The large pod-like structures under the aircraft wings are called Flap Track Fairings (FTFs). Sometimes known as the trailing edge fairings, the primary purpose of the FTFs is to enclose the actuation mechanism of wing flaps. The horizontal size of the fairing depends on the length of the flap track, which allows for extension and retraction.

In a retracted position, most of the FTF structure remains underneath the wing, with the rear box and the tail cone protruding behind the wing. The encapsulation prevents the flap track mechanism from damage during flight. Moreover, the aerodynamic shape of the fairings allows for drag reduction.

Why do flaps need to be extended?

A flap is a lifting device that essentially changes the shape of the wing. As an extension to the wing, flaps are used when reduced stall speeds are required. In order to increase lift coefficient of the wing at lower speeds, flaps are extended to increase the wing’s curvature. Extended flaps also increase the aerodynamic drag and help in slowing the aircraft.

Aircraft require a higher lift coefficient during takeoff, and hence a typical flap setting of 5-15 degrees is utilized. However, during landing, a greater flap setting of 25-40 degrees is selected to maximize both lift and drag. This enables the aircraft to descend at steeper angles and land at slower speeds. As the flaps extend, they protrude further aft of the wing structure.

How…