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touching down anywhere near the proper point, and very
often will result 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 will touch down headed in the direction in
which it is moving over the runway. This requires
timely action to discontinue 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 groundlooping 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 will swing too quickly into
line and the glider will tend 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 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 in a landing
approach over obstacles and in making short-field
landings, when 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.
The “forward slip” is a slip in which the glider’s direction
of motion continues the same as before the slip
was begun. [Figure 3-24] If there is any crosswind, the
slip will be 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 flight path. 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.
Forward slips with wing flaps extended should not be
done in gliders wherein the manufacturer’s operating
instructions prohibit such operation.
SIDE SLIP
A side slip, as distinguished from a forward slip
[Figure 3-24], is one during which the glider’s longitudinal
axis remains parallel to the original flight
path but in which the flight path changes direction
according to the steepness of the bank. To perform a
Figure 3-24. Two types of slips.
3-14
sideslip, the upwind wing is lowered and simultaneously
the opposite rudder is applied to maintain the
landing area alignment. The sideslip is important in
counteracting wind drift during crosswind landings
and is discussed in a later chapter.
STALLS
It is important to remember that a stall can occur at any
airspeed and at any flight attitude. A stall will occur when
the critical angle of attack is exceeded. [Figure 3-25]
The stall speed of a glider can be affected by many factors
including weight, load factor due to maneuvering,
and environmental conditions. As the weight of the glider
increases, a higher angle of attack is required to maintain
the same airspeed since some of the lift is sacrificed to
support the increase in weight. This is why a heavily
loaded glider will stall at a higher airspeed than it will
when lightly loaded. The manner in which this weight is
distributed also affects stall speed. For example, a forward
CG creates a situation that requires the tail to produce
a greater downforce to balance the aircraft. The
result of this configuration requires the wings to produce
more lift than if the CG were located further aft.
Therefore, a more forward CG also increases stall speed.
Environmental factors also can affect stall speed.
Snow, ice, or frost accumulation on the wing’s surface
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Glider Flying Handbook(30)
