Introduction to Glider Flying > Components and Systems > The Empennage

THE The empennage includes the entire tail section, con-sisting of fixed surfaces, such as the horizontal stabi-lizer and the vertical fin, or stabilizer. These two fixed surfaces act like the feathers on an arrow to steady the glider and help maintain a straight path through the air. The movable surfaces include the elevator and the rud-der. [Figure 2-4]

The elevator is attached to the back of the horizontal stabilizer. The elevator controls movement around the lateral axis. This is known as pitch. During flight, the elevator is used to move the nose up and down, which controls the pitch attitude of the glider. The trim tab normally located on the elevator of the glider lessens the resistance you feel on the flight controls due to the airflow over the associated control surface.

The rudder is attached to the back of the vertical stabilizer. The rudder controls movement about the vertical axis. This is known as yaw. The rudder is used in combination with the ailerons and elevator to coor-dinate turns during flight.

Some gliders use a stabilator, which is a one-piece horizontal stabilizer used in lieu of an elevator. The stabilator pivots up and down on a central hinge point. When you pull back on the control stick, the nose of the glider moves up; when you push forward, the nose moves down. Stabilators sometimes employ an anti-servo trim tab to achieve pitch trim. The anti-servo tab provides a control feel comparable to that of an elevator. [Figure 2-5]

Trim devices reduce pilot workload by relieving the pressure required on the controls to maintain a desired airspeed. One type of trim device found on gliders is called an elevator trim tab. The elevator trim tab is a small, hinged, cockpit-adjustable tab on the trailing edge of the elevator. Other types of elevator trim devices include bungee spring systems and ratchet trim systems. In these systems, fore and aft control stick pressure is applied by an adjustable spring or bungee cord.

Figure 2-5. Empennage components and trim tabs.

Over the years, the shape of the empennage has seen dif-ferent forms. Early gliders were most often built with the horizontal stabilizer mounted at the bottom of the verti-cal stabilizer. This type of tail arrangement is called the conventional tail. Other gliders were designed with a T-tail, and still others were designed with V-tail. T-tail gliders have the horizontal stabilizer mounted on the top of the vertical stabilizer, forming a T. V-tails have two tail surfaces mounted to form a V. V-tails combine elevator and rudder movements.