Development of high-rate, adaptive trailing edge control surface for the Smart Wing Phase 2 wind tunnel model

The DARPA/AFRL/NASA Smart Wing program, led by Northrop Grumman Corporation (NGC) under the DARPA Smart Materials and Structures initiative, addressed the development of smart technologies and demonstration of relevant concepts to improve the aerodynamic performance of military aircraft. In Phase 2, Test 2 of the program, the main objective was to demonstrate high-rate actuation of hingeless, spanwise, and chordwise deformable control surfaces using smart materials-based actuators on a 30% scale, full span wind tunnel model of a proposed NGC uninhabited combat air vehicle (UCAV). A minimum actuation rate of 25degrees flap deflection in 0.33 s, producing a slew rate of 75degrees/s, was desired. This slew rate is representative of many operational military aircrafts with hinged control surfaces. Numerous trade studies were performed on a variety of smart materials and flexible structure configurations before arriving at the final trailing edge structure design that consisted of a flexcore center and elastomeric outer skin actuated by high-power ultrasonic motors using an eccentric motion. The trailing edge control surface fitted onto the wind tunnel model comprised 10 eccentric-driven segments connected together by a continuous outer skin and a flexible hinge pin at the trailing edge tip. This pinned configuration allowed the segments partial freedom to rotate about each other, but constrained any lateral motion thus giving a smooth trailing edge shape for nonuniform spanwise deflections. To control the 10 segments of the trailing edge, a VME-based control system with high speed, simultaneously sampled A/D and D/A boards and a dedicated DSP board was developed. This paper describes the analysis and design of the flex structure, ultrasonic motor selection and performance, element and coupon tests to verify analysis, control system development, model integration, and results from the wind tunnel test.