High-Lift Devices

(in Russian, mekhanizatsiia kryla) a set of devices that alter the lift and drag of an aircraft wing. They reduce the landing speed of an airplane, and during takeoff they facilitate its lift-off from the ground. The lift may be increased by a factor of 1.5–2.0 or more, leading to a reduction of 20–50 percent and more in landing speed, depending on the type of device. Additional lift is produced by increasing the curvature of the wing section ([1] and [2] in Figure 1) and the surface area of the wing (2) or by improving the airflow around the wing by means of boundary-layer control (3) and the use of jet devices (4). Combinations of these methods, such as extensible slats and flaps (2,c), are often used.

The boundary layer is controlled in two ways: by blowing it off with compressed air from the engine that is brought through

Figure 1. High-lift devices: (1) increase in curvature of wing section (a—leading-edge flap, b-trailing-edge flap, c—plain flap), (2) increase in wing area and curvature of wing section (a—leading-edge slat, b—double-slotted flap, c—Kruger slat with triple-slotted flap), (3) boundary-layer control (a—vortex generator, b—boundary-layer suction), (4) jet device (jet flap), (5) spoiler

pipes with holes that are laid out along the wing or by drawing it off with a similar system. The flow of air around a wing is also substantially improved by a jet flap (4), which creates extra lift by feeding compressed air into a slot between its upper and lower surfaces. If the engine power is great enough, such a flap can provide a lift equal to the weight of the airplane (it can cause the airplane to hover in the air), and if the lift is greater than the weight, it can produce a vertical takeoff.

An airplane can be decelerated in the air by spoilers (5) or by drooped ailerons (1,c), which are deflected downward simultaneously and act as flaps.

In addition to the movable surfaces, whose position may be set manually or automatically, the Russian term mekhanizatsiia kryla also includes hydraulic and electric drives, control circuits (rods, bell cranks, and so on), and pipelines.