Aircraft

NASA turns to memory alloys for folding wings

NASA turns to memory alloys fo...
NASA used a remotely-controlled flight testbed called Prototype Technology-Evaluation Research Aircraft, or PTERA, to test the shape memory alloy
NASA used a remotely-controlled flight testbed called Prototype Technology-Evaluation Research Aircraft, or PTERA, to test the shape memory alloy
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NASA used a remotely-controlled flight testbed called Prototype Technology-Evaluation Research Aircraft, or PTERA, to test the shape memory alloy
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NASA used a remotely-controlled flight testbed called Prototype Technology-Evaluation Research Aircraft, or PTERA, to test the shape memory alloy
The Spanwise Adaptive Wing concept seeks to enhance aircraft performance through allowing the outboard portions of wings to adapt, or fold, according to different flight condition demands
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The Spanwise Adaptive Wing concept seeks to enhance aircraft performance through allowing the outboard portions of wings to adapt, or fold, according to different flight condition demands
PTERA in flight
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PTERA in flight
The subscale testbed PTERA flies over NASA Armstrong Flight Research Center in California with the outer portions of its wings folded 70 degrees upwards
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The subscale testbed PTERA flies over NASA Armstrong Flight Research Center in California with the outer portions of its wings folded 70 degrees upwards

NASA sees folding wings as a key aeronautical technology for the aircraft of tomorrow, and to make it practical, the space agency is looking to a cutting edge, lightweight memory alloy. Developed for the Spanwise Adaptive Wing (SAW) project, the new alloy allows an aircraft's wing and control surfaces to change their shape in flight without heavy hydraulic systems.

Aircraft wings have come a long way from the ones made out of spruce wood and duck for the 1903 Wright flyer, but they've also become very complicated. They're also limited in how efficient they can be, because they depend on shifting and tilting rigid control surfaces to work.

If a wing was a bit more "rubbery," it could reshape itself into a variety of forms to meet different flight conditions while maintaining a smooth, aerodynamic shape to minimize turbulence. It's not a new idea. The Wright flyer's flight controls worked by warping the wings using simple pulleys, and for decades aerospace engineers have explored the concept, including in a modified North American XB-70 Valkyrie in the 1960s.

The subscale testbed PTERA flies over NASA Armstrong Flight Research Center in California with the outer portions of its wings folded 70 degrees upwards
The subscale testbed PTERA flies over NASA Armstrong Flight Research Center in California with the outer portions of its wings folded 70 degrees upwards

The problem is that the hydraulic mechanisms used to fold wings are heavy, bulky, and energy-consuming to the point where their disadvantages offset any of their advantages. As part of a joint effort, NASA's Armstrong Flight Research Center, Glenn Research Center, Langley Research Center, Boeing Research & Technology, and Area-I Inc are studying how to replace the usual hydraulics and motors with actuators that are 80 percent lighter and run by shape memory alloy as a way of creating wings that work better at subsonic, transonic, and supersonic speeds.

Recently, NASA carried out a series of flight tests over Rogers Dry Lake at Edwards Air Force Base in California using the remotely-controlled Prototype Technology-Evaluation Research Aircraft (PTERA) fitted with wings with tips that can fold between zero and 70 degrees up and down while in flight. The carbon composite UAV is kitted out with extensive telemetry and sensors, and was flown in a racetrack pattern with the wings in the zero position, then in the 70 percent up and down positions on subsequent flights.

The drone was able to do this using an actuator consisting of a tube made of thermal shape memory alloy. A memory alloy is an alloy that is triggered by some outside stimulus, usually heat, and springs back into its original state. This means that you could, for example, take a strip of alloy, crumple it up, and then watch it uncrumple itself when heated.

The Spanwise Adaptive Wing concept seeks to enhance aircraft performance through allowing the outboard portions of wings to adapt, or fold, according to different flight condition demands
The Spanwise Adaptive Wing concept seeks to enhance aircraft performance through allowing the outboard portions of wings to adapt, or fold, according to different flight condition demands

In the PTERA's wings, heating the tube causes it to twist, causing the tips of the wings to bend up or down.

"The performance of this new alloy that we developed between NASA and Boeing really showed outstanding performance," says Jim Mabe, Technical Fellow with Boeing Research and Technology. "From the time we started initial testing here at Boeing, up to the flight tests, the material behaved consistently stable, and showed a superior performance to previous materials."

According to NASA, the ability to fold their wings may one day allow for lighter, simpler aircraft with longer and more slender wings, stabilizers, and rudders that make them not only more fuel-efficient, but better able to taxi at airports and to morph their wings to exploit different air conditions instead of suffering from them. In addition, it would make supersonic flight easier.

PTERA in flight
PTERA in flight

"There's a lot of benefit in folding the wing tips downward to sort of 'ride the wave' in supersonic flight, including reduced drag. This may result in more efficient supersonic flight," says SAW Principal Investigator Matt Moholt. "Through this effort, we may be able to enable this element to the next generation of supersonic flight, to not only reduce drag but also increase performance, as you transition from subsonic to supersonic speeds. This is made possible using shape memory alloy."

NASA will continue with SAW flights later this year, concentrating on folding wings between 70 degrees up to 70 degrees down in a single flight. This will be followed by scaling up the technology for installation on an F-18.

"We put the SAW technology through a real flight environment, and these flights not only proved that we can fly with this technology, but they validated how we went about integrating it," says Moholt. "We will use the data from these flights to continue to improve upon the actuation system, including speed and smoothness of actually folding the wings, and we'll apply them as we get ready to fly again in 2018."

The video below shows one of the PTERA flights.

Source: NASA

NASA Examines Technology To Fold Aircraft Wings In Flight

5 comments
highlandboy
Given the restriction of time a plane can fly “supersonic” due to heat build up (the Concord, for example, could only fly a little less than 3 hours supersonic, the blackbird on the other hand, had to stay supersonic for longer periods or its fule tanks leaked), using thermal memory metals is going to be fraught with problems for any plane which spends some of its time supersonic.
JonStron
Yes i agree, I really don't know why they even considering it, obviosuly the heat generated by supesonic flight will be a problem to the material used as well as what if the aircraft sits on the ground say in a parked position. The heat baking the wing, making it twist on it's own so you have a warped wing, the second thing is stress wear, bend anything up and down enough and it will break, seeing that these wings will bend at unusual angles all the time, my guess is that it will tear apart sooner rather than later. Good old rigid control surfaces stood the test of time for a reason.
Bob Flint
Nature has already figured this out thousands of years ago with the winged creatures being able to adjust theirs in split seconds...
JimFox
Please observe that supersonic flight was NOT the motivation for this development, only a possible future application. Current aviation both military & civilian is its primary aim. So you self-styled 'experts' are zoning in on the wrong thing...
Towerman
That is so but, nature can't build a megaton flying creature based on those principles.