Aeroelastic Modeling, Analysis and Testing of a Morphing Wing Structure

NextGen Aeronautics, Inc., of Torrance, CA, has been involved in all aspects of the design, development and testing of morphing aircraft structures, much of this in conjunction with NASA Langley Research Center. The single most substantial effort in this area has been the DARPA Next-Generation Morphing Aircraft Structures project, in which NextGen has been one of two prime contractors tasked with advancing the state of technology of morphing aircraft. NextGen developed an in-plane morphing geometry concept with mechanized four-bar linkages, and motion imparted by computer-controlled linear actuators. Flexible elastomeric skins with out-of-plane stiffeners accommodated the wing motion while transmitting air pressure loads to the wing substructure. The development process involved wind tunnel testing of a full-scale wing for a 2400-lb vehicle and flight testing of a subscale unmanned air vehicle. Among the more critical challenges has been that of addressing wing design for aeroelasticity, given the unique features of morphing wings. Specific relevant issues include: the need to address multiple geometries and flight envelopes to account for morphing shape changes; in-plane flexibility of the wing resulting from its mechanisms and soft (relative to typical fixed wing structure) restraint by linear actuators; nonlinearity and equivalent loss of stiffness in the wing’s out-of-plane direction as a result of multiple revolute joints in the structure. These unfamiliar features required, in some cases, the development of new analytical or testing approaches. In addition, due to a somewhat untried approach to mounting the half-span wind tunnel model of its size at the NASA Transonic Dynamics Tunnel, particular considerations of support structure dynamics had to be given particular attention prior to wind-on testing there. Ultimately, all of these challenges were overcome, and successful wind tunnel and flight demonstrations were completed.