Flight-testing is scheduled to begin in 2011 of a morphed wing prototype for unmanned air vehicles that uses in-built shape memory alloy actuators that deform the shape of the wing when heated.

The prototype is being developed by the University of Toronto's mechanical and industrial engineering unit on behalf of Singaporean defence research and development institution DSO National Laboratories.

"The major difference to the traditional discrete morphed wing design that uses flaps and ailerons with excessive complexity and weight penalty is that we're using smart materials such as shape memory alloys," says Professor Shaker Meguid, who is heading the research programme.

"We focus on planform change and instruct the wing to sweep backwards and achieve very high rates of deformation and change in area, even though the actuators undergo very small deformations. Furthermore, the actuators constitute part of the wing spar structure - this is the ingenuity of our new design."

Variable geometry wing concept UAV

These shape memory alloy actuators, when heated to a certain point, are able to morph into a preset shape. The actuators in Meguid's design are being deployed as part of an antagonistic rather than a compliant set-up, which means there are at least two actuators working in opposite directions to produce the desired effect.

"If you heat shape memory alloys, they change shape - if there are four and you heat two of them, the wing curves. This is continuous morphing," says Meguid. "Antagonistic structures have the advantage that they only require an external stimulus to morph into a new shape, and no external stimulus to maintain that shape."

One potential drawback of the design is that the in-built morphing capability will increase the weight of the UAV to which it is being applied. However, Meguid is confident that the resulting improvements in the aircraft's performance, such as reduced drag and increased lift, will cancel out the added weight penalty.

The first stage of the six-year morphed wing research project is to provide a prototype, which Meguid says will be concluded by the end of this year. "We are currently looking into covering the smart wing with an elastomeric skin to carry out its intended function," says Meguid. "Once the skin is selected, the prototype will be tested in a windtunnel and ultimately flight-tested."

Flight-testing is expected to begin in 2011, marking the beginning of the next three years of the wing morphing programme. Meguid is supervising Dr Aarash Sofla and Paul Galantai at the University of Toronto on the project, while the DSO team is being led by Dr Tan Koktin and Yeo Wei Kiong.

Source: Flight International