Minggu, 08 September 2013

Part of Aircraft (6)





Part of Aircraft (6)

ELEVATOR
At the rear of the fuselage of most aircraft
one finds a horizontal stabilizer and an
elevator. The stabilizer is a fixed wing section
whose job is to provide stability for the
aircraft, to keep it flying straight. The
horizontal stabilizer prevents up-and-down,
or pitching, motion of the aircraft nose. The
elevator is the small moving section at the
rear of the stabilizer that is attached to the
fixed sections by hinges. Because the elevator
moves, it varies the amount of force
generated by the tail surface and is used to
generate and control the pitching motion of
the aircraft. There is an elevator attached to
each side of the fuselage. The elevators work
in pairs; when the right elevator goes up, the
left elevator also goes up. This slide shows
what happens when the pilot deflects the
elevator.
The elevator is used to control the position of
the nose of the aircraft and the angle of attack
of the wing. Changing the inclination of the
wing to the local flight path changes the
amount of lift which the wing generates. This,
in turn, causes the aircraft to climb or dive.
During take off the elevators are used to
bring the nose of the aircraft up to begin the
climb out. During a banked turn, elevator
inputs can increase the lift and cause a tighter
turn. That is why elevator performance is so
important for fighter aircraft.
The elevators work by changing the effective
shape of the airfoil of the horizontal
stabilizer. As described on the shape effects
slide, changing the angle of deflection at the
rear of an airfoil changes the amount of lift
generated by the foil. With greater downward
deflection of the trailing edge, lift increases.
With greater upward deflection of the trailing
edge, lift decreases and can even become
negative as shown on this slide. The lift force
(F) is applied at center of pressure of the
horizontal stabilzer which is some distance
(L) from the aircraft center of gravity. This
creates a torque
T = F * L
on the aircraft and the aircraft rotates about
its center of gravity. The pilot can use this
ability to make the airplane loop. Or, since
many aircraft loop naturally, the deflection
can be used to trim or balance the aircraft,
thus preventing a loop. If the pilot reverses
the elevator deflection to down, the aircraft
pitches in the opposite direction.

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