Dec. 3, 2008 It's a bird, it's a plane, it's ... both! While aircraft have always borne a resemblance to their feathered counterparts in the sky, new research at U of T is bringing the two even closer together.
Inspired by nature, mechanical engineering professor Shaker Meguid is currently developing aircraft wing designs that imitate the amazing flight of birds by altering the planform of the wings in order to optimize the aerodynamics for a given flight stage.
"When you observe eagles in flight, you would notice that when they are high in the sky they soar and their wings are fully extended. They are gliding, attempting to increase lift and reduce drag. This helps them to glide effortlessly and navigate for long durations in their search for a prey. However, they fold their wings and go on a fast attack when they dive to catch a prey," Meguid explained.
After studying research on birds, in particular the Apus apus (common swift), a bird whose wing-morphing ability makes it an especially versatile flyer and allows it to eat, sleep and mate in the air, Meguid began plans to develop a more effective alternative to the traditional fixed-wing aircraft.
"Morphing implies large seamless shape change. Right now we have aircraft control surfaces that allow discrete morphing such as ailerons and flaps. What we want to do is undergo changes in a seamless fashion, resulting in increased efficiency," he said.
To achieve these seamless transitions in wing shape, Meguid and his research team are combining two types of advanced materials. The first is shape memory alloy (SMA), which contracts when heated above a certain temperature. The second are piezoelectrics, which compress or extend when an electric field is applied to them. They plan on using these materials to allow the wing to change shape and respond to an aircraft's changing mission with an overall reduced system complexity.
Meguid explained how this works using a model developed by one of his post-doctoral fellows, Aarash Sofla. "The shape morphing truss structure ... uses shape memory alloy actuators to achieve bending, twisting and undulating shape changes. The structure consists of tetrahedral truss unit cells, which are connected using a spherical freely rotating joint. The joint provides a means for connecting several struts at a node while ensuring sufficient rotational freedom.
"In addition to increasing an aircraft's performance and adaptability, morphing wings carry many other benefits, including lower costs, reduced pollution and noise during take-off," Meguid added.
Meguid's morphing wing research is funded by the DSO National Laboratories in Singapore, where he founded the aerospace division at Nanyang Technological University in 2004 while on leave from U of T. This three-year project, which was launched in April, is focusing on developing morphing wings specifically for unmanned aerial vehicles (UAVs), aircraft that are often used for surveillance, imaging and operation in locations where human safety is at risk.
Meguid is looking forward to seeing his morphing UAV wings literally take off as he and his team, consisting of one post-doctoral fellow, one doctoral student and three undergraduates, realize their designs. "It is design and build; it's not a paper exercise," he said. "We will be examining the aerodynamic performance and the mechanical integrity of the successful wing morphing designs and aerodynamic tests will be carried out in a wind tunnel in DSO National Laboratories in Singapore."
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