A flap is a

high-lift device In aircraft design and aerospace engineering, a high-lift device is a component or mechanism on an aircraft's wing that increases the amount of lift (force), lift produced by the wing. The device may be a fixed component, or a movable mechanism w ...

used to reduce the stalling speed of an

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...

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 expres ...

at a given weight. Flaps are usually mounted on the wing trailing edges of a

fixed-wing aircraft 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 distinc ...

. Flaps are used to reduce the take-off distance and the landing distance. Flaps also cause an increase in drag so they are retracted when not needed. The flaps installed on most aircraft are partial-span flaps; spanwise from near the wing root to the inboard end of the

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

s. When partial-span flaps are extended they alter the spanwise

lift distribution A fluid flowing around an object exerts a force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force parallel to the flow directi ...

on the wing by causing the inboard half of the wing to supply an increased proportion of the lift, and the outboard half to supply a reduced proportion of the lift. Reducing the proportion of the lift supplied by the outboard half of the wing is accompanied by a reduction in the

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

on the outboard half. This is beneficial because it increases the margin above the stall of the outboard half, maintaining aileron effectiveness and reducing the likelihood of asymmetric stall, and

spinning Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

. Extending the wing flaps increases the

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 * ...

or curvature of the wing, raising the maximum

lift coefficient In fluid dynamics, the lift coefficient () is a dimensionless quantity that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. A lifting body is a foil or a com ...

or the upper limit to the lift a wing can generate. This allows the aircraft to generate the required lift at a lower speed, reducing the minimum speed (known as stall speed) at which the aircraft will safely maintain flight. The increase in camber also increases the wing drag, which can be beneficial during approach and landing, because it allows the aircraft to descend at a steeper angle. For most aircraft configurations, a useful side effect of flap deployment is a decrease in aircraft pitch angle which lowers the nose thereby improving the pilot's view of the runway over the nose of the aircraft during landing. Another side effect however, depending on the type of flap, location on the wing and deployment speed during their extension, is that the flaps will cause the indicated (or relative to the unchanged airfoil) angle of attack to lower within a short time due to an increase in nose-down pitching moment which is characteristic to all trailing-edge flaps, as well as leading-edge flaps, then followed by a nose rise (

pitch-up In aerodynamics, pitch-up is an uncommanded nose-upwards rotation of an aircraft. It is an undesirable characteristic that has been observed mostly in experimental swept-wing aircraft at high subsonic Mach numbers or high angle of attack. History ...

) due to the increase in lift, thus obscuring the pilot's view of the runway if no action is taken over the pitch inputs. There are many different designs of flaps, with the specific choice depending on the size, speed and complexity of the aircraft on which they are to be used, as well as the era in which the aircraft was designed. Plain flaps,

slotted flap A flap is a high-lift device used to reduce the stalling speed of an aircraft wing at a given weight. Flaps are usually mounted on the wing trailing edges of a fixed-wing aircraft. Flaps are used to reduce the take-off distance and the landin ...

s, and

Fowler flap A flap is a high-lift device used to reduce the stalling speed of an aircraft wing at a given weight. Flaps are usually mounted on the wing trailing edges of a fixed-wing aircraft. Flaps are used to reduce the take-off distance and the landi ...

s are the most common.

Krueger flap Krueger flaps, or Krüger flaps, are lift enhancement devices that may be fitted to the leading edge of an aircraft wing. Unlike slats or droop flaps, the main wing upper surface and its nose is not changed. Instead, a portion of the lower wing i ...

s are positioned on the leading edge of the wings and are used on many jet airliners. The Fowler, Fairey-Youngman and Gouge types of flap increase the wing area in addition to changing the camber. The larger lifting surface reduces

wing loading In aerodynamics, wing loading is the total mass of an aircraft or flying animal divided by the area of its wing. The stalling speed of an aircraft in straight, level flight is partly determined by its wing loading. An aircraft or animal with a ...

, hence further reducing the stalling speed. Some flaps are fitted elsewhere. Leading-edge flaps form the wing leading edge and when deployed they rotate down to increase the wing camber. The

de Havilland DH.88 Comet The de Havilland DH.88 Comet is a British two-seat, twin-engined aircraft built by the de Havilland Aircraft Company. It was developed specifically to participate in the 1934 England-Australia MacRobertson Air Race from the United Kingdom to A ...

racer had flaps running beneath the fuselage and forward of the wing trailing edge. Many of the

Waco Custom Cabin series The Waco Custom Cabins were a series of up-market single-engined four-to-five-seat cabin sesquiplanes of the late 1930s produced by the Waco Aircraft Company of the United States. "Custom Cabin" was Waco's own description of the aircraft which des ...

biplanes have the flaps at mid- chord on the underside of the top wing.

Principles of operation

The general airplane lift equation demonstrates these relationships:Perkins, Courtland; Hage, Robert (1949). ''Airplane performance, stability and control'', Chapter 2, John Wiley and Sons. . :

L = \tfrac12 \rho V^2 S C_L

where: * ''L'' is the amount of ''Lift'' produced, * ''

\rho

'' is the air density, * ''V'' is the

true airspeed The true airspeed (TAS; also KTAS, for ''knots true airspeed'') of an aircraft is the speed of the aircraft relative to the air mass through which it is flying. The true airspeed is important information for accurate navigation of an aircraft. Tr ...

of the airplane or the ''Velocity'' of the airplane, relative to the air * S is the area of the wing *

C_L

is the ''

'', which is determined by the shape of the airfoil used and the angle at which the wing meets the air (or angle of attack). Here, it can be seen that increasing the area (S) and lift coefficient (

C_L

) allow a similar amount of lift to be generated at a lower airspeed (V). easyjet a319 wing g-ezav arp

Extending the flaps also increases the

drag coefficient In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equ ...

of the aircraft. Therefore, for any given weight and airspeed, flaps increase the drag force. Flaps increase the

of an aircraft due to higher

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 ...

caused by the distorted spanwise lift distribution on the wing with flaps extended. Some flaps increase the wing area and, for any given speed, this also increases the

parasitic drag Parasitic drag, also known as profile drag, is a type of aerodynamic drag that acts on any object when the object is moving through a fluid. Parasitic drag is a combination of form drag and skin friction drag. It affects all objects regardless of ...

component of total drag. Thus, flaps are extensively in use for short takeoffs and landings (

STOL A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh conditio ...

Flaps during takeoff

Depending on the aircraft type, flaps may be partially extended for

takeoff Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff. For aircraft that take off horizontally, this usually involves starting with a t ...

. When used during takeoff, flaps trade runway distance for climb rate: using flaps reduces ground roll but also reduces the climb rate. The amount of flap used on takeoff is specific to each type of aircraft, and the manufacturer will suggest limits and may indicate the reduction in climb rate to be expected. The ''

Cessna 172S The Cessna 172 Skyhawk is an American four-seat, single-engine, high wing, fixed-wing aircraft made by the Cessna Aircraft Company.Cessna Aircraft Company. ''Cessna Model 172S Nav III''. Revision 3-12, 2006, pp. 4–19 to 4–47.

Flaps during landing

Flaps may be fully extended for

landing Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing", "touchdown" or ...

to give the aircraft a lower stall speed so the approach to landing can be flown more slowly, which also allows the aircraft to land in a shorter distance. The higher lift and drag associated with fully extended flaps allows a steeper and slower approach to the landing site, but imposes handling difficulties in aircraft with very low

(i.e. having little weight and a large wing area). Winds across the line of flight, known as ''crosswinds'', cause the windward side of the aircraft to generate more lift and drag, causing the aircraft to roll, yaw and pitch off its intended flight path, and as a result many light aircraft land with reduced flap settings in crosswinds. Furthermore, once the aircraft is on the ground, the flaps may decrease the effectiveness of the brakes since the wing is still generating lift and preventing the entire weight of the aircraft from resting on the tires, thus increasing stopping distance, particularly in wet or icy conditions. Usually, the pilot will raise the flaps as soon as possible to prevent this from occurring.

Maneuvering flaps

Some gliders not only use flaps when landing, but also in flight to optimize the camber of the wing for the chosen speed. While

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

ling, flaps may be partially extended to reduce the stall speed so that the glider can be flown more slowly and thereby reduce the rate of sink, which lets the glider use the rising air of the thermal more efficiently, and to turn in a smaller circle to make best use of the core of the

. At higher speeds a negative flap setting is used to reduce the nose-down

pitching moment In aerodynamics, the pitching moment on an airfoil is the moment (or torque) produced by the aerodynamic force on the airfoil if that aerodynamic force is considered to be applied, not at the center of pressure, but at the aerodynamic center o ...

. This reduces the balancing load required on the

horizontal stabilizer A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplan ...

, which in turn reduces the trim drag associated with keeping the glider in longitudinal trim. Negative flap may also be used during the initial stage of an aerotow launch and at the end of the landing run in order to maintain better control by the

s. Like gliders, some

fighters Fighter(s) or The Fighter(s) may refer to: Combat and warfare * Combatant, an individual legally entitled to engage in hostilities during an international armed conflict * Fighter aircraft, a warplane designed to destroy or damage enemy warplan ...

such as the

Nakajima Ki-43 The Nakajima Ki-43 ''Hayabusa'' (, "Peregrine falcon", "Army Type 1 Fighter" ) is a single-engine land-based tactical fighter used by the Imperial Japanese Army Air Service in World War II. The Allied reporting name was "Oscar", but it was o ...

also use special flaps to improve maneuverability during air combat, allowing the fighter to create more lift at a given speed, allowing for much tighter turns. The flaps used for this must be designed specifically to handle the greater stresses and most flaps have a maximum speed at which they can be deployed.

Control line Control line (also called U-Control) is a simple and light way of controlling a flying model aircraft. The aircraft is connected to the operator by a pair of lines, attached to a handle, that work the elevator An elevator or lift is ...

model aircraft built for precision aerobatics competition usually have a type of maneuvering flap system that moves them in an opposing direction to the elevators, to assist in tightening the radius of a maneuver.

Flap tracks

Manufactured most often from PH steels and titanium, flap tracks control the flaps located on the trailing edge of an aircraft’s wings. Extending flaps often run on guide tracks. Where these run outside the wing structure they may be faired in to streamline them and protect them from damage. Some flap track fairings are designed to act as

anti-shock bodies Anti-shock body is the name given by Richard T. Whitcomb to a pod positioned on the upper surface of a wing. Its purpose is to reduce wave drag while travelling at transonic speeds (Mach number, Mach 0.8–1.0), which includes the typical cruising ...

, which reduce drag caused by local sonic shock waves where the airflow becomes

transonic Transonic (or transsonic) flow is air flowing around an object at a speed that generates regions of both subsonic and supersonic airflow around that object. The exact range of speeds depends on the object's critical Mach number, but transonic ...

at high speeds.

Thrust gates

Thrust gates, or gaps, in the trailing edge flaps may be required to minimise interference between the engine flow and deployed flaps. In the absence of an inboard aileron, which provides a gap in many flap installations, a modified flap section may be needed. The thrust gate on the

Boeing 757 The Boeing 757 is an American narrow-body airliner designed and built by Boeing Commercial Airplanes. The then-named 7N7, a twinjet successor for the 727 (a trijet), received its first orders in August 1978. The prototype completed its mai ...

was provided by a single-slotted flap in between the inboard and outboard double-slotted flaps. The

A320 The Airbus A320 family is a series of narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, first flew on 22 February 1987, and was introduced in April 1988 by Air France. The first member of the famil ...

A330 The Airbus A330 is a wide-body aircraft developed and produced by Airbus. Airbus conceived several derivatives of the A300, its first airliner in the mid-1970s. Then the company began development on the A330 twinjet in parallel with the A340 ...

A340 The Airbus A340 is a long-range, wide-body passenger airliner that was developed and produced by Airbus. In the mid-1970s, Airbus conceived several derivatives of the A300, its first airliner, and developed the A340 quadjet in parallel with ...

and

A380 The Airbus A380 is a large wide-body airliner that was developed and produced by Airbus. It is the world's largest passenger airliner and only full-length double-deck jet airliner. Airbus studies started in 1988, and the project was annou ...

have no inboard aileron. No thrust gate is required in the continuous, single-slotted flap. Interference in the go-around case while the flaps are still fully deployed can cause increased drag which must not compromise the climb gradient.

Types of flap

Airfoil lift improvement devices (flaps)

Plain flap

The rear portion of airfoil rotates downwards on a simple hinge mounted at the front of the flap. The

Royal Aircraft Factory Royal may refer to: People * Royal (name), a list of people with either the surname or given name * A member of a royal family Places United States * Royal, Arkansas, an unincorporated community * Royal, Illinois, a village * Royal, Iowa, a cit ...

and National Physical Laboratory in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

tested flaps in 1913 and 1914, but these were never installed in an actual aircraft.Taylor 1974, pp. 8–9. In 1916, the

Fairey Aviation Company The Fairey Aviation Company Limited was a British aircraft manufacturer of the first half of the 20th century based in Hayes in Middlesex and Heaton Chapel and RAF Ringway in Cheshire. Notable for the design of a number of important military a ...

made a number of improvements to a

Sopwith Baby The Sopwith Baby is a British single-seat floatplane that was operated by the Royal Naval Air Service (RNAS) from 1915. Development and design The Baby (also known as the Admiralty 8200 Type) was a development of the two-seat Sopwith Schneider. ...

they were rebuilding, including their Patent Camber Changing Gear, making the

Fairey Hamble Baby The Fairey Hamble Baby was a British single-seat naval patrol floatplane designed and built by Fairey Aviation for the Royal Naval Air Service Design and development Fairey Aviation built a number of Sopwith Baby floatplanes at its Hamble work ...

as they renamed it, the first aircraft to fly with flaps. These were full span plain flaps which incorporated ailerons, making it also the first instance of flaperons. Fairey were not alone however, as Breguet soon incorporated automatic flaps into the lower wing of their

Breguet 14 Breguet or Bréguet may refer to: * Breguet (watch), watch manufacturer **Abraham-Louis Breguet (1747–1823), Swiss watchmaker **Louis-François-Clement Breguet (1804–1883), French physicist, watchmaker, electrical and telegraph work * Bréguet ...

reconnaissance/bomber in 1917. Owing to the greater efficiency of other flap types, the plain flap is normally only used where simplicity is required.

Split flap

The rear portion of the lower surface of the airfoil hinges downwards from the leading edge of the flap, while the upper surface stays immobile. This can cause large changes in longitudinal trim, pitching the nose either down or up. At full deflection, a split flaps acts much like a spoiler, adding significantly to drag coefficient. It also adds a little to lift coefficient. It was invented by Orville Wright and James M. H. Jacobs in 1920, but only became common in the 1930s and was then quickly superseded. The Douglas DC-1 (progenitor to the DC-3 and C-47) was one of the first of many aircraft types to use split flaps.

Slotted flap

A gap between the flap and the wing forces high pressure air from below the wing over the flap helping the airflow remain attached to the flap, increasing lift compared to a split flap. Additionally, lift across the entire chord of the primary airfoil is greatly increased as the velocity of air leaving its trailing edge is raised, from the typical non-flap 80% of freestream, to that of the higher-speed, lower-pressure air flowing around the leading edge of the slotted flap. Any flap that allows air to pass between the wing and the flap is considered a slotted flap. The slotted flap was a result of research at

Handley-Page Handley Page Limited was a British aerospace manufacturer. Founded by Frederick Handley Page (later Sir Frederick) in 1909, it was the United Kingdom's first publicly traded aircraft manufacturing company. It went into voluntary liquidation a ...

, a variant of the slot that dates from the 1920s, but was not widely used until much later. Some flaps use multiple slots to further boost the effect.

Fowler flap

A split flap that slides backwards, before hinging downward, thereby increasing first chord, then camber. The flap may form part of the upper surface of the wing, like a plain flap, or it may not, like a split flap, but it must slide rearward before lowering. As a defining feature – distinguishing it from the Gouge Flap – it always provides a slot effect. Invented by Harlan D. Fowler in 1924, and tested by

Fred Weick Fred Ernest Weick (1899–1993) was an airmail pilot, research engineer, and aircraft designer. Working at the NACA, he won the 1929 Collier Trophy for his design of the NACA cowling for radial air-cooled engines. Weick's aircraft designs inc ...

NACA The National Advisory Committee for Aeronautics (NACA) was a United States federal agency founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved and its assets ...

in 1932. They were first used on the

Martin 146 The Martin Model 146 was an unsuccessful American bomber design that lost a 1934–1935 bomber design competition to the prototype for the Douglas B-18 Bolo (itself soon supplanted by the B-17 Flying Fortress). Design and development Although ...

prototype in 1935, and in production on the 1937

Lockheed Super Electra The Lockheed Model 14 Super Electra was an American civil passenger and cargo aircraft built by the Lockheed Aircraft Corporation during the late 1930s. An outgrowth of the earlier Model 10 Electra, the Model 14 was also developed into larger, ...

, and are still in widespread use on modern aircraft, often with multiple slots.

Junkers flap

A slotted plain flap fixed below the trailing edge of the wing, and rotating about its forward edge. When not in use, it has more drag than other types, but is more effective at creating additional lift than a plain or split flap, while retaining their mechanical simplicity. Invented by Otto Mader at Junkers in the late 1920s, they were most often seen on the

Junkers Ju 52 The Junkers Ju 52/3m (nicknamed ''Tante Ju'' ("Aunt Ju") and ''Iron Annie'') is a transport aircraft that was designed and manufactured by German aviation company Junkers. Development of the Ju 52 commenced during 1930, headed by German Aeros ...

and the Junkers Ju 87 ''Stuka'', though the same basic design can also be found on many modern ultralights, like the

Denney Kitfox The Denney Kitfox is a series of small side-by-side, two-seat, high-wing, single engine kit aircraft, designed and originally manufactured by Dan Denney and his company Denney Aerocraft of Boise, Idaho. The aircraft is amateur-built and ...

. This type of flap is sometimes referred to as an external-airfoil flap.

Gouge flap

A type of split flap that slides backward along curved tracks that force the trailing edge downward, increasing chord and camber without affecting trim or requiring any additional mechanisms. It was invented by

Arthur Gouge Sir Arthur Gouge (3 July 1890 – 14 October 1962) was a British engineer and aircraft designer from Kent, who worked notably for Short Brothers where he designed the "C-class" Empire and Sunderland flying boats. Early life He was born in North ...

for

Short Brothers Short Brothers plc, usually referred to as Shorts or Short, is an aerospace company based in Belfast, Northern Ireland. Shorts was founded in 1908 in London, and was the first company in the world to make production aeroplanes. It was particu ...

in 1936 and used on the

Short Empire The Short Empire was a medium-range four-engined monoplane flying boat, designed and developed by Short Brothers during the 1930s to meet the requirements of the growing commercial airline sector, with a particular emphasis upon its usefulness ...

and

Sunderland Sunderland () is a port city in Tyne and Wear, England. It is the City of Sunderland's administrative centre and in the Historic counties of England, historic county of County of Durham, Durham. The city is from Newcastle-upon-Tyne and is on t ...

flying boats, which used the very thick Shorts A.D.5 airfoil. Short Brothers may have been the only company to use this type.

Fairey-Youngman flap

Drops down (becoming a Junkers Flap) before sliding aft and then rotating up or down. Fairey was one of the few exponents of this design, which was used on the

Fairey Firefly The Fairey Firefly is a Second World War-era carrier-borne fighter aircraft and anti-submarine aircraft that was principally operated by the Fleet Air Arm (FAA). It was developed and built by the British aircraft manufacturer Fairey Avia ...

and

Fairey Barracuda The Fairey Barracuda was a British carrier-borne torpedo and dive bomber designed by Fairey Aviation. It was the first aircraft of this type operated by the Royal Navy's Fleet Air Arm (FAA) to be fabricated entirely from metal. The Barracuda ...

. When in the extended position, it could be angled up (to a negative angle of incidence) so that the aircraft could be dived vertically without needing excessive trim changes.

Zap flap

Commonly, but incorrectly, called the Zapp flap, it was invented by Edward F. Zaparka while he was with Berliner/Joyce and tested on a

General Airplanes Corporation A general officer is an Officer (armed forces), officer of highest military ranks, high rank in the army, armies, and in some nations' air forces, space forces, and marines or naval infantry. In some usages the term "general officer" refers t ...

Aristocrat in 1932 and on other types periodically thereafter, but it saw little use on production aircraft other than on the

Northrop P-61 Black Widow The Northrop P-61 Black Widow is a twin-engine United States Army Air Forces fighter aircraft of World War II. It was the first operational U.S. warplane designed as a night fighter, and the first aircraft designed specifically as a night fight ...

. The leading edge of the flap is mounted on a track, while a point at mid chord on the flap is connected via an arm to a pivot just above the track. When the flap's leading edge moves aft along the track, the triangle formed by the track, the shaft and the surface of the flap (fixed at the pivot) gets narrower and deeper, forcing the flap down.

Krueger flap

A hinged flap which folds out from under the wing's leading edge while not forming a part of the leading edge of the wing when retracted. This increases the camber and thickness of the wing, which in turn increases lift and drag. This is not the same as a leading edge droop flap, as that is formed from the entire leading edge. Invented by Werner Krüger in 1943 and evaluated in Goettingen, Krueger flaps are found on many modern swept wing airliners.

Gurney flap

A small fixed perpendicular tab of between 1 and 2% of the wing chord, mounted on the high pressure side of the trailing edge of an airfoil. It was named for racing car driver

Dan Gurney Daniel Sexton Gurney (April 13, 1931 – January 14, 2018) was an American racing driver, race car constructor, and team owner who reached racing's highest levels starting in 1958. Gurney won races in the Formula One, Indy Car, NASCAR, Can-Am, ...

who rediscovered it in 1971, and has since been used on some helicopters such as the

Sikorsky S-76B The Sikorsky S-76 is a medium-size commercial utility helicopter designed and produced by the American helicopter manufacturer Sikorsky Aircraft. It is the company's first helicopter specifically developed for the civilian market. The S-76 w ...

to correct control problems without having to resort to a major redesign. It boosts the efficiency of even basic theoretical airfoils (made up of a triangle and a circle overlapped) to the equivalent of a conventional airfoil. The principle was discovered in the 1930s, but was rarely used and was then forgotten. Late marks of the

Supermarine Spitfire The Supermarine Spitfire is a British single-seat fighter aircraft used by the Royal Air Force and other Allied countries before, during, and after World War II. Many variants of the Spitfire were built, from the Mk 1 to the Rolls-Royce Grif ...

used a bead on the trailing edge of the elevators, which functioned in a similar manner.

Leading edge flap

The entire leading edge of the wing rotates downward, effectively increasing camber and also slightly reducing chord. Most commonly found on fighters with very thin wings unsuited to other leading edge high lift devices.

Blown flap

A type of Boundary Layer Control System, blown flaps pass engine-generated air or exhaust over the flaps to increase lift beyond that attainable with mechanical flaps. Types include the original (internally blown flap) which blows compressed air from the engine over the top of the flap, the externally blown flap, which blows engine exhaust over the upper and lower surfaces of the flap, and upper surface blowing which blows engine exhaust over the top of the wing and flap. While testing was done in Britain and Germany before the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, and flight trials started, the first production aircraft with blown flaps wasn't until the 1957

Lockheed T2V SeaStar The Lockheed T2V SeaStar, later called the T-1 SeaStar, is a carrier-capable jet trainer for the United States Navy that entered service in May 1957. Developed from the Lockheed T-33 (itself derived from the Lockheed P-80 Shooting Star), it ...

. Upper Surface Blowing was used on the

Boeing YC-14 The Boeing YC-14 is a twinjet short take-off and landing (STOL) tactical military transport aircraft. It was Boeing's entrant into the United States Air Force's Advanced Medium STOL Transport (AMST) competition, which aimed to replace the Lockhe ...

in 1976.

Flexible flap

Also known as the FlexFoil. A modern interpretation of wing warping, internal mechanical actuators bend a lattice that changes the airfoil shape. It may have a flexible gap seal at the transition between fixed and flexible airfoils.

Flaperon

A type of aircraft control surface that combines the functions of both flaps and

Continuous trailing-edge flap

As of 2014,

U.S. Army Research Laboratory The U.S. Army Combat Capabilities Development Command Army Research Laboratory (DEVCOM ARL) is the U.S. Army's foundational research laboratory. ARL is headquartered at the Adelphi Laboratory Center (ALC) in Adelphi, Maryland. Its largest singl ...

(ARL) researchers at NASA's Langley Research Center developed an active-flap design for helicopter rotor blades. The Continuous Trailing-Edge Flap (CTEF) uses components to change blade camber during flight, eliminating mechanical hinges in order to improve system reliability. Prototypes were constructed for wind-tunnel testing. A team from ARL completed a live-fire test of a rotor blade with individual blade control technology in January 2016. The live fire experiments explored the ballistic vulnerability of blade control technologies. Researchers fired three shots representative of typical ground fire on a 7-foot-span, 10-inch-chord rotor blade section with a 4-foot-long CTEF at ARL's Airbase Experimental Facility.

Related devices

Leading edge slats Slats are aerodynamic surfaces on the leading edge of the wing of a 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, ...

and

slot Slot, the slot or Slots may refer to: People * Arne Slot (born 1978), Dutch footballer * Gerrie Slot (born 1954), Dutch cyclist * Hanke Bruins Slot (born 1977), Dutch politician * Tonny Bruins Slot (born 1947), Dutch association football coach wh ...

s are mounted on the top of the wings' leading edge and while they may be either fixed or retractable, when deployed they provide a slot or gap under the slat to force air against the top of the wing, which is absent on a Krueger flap. They offer excellent lift and enhance controllability at low speeds. Leading edge slats allow the wing to fly at a higher angle of attack which decrease takeoff and landing distances. Other types of flaps may be equipped with one or more slots to increase their effectiveness, a typical setup on many modern airliners. These are known as slotted flaps as described above. Frederick Handley Page experimented with fore and aft slot designs in the 20s and 30s. * Spoilers are intended to create drag and reduce lift by "spoiling" the airflow over the wing. A spoiler is much larger than a Gurney flap, and can be retracted. Spoilers are usually installed mid chord on the upper surface of the wing, but may also be installed on the lower surface of the wing as well. * Air brakes are used to increase drag, allowing the aircraft to decelerate rapidly. When installed on the wings they differ from flaps and spoilers in that they are not intended to modify the lift and are built strongly enough to be deployed at much higher speeds. *

Aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

s are similar to flaps (and work the same way), but are intended to provide lateral control, rather than to change the lifting characteristics of both wings together, and so operate differentially – when an aileron on one wing increases the lift, the opposite aileron does not, and will often work to decrease lift. When ailerons are designed to lower in conjunction with flaps, they are usually called

flaperon A flaperon (a portmanteau of flap and aileron) 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 s ...

s, while those that spoil lift (typically placed on the upper surface before the trailing edge) they are called

spoileron In aeronautics, spoilerons (also known as spoiler ailerons or roll spoilers) are spoilers that can be used asymmetrically as flight control surfaces to provide roll control. Operation Spoilerons roll an aircraft by reducing the lift of the ...

s. File:ILA 2008 PD 750.JPG, Plain flap at full deflection. File:Avro Lancaster flap Flickr 4841178432.jpg, Split flap on a World War II bomber File:A fully extended flap.jpg, Double slotted Fowler flaps extended for landing File:Undercarriage.b747.arp.jpg, Krueger flaps and triple-slotted trailing-edge flaps of a

Boeing 747 The Boeing 747 is a large, long-range wide-body airliner designed and manufactured by Boeing Commercial Airplanes in the United States between 1968 and 2022. After introducing the 707 in October 1958, Pan Am wanted a jet times its size, t ...

extended for landing File:Kitfox Lite.jpg, Junkers flaps, doubling as

ailerons An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in Flight dynamics, roll (or ...

References

Bibliography

* * Gunston, Bill, The Cambridge Aerospace Dictionary Cambridge, Cambridge University Press 2004, / * Windrow, Martin C. and René J. Francillon. ''The Nakajima Ki-43 Hayabusa''. Leatherhead, Surrey, UK: Profile Publications, 1965. {{DEFAULTSORT:Flap (Aircraft) Aircraft controls Aircraft wing components