Adaptive compliant wing

Last updated

An adaptive compliant wing is a wing which is flexible enough for aspects of its shape to be changed in flight. [1] [2] 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. [3] Flexible aerofoils can manipulate aerodynamic forces with less disruptions to the flow, resulting in less aerodynamic drag and improved fuel economy.


Shape adaptation

Classification of shape adaptation according to the motion Wing morphing classification.svg
Classification of shape adaptation according to the motion

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).

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


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 50-inch (1.3 m) 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. [4] Control methods are proposed. [5]

ETH Zurich

Adaptive compliant wings are also investigated at ETH Zurich in the frame of the Smart airfoil project. [6] [7]

EU Flexop and FLiPASED

The EU-funded Flexop program aims to develop to enable higher wing aspect ratio for less induced drag with lighter, more flexible airliner wings, along developing active flutter 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 in Germany. [8]

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. 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 FLiPASED program from September 2019 until December 2022, using all the movable surfaces. [8]

The glass fiber flutter wing should to be flown in 2020, with unstable aeroelastic modes under 55 m/s (107 kn) 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. [8]

See also

Related Research Articles

Wing Surface used for flight, for example by insects, birds, bats and airplanes

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 expressed as its lift-to-drag ratio. The lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift.

Aeroelasticity Interactions among inertial, elastic, and aerodynamic forces

Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classified into two fields: static aeroelasticity dealing with the static or steady state response of an elastic body to a fluid flow; and dynamic aeroelasticity dealing with the body's dynamic response.


Elevons or tailerons are aircraft control surfaces that combine the functions of the elevator and the aileron, hence the name. They are frequently used on tailless aircraft such as flying wings. An elevon that is not part of the main wing, but instead is a separate tail surface, is a stabilator.

Grumman X-29 1984 experimental aircraft family by Grumman

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 States Air Force. The aerodynamic instability of the X-29's airframe required the use of computerized fly-by-wire control. Composite materials were used to control the aeroelastic divergent twisting experienced by forward-swept wings, and to reduce weight. The aircraft first flew in 1984, and two X-29s were flight tested through 1991.

Aircraft flight control system How aircraft are controlled

A conventional fixed-wing aircraft flight control system consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. Aircraft engine controls are also considered as flight controls as they change speed.

Elevator (aeronautics) Aircraft flight control surface

Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's pitch, and therefore the angle of attack and the lift of the wing. The elevators are usually hinged to the tailplane or horizontal stabilizer. They may be the only pitch control surface present, and are sometimes located at the front of the aircraft or integrated into a rear "all-moving tailplane", also called a slab elevator or stabilator.

Wing warping

Wing warping was an early system for lateral (roll) control of a fixed-wing aircraft. The technique, used and patented by the Wright brothers, consisted of a system of pulleys and cables to twist the trailing edges of the wings in opposite directions. In many respects, this approach is similar to that used to trim the performance of a paper airplane by curling the paper at the back of its wings.

Flaperon Type of aircraft control surface that combines the functions of both flaps and ailerons

A flaperon on an aircraft's wing is a type of control surface that combines the functions of both flaps and ailerons. Some smaller kitplanes have flaperons for reasons of simplicity of manufacture, while some large commercial aircraft such as the Boeing 747, 767, 777, and 787 may have a flaperon between the flaps and aileron. The 787 has a configure known as SpoileFlaperon that combines the action of spoilers, flaps and ailerons into one control surface.

In aeronautics, spoilerons are spoilers that can be used asymmetrically as flight control surfaces to provide roll control.

Variable camber is a feature of some of aircraft wings that changes the camber of the main aerofoil during flight.

Boeing X-53 Active Aeroelastic Wing Experimental aircraft

The X-53 Active Aeroelastic Wing (AAW) development program is a completed American research project that was undertaken jointly by the Air Force Research Laboratory (AFRL), Boeing Phantom Works and NASA's Dryden Flight Research Center, where the technology was flight tested on a modified McDonnell Douglas F/A-18 Hornet. Active Aeroelastic Wing Technology is a technology that integrates wing aerodynamics, controls, and structure to harness and control wing aeroelastic twist at high speeds and dynamic pressures. By using multiple leading and trailing edge controls like "aerodynamic tabs", subtle amounts of aeroelastic twist can be controlled to provide large amounts of wing control power, while minimizing maneuver air loads at high wing strain conditions or aerodynamic drag at low wing strain conditions. This program was the first full-scale proof of AAW technology.

Parker variable wing

The Parker variable wing is a wing configuration in biplane or triplane aircraft designed by H.F. Parker in 1920. His design allows a supplement in lift while landing or taking-off. The system is depicted in the figure. The figure shows the biplane configuration. The lower airfoil is rigid. The upper airfoil is flexible. At high angle of attack the flow over the lower airfoil will cause the airflow to bend up and create an upward force at the lower surface of the upper airfoil. This upward force will cause the flexible section to be pushed upward. The flexible wing section is held at points A and B. The trailing edge is rigid and can rotate about point B. Due to this effect the camber of the airfoil is increased, and hence the lift it creates is increased.

Wingsail Variable-camber aerodynamic structure

A wingsail, twin-skin sail or double skin sail is a variable-camber aerodynamic structure that is fitted to a marine vessel in place of conventional sails. Wingsails are analogous to airplane wings, except that they are designed to provide lift on either side to accommodate being on either tack. Whereas wings adjust camber with flaps, wingsails adjust camber with a flexible or jointed structure. Wingsails are typically mounted on an unstayed spar—often made of carbon fiber for lightness and strength. The geometry of wingsails provides more lift, and a better lift-to-drag ratio, than traditional sails. Wingsails are more complex and expensive than conventional sails.

Wing configuration Describes the general shape and layout of an aircraft wing

The wing configuration of a fixed-wing aircraft is its arrangement of lifting and related surfaces.

Leading-edge slat Device increasing the lift of the wing at low speed (take-off and landing)

Slats are aerodynamic surfaces on wing leading edge of the of fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower speeds, or take off and land in shorter distances. They are used during takeoff and landing or while performing low speed maneuvers which may take the aircraft close to a stall, they are retracted in normal flight to minimize drag.

Flexible wing Flexible airfoil

In aeronautics, a flexible wing is an airfoil or aircraft wing which can deform in flight.

Distributed propulsion Engines placed along the wingspan of a plane

In aeronautics, Distributed propulsion is an arrangement in which the propulsive and related air flows are distributed over the aerodynamic surfaces of an aircraft. The purpose is to improve the craft's aerodynamic, propulsive and/or structural efficiency over an equivalent conventional design.

Lockheed Martin X-56 Type of aircraft

The Lockheed Martin X-56 is an American 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.

Adaptive compliant trailing edge

Adaptive Compliant Trailing Edge (ACTE) is a research project on shape-changing flaps for aircraft wings, intended to reduce the aircraft's fuel costs and reduce noise during take-off and landing. It is a join effort by NASA and the U.S. Air Force Research Laboratory and first airborne tests have been conducted in late 2014.

General Dynamics–Boeing AFTI/F-111A Aardvark American research aircraft

The General Dynamics–Boeing AFTI/F-111A Aardvark was a research aircraft modified from a General Dynamics F-111 Aardvark to test a Boeing-built supercritical mission adaptive wing (MAW). This MAW, in contrast to standard control surfaces, could smoothly change the shape of its airfoil in flight.


  1. "FlexSys Inc.: Aerospace". Archived from the original on 16 June 2011. Retrieved 26 April 2011.
  2. Kota, Sridhar; Osborn, Russell; Ervin, Gregory; Maric, Dragan; Flick, Peter; Paul, Donald. "Mission Adaptive Compliant Wing – Design, Fabrication and Flight Test" (PDF). Ann Arbor, MI; Dayton, OH, U.S.A.: FlexSys Inc., Air Force Research Laboratory. Archived from the original (PDF) on 22 March 2012. Retrieved 26 April 2011.
  3. "FlexFoil". FlexSys. Retrieved 2022-03-19.
  4. Scott, William B. (27 November 2006), "Morphing Wings", Aviation Week & Space Technology, archived from the original on 26 April 2011, retrieved 26 April 2011
  5. US 4899284,Lewis, George E.; Thomasson, Robert E.& Nelson, David W.,"Wing lift/drag optimizing system",published 6 February 1990
  6. Smart airfoil project "Archived copy". Archived from the original on 2013-06-23. Retrieved 2013-03-15.{{cite web}}: CS1 maint: archived copy as title (link)
  7. "ETH compliant wing". February 6, 2014.
  8. 1 2 3 Graham Warwick (Nov 25, 2019). "The Week In Technology, Nov. 25-29, 2019". Aviation Week & Space Technology.