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If a glider with tapered wings, as shown in Figure 3-14,  were to begin a slip to the left with the left wing lower, the left wing will have a relative wind more aligned with its chord line and effectively higher airflow (airspeed) that generates more lift as compared to the higher right wing with angled relative wind, resulting in lower effective airflow (airspeed) over that wing. This differential in airflow or relative airspeed of the wings when taken to the extremes of the flight envelope results in the higher wing stalling and often an inverted spin. 

Depending on the exact wing shape, an elliptical wing can have characteristics more like a tapered wing. [Figure 3-14] Pilots should always consult the GFM and know what the gliders limitations are concerning slips. 

The use of slips has limitations. Some pilots may try to lose altitude by violent slipping, rather than by smoothly maneuvering, exercising good judgment, and using only a slight or moderate slip. In short-field landings, this erratic practice invariably leads to trouble since enough excess speed may prevent touching down anywhere near the proper point, and very often results in overshooting the entire field. 

If a slip is used during the last portion of a final approach, the longitudinal axis of the glider must be aligned with the runway just prior to touchdown so that the glider touches down headed in the direction in which it is moving over the runway. This requires timely action to modify the slip and align the glider’s longitudinal axis with its direction of travel over the ground at the instant of touchdown. Failure to accomplish this imposes severe sideloads on the landing gear and imparts violent ground looping tendencies. 

Discontinuing the slip is accomplished by leveling the wings and simultaneously releasing the rudder pressure, while readjusting the pitch attitude to the normal glide attitude. If 

the pressure on the rudder is released abruptly, the nose swings too quickly into line and the glider tends to acquire excess speed. 

Because of the location of the pitot tube and static vents, airspeed indicators in some gliders may have considerable error when the glider is in a slip. The pilot must be aware of this possibility and recognize a properly performed slip by the attitude of the glider, the sound of the airflow, and the feel of the flight controls. 

## Forward Slip 

The forward slip is a slip in which the glider’s direction of motion is the same as before the slip was begun. [Figure 3-30] The primary purpose of a forward slip is to dissipate altitude without increasing the glider’s speed, particularly in gliders not equipped with flaps, or if the spoilers are inoperative. There are many circumstances requiring the use of forward slips, such as a landing approach over obstacles and short- field landings, in which it is always wise to allow an extra margin of altitude for safety in the original estimate of the approach. In the latter case, if the inaccuracy of the approach is confirmed by excess altitude when nearing the boundary of the selected field, slipping can dissipate the excess altitude. If there is any crosswind, the slip is much more effective if made toward the wind. 

Assuming the glider is originally in straight flight, the wing on the side toward which the slip is to be made should be lowered by use of the ailerons. Simultaneously, the airplane’s nose must be yawed in the opposite direction by applying opposite rudder so that the glider’s longitudinal axis is at an angle to its original flightpath. The degree to which the nose is yawed in the opposite direction from the bank should be such that the original ground track is maintained. The nose should also be raised as necessary to prevent the airspeed from increasing. 

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