Development and Testing of a Swashplateless Rotor with Compact Brushless Motor Actuated Flaps for Primary Control

A novel system of actuating the trailing edge flap using a compact brushless dc motor is presented. By electronically controlling the motor, a control strategy to actuate the flap at desired frequency and amplitude was developed and large flap amplitudes (instead of rotational motion) from the motor were obtained. A 6-ft diameter, 2-bladed Mach scale rotor with motor-flap system integrated into the NACA 0012 airfoil section was built. Systematic testing of Maxon EC-10 brushless dc motor on bench-top, in the 10-ft vacuum chamber and on the hover tower was carried out. Large controllable amplitudes were obtained at 40 Hz for a range of load conditions. For instance, in hover peak-to-peak amplitude of 18° were obtained at 1200 rpm, with tests planned to operate the flaps at rotor design rpm of 2400. Results show that the brushless dc motors can provide sufficient control authority, require low input voltages, show no hysteresis and have structural strength to withstand centrifugal loads, while fitting in the airfoil profile and causing a minimal weight penalty. The concept of using brushless dc motors as on-blade actuators has the potential to replace the swashplate as a hydraulic-free system.