: 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(exp 5) cycles. Flight tests are planned to fully prove the benefits of the morphing actuation over a servo-actuated design.

Piezoelectric Morphing versus Servo-Actuated MAV Control Surfaces

Aircraft wings with smooth, hinge-less morphing ailerons exhibit increased chordwise aerodynamic efficiency over conventional hinged ailerons. Ideally, the wing would also use these morphing ailerons to smoothly vary its airfoil shape between spanwise stations to optimize the lift distribution and further increase aerodynamic efficiency. However, the mechanical complexity or added weight of achieving such a design has traditionally exceeded the potential aerodynamic gains. By expanding upon the previously developed cascading bimorph concept, this work uses embedded Macro-Fiber Composites and a flexure box mechanism, created using multi-material 3D printing, to achieve the Spanwise Morphing Trailing Edge (SMTE) concept. The morphing actuators are spaced spanwise along the wing with an elastomer spanning the gaps between them, which allows for optimization of the spanwise lift distribution while maintaining the continuity and efficiency of the morphing trailing edge. The concept is implemented in a representative section of a UAV wing with a 305 mm chord. A novel honeycomb skin is created from an elastomeric material using a 3D printer. The actuation capabilities of the concept are evaluated with and without spanning material on a test stand, free of aerodynamic loads. In addition, the actuation restrictions of the spanning elastomer, necessary in adapting the morphing concept from 2D to 3D, are characterized. Initial aerodynamic results from the 1’×1’ wind-tunnel also show the effects of aerodynamic loading on the actuation range of the SMTE concept for uniform morphing.

Experimental testing of spanwise morphing trailing edge concept

Smart Material Wing Morphing for Unmanned Aerial Vehicles.

‡‡ 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 been extended to include flight test comparisons. Flight agility and control response of the morphing-actuated and servo-actuated configurations were quantified through state measurement during identical automated maneuvers. The morphing actuation scheme demonstrated superior response times and a fully controllable vehicle, but was unable to match the magnitude of roll and pitch rates attained by the servo-actuated baseline aircraft. The servo-actuated aircraft exhibited velocity deficits during doublet maneuvers, while the morphing actuation negligibly decreased velocity, demonstrating lower drag and more efficient production of control forces and moments. Reliability cycle testing of an MFC bimorph achieved 1 million cycles without failure and minimal degradation in performance.

Piezoelectric Morphing versus Servo-Actuated MAV Control Surfaces, Part II: Flight Testing

Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2012

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.

Chris C. Olien

Papers

Piezoelectric composite morphing control surfaces for unmanned aerial vehicles