Flaps are, like slots and slats, secondary control surfaces. Flaps are placed at the back of the wing, where they are used to change the wing's profile during takeoff and landing.
Flaps are used to increase the wing's lift during takeoff and landing, but they also increase drag, which is why full flaps are never used during takeoff.
Simple flaps are, as the name suggests, the most basic flap type.
This type of flap is hinged directly to the back of the wing, and it is the flap type that provides the least extra lift, and is typically found on smaller aircraft. It will normally provide an increase in lift of about 50%.
Split flaps are, like plain flaps, hinged to the wing.
In contrast to simple flaps, here it is only the underside of the wing, which also gives it more lift. Split flaps were used on the DC-3, but today they are mainly used on smaller aircraft.
This type of flap is the most commonly used (when variants are included), and they are used on both small and large aircraft.
Slotted flaps work like simple flaps with the difference that here a gap is formed between the wing and the flaps. The gap to the wing delays the separation of the airflow from the wing, and thus delays stall.
Because the wing must be moved backward, it requires a much more advanced mechanism than simple flaps. These flaps are found on both small and medium-sized aircraft, and they provide significantly more lift than both simple flaps and split flaps.
Fowler flaps are a variant of slotted flaps that considerably increase the wing surface area.
This type is primarily used on larger aircraft, and it is often divided into several sections. In the first positions (5°-15°), fowler flaps generate only very little drag.
Flaps are controlled from the cockpit. On small aircraft, they will most often be located on the instrument panel, while on larger aircraft they will be located on the center panel between the pilots.
Most flaps can normally be set from 0° to 30° or 40°. These numbers are shown on some controls as shown above, but instead there may be markings for the steps they can be set to as shown below.
