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Consider the example of an airplane that requires 23" of
manifold pressure (Hg) to maintain a normal cruising airspeed
of 120 knots, and 18" Hg to maintain an airspeed of 100 knots.
The reduction in airspeed from 120 knots to 100 knots while
maintaining straight-and-level flight is discussed below and
illustrated in Figures 5-57, 5-58, and 5-59.
Instrument indications, prior to the power reduction, are
shown in Figure 5-57. The basic attitude is established and
maintained on the attitude indicator. The specific pitch,
bank, and power control requirements are detected on these
primary instruments:
Altimeter—Primary Pitch
Heading Indicator—Primary Bank
Airspeed Indicator—Primary Power
Supporting pitch and bank instruments are shown in
Figure 5-57. Note that the supporting power instrument is
the manifold pressure gauge (or tachometer if the propeller
is fixed pitch). However, when a smooth power reduction to
approximately 15" Hg (underpower) is made, the manifold
pressure gauge becomes the primary power instrument.
[Figure 5-58] With practice, power setting can be changed
with only a brief glance at the power instrument, by sensing
the movement of the throttle, the change in sound, and the
changes in the feel of control pressures.
As the thrust decreases, increase the speed of the cross-check
and be ready to apply left rudder, back-elevator, and aileron
control pressure the instant the pitch-and-bank instruments
show a deviation from altitude and heading. As proficiency
is obtained, a pilot will learn to cross-check, interpret, and
control the changes with no deviation of heading and altitude.
Assuming smooth air and ideal control technique, as airspeed
decreases, a proportionate increase in airplane pitch attitude
is required to maintain altitude. Similarly, effective torque
control means counteracting yaw with rudder pressure.
As the power is reduced, the altimeter is primary for pitch,
the heading indicator is primary for bank, and the manifold
pressure gauge is momentarily primary for power (at 15"
Hg in Figure 5-58). Control pressures should be trimmed
off as the airplane decelerates. As the airspeed approaches
the desired airspeed of 100 knots, the manifold pressure
is adjusted to approximately 18" Hg and becomes the
supporting power instrument. The ASI again becomes
primary for power. [Figure 5-58]
Airspeed Changes in Straight-and-Level Flight
Practice of airspeed changes in straight-and-level flight
provides an excellent means of developing increased
proficiency in all three basic instrument skills, and brings
out some common errors to be expected during training
in straight-and-level flight. Having learned to control the
airplane in a clean configuration (minimum drag conditions),
increase proficiency in cross-check and control by practicing
speed changes while extending or retracting the flaps and
landing gear. While practicing, be sure to comply with the
airspeed limitations specified in the POH/AFM for gear and
flap operation.
5-41
Figure 5-58. Straight-and-Level Flight (Airspeed Decreasing).
Figure 5-59. Straight-and-Level Flight (Reduced Airspeed Stabilized).
5-42
Figure 5-60. Cross-check Supporting Instruments.
2. Reduce manifold pressure to 10" Hg. As the airspeed
decreases, increase cross-check speed.
3. Make trim adjustments for an increased angle of attack
and decrease in torque.
4. Lower the gear at 115 knots. The nose may tend to
pitch down and the rate of deceleration increases.
Increase pitch attitude to maintain constant altitude,
and trim off some of the back-elevator pressures.
If full flaps are lowered at 105 knots, cross-check,
interpretation, and control must be very rapid. A
simpler technique is to stabilize attitude with gear
down before lowering the flaps.
5. Since 18" Hg manifold pressure will hold level
flight at 100 knots with the gear down, increase
power smoothly to that setting as the ASI shows
approximately 105 knots, and retrim. The attitude
indicator now shows approximately two-and-a-half
bar width nose-high in straight-and-level flight.
6. Actuate the flap control and simultaneously increase
power to the predetermined setting (25" Hg) for the
desired airspeed, and trim off the pressures necessary
to hold constant altitude and heading. The attitude
indicator now shows a bar width nose-low in straightand-
level flight at 95 knots.
Sudden and exaggerated attitude changes may be necessary
in order to maintain straight-and-level flight as the landing
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Instrument Flying Handbook仪表飞行手册上(103)
