If you’ve flown in the passenger seat of an airliner, you’ve surely caught yourself gazing out the window at the system of flight controls moving up and down. These flight controls are known as flaps, but what exactly do they do? This blog will explain what flaps are, how they work, and their types.
Flaps are trailing-edge high-lift devices. In simpler terms, they are moveable surfaces on the back of wings that assist the plane in generating more lift. They are also used to help high speed planes fly slowly for takeoff and landing. The way flaps are used varies from aircraft to aircraft, depending on factors such as speed profiles and basic design. Despite this, nearly all aircraft use flaps during landing to help them slow down. Certain aircraft also use their flaps during takeoff. If an aircraft has a low profile wing designed for high speed flight, flaps will help it get off the ground sooner. As such, the aircraft requires less runway and can leave the ground at a slower speed than it could without flaps.
Even in aircraft that use flaps for takeoff, they are still very scarcely used. Flaps cause lift to increase, but also contribute to drag. The extra lift is helpful, but any amount of drag has a negative effect. Prior to landing, flaps benefit the plane because they allow it to descend rapidly without increasing airspeed. Because of this, the pilot can fly a steeper approach while still maintaining a low airspeed. This steeper approach allows the aircraft to avoid obstacles on their approach path (mountains, tall buildings, etc.) while remaining on their flight path near the airport.
There are four main types of flaps used on aircraft: plain flaps, split flaps, slotted flaps, and Fowler flaps. Plain flaps look very similar to inboard ailerons. They are made up of the trailing section of the wing’s airfoil. When plain flaps are deployed, a small section of the back of the wing deflects downward. When a split flap is deployed, the top of the wing above it remains the same. Instead of the entire trailing edge moving down, only the bottom section does. Split flaps are commonly used in areas where other structures make the use of plain or slotted flaps more difficult. A good example of this is in twin-engine aircraft, where the nacelle extends up to or beyond the trailing edge.
Slotted flaps move away from the main wing and are considered lift-creating airfoils. This means that air can flow both above and below them, allowing them to generate a significant amount of lift when compared to other flap types. Fowler flaps have a lot in common with slotted flaps, with aerodynamic flow created over both the flap and the wing. However, the defining characteristic of Fowler flaps is that, in addition to moving down, they can move aft as well. Therefore, as Fowler flaps are extended, the wing’s area increases and creates more lift. Fowler flaps are common on airliners and aircraft that have significant speed differences between cruise and terminal operations.
Aircraft frequently have multiple types of flaps built into them. For instance, some light twin-engine aircraft have inboard split flaps connected to outboard plain flaps. Additionally, airliners often use a combination of slotted and Fowler flaps. On smaller aircraft, flaps are usually controlled by a flap actuator. Large aircraft often utilize a sophisticated hydraulic system to operate the aircraft flap switch. For high-quality aircraft flap parts and much more, Aerospace Buying is the ultimate source.
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