Wind Tunnel Testing of a Swashplateless Rotor with Compact Brushless Motor Actuated Flaps for Primary Control

Blade pitch response to a brushless dc motor actuated trailing edge flap on a Mach scale rotor in hover is presented. A 6-ft diameter, 2-bladed rotor with motor-flap system integrated into the NACA 0012 airfoil section was built. A soft pitch link was used to allow for pitch motion with desired torsion stiffness. First experiments with stiff pitch links were carried out to demonstrate trailing edge flap mean position and the peak-peak amplitude control. Large peak-peak trailing edge amplitudes were observed at 2000 rotor rpm in hover. Further, blade pitch response due to both steady as well as sinusoidal flap deflections are presented. At 1500 rotor rpm, about 8 deg. peak-peak blade pitch was obtained with about 18 deg. peak-peak trailing edge flap deflections at 25 Hz (1/rev) excitation. Results show that the brushless dc motors can provide sufficient control authority, 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 current swashplate with a hydraulic-free swashplateless system.