| An approach to develop a piezoelectric actuator for blade trailing-edge flaps on full-scale rotor systems is considered for helicopter vibration suppression. The actuator is located in the blade because it is effective to cancel the vibratory force close to its source. The objective of the present research is to systematically investigate the feasibility of the trailing-edge flap mechanism actuated by piezoelectric stacks in conjunction with efficient stroke amplifier. It includes the characterization of the piezostack, the design and the validation of a stroke amplification mechanism for the piezostack, and the development and the experimental evaluation of the on-blade trailing-edge flap actuator. Two-stage piezostack down-selection approach through the experimental evaluation was conducted to select an appropriate commercial piezostack, which has a high stiffness as well as a good strain/block force capability. A new mechanical amplification concept utilizing two-stage lever-fulcrum mechanism was designed, which extends the capability of lever-fulcrum stroke amplifier. The first prototype actuator was designed and fabricated by using two piezostacks with the double-lever amplification mechanism. The prototype actuator was tested on bench-top as well as in vacuum chamber that simulates full-scale centrifugal force environment of 700g. An experimental validation showed a quasi-static displacement amplification factor of 19.4, the uniform response up to 8/rev (52.3 Hz), and the consistent performance up to 600g of centrifugal loading. With a design refinement, the second prototype actuator was designed using five piezostack segments. The bench-top testing showed 73.7 mils of free stroke and uniform performance up to 150 Hz. In vacuum spin testing, the second prototype actuator showed approximately 13% loss in actuation stroke at 700g of centrifugal loading, and no further degradation up to 800g overloading condition. At the freestream velocity of 120 ft/sec in the Open-jet wind tunnel, the peak-to-peak flap deflections of 13, 19, 17.5 and 8 degrees were measured for 1, 2, 3 and 4/rev excitation, respectively. The present actuator has a capability of oscillating the trailing edge flap with the required deflection/frequency in a rotating environment. |
