Airplanes, whether manned or unmanned, need to travel at various speeds. For example, a surveillance plane needs to fly fast to reach its destination point. Then, it needs to reduce its speed to achieve its surveillance mission. But with its fixed wings, it doesn't offer the same level of efficiency during these two phases. That's why Penn State engineers have devised airplane wings that change shape like a bird and have scales like a fish. Right now, the team has only built a tabletop model. So it will be a long time before you catch a plane and watch the wings disappear by looking through the window.
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.
So how did these engineers design these morphing wings?
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.
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.
Here is a couple of images describing the work done so far, which is limited to a tabletop model of the compliant cellular truss structure and a computer graphic model of the wing structure (Credit: Penn State).
|Here is the wing structure, made of octahedral unit cells. "The unit cell used in the top surface is different from that used in the bottom surface. Since on the top surface the chordwise and spanwise strains increase simultaneously as the the wing morphs, whereas on the bottom surface the chordwise strain increases and the spanwise strains decreases as the wing morphs."
|And here is the tabletop model of the complaint cellular truss structure.
For more information, you can visit two other pages from the Penn State website, one containing morphing wing photos (slow loading, 1.6 MB), the other giving more details about morphing aircraft structures.
Finally, if you have a broadband connection, here is a link to a movie showing the tabletop model expanding (5.1 MB).
Source: Penn State news release, April 20, 2004, via EurekAlert!; Penn State website