Analysis and Design of a Hyper-Elliptical Cambered Span Morphing Aircraft Wing

Abstract

Morphing aircraft are a focus today due to their ability to combine multiple mission flexibility with a single vehicle. The Hyper-Elliptical Cambered Span (HECS) wing is one such wing being developed as a testbed for morphing technologies, due to its ability to vary the spanwise curvature in order to alter a craft's lift-to-drag performance. Through analysis of the aft-swept wing geometry and review of theory, predictions of aerodynamic performance are benchmarked against quasi-static rigid wing models in the Cornell University low-speed wind tunnel facility. Models assume a discretized approximation of the continuously varying spanwise curvature, with system order reduced significantly via a spool-and-tendon mechanism linking motions proportionally. The traditional rib-and-skeleton framework is replaced by a composite structure more adept at withstanding compressive loads due to actuation as verified through finite element analysis. Actuation methods are contrasted between a DC motor driven system and one employing shape memory alloy (SMA) wires, which generate proportional motion by linking sections electrically rather than mechanically. An energy comparison reveals the SMA wire to be more efficient, resulting in a prototype with embedded SMA wire actuators. The prototype employs a nonlinear proportional-integral controller to reach desired wing setpoints, which can be modified to user specifications based on flight conditions. A thermomechanical system model for the SMA is detailed and implemented in the feedback law, which relates well to observed actuation. The prototype half-wing is dynamically tested over a range of angle of attack in the wind tunnel facility. Results confirm the hypothesis that the planar wing will perform better than an elliptical wing of comparable characteristics, while morphing to the 'furled' state further increases lift-to-drag only over a small range of angle of attack. The SMA mechanism is demonstrated to be a viable means of morphing the wing, capable of overcoming aerodynamic loads and holding a desired wing shape based on the feedback law. Metrics of success are delineated and future revisions and inclusions are discussed.