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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 the
turn is established will cause the airplane 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 airplane to
yaw opposite its turning path, causing the airplane to
slip to the inside of the turn. The ball in the turn-andslip
indicator will be displaced off-center whenever
the airplane is skidding or slipping sideways. [Figure
3-8] In proper coordinated flight, there is no skidding
or slipping. An essential basic airmanship skill is the
ability of the pilot to sense or “feel” any uncoordinated
condition (slip or skid) without referring to instrument
reference. During this stage of training, the flight
instructor should stress the development of this ability
and insist on its use to attain perfect coordination in all
subsequent training.
In all constant altitude, constant airspeed turns, it is
necessary to increase the angle of attack of the wing
when rolling into the turn by applying up elevator.
This is required because part of the vertical lift has
been diverted to horizontal lift. Thus, the total lift must
be increased to compensate for this loss.
To stop the turn, the wings are returned to level flight
by the coordinated use of the ailerons and rudder
applied in the opposite direction. To understand the
relationship between airspeed, bank, and radius of
turn, it should be noted that 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
Figure 3-6. Change in lift causes airplane to turn.
More lift
Additional
induced drag
Rudder overcomes
adverse yaw to
coordinate the turn
Reduced lift
Figure 3-7. Forces during a turn.
Ch 03.qxd 7/13/04 11:08 AM Page 3-8
3-9
to become slower. [Figure 3-9 on next page] Therefore,
at a given angle of bank, a higher true airspeed will
make the radius of turn larger because the airplane will
be turning at a slower rate.
When changing 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 as the radius of
turn decreases. The additional lift developed because
of this increase in speed of the wing balances the
inherent lateral stability of the airplane. At any given
airspeed, aileron pressure is not required to maintain
the bank. If the bank is allowed to increase from a
medium to a steep bank, the radius of turn decreases
further. The lift of the outside wing 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
wing and the speed of the outside wing. The wing on
the outside of the turn travels a longer circuit than the
inside wing, yet both complete their respective circuits
in the same length of time. Therefore, the outside wing
travels faster than the inside wing, and as a result, it
develops more lift. This creates an overbanking
tendency that must be controlled by the use of the
ailerons. [Figure 3-10] Because the outboard wing is
developing more lift, it also has more induced drag.
This causes a slight slip during steep turns that must be
corrected by use of the rudder.
Sometimes during early training in steep turns, the
nose may be allowed to get excessively low resulting
in a significant loss in altitude. To recover, the pilot
should first reduce the angle of bank with coordinated
use of the rudder and aileron, then raise the nose of the
airplane to level flight with the elevator. If recovery
from an excessively nose-low steep bank condition is
attempted by use of the elevator only, it will cause a
steepening of the bank and could result in overstressing
the airplane. Normally, small corrections for pitch
during steep turns are accomplished with the elevator,
and the bank is held constant with the ailerons.
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(28)
