Induced-shear piezoelectric actuators for rotor blade trailing edge flaps and active tips

One of the most promising active control solutions being investigated to solve the rotorcraft vibration problem is an active trailing edge flap and/or active blade tip. In the present work, induced-shear piezoelectric tube actuators are used in conjunction with simple lever/cusp hinge amplification devices to generate useful combinations of trailing edge flap and blade tip deflections and hinge moments. A finite element model of the actuator tube and trailing edge flap (including aerodynamic and inertial loading) was used to guide the design of the actuator/flap system. Both a Mach scale induced shear tube actuator flap system and a Mach scale induced shear blade tip system were fabricated. Experimental bench top testing was conducted to validate the analysis. In experimental testing at an applied electric field of 4 kV/cm of a Mach scale induced shear tube actuator, a 1.5 inch long flap was deflected +/- 12° in a no-load condition and +/- 8.5° for a hinge moment simulating a rotor speed of 2000 RPM. The percent error between the predicted and experimental flap deflections ranged from 2% (low RPM) to 8% (large RPM). In addition, a 10% radius blade tip (3.6 inches) was deflected +/-3.15° and +/- 2.50° for hinge moments that simulated the 0 and 2000 RPM rotor speed conditions.