An adaptive compliant wing is a

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...

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 reduction) or to perform maneuvers (e.g.

roll Roll or Rolls may refer to: Movement about the longitudinal axis * Roll angle (or roll rotation), one of the 3 angular degrees of freedom of any stiff body (for example a vehicle), describing motion about the longitudinal axis ** Roll (aviation) ...

). 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 Sweep or swept may refer to: Cleaning * Sweep, the action of using a brush to clean * Chimney sweep, a worker who clears ash and soot from chimneys * Street sweeper, a person's occupation, or a machine that cleans streets * Swept quartz, a cleani ...

(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 Camber may refer to a variety of curvatures and angles: * Camber angle, the angle made by the wheels of a vehicle * Camber beam, an upward curvature of a joist to compensate for load deflection due in buildings * Camber thrust in bike technology * ...

and thickness distribution.

Ongoing research

FlexSys

An adaptive compliant wing designed by FlexSys Inc. features a variable-

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 199 ...

which can be deflected up to ±10°, thus acting like a

flap Flap may refer to: Arts, entertainment, and media * ''Flap'' (film), a 1970 American film * Flap, a boss character in the arcade game ''Gaiapolis'' * Flap, a minor character in the film '' Little Nemo: Adventures in Slumberland'' Biology and he ...

-equipped wing, but without the individual segments and gaps typical in a

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 The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of aerospace warfighting technologies, pl ...

. Initially, the wing was tested in a

wind tunnel Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

, and then a section of wing was flight tested on board the

Scaled Composites White Knight The Scaled Composites Model 318 White Knight (now also called ''White Knight One'') is a jet-powered carrier aircraft that was used to launch its companion SpaceShipOne, an experimental spaceplane. The White Knight and SpaceShipOne were designed b ...

research aircraft in a seven-flight, 20-hour program operated from the

Mojave Spaceport The Mojave Air and Space Port at Rutan Field is in Mojave, California, United States, at an elevation of . It is the first facility to be licensed in the United States for horizontal launches of reusable spacecraft, being certified as a spa ...

. Control methods are proposed.

ETH Zurich

Adaptive compliant wings are also investigated at ETH Zurich 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 In aeronautics, the aspect ratio of a wing is the ratio of its span to its mean chord. It is equal to the square of the wingspan divided by the wing area. Thus, a long, narrow wing has a high aspect ratio, whereas a short, wide wing has a low a ...

for less

induced drag In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or ...

with lighter, more flexible airliner wings, along developing active flutter suppression for flexible wings. Partners include Hungary's

MTA SZTAKI The Institute for Computer Science and Control (in short SZTAKI, hu, Számítástechnikai és Automatizálási Kutatóintézet) is a Hungarian research institute in Budapest, founded in 1964. Scope Its primary tasks include basic and applicati ...

Airbus Airbus SE (; ; ; ) is a European multinational aerospace corporation. Airbus designs, manufactures and sells civil and military aerospace products worldwide and manufactures aircraft throughout the world. The company has three divisions: ' ...

, Austria's FACC, Inasco of Greece,

Delft University of Technology Delft University of Technology ( nl, Technische Universiteit Delft), also known as TU Delft, is the oldest and largest Dutch public technical university, located in Delft, Netherlands. As of 2022 it is ranked by QS World University Rankings among ...

German aerospace center The German Aerospace Center (german: Deutsches Zentrum für Luft- und Raumfahrt e.V., abbreviated DLR, literally ''German Center for Air- and Space-flight'') is the national center for aerospace, energy and transportation research of Germany ...

DLR, TUM, the UK's

University of Bristol , mottoeng = earningpromotes one's innate power (from Horace, ''Ode 4.4'') , established = 1595 – Merchant Venturers School1876 – University College, Bristol1909 – received royal charter , type ...

and RWTH Aachen University in Germany. On 19 November 2019, a 7 m (23 ft) span jet-powered

UAV An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controlle ...

demonstrator with an aeroelastically tailored wing for passive load alleviation was flown in

Oberpfaffenhofen Oberpfaffenhofen is a village that is part of the municipality of Weßling in the district of Starnberg, Bavaria, Germany. It is located about from the city center of Munich. Village The village is home to the Oberpfaffenhofen Airport and a m ...

, Germany, previously flown with a

carbon-fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

, rigid wing to establish baseline performance. It has a conventional tube-and-wing configuration, unlike the

blended wing body A blended wing body (BWB), also known as blended body or hybrid wing body (HWB), is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft. The aircraft has distinct wing and body structures, which ar ...

of the Lockheed Martin X-56. It follows the

Grumman X-29 The Grumman X-29 was an American experimental aircraft that tested a forward-swept wing, canard control surfaces, and other novel aircraft technologies. The X-29 was developed by Grumman, and the two built were flown by NASA and the United St ...

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 Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

flutter wing should to be flown in 2020, with unstable aeroelastic modes under that must be actively suppressed. With optimized aeroelastic tailoring 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 The Office National d'Etudes et de Recherches Aérospatiales (ONERA) is the French national aerospace research centre. It is a public establishment with industrial and commercial operations, and carries out application-oriented research to supp ...

References