Wing with a bent for efficiency

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NASA has demonstrated a prototype wing that folds in flight by using shape memory alloy (SMA).

Engineers used a 135 kg folding wing section from a NASA F/A-18 and replaced its electric motor folding actuator with a newly developed nickel-titanium-hafnium high temperature SMA torque-tube actuator.

Beginning at the horizontal position, the SMA mechanism was electrically heated and cooled on command to allow the wing to move 90 degrees up and down. More importantly, researchers were able to move the wing section to any selected position within that sweep with very precise control.

This successful test is another milestone for NASA’s Spanwise Adaptive Wing Project, which is studying the in-flight bending or shaping sections of an aircraft’s wings. The ability to shape wings could increase aircraft performance by reducing weight and drag, while improving aircraft control.

NASA concedes in-flight wing folding, like most novel technologies in aviation, is not new; the XB-70 Valkyrie supersonic bomber prototype used it more than 50 years ago. (Folding wings are particularly useful in supersonic flight, where there is an excess of lift, and a deficit of yaw control.) But replacing traditional actuators with SMA actuators, or, possibly building wings of SMA itself could allow the technology to become lighter by up to 80 per cent, cheaper and more reliable. Early this year NASA tested the technology on a small unmanned aircraft.

NASA says: ‘Advanced actuation could make possible a design that is both compact and lightweight, minimising stress on the wing and allowing for more compact packaging. Conventional systems have proven to be heavy, bulky systems, too large for practical use on an aircraft. These have included gear boxes and hydraulic, pneumatic or magnetic motors. NASA engineers believe actuator technology has advanced and may be dramatically reduced in size and weight.’

Testing using SMA actuators and the F/A-18 wing at NASA Glenn research Centre will continue through the summer.

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