Introduction to Glider Flying > Components and Systems > Lift/Drag Devices.

Gliders are equipped with devices that modify the lift and drag of the wing. High drag devices include spoil-ers, dive brakes, and flaps. Spoilers extend from the upper surface of the wing interrupting or spoiling the airflow over the wings. This action causes the glider to descend more rapidly. Dive brakes extend from both the upper and lower surfaces of the wing and help to increase drag. [Figure 2-2]

Flaps are located on the trailing edge of the wing, inboard of the ailerons, and can be used to increase lift, drag, and descent rate. When the glider is cruising at moderate air-speeds in wings-level flight, the flaps are set to zero degree deflection and are in trail with the wing. When the flap is extended downward, wing camber is increased, and the lift and the drag of the wing increase.

There are several different types of flaps. [Figure 2-3] The plain flap is the simplest of the four types. When deflected downward, it increases the effective camberand changes the wing’s chord line. Both of these factors increase the lifting capacity of the wing. The slotted flap is similar to the plain flap. In addition to changing the wing’s camber and chord line, it also allows a portion of the higher pressure air beneath the wing to travel through a slot. This increases the velocity of the airflow over the flap and provides additional lift.

Another type of flap is the Fowler flap. When extended, it moves rearward as well as down. This rearward motion increases the total wing area, as well as the camber and chord line. Negative flap is used at high speeds where wing lift reduction is desired to reduce drag.When the flaps are extended in an upward direction, or negative setting, the camber of the wing is reduced, resulting in a reduction of lift produced by the wing at a fixed angle of attack and airspeed.

Figure 2-3. The four different types of flaps.

Figure 2-4. The empennage components.