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the direction of ball displacement. If the ball is to the left of
center and the left wing is low, apply left rudder pressure
to center the ball and correct the slip. At the same time
apply right aileron pressure as necessary to level the wings,
cross-checking the heading indicator and attitude indicator
while centering the ball. If the wings are level and the ball is
displaced from the center, the airplane is skidding. Note the
direction of ball displacement, and use the same corrective
technique as for an indicated slip. Center the ball (left ball/left
rudder, right ball/right rudder), use aileron as necessary for
bank control, and retrim.
To trim the airplane using only the turn coordinator, use
aileron pressure to level the miniature aircraft and rudder
pressure to center the ball. Hold these indications with control
pressures, gradually releasing them while applying rudder
trim sufficient to relieve all rudder pressure. Apply aileron
trim, if available, to relieve aileron pressure. With a full
instrument panel, maintain a wings level attitude by reference
to all available instruments while trimming the airplane.
Turn-and-Slip Indicator (Needle and Ball)
Unlike the turn coordinator that provides three indications
(roll, turn, and trim), the turn-and-slip indicator provides
two: turn-rate and trim. Although the turn-and-slip indicator
needle provides an indication of turn only, it provides an
indirect indication of aircraft attitude when used with roll
indicators such as a heading indicator or magnetic compass.
As with the turn coordinator (after stabilizing from a roll),
when the turn-and-slip indicator’s needle is aligned with the
alignment marks the aircraft is in a standard turn of 3° per
second or 360° in 2 minutes.
The ball of the turn-and-bank indicator provides important
trim in the same manner that the ball in the turn coordinator
does. Figures 5-18 and 5-19 provide a comparison of the
two instruments.
Power Control
Power produces thrust which, with the appropriate angle of
attack of the wing, overcomes the forces of gravity, drag,
and inertia to determine airplane performance.
Power control must be related to its effect on altitude and
airspeed, since any change in power setting results in a change
in the airspeed or the altitude of the airplane. At any given
airspeed, the power setting determines whether the airplane
is in level flight, in a climb, or in a descent. If the power is
increased in straight-and-level flight and the airspeed held
constant, the airplane climbs. If power is decreased while
the airspeed is held constant, the airplane descends. On the
other hand, if altitude is held constant, the power applied will
determine the airspeed.
The relationship between altitude and airspeed determines the
need for a change in pitch or power. If the airspeed is not the
desired value, always check the altimeter before deciding that
a power change is necessary. Think of altitude and airspeed
as interchangeable; altitude can be traded for airspeed by
lowering the nose, or convert airspeed to altitude by raising
the nose. If altitude is higher than desired and airspeed is
5-9
Figure 5-20. Airspeed Low and Altitude High—Lower Pitch.
Figure 5-21. Airspeed and Altitude High—Lower Pitch and Reduce Power.
low, or vice versa, a change in pitch alone may return the
airplane to the desired altitude and airspeed. [Figure 5-20] If
both airspeed and altitude are high or if both are low, then a
change in both pitch and power is necessary in order to return
to the desired airspeed and altitude. [Figure 5-21]
For changes in airspeed in straight-and-level flight, pitch,
bank, and power must be coordinated in order to maintain
constant altitude and heading. When power is changed to
vary airspeed in straight-and-level flight, a single-engine,
propeller-driven airplane tends to change attitude around all
axes of movement. Therefore, to maintain constant altitude
and heading, apply various control pressures in proportion
to the change in power. When power is added to increase
airspeed, the pitch instruments indicate a climb unless
forward elevator control pressure is applied as the airspeed
changes. With an increase in power, the airplane tends to
yaw and roll to the left unless counteracting aileron and
rudder pressures are applied. Keeping ahead of these changes
requires increasing cross-check speed, which varies with the
type of airplane and its torque characteristics, the extent of
power and speed change involved.
Power Settings
Power control and airspeed changes are much easier when
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Instrument Flying Handbook仪表飞行手册上(82)
