NASA engineers have added a new twist to a cutting edge aerospace technology by demonstrating how a new Shape Memory Alloy (SMA) actuator can fold a 300-lb (136 kg) wing section from an F/A-18 Hornet supersonic fighter plane. Taking place at NASA's Armstrong Flight Research Center in Edwards, California, the test involved replacing the folding mechanism a Hornet wing tip with a high-temperature SMA torque-tube actuator made of a newly developed nickel-titanium-hafnium alloy that generated 5,000 in-lb (564 Nm) of torque.
According to NASA, the recent test was the latest step in the agency's Spanwise Adaptive Wing (SAW) Project. This aims to simplify aircraft design by replacing the complicated mechanical, hydraulic, and electromechanical actuators that move wing surfaces with components or even whole wing sections made of memory alloys that bend themselves. A joint effort from NASA's Armstrong Flight Research Center, Glenn Research Center, Langley Research Center, Boeing Research & Technology, and Area-I Inc, SAW could see an 80 percent reduction in actuator weight.
The key to this is memory alloy, which is a special combination of metals that retains a "memory" of its shape. In other words, if you take a spring made of memory alloy, stretch it out of shape, mangle it into a lump, and then heat it, it will spring back into its original shape.
SMA actuators work on the same principle. By applying heat or some other stimulus, the actuator can change shape and perform work without the need for motors, pulleys, or hydraulics. The current focus of NASA's work is on producing folding wings that could one day lead to lighter, simpler aircraft with longer and more slender wings, as well as stabilizers, and rudders that are more fuel-efficient. Such technology could also enable aircraft that morph their wings to exploit different air conditions, and could even improve the performance of supersonic aircraft.
So far, SMA actuators have been tested on the remote controlled Prototype Technology-Evaluation Research Aircraft (PTERA), but now NASA is taking things further by installing an SMA actuator in a wing section of an F/A-18 Hornet. During the test, the actuator was not only able to fold the wing 90 degrees up and down, but did so with very precise control. It managed this in a folding up maneuver used to park the fighter on an aircraft carrier, and also in folding it down, as the aircraft would in flight under conditions that simulated actual flight loads.
NASA says that the F/A-18 tests will continue over the next few months leading up to the installation of a new actuator capable of generating 20,000 in-lb (2,260 Nm) of torque that can be applied to the wing's leading and trailing sections.
The video below discusses the F/A-18 Hornet test.
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