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maintain the angle.
• Steep turns are those resulting from a degree
of bank (45° or more) at which the “overbank
ing tendency” of a glider overcomes stability,
and the bank increases unless aileron is
applied to prevent it.
Before starting any turn, the pilot must clear the airspace
in the direction of the turn. A glider is turned by
banking (lowering the wing in the direction of the
desired turn, thus raising the other). When the glider is
flying straight, the total lift is acting perpendicular to
the wings and to the earth. As the glider is banked into
a turn, total lift becomes the resultant of two components.
One, the vertical lift component, continues to act
perpendicular to the earth and opposes gravity. Second,
the horizontal lift component (centripetal) acts parallel
to the earth’s surface and opposes inertia (apparent centrifugal
force). These two lift components act at right
angles to each other, causing the resultant total lifting
force to act perpendicular to the banked wing of the
glider. It is the horizontal lift component that actually
turns the glider, not the rudder.
When applying aileron to bank the glider, the aileron
on the rising wing is lowered produces a greater drag
than the raised aileron on the lowering wing. This
increased drag causes the glider to yaw toward the rising
wing, or opposite to the direction of turn. To counteract
this adverse yawing moment, rudder pressure
must be applied in the desired direction of turn simultaneously
with aileron pressure. This action is required
to produce a coordinated turn.
After the bank has been established in a medium
banked turn, all pressure applied to the aileron may be
relaxed. The glider will remain at the selected bank
with no further tendency to yaw since there is no longer
a deflection of the ailerons. As a result, pressure may
also be relaxed on the rudder pedals, and the rudder
allowed to streamline itself with the direction of the
slipstream. Rudder pressure maintained after establishing
the turn will cause the glider to skid to the outside
of the turn. If a definite effort is made to center the rudder
rather than let it streamline itself to the turn, it is
probable that some opposite rudder pressure will be
exerted inadvertently. This will force the glider to yaw
opposite its turning path, causing the glider to slip to
the inside of the turn. The yaw string or ball in the slip
indicator will be displaced off-center whenever the
glider is skidding or slipping sideways. In proper coordinated
flight, there is no skidding or slipping.
In all gliding, constant airspeed turns, it is necessary to
increase the angle of attack of the wing as the bank
progresses by adding nose-up elevator pressure. This is
required because the total lift must be equal to the vertical
component of lift plus the horizontal lift component.
To stop the turn, coordinated use of the aileron
and rudder pressure are added to bring the wings back
to level flight, and elevator pressure is relaxed.
There is a direct relationship between, airspeed, bank
angle, and rate and radius of turn. The rate of turn at
any given true airspeed depends on the horizontal lift
component. The horizontal lift component varies in
proportion to the amount of bank. Therefore, the rate of
turn at a given true airspeed increases as the angle of
bank is increased. On the other hand, when a turn is
made at a higher true airspeed at a given bank angle, the
inertia is greater and the horizontal lift component
required for the turn is greater, causing the turning rate
20°
45°
60°
Figure 7-25. Shallow, medium, and steep turns.
7-24
to become slower. Therefore, at a given angle of bank, a
higher true airspeed will make the radius of turn larger
because the glider will be turning at a slower rate.
As the angle of bank is increased from a shallow bank
to a medium bank, the airspeed of the wing on the outside
of the turn increases in relation to the inside wing.
The additional lift so developed balances the lateral
stability of the glider. No aileron pressure is required
to maintain the bank. At any given airspeed, aileron
pressure is not required to maintain the bank.
If the bank is increased from a medium bank to a steep
bank, the radius of turn decreases even further. The
greater lift of the outside wing then causes the bank to
steepen and opposite aileron is necessary to keep the
bank constant.
As the radius of the turn becomes smaller, a significant
difference develops between the speed of the inside
　
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本文鏈接地址：Glider Flying Handbook(71)