Flutter control of wing boxes using piezoelectric actuators

This paper examines the use of piezoelectric actuators to control supersonic nutter of wing boxes. Aluminum built-up wing boxes are used as examples to analyze the free-vibration, aeroelastic, and control concepts associated with nutter control. Finite elements are used to calculate deflections caused by input forces, the member stresses and strains, natural frequencies, and mode shapes. Linear strip theory with steady aerodynamics is applied to find the frequency coalescence of modes indicating nutter. The variables of interest are the skin, web, and rib thicknesses associated with torsional rigidity, and the spar cap and vertical post areas associated with bending rigidity. Piezoelectric actuators are implemented in a configuration that generates torsional control of the wing box. Pole assignment concepts are applied to change the free-vibration frequencies. A parametric study changing the free-vibration frequencies using piezoelectric actuators is conducted to determine which thicknesses of skins, webs, and ribs will meet a specified nutter requirement, The addition of piezoelectric actuators will allow the nutter requirements to be met at smaller thicknesses of skins, webs, and ribs so that the overall weight of the wing box, including actuators, is decreased.