Figure 3-9.  Weight-shift control aircraft use the shifting of weight  for control.  portions of the trailing edge of the control surface. These  movable trim tabs, which are controlled from the flight deck,  reduce control pressures. Trim tabs may be installed on the  ailerons, the rudder, and/or the elevator.  A second type of empennage design does not require an  elevator. Instead, it incorporates a one-piece horizontal  stabilizer that pivots from a central hinge point. This type of  design is called a stabilator and is moved using the control  wheel, just as the elevator is moved. For example, when a  pilot pulls back on the control wheel, the stabilator pivots so  the trailing edge moves up. This increases the aerodynamic  tail load and causes the nose of the airplane to move up.  Stabilators have an antiservo tab extending across their  trailing edge.  [Figure 3-11]  The antiservo tab moves in the same direction as the trailing  edge of the stabilator and helps make the stabilator less  sensitive. The antiservo tab also functions as a trim tab to  relieve control pressures and helps maintain the stabilator in  the desired position.  The empennage includes the entire tail group and consists  of fixed surfaces, such as the vertical stabilizer and the  horizontal stabilizer. The movable surfaces include the  rudder, the elevator, and one or more trim tabs.  [Figure 3-10]  The rudder is attached to the back of the vertical stabilizer.  During flight, it is used to move the airplane’s nose left  and right. The elevator, which is attached to the back of the  horizontal stabilizer, is used to move the nose of the airplane  up and down during flight. Trim tabs are small, movable  Figure 3-10.  Empennage components.  Figure 3-8.  Types of flaps.  Empennage  3-6  Horizontal stabilizer  Rudder  Elevator  Vertical stabilizer  Trim tabs  Plain flap  Basic section  Split flap  Slotted flap  Fowler flap  Slotted Fowler flap 