Flexible wing

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The NASA Paresev was one of the first powered Rogallo-winged aircraft to fly Paresev 1-B in Tow Flight - GPN-2000-000212.jpg
The NASA Paresev was one of the first powered Rogallo-winged aircraft to fly

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

Contents

Early pioneer aeroplanes such as the Wright flyer used the flexible characteristics of lightweight construction to control flight through wing warping. Others made collapsible wings for folding away, such as the flying car designs by Gustave Whitehead.

Since the 1960s flexible wings have dominated hang glider and ultralight aircraft designs, with such types as the delta-shaped Rogallo wing and the fully collapsible paraglider.

More recently, the advent of high-strength flexible materials and other advanced technologies has renewed interest in the use of flexing for control purposes.

Pioneer aircraft

Control

The first effective control system on a powered aircraft allowed one to fly for the first time. The Wright Flyer used wing warping for lateral or roll control, by twisting one wing tip to increase its angle to the air while twisting the other to reduce its angle. The Wright brothers patented system was widely copied.

However, as engine powers and air speeds rose, so too did the forces needed to operate the pilot controls and by 1914 warping was all but abandoned.

Collapsibility

Predating successful controlled and powered flight, collapsible wings had been developed in an attempt to solve the problems of ground storage and transport. A system of radial ribs like a giant folding fan, sometimes described as bat-like, was used by some pioneers, notably Gustave Whitehead in his attempts to build a flying car.

Aeroelasticity

Aeroelasticity is the natural tendency of any wing to flex under aerodynamic and inertial loads while in flight. Most designs seek to minimise the effects by making the wing structure as stiff as possible. However some have sought to use the effect to advantage.

A relatively early example is provided by the flying-wing gliders of the Horten brothers during the 1930s, whose wing tips flexed upwards in flight to act as stabilising surfaces.

The advent of the jet engine and transonic flight speeds brought a sharp increase in aerodynamic forces, made worse by the innate structural inefficiency of the swept wing, with the combination leading to dangerous characteristics in extreme flight conditions. The aeroisoclinic wing, developed by Geoffrey T. R. Hill in the 1950s and flown on the Short SB.4 Sherpa, was an attempt control the flexing in such a way as to maintain handling characteristics in all flight regimes. Similar aeroelastic tailoring was later applied to experimental forward-swept wings, where it is a necessity for any safe design.

Lightweight aircraft

In 1948 the husband-and-wife team of Francis and Gertrude Rogallo developed a flexible kite which could be collapsed for storage. A key part of their design is the mixed use of tension lines and aerodynamic forces to stabilise and control the wing. The wing remains a constant shape in flight under wind pressure, and the lines are used to control its position.

Over the following years they developed the design and then Francis, working at NASA's Langley research centre, further developed the concept into proposals for manned aircraft such as a space vehicle re-entry system.

Following a series of talks in 1959 and 1960 his ideas spread rapidly and two designs in particular, the Rogallo delta and the paraglider, were soon being used for kites, hang gliders and ultralight aircraft. Types with an engine backpack for the pilot are known as powered gliders. Although tested for spacecraft descent, no Rogallo types have been used by NASA.

Rogallo wing

Francis Rogallo evolved his trademark double-delta "parawing" during the 1950s. Unlike the earlier kites it uses several struts to maintain its planform, while still relying on air pressure from beneath to develop its conical upper profile.

Parafoil

Like the original Rogallo kites, the parafoil is fully collapsible. But unlike them it is double-skinned. Comprising an open-fronted aerofoil wing, it is held in shape by the pressure of air from in front. Many flexible ribs are needed to hold its aerofoil shape.

Advanced concepts

In the 21st. century, new materials possessing both flexibility and strength are being experimented with, in order to merge control surfaces into the main wing surface. [1] [2] For example, a flexible wing flap has been test flown on a Gulfstream III. [3] Flexible aerofoils and control surfaces operate by regular deformation of the wing material. Current challenges are centred around deforming the material to manipulate aerodynamic loads without exceeding the materials elastic limit. [4]

The key benefits of flexible aerofoils are the reductions in aerodynamic drag. [5] Current flight control mechanisms operate using hinges, which significantly disrupt the airflow and even generate vortices between the control surface and wing boundary. A flexible aerofoil can smoothly alter its shape to deflect the airflow, allowing the aerodynamic forces to be controlled without creating 'gaps' between hinges. [6]

For smaller craft, the increasing sophistication of smart control systems is being combined with flexible technologies to create articulated wings which mimic the natural flexing of birds' wings in flight. It is now even practicable to use a bird-like flapping action to provide thrust as an ornithopter. The UTIAS Snowbird ornithopter of 2010 was human-powered.

See also

Related Research Articles

<span class="mw-page-title-main">Aircraft</span> Vehicle or machine that is able to fly by gaining support from the air

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<span class="mw-page-title-main">Hang gliding</span> Unpowered glider air sport

Hang gliding is an air sport or recreational activity in which a pilot flies a light, non-motorised foot-launched heavier-than-air aircraft called a hang glider. Most modern hang gliders are made of an aluminium alloy or composite frame covered with synthetic sailcloth to form a wing. Typically the pilot is in a harness suspended from the airframe, and controls the aircraft by shifting body weight in opposition to a control frame.

<span class="mw-page-title-main">Wing</span> 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.

<span class="mw-page-title-main">Fixed-wing aircraft</span> Heavier-than-air aircraft with fixed wings generating aerodynamic lift

A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinct from rotary-wing aircraft, and ornithopters. The wings of a fixed-wing aircraft are not necessarily rigid; kites, hang gliders, variable-sweep wing aircraft and airplanes that use wing morphing are all examples of fixed-wing aircraft.

<span class="mw-page-title-main">Rogallo wing</span>

The Rogallo wing is a flexible type of wing. In 1948, Francis Rogallo, a NASA engineer, and his wife Gertrude Rogallo, invented a self-inflating flexible wing they called the Parawing, also known after them as the "Rogallo Wing" and flexible wing. NASA considered Rogallo's flexible wing as an alternative recovery system for the Mercury and Gemini space capsules, and for possible use in other spacecraft landings, but the idea was dropped from Gemini in 1964 in favor of conventional parachutes.

<span class="mw-page-title-main">Francis Rogallo</span> American aeronautical engineer

Francis Melvin Rogallo was an American aeronautical engineer inventor born in Sanger, California, U.S. Together with his wife, he is credited with the invention of the Rogallo wing, or "flexible wing", a precursor to the modern hang glider and paraglider. His patents were ranged over mechanical utility patents and ornamental design patents for wing controls, airfoils, target kite, flexible wing, and advanced configurations for flexible wing vehicles.

<span class="mw-page-title-main">Ornithopter</span> Aircraft which use flapping movement of the wings to generate lift

An ornithopter is an aircraft that flies by flapping its wings. Designers sought to imitate the flapping-wing flight of birds, bats, and insects. Though machines may differ in form, they are usually built on the same scale as flying animals. Larger, crewed ornithopters have also been built and some have been successful. Crewed ornithopters are generally either powered by engines or by the pilot.

Kite types, kite mooring, and kite applications result in a wide variety of kite control systems. Contemporary manufacturers, kite athletes, kite pilots, scientists, and engineers are expanding the possibilities.

<span class="mw-page-title-main">Aircraft flight control system</span> How aircraft are controlled

A conventional fixed-wing aircraft flight control system (AFCS) 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.

<span class="mw-page-title-main">Early flying machines</span> Aircraft developed before the modern aeroplane

Early flying machines include all forms of aircraft studied or constructed before the development of the modern aeroplane by 1910. The story of modern flight begins more than a century before the first successful manned aeroplane, and the earliest aircraft thousands of years before.

<span class="mw-page-title-main">Wing warping</span> Early system for lateral control of a fixed-wing aircraft

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.

<span class="mw-page-title-main">Ultralight trike</span>

An ultralight trike is a type of powered hang glider where flight control is by weight-shift. These aircraft have a fabric flex-wing from which is suspended a tricycle fuselage pod driven by a pusher propeller. The pod accommodates either a solo pilot, or a pilot and a single passenger. Trikes grant affordable, accessible, and exciting flying, and have been popular since the 1980s.

<span class="mw-page-title-main">History of hang gliding</span>

Hang gliding is an air sport employing a foot-launchable aircraft. Typically, a modern hang glider is constructed of an aluminium alloy or composite-framed fabric wing. The pilot is ensconced in a harness suspended from the airframe, and exercises control by shifting body weight in opposition to a control frame.

<span class="mw-page-title-main">NASA Paresev</span> Experimental NASA glider using the Rogallo airfoil

The NASA Paresev was an experimental NASA glider aircraft based upon the kite-parachute studies by NASA engineer Francis Rogallo.

<span class="mw-page-title-main">Boeing X-53 Active Aeroelastic Wing</span> 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.

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.

<span class="mw-page-title-main">Glider (aircraft)</span> Aircraft designed for operation without an engine

A glider is a fixed-wing aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend on an engine. Most gliders do not have an engine, although motor-gliders have small engines for extending their flight when necessary by sustaining the altitude with some being powerful enough to take off by self-launch.

<span class="mw-page-title-main">Tailless aircraft</span> Aircraft whose only horizontal aerodynamic surface is its main wing

In aeronautics, a tailless aircraft is an aircraft with no other horizontal aerodynamic surface besides its main wing. It may still have a fuselage, vertical tail fin, and/or vertical rudder.

<span class="mw-page-title-main">Kite types</span>

Kites are tethered flying objects which fly by using aerodynamic lift, requiring wind for generation of airflow over the lifting surfaces.

<span class="mw-page-title-main">Wing configuration</span> 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.

References

  1. NASA Boeing study flexible wing control: Aviation Week blog
  2. Flying on flexible wings: Scientific American
  3. first flexible airplane wing takes flight Scientific American blog
  4. "Aero". FlexSys. Retrieved 2022-03-19.
  5. "Aero". FlexSys. Retrieved 2022-03-19.
  6. Tamai, Masatoshi (2008). "An Experimental Study of Flexible Membrane Airfoils at Low Reynolds Numbers" (PDF). Iowa State University.