Thrust Control and Vibration Damping Using a Wingtip Electric Proprotor

Vibration damping in rotorcraft structures can reduce failures and instabilities and improve the ride comfort for passengers. This paper introduces the novel idea of damping vibration using electric proprotors on eVTOL aircraft without compromising the rotors ability to provide thrust. Feeding back the beam tip angular rate to the motor voltage is shown to stabilize all transverse beam vibration modes. The experimental results show that the closed loop damping in the first mode is three times higher than open loop. The torque bandwidth of the electric motor exceeds 100 Hz so the damping performance on the first mode (5.6 Hz) is very good. Damping on the second mode, however, is not improved due to the 40 Hz bandwidth of the angular rate sensor. The rotor speed frequency response rolls off at 20 dB/dec, indicating smaller vibration induced rotor speed variations at high frequency. Experimental step response results match the frequency domain damping predictions and show only 0.8% rotor speed variation for a 3% initial tip displacement.