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Any airspeed in excess only causes the approach area
and runway needed for approach and landing to
increase.
The tailwind increases the touchdown groundspeed and
lengthens the landing roll. The increased distance for
landing can be determined by dividing the actual touchdown
speed by the normal touchdown speed, and
squaring the result. For example, if the tailwind is 10
knots and the normal touchdown speed is 40 knots, the
actual touchdown speed is 50 knots. This touchdown
speed is 25 percent more than the normal speed, a factor
of 1.25. A factor of 1.25 squared equals 1.56. This
means the landing distance will increase 56 percent
over the normal landing distance.
On downwind approaches, a shallower approach angle
should be used, depending on obstacles in the approach
path. Use the spoilers/dive brakes and perhaps a forward
slip as necessary to achieve the desired glide path.
After touchdown, use the wheel brake to reduce
groundspeed as soon as is practical. This is necessary
to maintain aerodynamic control of the glider.
COMMON ERRORS
• Improper glide path control.
• Improper use of slips.
• Improper airspeed control.
• Improper correction of crosswind.
• Improper procedure for touchdown/landing.
• Poor directional control during/after landing.
• Improper use of wheel brakes.
8-1
Training for abnormal and emergency procedures is an
essential element in becoming a glider pilot.
Knowledge of procedures for coping with control problems
and instrument or equipment malfunction is especially
important in soaring activities. Knowing how to
use emergency equipment and survival gear is a practical
necessity.
PORPOISING
Porpoising is a general term that refers to pitch oscillations
that can occur in gliders. In most cases, pilots
induce these oscillations through over-controlling the
glider as they attempt to stop the oscillations from
occurring in the first place.
PILOT—INDUCED OSCILLATIONS
The instability of a glider’s attitude that arises when
the pilot fails to recognize the lag time inherent in
controlling the glider is known as a pilot-induced
oscillation (PIO). Typically, PIOs occur when the
glider fails to respond instantly to control input and
the pilot quickly increases the pressure on the controls.
By the time the pilot judges that the glider is
responding satisfactorily, the extra control pressures
have resulted in such a vigorous response that the
glider overshoots the desired flight attitude.
Alarmed, the pilot moves the controls rapidly in the
opposite direction, overcompensating for the mistake.
The undesired glider motion slows, stops for an
instant, and then reverses. The alarmed pilot maintains
significant control pressures to try to increase
the rate of response. The glider, now in rapid motion
in the desired direction in response to heavy-handed
control inputs, again shoots past the desired attitude
as the now thoroughly alarmed pilot jerks the flight
controls in the opposite direction. Unless the pilot
understands that these oscillations are the direct
result of over-controlling the glider, it is unlikely that
the oscillations will cease. More likely, they will
increase in intensity until there is a complete loss of
control.
Although pilot-induced oscillations can occur at any
time, these situations arise most commonly during
primary training. They tend to disappear as pilot
experience grows because pilots gain familiarity with
the lag time inherent in the flight controls. These
types of oscillations may also occur when a pilot is
making flights in unfamiliar types of gliders. For this
reason, particular care must be taken when the pilot is
preparing to fly a single seat glider in which the pilot
has no prior experience. When checking out in a new
type of single seat glider, the lag time of the flight controls
must be learned without the obvious benefit of
having an experienced glider flight instructor aboard
during flight to offer advice or, if necessary, to intervene.
While most PIO discussions are devoted to pitch
oscillations, consideration will be given to roll and yaw
induced oscillations.
The first step toward interrupting the PIO cycle is to
recognize the lag time inherent in the glider’s
response. Any change in glider flight attitude takes an
appreciable amount of time to accomplish as the flight
controls take affect, and the mass of the glider
responds to the pilot’s control inputs. The second step
is to modify control inputs to avoid over-controlling
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Glider Flying Handbook(86)
