Improved design and performance of the SMA torque tube for the DARPA Smart Wing program

recent Smart Wing wind tunnel tests at NASA Langley, we demonstrated over 5 degrees of span-wise wing twist at M=0.205. This was a considerable improvement over the 1.25 degrees of twist demonstrated during the initial tunnel test. Key to the improvements were two developments. First a different torque loading path in the structure, which resulted in torque being directly reacted from root to wing tip. Secondly, a new SMA actuator was developed, with a measured blocking torque of 3500 +/-100 in-lb. The second round of tunnel tests not only demonstrated increased wing twist; we also were able to command a variety of twist angles and were able to show that the wing could maintain a predetermined twist for over an hour with a stability of 0.05 degrees. Power consumption was recorded, with maximum power of 200W during twisting, and a power demand of 20W for maintaining wing twist.