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require constant, rapid cross-check and control during turns to
correct overbanking tendencies. Due to the interrelationship
of pitch, bank, and airspeed deviations during turns, crosscheck
must be fast in order to prevent an accumulation of
errors.
Turns to Predetermined Headings
As long as an airplane is in a coordinated bank, it continues
to turn. Thus, the roll-out to a desired heading must be started
before the heading is reached. The amount of lead varies with
the relationship between the rate of turn, angle of bank, and
rate of recovery. For small heading changes, use a bank angle
that does not exceed the number of degrees to be turned.
Lead the desired heading by one-half the number of degrees
of bank used. For example, if a 10° bank is used during a
change in heading, start the roll-out 5° before reaching the
desired heading. For larger changes in heading, the amount
5-21
Figure 5-34. Turn Coordinator Calibration.
of lead varies since the angle of bank for a standard rate turn
varies with the true airspeed.
Practice with a lead of one-half the angle of bank until the
precise lead a given technique requires is determined. If
rates of roll-in and roll-out are consistent, the precise amount
of lead suitable to a particular roll-out technique can be
determined.
Timed Turns
A timed turn is a turn in which the clock and the turn
coordinator are used to change heading by a specific number
of degrees in a given time. For example, in a standard rate turn
(3° per second), an airplane turns 45° in 15 seconds; in a half
standard rate turn, the airplane turns 45° in 30 seconds.
Prior to performing timed turns, the turn coordinator should
be calibrated to determine the accuracy of its indications.
[Figure 5-34] Establish a standard rate turn as indicated by
the turn coordinator, and as the sweep-second hand of the
clock passes a cardinal point (12, 3, 6, 9), check the heading
on the heading indicator. While holding the indicated rate
of turn constant, note the indicated heading changes at 10
second intervals. If the airplane turns more than or less than
30° in that interval, a respectively larger or smaller deflection
of the miniature aircraft of the turn coordinator is necessary
to produce a standard rate turn. After calibrating the turn
coordinator during turns in each direction, note the corrected
deflections, if any, and apply them during all timed turns.
The same cross-check and control technique is used in making
a timed turn that is used to execute turns to predetermined
headings, except the clock is substituted for the heading
indicator. The miniature aircraft of the turn coordinator is
primary for bank control, the altimeter is primary for pitch
control, and the ASI is primary for power control. Start the
roll-in when the clock’s second hand passes a cardinal point,
hold the turn at the calibrated standard rate indication (or
half-standard rate for small heading changes), and begin the
roll-out when the computed number of seconds has elapsed.
If the rates of roll-in and roll-out are the same, the time taken
during entry and recovery does not need to be considered in
the time computation.
Practice timed turns with a full instrument panel and check
the heading indicator for the accuracy of turns. If the turns are
executed without the gyro heading indicator, use the magnetic
compass at the completion of the turn to check turn accuracy,
taking compass deviation errors into consideration.
Compass Turns
In most small airplanes, the magnetic compass is the only
direction-indicating instrument independent of other airplane
instruments and power sources. Because of its operating
characteristics, called compass errors, pilots are prone to
use it only as a reference for setting the heading indicator,
but knowledge of magnetic compass characteristics permits
full use of the instrument to turn the airplane to correct and
maintain headings.
5-22
Figure 5-35. North and South Turn Error.
Remember the following points when making turns to
magnetic compass headings or when using the magnetic
compass as a reference for setting the heading indicator:
1. If on a north heading and a turn is started to the east
or west, the compass indication lags, or indicates a
turn in the opposite direction.
2. If on a south heading and a turn is started toward the
east or west, the compass indication precedes the turn,
indicating a greater amount of turn than is actually
occurring.
3. When on an east or west heading, the compass
indicates correctly when starting a turn in either
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Instrument Flying Handbook仪表飞行手册上(89)
