Adaptive Wings Could Improve Aircraft Fuel Consumption 5% to 15%
23 November 2006
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| The leading and trailing edge of the wing contain embedded compliant systems that trigger the actuators when flight conditions change. Click to enlarge. |
FlexSys, with funding from the US Air Force, is developing shape-morphing adaptive aircraft wings that alter their shape in response to changing flight conditions.
Such technology could result in fuel savings in the range of 5% to 15% for long-range military and commercial fixed-wing aircraft, according to the company.
The FlexSys Mission Adaptive Compliant Wing (MACW) is a smooth, hinge-free wing whose trailing and/or leading edges morph on demand to adapt to different flight conditions. The wing was flight-tested at Scaled Composites in Mojave, California at the end of October 2006.
FlexSys is also developing wings with compliant leading or trailing edges. The Mission Adaptive Compliant Wing combines both.
The compliant trailing edge flap produces a smooth shape change as it deflects from -10° to +10°, can twist along the span to tailor wing loading, and can be actuated at rates fast enough to be used as a control surface. Full-scale numerical studies have shown that the technology is weight and power competitive with conventional mechanical flaps, without the increase in aerodynamic drag caused by conventional flaps.
Earlier wind tunnel testing on the leading edge compliant flap demonstrated a 25% increase in the lift coefficient and a 51% increase in lift-to-drag ratio. These performance improvements were primarily observed at high angles of attack (up to 15 degrees) as the leading edge camber was shifted from zero to six degrees.
(A hat-tip to Allen!)
Resources:
New York Times graphic
A few months ago we had a thread about managing the thickness of the boundary layer of an airfoil by applying a vacuum inside the hollow structure via a special pattern of perforations.
This is an alternate approach to adapting effective airfoil cross-section. Birds, of course, have been twisting their wings as needed for ages. It's a bit harder to do in metal, though.
Helicopters should benefit in terms of the range of their cyclic control, which vectors the available thrust. The actuation mechanics should be interesting, though. Perhaps they'll have to resort to piezo electricity or memory metals to obtain the necessary deformations.
For fixed-wing aircraft, actuation can be mechanical. Bending the tail end of the wings downward would help during take-off and initial ascent, as well as landing approach. It probably won't eliminate brake flaps and thrust reversers, though.
Posted by: Rafael Seidl | 23 November 2006 at 12:23 PM
This is not an alternate approach to boundary-layer management, it is complementary. Smooth airfoils benefit from BLC techniques and all this scheme does is to preserve airfoil smoothness while changing its shape.
That said, the Wright brothers would be smiling about now.
Posted by: Engineer-Poet | 23 November 2006 at 02:07 PM
Engineer-Poet,
Perhaps the Wrights were on to something, but materials and control equipment of the age could not follow them. Now, can they work leading edge blades onto wings, to take advantage of leading edge vortices?
_On a side note, one of the descendants of the Wright brothers was a contributer on an experimental IEC fusion reactor with Dr. Bussard. It was funded by the Navy, and results have recently been declassified. Currently, it needs ~10 years, and $200+ million to complete R&D, and to move onto commercialization. They need engineers and physicists adept with 1950's technology and equipment; more vacuum tubes, less solid state.
Posted by: allen_Z | 23 November 2006 at 05:58 PM
Very neat -- like the old Wright brothers idea but even more so. This is not just wing warping to create an aileron-like effect, but the ability to change the entire camber of the airfoil in flight.
One of the fundamental choices (i.e. tradeoffs) that goes into designing an airplane is choosing a airfoil profile that has the right mix of properties (i.e. lift to drag ratio) across the slow-speed performance regime (takeoff and landing), high speed performance regmine (cruise), has proper wing loading (wing surface area to total weight ratio), etc. In the 1930s, NACA published a large catalogue of airfoil designs and their associated wind-tunnel test results. Designers could choose the shape with the properties that best suited their goals. That overall design strategy still holds today.
With this, not only can you dispose of flaps (which are a much cruder way of changing airfoil shape for the purposes of easing takeoff and landing), you could adapt the airfoil to differences in payload, differences in weather conditions, whatever. The airplane geek in me is happy.
Posted by: NBK-Boston | 23 November 2006 at 09:06 PM
I assume that the adaptive wings would have a finite (possibly large) number of pre-programmed configurations for specific functions and conditions rather than attempting to continuously monitor and react to airflow over the wing. Anyone heard differently?
Posted by: Neil | 23 November 2006 at 09:15 PM
Neil: Adaptive wing use is an area where no one is yet an expert. But my experience optimizing fuel consumption on longe range cargo jets leads me to believe that your assumption is right.
Air conditions change slowly once a cruise altitude is reached. The other factor is fuel burnoff which continuously reduces weight. So the plane has a slight tendency to climb as the flight progresses. This is prevented (see next).
Air traffic control prefers that planes stay at a fixed altitude. So climb is delayed until the plane becomes light enough - perhaps an hour. Then a 'step' climb is made to the new fixed altitude.
Of course what I mentioned are only constraints today. In the long term constraints get overcome.
Posted by: K | 24 November 2006 at 06:05 AM
This is really interesting timing - I just got an assignment in my advanced aerodynamics course about adaptive wings. It's pretty cool technology, but apparently is about 5-10 years off in UAVs, longer in manned aircraft. FlexSys is leading the pack in compliant structures, though, and Dr. Kota has been working on this for an awfully long time.
Hopefully this is technology that we see much sooner than the estimates; think about what it would do to already-efficient designs like the 787 or some of the turboprops in use today.
Posted by: Eric | 25 November 2006 at 10:34 AM