Wing Flaps for Lift Augmentation in Aircraft

Why does a plane have flaps on its wings?

Commercial airline jets tend to fly at both high altitudes and at high airspeeds so as to cover a maximum distance in the shortest possible time, but require a much lower airspeed to land safely. Consequently the cruise speed of a passenger jet is higher than its climb speed.

This conflicting requirement of high speed for cruise, and a lower speed for landing, affects the plane’s wing design. For increased flight efficiency, the wings are engineered to accommodate the plane’s high-speed cruise, but have wing flaps for low-speed high lift maneuvers.

The primary purpose of the controllable hinged aerofoils (flaps) attached near the wing-root (inboard of the wing) and at the trailing edge is to create additional lift from the already lift-producing wing.

Wing Flaps – What They Actually Do

The wing flaps of any aircraft have two very important functions:

1. Flaps increase the lifting capability of a wing.
2. Flaps increase drag.

Some flight maneuvers require an aircraft to maintain its altitude at a lower airspeed, which results in a lesser degree of  lift generated by the airplane wings, and a loss of altitude. Using flaps increases the effective wing area used for generating lift, and increase the camber (curvature) of an airplane wing.

Wing flaps also play a crucial role in slowing down the aircraft’s airspeed and/or increasing its rate of descent by increasing the parasite drag produced by the wing.

Contrary to how the ailerons work to steer the plane – one aileron goes down while the other goes up to produce a couple that rolls an airplane – wing flaps act symmetrically on both the wings. There is no roll or yaw effect as a consequence of using flaps.

Using Flaps for Flight Maneuvers

By increasing the curvature (camber) of the aircraft wings; wing flaps contribute to safe flight in vital maneuvers such as the takeoff and landing.

• Using appropriate deflection of wing flaps on takeoff, the aircraft will lift-off the ground at a lower airspeed thereby decreasing the takeoff run required to liftoff. The flap setting for an efficient takeoff is given in an aircraft’s Operating Handbook and is different for different airplanes.
• During the landing phase, flaps contribute to a steeper descent angle by increasing the parasite drag produced by the wing. A slower approach speed and a shorter landing distance (as a consequence of reduced stall speed and increased aerodynamic braking) is also achieved by an appropriate deflection of wing flaps.

Wing flaps can also be useful in a variety of other situations:

• Pilots use flaps to increase lift at a constant airspeed.
• Flaps can decrease the plane’s lift to drag ratio.
• Flaps can increase parasite drag on the airplane wings.
• Pilots use flaps to lower the stall angle of attack and the stall speed.
• Flaps increase the forward visibility from the cockpit, as using flaps require a nose-down pitch attitude.