NASA is exploring the feasibility of a system that would allow part of an aircraft’s wing to fold in flight, to increase flying efficiency through wing adaptation.

Engineers at NASA’s Armstrong Flight Research Center, in California, Langley Research Center, in Virginia, and Glenn Research Center, in Ohio, are working on the Spanwise Adaptive Wing (SAW) concept. Their design, if feasible, would permit the outboard portions of the wings to move to the optimal position during operation. This could potentially result in an increase in efficiency by reducing drag and increasing lift and performance.

In theory, the design would permit the outboard portions of the wings to move to the optimal position during operation. Image credit: NASA.Through advanced actuation, SAW aims to use control surfaces to allow the outboard portions of wings to adapt as much as 75 degrees to more effectively meet the demands of various operating conditions throughout a flight. A mechanical joint, acting as a hinge line for rotation, makes the freedom of movement possible.

“Let’s say you’re in a condition that requires a climb-out. The optimal position might be up 15 degrees or down 15 degrees, and you would be able to get that,” says Matt Moholt, NASA Armstrong principal investigator for SAW.

According to NASA, the ability to achieve optimal wing position for different aspects of flight may also produce enough yaw control to allow for rudder reduction on both subsonic and supersonic aircraft, which may provide additional benefits to aircraft efficiency, such as reduced drag and weight.

While folding wing capabilities have been around for decades, wing folding articulation, or shaping, has generally been used only as a method for the conservation of deck space on aircraft carriers and aircraft storage areas. Moholt says that the benefits of wing articulation spans across several regimes, from taxiing on the ground to takeoff, cruising and even supersonic flight.

“In supersonic flight, yaw stability becomes a big issue,” said Moholt. “If you’re flying supersonically, you have tons of lift. Let’s say you need more yaw control. Well, if I fold the wing portion all the way down, I may be able to trade lift in favor of more yaw control where I need it and less lift where I don’t need it.”

The concept may be flight tested on NASA's subscale Prototype Technology Evaluation and Research Aircraft as early as Spring 2017. Testing objectives would include the validation of tools and vetting of the system’s integration, vehicle control law evaluation and analysis of SAW’s airworthiness and potential benefits to in-flight efficiency.