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recover at the onset of a stall at other-than-normal stall
speed or flight attitudes. An accelerated stall, although
usually demonstrated in steep turns, may actually be
encountered any time excessive back-elevator pressure
is applied and/or the angle of attack is increased too
rapidly.
From straight flight at maneuvering speed or less, the
glider should be rolled into a steep banked (maximum
45°) turn and back-elevator pressure gradually applied.
After the bank is established, back-elevator pressure
should be smoothly and steadily increased. The resulting
apparent centrifugal force pushes the pilot’s body
down in the seat, increases the wing loading, and
decreases the airspeed. Back-elevator pressure should
be firmly increased until a definite stall occurs.
When the glider stalls, recovery should be made
promptly by releasing back-elevator pressure. If the
greater lift on that wing. To keep that wing from rising
and to maintain a constant angle of bank, opposite
aileron pressure is required. The added inside rudder
pressure will also cause the nose to lower in relation to
the horizon. Consequently, additional back-elevator
pressure would be required to maintain a constantpitch
attitude. The resulting condition is a turn with
rudder applied in one direction, aileron in the opposite
direction, and excessive back-elevator pressure—a
pronounced cross-control condition.
Since the glider is in a skidding turn during the crosscontrol
condition, the wing on the outside of the turn
speeds up and produces more lift than the inside wing;
thus, the glider starts to increase its bank. The down
aileron on the inside of the turn helps drag that wing
back, slowing it up and decreasing its lift. This further
causes the glider to roll. The roll may be so fast that it
is possible the bank will be vertical or past vertical
before it can be stopped.
For the demonstration of the maneuver, it is important
that it be entered at a safe altitude because of the possible
extreme nose down attitude and loss of altitude
that may result. Before demonstrating this stall, the
pilot should clear the area for other air traffic. While
the gliding attitude and airspeed are being established,
the glider should be re-trimmed. When the glide is stabilized,
the glider should be rolled into a mediumbanked
turn to simulate a final approach turn that
would overshoot the centerline of the runway. During
the turn, excessive rudder pressure should be applied
in the direction of the turn but the bank held constant
by applying opposite aileron pressure. At the same
time, increased back-elevator pressure is required to
keep the nose from lowering.
All of these control pressures should be increased until
the glider stalls. When the stall occurs, releasing the
control pressures, simultaneously decreasing the angle
of attack initiates the recovery. In a cross-control stall,
the glider often stalls with little warning. The nose
may pitch down, the inside wing may suddenly drop,
and the glider may continue to roll to an inverted position.
This is usually the beginning of a spin. It is obvious
that close to the ground is no place to allow this to
happen.
Recovery must be made before the glider enters an
abnormal attitude (vertical spiral or spin); it is a simple
matter to return to wings-level, straight flight by
coordinated use of the controls. The pilot must be able
to recognize when this stall is imminent and must take
immediate action to prevent a completely stalled condition.
It is imperative that this type of stall not occur
during an actual approach to a landing, since recovery
7-30
turn is uncoordinated, one wing may tend to drop suddenly,
causing the glider to roll in that direction. If this
occurs, the glider should be returned to wings-level,
straight flight with coordinated control pressure.
A glider pilot should recognize when an accelerated
stall is imminent and take prompt action to prevent a
completely stalled condition. It is imperative that a prolonged
stall, excessive airspeed, excessive loss of altitude,
or spin be avoided.
CROSSED-CONTROL STALL
The objective of a crossed-control stall demonstration
maneuver is to show the effect of improper control
technique and to emphasize the importance of using
coordinated control pressures whenever making turns.
This type of stall occurs with the controls crossed—
aileron pressure applied in one direction and rudder
pressure in the opposite direction, and the critical angle
of attack is exceeded. [Figure 7-30]
　
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本文鏈接地址：Glider Flying Handbook(78)