Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 80

An elevator or stabilator controls pitch about the lateral axis, allowing for varying angles of attack during flight. An elevator is attached to the trailing edge of the horizontal stabilizer, which is usually fixed to the empennage, sometimes with an angle of incidence built in. A stabilator is a one‐piece horizontal stabilizer which moves as a unit around a pivot point in order to allow the pilot to control the angle of attack by adjusting the tail‐down force resulting in pitch variations of the nose of the aircraft.

The elevator is controlled by the pilot through various mechanical linkages; when the pilot pulls aft on the stick, the elevator forces the tail down, so the nose pitches up, and when the pilot pushes forward the elevator forces the tail up, so the nose goes down. As discussed in Chapter 2, the tail‐down force provides a moment that moves the nose of the aircraft around the aircraft’s center of gravity. In the example of an up elevator, when the pilot pulls aft on the stick, a larger “camber” is created on the tail and thus a greater aerodynamic force is created (Figure 3.5).

Figure 3.5 Elevator movement.

Source: U.S. Department of Transportation Federal Aviation Administration (2008a).

A stabilator essentially works like the elevator, but due to the fact the entire rear horizontal piece is movable, more force is created when the pilot moves the stick fore and aft and sensitivity is increased. This leads to greater chances of the pilot overcontrolling the aircraft; so, components like an antiservo tab and balance weight are added to reduce the sensitivity.

Some larger aircraft incorporate an adjustable horizontal stabilizer controlled by a jackscrew through a wheel in the cockpit or a motor. Though an elevator is still located on the trailing edge, the usually fixed horizontal stabilizer is adjustable, in this case allowing the pilot to move the stabilizer to reduce control pressures on the stick (Figure 3.6).