What Are Common Types of High Lift Devices

Flaps
 
Flaps are considered the most common high-lift device which may be employed for the means of reducing the stalling speed of an aircraft wing. For their installation, flaps are typically situated on the trailing edge of wings. Controllable by the pilot from within the cockpit, flaps are capable of extending outwards into the air, causing the camber or curvature of the wing to increase. As a result, the maximum lift coefficient is raised, permitting the aircraft to generate more lift at low speeds. Flaps are used for multiple operations, typically serving to reduce take-off and landing distances. As they can cause increased drag when deployed, flaps should not be used when they are not required.
 
Depending on an aircraft’s size, speed, and complexity, there are a few common flap variations that one may use. Generally speaking, the most common forms of flaps that are found on fixed-wing aircraft include plain, split, slotted, fowler, junkers, Gouge, Fairey-Youngman, Zap, Krueger, Gurney, leading edge, blown, and flexible flaps. While each flap type serves a similar role in reducing stalling speeds, each may differ in its construction with the possible use of movable slots or adjustable positions for increased capabilities.
 
Slats and Slots
 
Slats and slots are also common high-lift components, each serving as a leading edge device. Slats in particular are small and aerofoil shaped, designed to redirect air at the front of the wing. Through this redirection of airflow, air will move smoothly over the upper wing surface even when the aircraft is traveling at a high angle of attack. While slats are quite useful for flying at lower speeds, they can also reduce the distance needed for take-off and landing procedures. In general, slats may either be automatic, fixed, or powered.
 
Slots are the gap area present between wings and slats, serving to assist in the reduction of stall speeds for more optimal aircraft handling during low speed flying. Slots permit air to flow from the lower side of the wing to the upper surface, reducing stall speeds and assisting in high angles of attack. While most aircraft wings are only capable of reaching an angle of attack of 15 degrees, the use of slots can increase the permissible angle to a value upwards of 25 degrees.
 
Boundary Layer Control and Blown Flaps
 
Boundary layer control and blown flaps serve as an alternative to flaps or may assist in their operations. With blown flaps, bleed air from the engine is directed to the back portion of the upper wing surface, resulting in a reenergized boundary layer that maintains airflow attachment while flying at higher angles of attack. Engine exhaust may also be used alongside flaps, allowing for significant lift when the flap is deployed in the flow of exhaust.
 
Leading Edge Root Extensions
 
Leading edge root extensions such as the leading-edge root extension (LERX) are more common to fighter aircraft, though may also be seen on some civil models as well. A LERX typically comes in the form of a triangular fillet that is mounted to the leading edge root and fuselage, generating a vortex during high angles of attack to increase airflow speed over the wing. As a result, pressure is reduced and lift can be increased.
 
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