Wing Flaps: How Do They Function and What Is Their Purpose?

The first step to growing as a safe and competent pilot is to fully understand how an aircraft works. This includes understanding every part of an airplane, especially its control surfaces and how they affect performance. Fully comprehending the ways in which various sections of the airplane affect aerodynamics, as well as how the laws of aerodynamics work on the aircraft, is the best way to remain calm in an emergency and pilot effectively when in normal flight.

This includes wing flaps. The flaps on an airplane wing are usually not much noticed by those outside of aviation, but they play a vital role in getting—and keeping– an airplane aloft. Flaps are also an important part of making a safe and controlled landing.

 

What Is a Wing Flap?

The flap is placed on the outside edge of an airplane’s wing. You can find it between the fuselage and ailerons. Large jetliners have as many as three parts to their flaps; these are extended in sections on takeoff and landing, as needed. Small aircraft have appropriately sized flaps which attach to the wing with a hinge.

Flaps help to either increase or decrease the camber, or surface area, of the airplane wing. Camber includes how convex the upper part of the wing is, as well as the concavity of the lower half.  Wing flaps are a significant part of the takeoff and landing process. When the airplane is taking off, the flaps help to produce more lift. Conversely, flaps allow for a steep but controllable angle during landing. During both, efficient use of flaps help to shorten the amount of runway length needed for takeoff and landing.

 

How Wing Flaps Work

Wing flaps change the shape of the airplane wing. They divert the air around the wing as necessary. The setting of the flap determines whether they are used to increase lift (as on takeoff) or increase drag (used on landing.) When the airplane’s flaps are up, the camber of the airplane is such that the wings can produce more lift. Depending on the aircraft, the flap settings are usually between five and fifteen degrees. After liftoff, the wing flaps are retracted completely so that they do not begin to produce drag.

Conversely, extending the flaps of the airplane creates a “broken wing,” which increases drag. This also lower’s the airplane’s stall speed. It helps the airplane to slow down. Pilots usually place the flap setting between twenty five and forty degrees. This allows the pilot to take a steeper angle of attack to the landing field. Pilots who are flying high wing airplanes might notice a significant pitch up in the aircraft’s nose if the increase in drag is sudden.

 

Four Types of Wing Flaps

Smaller, simpler airplanes, usually sport airplanes or those used to train pilots, use a plain flap. These don’t create an enormous amount of lift, but it’s not usually needed. When a plain flap is extended, it swings down from a hinge to the back of the wing. You might also hear these referred to as “barn door flaps.”

Split flaps extend from the lower part of the wing’s surface. These are more complex and produce a greater amount of lift than plain flaps. Split flaps were partially invented by one of the Wright Brothers, Orville, but they were not in use much past the 1930’s due to the rapidly accelerating technology of the airplane industry. They were more effective at producing drag than providing lift. The Douglas DC-1 is the most famous type of airplane to use split flaps. They are now usually only seen on vintage aircraft.

Slotted flaps are seen on most modern aircraft. Training, passenger, and cargo airplanes all use them, both jet and propeller-powered. Wing camber is noticeably increased by slotted flaps. Instead of simply folding down from the wing, slotted flaps allow a small opening between the flap and the rest of the wing. This creates additional lift, because it allows the high pressure beneath the wing to rush above the wing. Airflow separation is then delayed.

Finally, Fowler flaps are used on large jets to create massive lift and drag as necessary. While Fowler flaps were invented around the same time as split flaps, and various engineers and pilots worked with the idea, the modern concept of them did not come into use until Harlan Fowler convinced Lockheed to employ it on its 14 Super Electra (popularly known as the “Super 14”) in the latter part of the 1930’s. Fowler flaps extend in stages. Depending on the type of aircraft, the flaps run on racks or rails in a series controlled by the pilot. Fowler flaps sometimes also have slots, and are known as slotted Fowler flaps. All are far more complex than plain flaps.

You may also hear the phrase “flaperon.” A flaperon is a surface which functions as both a wing flap and an aileron. Using a flaperon instead of a separate aileron and wing flap helps to reduce with aircraft’s weight—when employed properly, use of a flaperon can result in the use of less fuel. Flaperons appear on both small and large aircraft (even experimental and kitplanes) and, just like the Wright Flyer, were inspired by the way the wings of a bird work.

 

Practical Purpose and Function of Flaps

No matter the type of aircraft or style of flaps, pilots must understand the effect that use of them will have on their flight. Especially while landing, pilots must think ahead, anticipate, and make educated judgments about wind speed and runway conditions.

It’s also important to understand that flaps work in concert with the aircraft’s power, pitch, and altitude. For example, flaps cannot alone make for a safe landing—if an aircraft seems as if it might land beyond an intended landing area, pilots must increase the angle of the flaps in addition to lowering the airplane’s pitch and power. The reverse is true if the landing area seems to rush up faster than expected.