To maximize a plane's efficiency over a broader range of flight speeds, Penn State engineers have developed a concept for morphing airplane wings that change shape like a bird's and are covered with a segmented outer skin like the scales of a fish.
Dr. George Lesieutre, professor of aerospace engineering who leads the project, says, "Airplanes today are a design compromise. They have a fixed-wing structure that is not ideal for every part of a typical flight. Being able to change the shape of the wings to reduce drag and power, which vary with flight speed, could optimize fuel consumption so that commercial planes could fly more efficiently."
Morphing wings can also be useful for military defense and homeland security when applied to unmanned surveillance planes that need to fly quickly to a distant point, loiter at slow speed for a period of time and then return, Lesieutre explains. Flying efficiently at high speed requires small, perhaps, swept wings. Flying at slow speed for long periods requires long narrow wings. The morphing wings designed by the Penn State team can change both wing area and cross section shape to accommodate both slow and fast flight requirements.
Lesieutre and the wing design team will detail their concept in a paper, "Tendon Actuated Compliant Cellular Truss For Morphing Aircraft Structures," on Tuesday, April 20, at the 45th AIAA/ASME/ASCE/AHA/ASC Structures, Structural Dynamics and Materials Conference in Palm Springs, Calif. The authors are Lesieutre; Dr. Mary Frecker, associate professor of mechanical engineering; Deepak Ramrakhyani, doctoral candidate in aerospace engineering; and Smita Bharti, doctoral candidate in mechanical engineering.
The essential features of the Penn State concept are a small-scale, efficient compliant cellular truss structure, highly distributed tendon actuation and a segmented skin. The cellular truss structure is the skeleton of the wing. The skeleton is formed of repeating diamond-shaped units made from straight metal members connected at the angles with bendable or "compliant" shape memory alloys. Tendons in each unit, like the ropes that shape a tent, can pull the units into new configurations that will spring back, thanks to the shape memory alloys, when the tendon tension is released.
Since the underlying structure can undergo radical shape change, the overlaying skin of the wing must be able to change with it. Lesieutre says a concept that he thinks holds great promise is a segmented skin composed of overlapping plates, like the scales of a fish. He notes that conveyers on the baggage carousel in airports are composed of a similar pattern of plates.
So far, the design team has built a tabletop model of the compliant cellular truss structure and a computer graphic model of the wing structure.
The project is supported by grants from NASA and the Defense Advanced Research Projects Agency (DARPA).