Active aeroelastic tailoring of an adaptive Flexspar stabilator

Abstract

The aeroservoelastic properties of a new class of adaptive aeronautical surfaces are detailed. These new active surfaces use the newly invented Flexspar configuration which employs a high-strength main spar around which an aerodynamic shell is pivoted. Within the aerodynamic shell, a piezoelectric actuator is mounted with one end bonded rigidly to the spar and the other attached to a point on the shell. As the piezoelectric element is energized, the pitch angle of the shell is changed. Adjacent to the piezoelectric element, a sensor is used to determine the position of the shell. A simple feedback loop connecting the sensor and actuator provides a high degree of stability. Inertial and aerodynamic coupling are minimized by collocating the pitch axis, aerodynamic center and center of gravity. Laminated plate theory estimations are used with basic kinematic expressions for relating piezoelectric flexure to shell pitch angle change. Wind tunnel test results demonstrate that stable deflections up to are possible. By using an adaptive positioning system, the aerodynamic shell may be moved with respect to the main spar. This modification lends aeroservoelastic characteristics to the system. Accordingly, as the quarter-chord of the shell is moved forward of the pitch axis, small pitch deflections are effectively magnified with increasing air speed. Experimental testing of an aeroservoelastically coupled wing specimen showed magnification of pitch deflections from to and good correlation with theory.