An adaptive compliant wing is a wing which is flexible enough for aspects of its shape to be changed in flight. Flexible wings have a number of benefits. Conventional flight control mechanisms operate using hinges, resulting in disruptions to the airflow, vortices, and in some cases, separation of the airflow. These effects contribute to the drag of the aircraft, resulting in less efficiency and higher fuel costs. Flexible aerofoils can manipulate aerodynamic forces with less disruptions to the flow, resulting in less aerodynamic drag and improved fuel economy.

Shape adaptation

Changing the shape of an aerodynamic surface has a direct effect on its aerodynamic properties. According to the flow condition and to the initial shape of the part, each shape variation (curvature, incidence, twist...) can have a different impact on the resulting forces and moments. This characteristic is actively pursued in adaptive wings which – by nature of their distributed compliance – can attain shape changes in a continuous, smooth, gap-free manner. By altering these geometrical parameters, the forces and moments can be modified, permitting to tailor them to the specific flight condition (e.g. for

drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adj ...

reduction) or to perform maneuvers (e.g. roll). Shape adaptation can be classified according to the motion it enables. Motions that affect the overall planform of the wing "as seen from above" include changes in span (thus changing the length of the wings), in sweep (altering the angle between the wing and the fuselage axis), in chord length (increasing or reducing the length of the wing cross-section) and dihedral (changing the angle between the wings and the horizontal plane of the vehicle). Changes of the airfoil shapes include altering its twist, and changing its camber and thickness distribution.

Ongoing research

FlexSys

An adaptive compliant wing designed by FlexSys Inc. features a variable- camber trailing edge which can be deflected up to ±10°, thus acting like a flap-equipped wing, but without the individual segments and gaps typical in a flap system. The wing itself can be twisted up to 1° per foot of span. The wing's shape can be changed at a rate of 30° per second, which is ideal for gust load alleviation. The development of the adaptive compliant wing is being sponsored by the U.S. Air Force Research Laboratory. Initially, the wing was tested in a wind tunnel, and then a section of wing was flight tested on board the Scaled Composites White Knight research aircraft in a seven-flight, 20-hour program operated from the Mojave Spaceport. Control methods are proposed.

ETH Zurich

Adaptive compliant wings are also investigated at

ETH Zurich (colloquially) , former_name = eidgenössische polytechnische Schule , image = ETHZ.JPG , image_size = , established = , type = Public , budget = CHF 1.896 billion (2021) , rector = Günther Dissertori , president = Joël Mesot , ac ...

in the frame of the Smart airfoil project.

EU Flexop and FLiPASED

The EU-funded program aims to develop to enable higher wing aspect ratio for less induced drag with lighter, more flexible

airliner An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines. Although the definition of an airliner can vary from country to country, an airliner is typically defined as an ...

wings, along developing active

flutter Flutter may refer to: Technology * Aeroelastic flutter, a rapid self-feeding motion, potentially destructive, that is excited by aerodynamic forces in aircraft and bridges * Flutter (American company), a gesture recognition technology company acqu ...

suppression for flexible wings. Partners include Hungary's MTA SZTAKI, Airbus, Austria's FACC, Inasco of Greece, Delft University of Technology, German aerospace center DLR, TUM, the UK's University of Bristol and

RWTH Aachen University RWTH Aachen University (), also known as North Rhine-Westphalia Technical University of Aachen, Rhine-Westphalia Technical University of Aachen, Technical University of Aachen, University of Aachen, or ''Rheinisch-Westfälische Technische Hoch ...

in Germany. On 19 November 2019, a 7 m (23 ft) span jet-powered UAV demonstrator with an aeroelastically tailored wing for passive load alleviation was flown in Oberpfaffenhofen, Germany, previously flown with a carbon-fiber, rigid wing to establish baseline performance. It has a conventional tube-and-wing configuration, unlike the blended wing body of the

Lockheed Martin X-56 The Lockheed Martin X-56 is an American Modularity, modular unmanned aerial vehicle that is being designed to explore High-Altitude Long Endurance (HALE) flight technologies for use in future military unmanned reconnaissance aircraft. Design and d ...

. It follows the Grumman X-29 demonstrator in 1984, with more refined fiber orientations. The flexible wing is 4% lighter than the rigid one. The 54-month, €6.67 million ($7.4 million) project ends in November 2019, followed by the €3.85 million program from September 2019 until December 2022, using all the movable surfaces. The glass fiber flutter wing should to be flown in 2020, with unstable aeroelastic modes under that must be actively suppressed. With optimized

aeroelastic tailoring Aeroelastic tailoring is defined as "the embodiment of directional stiffness into an aircraft structural design to control aeroelastic deformation, static or dynamic, in such a fashion as to affect the aerodynamic and structural performance of that ...

and active flutter suppression, an aspect ratio of 12.4 could reduce fuel-burn by 5%, and 7% are targeted. FLiPASED is also led by MTA SZTAKI and include partners TUM, DLR and French aerospace research agency ONERA.

References