Adaptive Flutter Test Vane: Low Net Passive Stiffness (LNPS) Techniques for Deflection Amplification of Piezoelectric Actuators

Abstract

This document outlines the design, development and testing of an adaptive flutter test surface utilizing low net passive stiffness (LNPS) actuator configurations for deflection amplification. The device uses a tapered piezoelectric bender actuator in an aerodynamic shell which pivots about the quarter-chord. Laminated plate theory is used to capture the unamplified deflection levels. A unique reverse-bias spring mechanism enables LNPS techniques, generating a 5:1 amplification ratio from baseline deflection levels with negligible weight penalty and no degradation in blocked moments. The adaptive flutter test vane and associated spar-mounting hardware have a combined weight of only 2 lb and consume less than 1W of peak power at maximum actuation voltage. The significance of the relatively low installed weight is apparent when considering the effect on the modal mass of the aircraft. It can be shown that a reduction in weight from the current state-of-the-art 18+ lb (installed) DEI vane to a 2 lb adaptive flutter test vane (installed) improves the normalized first natural frequency of flap in a wing from approximately 60% to 90% in light aircraft classes - all but eliminating the detrimental effect of additional mass on the accuracy of flutter prediction. Quasi-static and dynamic wind tunnel testing shows excellent correlation with bench tests and theory. Maximum deflection levels were recorded in excess of 8 deg. peak-to-peak, with a corner frequency in excess of 50 Hz. Wind tunnel tests were performed up to 110 ft/s with change in lift forces on the order of 1.45 lbf. This paper focuses on the testing and evaluation of the aforementioned hardware for applications in certification of small aircraft in the general aviation (GA), light sport (LSA), homebuilt and ultralight classes.