Abstract. This paper presents the development of electromechanical actuators based on the concept of mechanical amplification with piezo and electrostrictive stacks as drivers to achieve high force and high displacement actuation. The actuators were designed for two different applications. The first actuator, with an piezo stack, was developed to actuate a `Flaperon' which consisted of a small movable surface to trip the boundary layer, located on the top surface of a wing model with span and chord of 12 in each and of NACA 0012 airfoil. The actuator was designed to produce 8 lbs of force with peak displacement of 10 mils at a maximum frequency of 40 Hz. The second actuator, with an electrostrictive stack as a driver, was designed to move a leading edge droop flap hinged at 25% chord of a wing model with span of 8 in, chord of 4 in and a VR-12 airfoil. This actuator was designed to produce 8.5 lbs of force with peak displacement of 10 mils at a maximum frequency of 45 Hz. Experiments were performed on both stacks to evaluate their important characteristics such as block force, free displacement and stiffness, that were essential in the design of the actuators. The results showed that the block force obtainable from a piezo stack was higher and that of an electrostrictive stack was lower than that specified by the respective manufacturers, while the free displacements are about the same. The dynamic response of the actuators over a frequency range of 33 Hz was evaluated. Results showed that 7 lbs of actuator force was obtainable in both cases, with the flaperon actuator producing 15 mils of dynamic displacement at 15 Hz and the droop flap actuator producing about 6 mils of displacement at 16 Hz. The results were inconclusive beyond 16 Hz due to the setup resonance. The droop flap actuator did not achieve the desired performance because the design calculations were based on the block force listed by the manufacturer which was about 20% higher than the measured value. This led to the conclusion that before the design process begins, the performance of the stack alone should be carefully measured in order to achieve the required performance. Thus, a simple actuator based on a mechanical amplification concept could be effectively designed to produce high force and high displacements.

Print publication: Issue 1 (February 1996)
Received 27 October 1994, accepted for publication 28 August 1995