A novel morphing control surface design employing piezoelectric Macro Fiber Composite (MFC) actuators is compared to a servo-actuated system. The comprehensive comparison including aerodynamics, size, weight, power, bandwidth, and reliability has revealed several observations. The conformal morphing airfoil geometry increases the lift-to-drag ratio over a servo-actuated flapped airfoil design, showing benefits in aerodynamic efficiency. The embedded MFC actuators eliminate the servo actuator volume from vehicle packaging; however, the MFC drive electronics must be taken into consideration. While the weight of the current prototype morphing system exceeds that of a traditional servo and linkage implementation, the weight is comparable and may not be prohibitive for some applications. The comparable power requirement and superior bandwidth make the morphing actuation a feasible and attractive approach for certain air vehicle designs. An order of magnitude increase in bandwidth was observed using the morphing flight control actuation. Ongoing reliability testing of the morphing specimens has demonstrated that solid-state morphing actuation has not failed within 10 5 cycles. Flight tests are planned to fully prove the benefits of the morphing actuation over a servo-actuated design. NomenclatureA = Airfoil planform area, ft 2 C d = Drag coefficient (2D), D/(0.5!V 2 A) C l = Lift coefficient (2D), L/(0.5!V 2 A) D = Drag, lb L = Lift, lb ! = Angle of Attack, degrees "= Airfoil support angle, degrees # = Air density, slug/ft 3

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The use of piezo-ceramic actuators for UAV flight control has been shown to be effective both in the wind tunnel and in flight test. Macro fiber composite (MFC) actuators are a high strain variant of the lead zirconate titanate (PZT) actuator, and have been employed in a bimorph configuration to cause morphing camber control of aerodynamic surfaces in less than 0.5 m wingspan UAV applications. One of the challenges of operating these conformal actuators is to quantify the voltage input/displacement output relationship given hysteresis and aerodynamic loading effects. The work presented provides a framework for the practical implementation of these actuators by using both open and closed loop feedback systems for displacement control. Results are presented for thick airfoil designs where only the trailing edge is deflected using smart materials. The two main sources of non-linear behavior include dynamic pressure and actuator hysteresis, and knowledge of these parameters can be used for reasonably good open loop displacement control. Results are presented for 2-D airfoil section testing. Nomenclatureb airfoil spanwise length V free stream wind velocity L lift force D drag force β wind tunnel support angle α angle of attack A airfoil area C L coefficient of lift C D coefficient of drag c chord ρ air density TE trailing edge t time

The authors have explored the use of morphing control surfaces to replace traditional servo-actuated control surfaces in UAV applications. The morphing actuation is accomplished using Macro Fiber Composite (MFC) piezoelectric actuators in a bimorph configuration to deflect the aft section of a control surface cross section. The resulting camber change produces forces and moments for vehicle control. The flexible piezoelectric actuators are damage tolerant and provide excellent bandwidth. The large amplitude morphing deflections attained in bench-top experiments demonstrate the potential for excellent control authority. Aerodynamic performance calculations using experimentally measured morphed geometries indicate changes in sectional lift coefficients that are superior to a servo-actuated hinged flap airfoil. This morphing flight control actuation technology could eliminate the need for servos and mechanical linkages in small UAVs and thereby increase reliability and reduce drag.

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