Types of flaps

WORKING OF FLAPS AND ITS DIFFERENT TYPES

Will an aircraft produce the same amount of lift or could the lift produced by it be increased? An aircraft could produce the different magnitude of lift depending upon the angle of attack and wing configuration. The angle of attack is the angle in which the relative wind velocity makes with the chord line. Chord line is the line joining the leading and the trailing edge of the wing.

The concept of high lift devices:

As the birds are able to change the configuration of their feathers, similarly an aircraft could make use of the high lift devices to increase the amount of lift generated. High lift devices include slats, slots, and flaps. Wings have to generate a lot of lift during take-off and landing to reduce the chances of a stall.

The speed below which the aircraft goes into a stall is known as stall speed. So the aircraft must always fly at a speed greater than stall speed. Stall speed would be more if the wings are producing more lift. Therefore high lift devices are used to decrease the stall speed, which would result in the decreased requirement of runway length for take-off and landing.

Different high lift devices:

Trailing edge flaps are extended and moved downwards to increase the curvature of the wings. Leading edge flaps are present on the front of the wings and are moved out to increase the lift. Leading edge slats extend out from the front of the wing. When the high lift devices are extended, then the net area and the curvature of the wing are increased. This causes increased lift but also creates a lot of drag. Both these things are desirable during landing.

High lift devices are used during landing as well as take-off but their configuration is different for different purposes. Higher flap settings are used for landing whereas lower flap settings are used for take-off, because higher drag, which is desirable during landing, is created through higher flap settings.

Understanding Flaps:

Flaps are the secondary control surfaces. These are usually present on the trailing edge of the wing. Chord line gets altered when the flaps are extended. The effective angle of attack increases when the flaps are extended. Lift varies with varying lift coefficient which in turn is dependent upon the angle of attack.

With flaps down larger lift could be generated at the same speed as compared to flaps up configuration. Stall speed is decreased with flaps down configuration; therefore the aircraft would now be able to fly at a slower speed without stalling. The pilot gets improved visibility as the pilot could now fly at a lower nose attitude without stalling.

Different types of flaps:

Plain Flaps are the simplest form of flaps. They are hinged at the rear part of the wing. When extended they help in changing the curvature of the wing. They provide more lift but at the same time chances of flow separation increases. Chances of flow separation is increased as the flow losses energy because now it has to travel a larger distance. Fairey Hamble Baby was the first aircraft to fly with flaps.  Cessna A185F is one of the aircraft which use plain flaps.

Cessna A185F

Split Flaps are hinged below the wings. When these are rotated they increase lift but causes more drag as compared to the plain flap design due to disturbance of airflow around the wings. Split Flaps when fully extended could also work as a spoiler. Split flaps are used by many aircraft and Douglas DC-1 was one of the first aircraft to use them. 

Douglas DC-1

Slotted Flaps are similar to the plain flap design but there is a slot or gap which helps in reducing the chance of flow separation. Chances of flow separation are reduced as the higher pressure air from below the wings flows up and energizes the boundary layer. There are many aircraft which are installed with slotted flaps, most of the commercial airliners use slotted flaps.

Fowler Flaps are similar to slotted flaps but unlike slotted flaps, they could be extended both back and down. This increases affected wing surface area as well as the effective angle of attack. Fowler Flaps increases effective chord length as well as curvature of the wing. P-47d thunderbolt and many other aircraft use fowler flaps. 

P-42d thunderbolt

Krueger Flaps are installed on the leading edge of the aircraft, unlike other flaps which are present on the trailing edge. The total chord length of the wing is increased when Krueger flaps are deployed. Wings get a new leading edge when the Krueger flaps are deployed. Some of the portions of lower wing is rotated so as to bring it in the front of leading edge of the main wing. A mixture of inboard Krueger flaps and outboard slats are used in Boeing 727.

Boeing 727

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