NASA's Glenn Research Center developed a novel means of articulating the outboard portion of an aircraft wing to create the optimal geometry for given flight conditions. The Spanwise Adaptive Wing (SAW) concept employs a high-force, solid-state Shape Memory Alloy (SMA)-based actuator to develop a structurally efficient and reliable method of deflecting a portion of the wing in flight. This ability enables significant increases in lateral-directional stability and control augmentation, thereby enhancing aircraft efficiency by reducing the rudder motion to control yaw.
Particularly in supersonic flight, the SAW's benefits include increased compression lift and reduced wave drag. Compared to prior hydraulic-based actuators, the SMA-based actuator features significantly reduced size and weight, high specific work output, solid-state actuation, low maintenance, and high reliability.
Prior efforts to actuate wing articulation were unsuccessful, largely because the systems designed were too large, heavy, and complex to be practical for use. NASA's comparatively simple SAW concept centers on a wing actuator fabricated from lightweight SMA material, which is trained to deform to a specific shape as it becomes heated. SMA actuators are composed of high-strength alloys, such as nickel-titanium-hafnium, and can feature elements such as trained tubes, wires, cables, or sheets. For example, a high-temperature, high-force SMA torque tube can be embedded in an outboard chordwise hinge line of a wing.
Every embodiment of the SMA actuator features integrated heaters and cooling devices that enable better control authority. A novel hinge line mechanism both provides a two-piece wing connection and houses the actuator assembly. When the actuator is heated, the SMA apparatus triggers the articulation of the wing to a predefined position. Once the desired position is reached, the heater maintains a constant temperature, causing the SMA to maintain its deformity.
As needed, the cooling system can be used to allow the wing to return to its original geometry. Multiple actuators can be employed on a single wing, allowing the various parts of the wing to articulate independently. By adapting the geometry of the wing during all phases of operation, from ground to subsonic and supersonic/hypersonic flight, NASA's SAW offers the first practical method of using wing articulation to improve aircraft performance and fuel efficiency.