Second generation inflatable/rigidizable wings for low-density flight applications

Recent projects involving unfolding rigid-wing aircraft have demonstrated high-altitude, low-density flight capabilities, moving the concept of an unmanned aircraft exploring Mars or Venus nearer to reality. An alternative approach for the wing design is an inflatable wing impregnated with a UV-curable composite. Once rigid, the wings no longer require pressurization to maintain their shape and so are less vulnerable to catastrophic failure due to loss of pressurization. The initial effort to demonstrate the feasibility of inflatable, rigidizable wing technologies culminated in a balloon-launched experiment on May 3, 2003. The first-generation wing design was a uniform two-layer woven composite impregnated with curing vinyl ester resin. After the first feasibility experiment, a second generation wing design was undertaken to minimize the weight by tailoring the composite layering for the expected loads. This paper presents details of the design, along with stress analyses and optimization studies performed to determine the second generation design. A series of low-temperature cure tests were completed to define the flight test protocol. Wings fabricated following the new design were launched on May 1, 2004 via weather balloon, inflated, cured and then recovered after a premature balloon burst and parachute return to ground. This flight test demonstrated the successful inflation deployment and UV-rigidization of the second-generation wing. Postflight evaluation results are also included in the paper.