Scaling of Performance, Weight and Actuation of a 2-D Compliant Cellular Frame Structure for a Morphing Wing

摘要

A typical mission profile for a fixed-wing aircraft consists of several phases: take off, climb, cruise, dash, loiter, descent, and landing. Corresponding to each phase of flight is a specific wing configuration that yields optimal performance. Conventional aircraft employ a single fixed structure, necessarily a compromise. Morphing structures provide the possibility to make large global changes to the wing shape, ideally enabling optimum performance over a larger range of flight conditions. Although structural and actuator weight necessarily increases with morphing capability, overall performance gains can offset these with fuel savings or by enabling new aircraft missions. One benefit of morphing is described by the absolute difference between a maximum dash speed (at minimum drag), and a minimum loiter speed (for maximum time on station). For comparable morphing capability, this benefit is roughly proportional to W_o~(1/6). A 2-D compliant cellular truss structure was designed to replace the fixed internal structure of a wing. This structure is able to achieve large changes in both aspect ratio and planform area. The capability of this design was determined for aircraft of varying scale. RC model-sized aircraft, approximately 1-10 lbs, were used as a starting point. At this scale, the wing structure was capable of an 85% decrease in the planform area (and aspect ratio) with a structural weight of 2.9% of the gross weight. As the gross weight of the aircraft increases, the achievable span reduction decreases while the structural weight fraction increases. For a 100 and 1000 lb aircraft the decrease in planform area was 74% and 48%, respectively. A't 100 lbs the wing structure comprises 7.4% of the gross weight, while at 1000 lbs this increases to 8.9% of the gross weight. The difference between weight of the morphing structure and a similar passive structure is a weight penalty: the price we pay for the ability to morph. Actuation systems including a single actuator and a system of parallel actuators were considered for their ability to deform the structure. The weight fraction of the actuators required to deform the structure was found to increase with increasing gross weight. A system of parallel actuators was found to have a significant advantage over a single actuator, especially at higher gross weights. The benefit of morphing increases with the gross weight, however, structural morphing capability decreases with gross weight. This suggests, for a given structural paradigm, that there may be a gross weight for which morphing is most advantageous and practical.