Wing Flaps for Lift Augmentation in Aircraft

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A Lufthansa Boeing 747-400 taxiing at Hong Kong International Airport. Flaps and spoilers can also provide aerodynamic braking. Photo Credit: Tahir Hashmi.

Types of Wing Flaps (Trailing Edge Only)

Flaps are airflow-modifying structures attached to the trailing edge of the wing (behind the wing), and are used for increasing lift. Types:

  • Plain: The plain flap is simply a hinged portion of the wing that moves downward when operated. This increases lift by 50% approximately.
  • Split: Split flaps are movable flaps, only on the lower surface of the trailing edge of the wing. Their contribution to lift augmentation is about 60%.
  • Slotted: These types of flaps are surfaces that move downwards to form a slot between the trailing edge of the wing (back of the wing) and the leading edge of the flap (front of the flap). The increase in lift due to these flaps in roughly about 65%.
  • Double Slotted: In these type of flaps, a secondary slot is formed just behind the leading edge of the flap. Two slots; 70% lift augmentation, stalling angle delayed by 18 degrees.
  • Zap Flaps: The under-surface of the trailing edge of the wing moves backwards and downwards (without forming any slots), thereby contributing to a 90% increase in the wing’s lifting capability.
  • Fowler: Fowler flaps are used most commonly in jetliners. These flaps are shaped like aerofoils. They move downwards and aft to increase the wing area, thereby contributing to a 90% lift augmentation.
  • Double Slotted Fowler Flaps: These are wing-shaped structures moving downwards and aft of the wing, creating two slots between the trailing edge of the wing and that of the flap itself. These produce a 100% lift augmentation.

Pilot’s Control of Flaps

Flaps can be controlled from the cockpit via the following systems:

  1. Planes include a mechanical linkage between the cockpit controls and the wing flaps themselves.
  2. Pilots operate hydraulic actuators and hydraulic motors from the cockpit.

Wing flaps are used in a number of maneuvers other than the plain takeoff and landing. These surfaces primarily ensure safe flight in terms of  slow-speed maneuvers, regardless of what type is installed in an aircraft.

Resources:

Aviation Theory Centre. Aeroplane General Knowledge and Aerodynamics. (2004).

Federal Aviation Administration. Pilots Handbook of Aeronautical Knowledge. (2008). Accessed March 28, 2012.

Federal Aviation Administration. Airplane Flying Handbook. (2004). Accessed March 28, 2012.

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