DEVELOPMENT OF A SMART MOVING-BLADE-TIP AND AN ACTIVE-TWIST ROTOR BLADE DRIVEN BY A PIEZO-INDUCED BENDING-TORSION COUPLED BEAM

This paper presents two active rotor blade concepts, using a piezo-induced bending-torsion coupled composite actuator beam. The first is an active moving blade, and the second is a rotor blade with active linear twist. A novel spanwise variation in the beam layup and piezoceramic element phasing is used to maximize the twist response, while minimizing the bending response. Two operational 1/8th Froude scale model rotor blades, with a 90% main blade section and 5% and 10% span active tips were manufactured for hover testing. In the controllable twist configuration, a non-rotating twist amplitude of 0.8 deg is achieved, at 100Vrms and 75 Hz. In hover, at 875 rpm, this reduces to 0.5 deg at 5/rev. The actuation power per blade is estimated at 1.2% of the hover power required at 8 deg collective. In the moving blade tip configuration, a non-rotating deflection amplitude of 1.7 deg is achieved at 100Vrms. Non-rotating dynamic tests show resonant amplification for all frequencies up to 5/rev. The deflection at 120Vrms increases from a low frequency 2.25 deg to 3.5 deg at 4/rev, and for 90Vrms the low frequency deflection amplitude of 1.5 deg doubles to 3.0 deg at 5/rev. The rotor blades with non-activated moving tips were successfully flown in hover, at 900 rpm and collective setting from 4-8 deg.