How does Aircraft Elevator Functions? - اسأل الطيار ask pilot

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Friday, July 10, 2020

How does Aircraft Elevator Functions?

Aircraft Elevator Functions


Elevators - Located on the edge of the horizontal part of the tail
The Elevator is like the Rudder except it makes the plane descend or rise. If the Elevators go down, the plane goes down, if they go up, the plane goes up.
The elevator controls pitch about the lateral axis. Like the ailerons on small aircraft, the elevator is connected to the control column in the flight deck by a series of mechanical linkages. Aft movement of the control column deflects the trailing edge of the elevator surface up. This is usually referred to as the up elevator position.
Aircraft Elevator Functions
The up-elevator position decreases the camber of the elevator
and creates a downward aerodynamic force, which is greater than the normal tail-down force that exists in straight-and level flight. The overall effect causes the tail of the aircraft to move down and the nose to pitch up. The pitching moment occurs about the center of gravity (CG). The strength of the pitching moment is determined by the distance between the CG and the horizontal tail surface, as well as by the aerodynamic effectiveness of the horizontal tail surface.
Moving the control column forward has the opposite effect. In this case, elevator camber increases, creating more lift (less tail-down force) on the horizontal stabilizer/elevator. This moves the tail upward and pitches the nose down. Again, the pitching moment occurs about the CG.
As mentioned earlier, stability, power, thrust line, and the position of the horizontal tail surfaces on the empennage are factors in elevator effectiveness controlling pitch. For example, the horizontal tail surfaces may be attached near the lower part of the vertical stabilizer, at the midpoint, or at the high point, as in the T-tail design.

**T-Tail
In a T-tail configuration, the elevator is above most of the effects of downwash from the propeller, as well as airflow around the fuselage and/or wings during normal flight conditions. Operation of the elevators in this undisturbed air allows control movements that are consistent throughout most flight regimes. T-tail designs have become popular on many light and large aircraft, especially those with aft fuselage mounted engines because the T-tail configuration removes the tail from the exhaust blast of the engines.Seaplanes and amphibians often have T-tails in order to keep the horizontal surfaces as far from the water as possible. An additional benefit is reduced noise and vibration inside the aircraft.
In comparison with conventional-tail aircraft, the elevator on a
T-tail aircraft must be moved a greater distance to raise the nose
a given amount when traveling at slow speeds. This is because
the conventional-tail aircraft has the down wash from the propeller pushing down on the tail to assist in raising the nose.
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 stabilizer 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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