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lift assistance during the landing and the takeoff, more rarely also in the climb and when maneuvering an airplane are in particular used. Only in rare cases (see Douglas DC-8) they are used also during the cruising. A goal of the use of lift assistance is it above all to reduce the landing and lift-off speed and thus the starting and landing distance to increase in the climb climb gradient and to reduce in the turning flight the turning radius. Lift assistance increase in different measure the air resistance of the airplane and therefore also for the reduction or delimitation of the airspeed, in particular in descending flight, are used. Airbrakes are however no lift assistance.
The manufacturers of the airplane specify permissible maximum speeds for the use of the lift assistance . Above a certain speed landing flaps cannot be driven out typically any longer, because the control drive is not enough to overcome the aerodynamic forces. At still higher speeds, which depend also on the present/immediate driving out angle of the landing flaps, even damages of the flaps threaten. Some airplanes therefore have landing flaps which are brought in automatically by the aerodynamic forces at increasing speed (z. B. Grumman F4F).
kinds of lift assistance
lift assistance differ in your structure and the position at the wing. Lift assistance affect either on the wing curvature, the wing area, the boundary layer of the air flow around a wing or by detour of the jet.
lift assistance at the Flügelvorderkante
the Krügerklappe is a relatively simple mechanism, both the wing curvature, and the wing area changed
of the slats is an extendable or rigid small wing, which is at the front of the wing. It leaves by an air gap air of the lower surface on the top side of the wing and prevents thereby an flow separation with high angles of incidence. If it is mobile implemented, the wing area becomes larger at the same time. Some airplanes have the situation slats, which retract themselves and extend due to aerodynamic forces the affecting them automatically, like it required (z. B. Messerschmitt BF 108).
tilting nose (LEADING EDGE FLAP)
lift assistance at the Flügelhinterkante
landing flap (also curving flap)
a landing flap, also Flap mentioned, is the simplest form of the lift assistance. It is an extendable extension at the rear end of the bearing area. It produces the lift necessary with the approach flight and makes thus (on) the flight possible with decreased speed of the airplane. With gliders the sliding qualities are optimized by optimal attitude of the curving flap between the positive landing setting and the negative high-speed flight position. With aerobatics witnesses the landing flaps can be deflected in the same direction with the elevator (z. B. Hirth Acrostar), with sail aerobatics witnesses were headed for even already completely automatically them.
Flaps are normally driven out on both sides of the wings in the same angle. If they are coupled with the aileron however, one speaks of the Flaperon, as for instance with the F-16 Fighting Falcon used. With some airplanes when driving the landing flaps out also the ailerons are in the same direction lowered (z. B. Messerschmitt BF 109).
with the Spaltklappe is folded downward as with the landing flap a rudder. At the same time this movement releases however an air gap, to air on the top side of the wing leaves prevented and so an flow separation. Spaltklappen can be so developed that they release up to three columns. With the Spaltklappe the bearing area curvature is changed.
with the Fowlerklappe concerns it a flap, which is to the rear driven and employed below the wing trailing edge. Thus as with the Spaltklappe an air gap between top side of the wing and lower surface freely, the bearing area curvature becomes larger. In addition, additionally the wing area is increased. Also Fowlerklappen were in such a way implemented that they release up to 3 column, used at Boeing B727, B737, to find B747 and likewise at the airbus A321.
with the Spreizklappe is folded downward a part of the rear wing lower part. Thus the wing curvature becomes larger.
with the Junkers Doppelflügel is behind the actual wing still another additional small wing. Thus the bearing area curvature can be increased. Junkers Doppelflügel can be used not only as lift assistance, but also as control surfaces (ailerons) (z. B. Junkers Ju 52/3m).
by an influence of the boundary layer on a wing can the tearing off speed be reduced and the maximum angle of incidence be increased. Either a part of the air flow on the wing area is sucked off, or injected by a blower air on the bearing area top side.
control and drive
lift assistance at the Flügelvorderkante work partially automatically as a function of the angle of incidence and the airspeed. Other lift assistance are used by the pilot or the Fly by wire - control purposefully or are compelling part of the landing procedure. The drive of landing flaps takes place usually manually, hydraulically, pneumatically or electrically.
lift assistance end of the 1920er years were introduced, when the airplanes reached speeds beyond 300 km/h. With the thin wing profiles necessary thereby those increased start and landing speed so strongly, which became landing for the normal pilot on at that time still frequently fastened airfields a risk.
- encyclopedia of aviation, Transpress, ISBN 3-344-70711-6