The part on the trailing edge of a wing is called a flap; together with the leading-edge slat, it forms a high-lift system that increases wing camber, delays stall at higher angles of attack, and supplies the extra lift and drag needed for short-field takeoffs and steep, low-speed landings. To perform these tasks, flaps and slats move along metal tracks built into the wings: the slat extends forward while the flap pivots downward and aft, enlarging the effective wing area and reshaping the airfoil for maximum aerodynamic effect.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What are flaps on an airplane’s wings?
The flaps on airplane wings play a vital part in getting and keeping an airplane aloft, and they move along metal tracks built into the wings. Moving the flaps aft and the slats forward increases the wing area. Split flaps extend from the lower part of the wing's surface. Flaps are an important part of making a safe and controlled landing. Flaps are control surfaces, and their part-name identifies their location: the panel on the trailing edge is called a flap.
When an aileron is built so that it can droop with the flaps, that combination surface is termed a flaperon. Flaperons are ailerons designed to lower in conjunction with flaps. By serving both roll and high-lift duties, flaperons reduce aircraft weight and simplify the wing structure.
Ahead of the main wing, the leading-edge devices are called slats. Slats are on the leading edge of a wing, and when they are moved forward they increase wing area while pivoting their noses downward to increase the effective camber of the airfoil. This action lets airplane designers change airfoil shape in flight, so slats increase lift at low speed. Together, trailing-edge flaps and leading-edge slats give pilots the extra lift demanded for safe take-off and landing.
I understand the difference in terminology when referring to flaps. The surfaces hinged to the wing’s trailing edge are called flaps and are responsible for keeping the plane aloft. Flaperons are a combination of ailerons and flaps, responsible for roll and lift. Slats are the leading edge devices responsible for increasing the camber of the airfoil.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What are the types of flaps on an airplane?
The types of flaps on an airplane are provided in the list below.
- Plain Flaps
- Split Flaps
- Slotted Flaps
- Fowler Flaps
- Slotted Fowler Flaps
- Zap Flaps
- Gouge Flaps
- Junkers Flaps
- Fairey-Youngman Flaps
- Krueger Flaps
- Gurney Flaps
1. Plain Flaps
Plain flaps are the simplest type of flaps in design and were the first type of wing flaps developed. They hinge to the back of the wing and rotate downwards on a simple hinge arrangement, maintaining the surface area of the fixed portion of the wing even when deflected. As a high-lift device, they increase the wing's camber when deployed, which helps reduce the stalling speed of an aircraft at a given weight. Plain flaps are part of the control surface and are lightweight, easy to maintain, and simple in construction, making them best suited for use on small, light general aviation aircraft like early Cessna 150s and Piper Cubs.
Despite their simplicity, plain flaps produce drag relative to the lift gained, which allows pilots to fly steeper descents without increasing airspeed - especially useful during landing. However, this drag also makes the aircraft work harder to get into the air during takeoff. While they increase lift at slower speeds, plain flaps are limited in the amount of lift they can create, and their popularity peaked when they debuted in 1916. They remain in use today on many older or basic training aircraft where simplicity outweighs performance.
I understand both the pros and cons of using a plain flap. While they increase the wing’s camber and help in stall, the drag that accompanies it poses an issue during takeoff. The working of the flaps produces an opening that disrupts airflow, increasing lift and drag.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
2. Split Flaps
Split flaps are a type of high-lift device located on the lower surface of the wing. The upper portion of the split flap is a fixed extension of the top trailing edge of the wing, while the mobile portion is mounted on the lower surface of the wing. As the split flap hinges down from the wing's lower surface, the upper surface remains immobile. The wing’s lower surface drops down, leaving the upper surface intact.
Split flaps add a little to the lift coefficient, yet they produce a lot of drag relative to lift gained. At full deflection a split flap acts much like a spoiler, adding significantly to the drag coefficient. This strong ‘airbrake’ effect lets you fly a steeper descent to landing without increasing airspeed, so split flaps are good for short-field performance and steep approaches.
Split flaps were invented by Orville Wright and James M. H. Jacobs in 1920, became common in the 1930s, and were popular on World War II airplanes. The Supermarine Spitfire and Douglas DC-1 are two of the many 1930s aircraft types to use split flaps. Split flaps are simple, lightweight, and easy to maintain, but today they are uncommon. Split flaps still exist on many light twins.
3. Slotted Flaps
A slotted flap is a high-lift device that is similar to a plain flap but incorporates a gap between the flap and the wing. When the flap is extended, the gap opens and allows high-pressure air from the underside of the wing to flow through to the top surface of the flap. This slot re-energizes the boundary layer, delays airflow separation, and allows the airflow over the flap to remain laminar. By delaying the boundary layer separation that leads to stall, the slotted flap permits a higher angle of attack and produces more lift without creating excessive drag.
Slotted flaps have one or more slots and are found on small and large aircraft. The most common configuration is the single-slotted flap, but double-slotted flaps add another slot for more lift at low speeds and are used on large airliners. The slotted flap was the result of research at Handley-Page in the 1920s and is now the most commonly used flap type.
A slotted flap is a simple method in airflow administration that makes a thin slit between the wing and the flap, slowing airflow and stimulating the boundary region so that airflow detachment is delayed and lift is increased. This gives substantial performance increase for takeoff and landing.
4. Fowler Flaps
Fowler flaps were invented by Harlan D. Fowler in 1924 and first tested at NACA in 1932 by Fred Weick. Their action is to slide backward on rails or tracks and then hinge downwards. This slide-back momentarily leaves a slot that re-energizes the boundary layer and delays airflow separation. Because of this effect, lift rises strongly while drag rises only a little during the first stages of extension.
By increasing both camber and effective wing area, Fowler flaps increase lift with little increase in drag in the first stages of extension. First stages of a Fowler flap's extension produce a large increase in lift and make the setting best suited for takeoff in a large jet. At greater deflections the same surface continues to create more drag, so further extension generates more drag while lift gains taper off. This extra drag suits steep descents and final landing approaches.
Fowler flaps are used on modern aircraft and are often used on large jets. They appear on light twins and on aircraft like the Nakajima Ki-43. Whether on a heavy transport or a small twin, the Fowler flap reduces stalling speed, provides drag control, and allows tighter turns while giving boosted lift for low-speed flight and landing.
From my view, the Fowler flap's configuration serves an ideal proportion between streamlined economy and functionality. Performance advantages appear during stages of takeoff and landing, letting the aircraft function safely at steeper inclinations and from shorter airstrips. The configuration is heavier than a plain flap, yet the mechanical complication needed is a worthy trade-off for the performance advantages.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
5. Slotted Fowler Flaps
Slotted-Fowler flaps hinge downwards while sliding backward, increasing both wing area and camber. The gap that opens between the flap and the wing forms a narrow slot which allows high-pressure air from beneath the wing to move to the top and re-energizes the boundary layer over the flap. Re-energized, the boundary layer delays airflow separation and preserves lift at higher angles of attack. Large increases in lift and little increase in drag make the setting best suited for take-off in a large jet.
The slotted Fowler flap is a dual-action device that spans the back end of the wing and comprises a mixture of extension and camber increase. By extending aft and downward, it enlarges wing area, allowing higher angles of attack without stall. This configuration gives considerable lift at slower airspeeds, producing elevation. The lift created allows for steeper descents and shorter runways.
6. Zap Flaps
Zap flaps are a type of split flap invented by Edward F. Zaparka while he was with Berliner/Joyce and first flight-tested on a General Airplanes Corporation Aristocrat in 1932. They operate on a split-flap design whose movable bottom portion slides aft on tracks and simultaneously hinges downward, so the panel moves aft and down. This dual articulation increases both chord and camber, enlarging the effective surface area of the wing and re-energizing the boundary layer. The flap chord is 30% of the wing chord, and the flap area is 30% of the total wing area.
Because the toggle arrangement is concealed in the wing with one end near the center of pressure of the flap, the Zap flap provides a sizable increase to both the maximum lift and drag capacities of the aircraft. However, the large operating forces required 45 turns of the crank to lower the flap to 45 degrees, yielding only a 35% lift increase, so the mechanism was rarely used commercially. Apart from experimental installations, the type saw little use on production aircraft other than the Northrop P-61 Black Widow, where it was employed in conjunction with Zap ailerons that produce favorable rolling moments at speeds far below those at which a conventional-wing airplane can be controlled.
The Zap flap constitutes a method of increasing lift by moving the whole plane back before deploying. This enlarges the wing region and raises the convexity, giving a considerable boost in lift.
7. Gouge Flaps
Gouge flaps are a type of split flap invented by Arthur Gouge of Short Brothers in 1936 and patented as British Patent no. 443,516 awarded jointly to Short Bros. Ltd. and Arthur Gouge. In the closed position, the sharp-nosed aerofoil forms part of the wing profile. When raised or lowered in level flight the assembly slides backward along curved tracks, increasing chord, camber and planform area. The movement increases lift and drag and reduces stalling speed at a given weight while providing a slot effect similar to Fowler flaps but without the extra lift-generating slots.
The device was installed on the Short Empire, Short Sunderland and Short Stirling, but remained specific to Short Brothers aircraft and ultimately failed to be widely adopted. Flight-test data showed that fully open Gouge flaps decrease take-off distance by 23% and clear a 50 ft (15.24 m) obstacle 23% sooner, half-open settings give 14% shorter roll and 21% lower obstacle-clearance distance.
8. Junkers Flaps
Junkers flaps are a type of wing flap and high lift device invented by Otto Mader at the Junkers aircraft company. They constitute slotted plain flaps mounted beneath the wing's trailing edge and are sometimes referred to as external airfoil or droop flaps. Similar in principle to slotted flaps, they increase wing camber, delay airflow separation, and generate more lift and drag than plain or split flaps, thereby refining takeoff and landing performance. They were most often seen on the Junkers Ju-52 and Junkers Ju-87 Stuka and are found on many modern ultralights like the Denney Kitfox. Junkers flaps do not retract, remaining aligned with airflow when stowed.
9. Fairey-Youngman Flaps
The Fairey-Youngman flap is a high lift device, a type of flap that increases camber and wing area. It is a hydraulically operated retractable flap system: the panel first moves bodily down, then aft, then rotates, giving four distinct positions. Developed by Fairey, it was used on naval aircraft like the Firefly FR1 and the Fairey Barracuda. On the Barracuda the same mechanism acted as a second wing, generating greater lift yet also greater drag. Engine power compensated for the extra drag when the flap could not be retracted. The clear advantage is mechanical simplicity, which increases durability and makes repair and design easier. In service, the system provided greater maneuverability and a tighter turning circle in combat.
10. Krueger Flaps
Krueger flaps are a type of leading-edge high-lift device mounted on the bottom surface of the wing. They hinge forwards from the under surface of the wing and extend forward from the wing's leading edge. Krueger flaps increase wing camber and maximum coefficient of lift, generating additional lift during takeoff and landing.
Krueger flaps were invented by Werner Krueger in 1943. Variable-camber Krueger flaps protrude just ahead of the leading edge when deployed. The left wing was modified to include a 6.7 m-wide (22 ft) glove section aiding a variable-camber Krueger flap.
Early generation jet airliners like the B707 Series utilized Krueger flaps as their sole leading edge high lift devices. The Boeing 707 and Boeing 747 used Krueger flaps on the wing leading edge. Current generation aircraft use either all slats or a combination of slats and Krueger flaps.
11. Gurney Flaps
A Gurney flap is a fixed, right-angle tab one to two percent of chord high, attached to the lower trailing edge of an airfoil. It increases lift by altering the Kutta condition, creates two counter-rotating vortices, and delays separation while adding only modest drag. The device produces a nose-down pitching moment and extends structural depth aft.
Optimum height is about 3% of chord, gains peak near 5% chord, beyond which drag rises sharply. Rediscovered by race-car driver Dan Gurney in 1971, the flap entered production on the 1937 Lockheed Super Electra and is now common on helicopters like the Sikorsky S-76B to cure control issues without major redesign.
What is the purpose of flaps on an airplane?
Flaps are high-lift devices that reshape the wing to increase lift at lower speeds. By increasing camber and wing area, flaps raise the lift coefficient, allowing an aircraft to fly slower while maintaining lift during take-off and landing. Flaps produce greater lift at lower speeds, which gives a lower take-off speed and helps avoid obstacles from short runways. Flaps are used during landing to permit lower landing speed and allow steeper, slower approaches. They increase drag, reducing landing distance and shortening landing roll, so the brakes are more effective. Flaps thus play a vital part in making safe, controlled landings. Slats work with flaps to provide greater lift at lower speeds, while spoilers, deployed after landing, reduce lift and increase drag to assist braking.
The main function of flaps is to change the wing's camber by expanding the airfoil's surface region, generating lift at faster airspeeds. This allows the aircraft to operate safely at airspeeds that would otherwise be unworkable. During departure and touchdown, an aircraft needs to have varied streamlined cross-sectional properties different from those required during high-speed cruise. Deploying flaps provides an aviator the ability to keep a steeper slope, controlling advance tilt and movement tilt. This allows for a steady landing.
What controls the flaps on an airplane?
Pilots control the flaps on an airplane. The control placement depends on the airplane. Most airplanes built after the late 1970s mount an electric switch on the instrument panel. When the pilot moves this cockpit switch, an electric motor extends or retracts the flaps. In airplanes built prior to the 1970s, the pilot instead uses a handle located near the seat, and the lever between the seats powers the motor to move the flaps. Some light planes like the Cessna 172 still utilize pulleys, cables, and bellcranks to move the surfaces, yet even these aircraft retain a flap control switch on the panel that activates an electric actuator. Detents built into the control allow the pilot to set precise flap angles, and each detent corresponds to a specific airplane flap number. Thus, from the cockpit the pilot can command any flap angle needed for take-off, approach, or landing.
What is the structural design of aircraft flaps?
Flaps are incorporated into the aerodynamic and structural design of the wing and are typically made from an aluminum alloy structure built around a single spar member or torque tube. Sometimes made from composite honeycomb materials, they are part of an airframe’s structure.
Flap side loads are transmitted through an A-frame type structure attached to the forward and aft links to the aft link support ribs, while rear spar carries shear and supports the trailing-edge structure including flaps and ailerons.
Flap design involves trade-off analysis between track misalignment, flap panel stiffness, and assembly pretension, as flap actuation forces increase with flap stiffness and minimum clearances. Thus, flaps are a design trade-off between structural weight and actuation force.
Does every plane have flaps?
The majority of aircraft have flaps, yet the extent and complexity of the system vary with size and mission. Flaps are a common feature on small general aviation airplanes, and Cessna and Piper planes have flaps. Some aircraft like the Piper Archer have a manual flap system. On these light types they are typically hinged panels that the pilot extends to preset angles; max flaps usually equals about thirty degrees. Because speeds are modest, partial settings give enough extra lift for short-field departures and steeper approaches.
Flaps are a common feature on larger commercial jets and Airbus airliners have flaps. Larger airplanes require flaps for every takeoff and every landing. On jetliners, flaps shift the center of lift backwards and change zero lift angle-of-attack, allowing the same wing to carry far more weight at low speed. Pilots employ full flaps on every landing. Designers certify a big jet without flaps in theory, but performance rules, runway length, and fuel economics make such a choice unrealistic, so in practice every transport-category airplane has a multi-segment flap system installed.
