The U.S. Air Force is examining how wing warping technology can be applied to future fighter jets. Ironically, Wilbur and Orville Wright developed the concept more than 100 years ago while they were tinkering in the back of their little bicycle shop in Dayton, OH. In fact, wing warping is what allowed them to achieve their historic flight on Dec. 17, 1903.

By studying birds and bicycles, the Wrights discovered that wing warping could allow them to actively control the lateral movement of their aeroplane. In 1899, Wilbur Wright used a long, narrow bicycle inner tube box to demonstrate the basic principles of wing warping. By twisting the box, he discovered that the entire wing structure could be twisted in a helical motion to achieve the desired direction.

The Wright Flyer used cables attached to a wing-warping cradle. The pilot pulled on the cable to warp the fabric wings up or down. Wing warping also played a key role in successfully defending the Wrights’ “flying machine” patent during a lengthy legal battle.

Ever since, aeronautical engineers have used ailerons instead of wing warping. But, that may be about to change, as engineers rediscover the benefits of wing warping and head back to the future.

Traditional mechanical flaps on the trailing edge of aircraft wings disrupt airflow and increase aerodynamic drag, which increase fuel consumption. Sridhar Kota, a professor of mechanical engineering at the University of Michigan, has been working with the Air Force Research Laboratory to develop a mission-adaptive compliant wing that can change shape in response to changing flight conditions. The goal is to improve efficiency, increase maneuverability and cut operating costs.

FlexSys Inc. is currently commercializing the technology developed at the University of Michigan’s Compliant Systems Design Lab. The smooth, hinge-free FlexSys wing can flex its trailing edge up or down 10 degrees. Air flows smoothly over the seamless wing, which uses internal actuators to alter its shape as conditions change. The wing can reduce fuel consumption by 5 percent to 15 percent for long-range military aircraft.

The U.S. Air Force has invested $6 million to test the adaptive compliant trailing edge technology that Kota and his colleagues have developed to replace conventional aircraft control surfaces. In addition, they have developed shape-morphing rotor blades for helicopters.”

Another company, ADA Technologies Inc. (ADA), recently received a contract from the U.S. Air Force to conduct research on a new method of creating a wing skin for use on morphing unmanned air vehicles (UAVs). Morphing UAVs would have the ability to dramatically alter their wing shape during flight to maintain optimal aerodynamic efficiency over a wide range of flight conditions.

“To perform, morphing wings skins must be sufficiently compliant to allow for substantial changes in wing shape, while having sufficient stiffness to carry aerodynamic loads,” says Steven Arzberger, ADA’s senior research scientist and project manager. “Shape memory polymers (SMPs) show substantial promise in meeting these conflicting requirements, due to their ability to quickly transition between rubber- and rigid-like behaviors through the application of heat.

“Efficient heat transfer within a timeframe that is consistent with UAV flight control needs is critical to the successful application of SMPs for morphing wing skins,” adds Arzberger. “Traditional resistive heating techniques have thus far proven unable to meet this requirement.”

According to Arzberger, ADA’s research will focus on nanotechnology, shape-memory polymer and thermal modeling to develop wing skins that are capable of rapid shape change enabled through highly efficient means of heat transfer.

“A key distinction of [our] approach compared to prior work is the use of a novel approach to transmitting heat within a nanoparticle reinforced SMP wing skin,” claims Arzberger. “Specifically, our approach will improve the thermal conductivity at the interface between the nanoparticles and the SMP resin, thereby increasing the heat transfer efficiency and, ultimately, the performance and effectiveness of the morphing UAV.”