Aircraft maneuverability depends heavily on the movement of flaps found at the rear or trailing edge of the wings. The efficiency and reliability of operating these flaps is of critical importance.
Most aircraft in the air today operate these flaps using extensive hydraulic systems. These hydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order to maintain reliability of operation, multiple hydraulic lines must be run to each set of flaps. This complex system of pumps and lines is often relatively difficult and costly to maintain.
Many alternatives to the hydraulic systems are being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memory alloys.
The flaps on a wing generally have the same layout shown on the left, with a large hydraulic system like the one shown in Figure 2 attached to it at the point of the actuator connection. "Smart" wings, which incorporate shape memory alloys, are generally shaped like the wing shown in Figure 3, this system is much more compact and efficient, in that the shape memory wires only require an electric current for movement.
Figure 1: Typical Wing and Flap Figure 2: Electromechanical Actuator
The shape memory wire is used to manipulate a flexible wing surface. The wire on the bottom of the wing is shortened through the shape memory effect, while the top wire is stretched bending the edge downwards, the opposite occurs when the wing must be bent upwards. The shape memory effect is induced in the wires simply by heating them with an electric current which is easily supplied through electrical wiring, eliminating the need for large hydraulic lines. By removing the hydraulic system, aircraft weight, maintenance costs, and repair time are all reduced. The smart wing system is currently being developed cooperatively through the Defense Advanced Researched Project Agency (DARPA, a branch of the United States Department of Defense), and Boeing.
Figure 3: Hinge less shape memory alloy Flap
The video clip shown on the right is of a hydraulic system in use on an airplane wing, while the link on the left takes you to an interactive Applet which will allow you to experiment with a computer modeled piece of shape memory alloy similar to that found in the "smart" wing system described above.