Spanwise Adaptive Wing: An Overview and Challenges of In-Flight Wing Flooding using Shape Memory Alloys

The Spanwise Adaptive Wing (SAW) project, consisting of members from NASA, Boeing, and AREA-I, are evaluating inflight wing folding using advanced actuation systems based on shape memory alloys (SMAs). The team conducted a series of subscale flight tests on the Prototype-Technology Evaluation and Research Aircraft (PTERA) airplane, and ground tests on a full-scale F/A-18 outer wing section. Actuation systems were based on a precipitation-strengthened, high temperature NiTi-20Hf shape memory alloys developed at NASA Glenn Research Center in the form of torque tubes. The flight test consisted of an actuation system designed for an output torque of 56 N-m with angular displacement of 90 degrees using a single tube, while the ground test was designed for a bigger system rated for 2260 N-m torque with the same angular displacement using a combination of tubes. The actuators were instrumented and integrated within the hinge line of each test bed. Preliminary data shows that the actuator was precisely controlled to within a fraction of a degree, but actuation rates can still be improved. In this work, an overview and lessons learned from the flight and ground tests are discussed. Challenges that were solved are highlighted and those that remain are addressed in the context of future SAW activities.