission weight are also highlighted. Depending on the aircraft, significant power savings are possible at certain flight regimes.