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turns, a pilot needs to adjust for the lead or lag created by
acceleration and deceleration errors so that the helicopter
rolls out on the desired heading. When turning to a heading
of north, the lead for the roll-out must include the number of
degrees of latitude plus the lead normally used in recovery
from turns. During a turn to a south heading, maintain the
turn until the compass passes south the number of degrees
of latitude, minus the normal roll-out lead. For example,
when turning from an easterly direction to north, where the
latitude is 30°, start the roll-out when the compass reads
37° (30° plus one-half the 15° angle of bank, or whatever
amount is appropriate for the rate of roll-out). When turning
from an easterly direction to south, start the roll-out when
the magnetic compass reads 203° (180° plus 30° minus onehalf
the angle of bank). When making similar turns from a
westerly direction, the appropriate points at which to begin
the roll-out would be 323° for a turn to north, and 157° for
a turn to south.
30° Bank Turn
A turn using 30° of bank is seldom necessary or advisable
in instrument meteorological conditions (IMC), and is
considered an unusual attitude in a helicopter. However, it
is an excellent maneuver to practice to increase the ability to
react quickly and smoothly to rapid changes of attitude. Even
though the entry and recovery techniques are the same as for
any other turn, it is more difficult to control pitch because
of the decrease in vertical lift as the bank increases. Also,
because of the decrease in vertical lift, there is a tendency
to lose altitude and/or airspeed. Therefore, to maintain a
constant altitude and airspeed, additional power is required.
Do not initiate a correction, however, until the instruments
indicate the need for one. During the maneuver, note the
need for a correction on the altimeter and VSI, check the
attitude indicator, and then make the necessary adjustments.
After making a change, check the altimeter and VSI again to
determine whether or not the correction was adequate.
Climbing and Descending Turns
For climbing and descending turns, the techniques described
previously for straight climbs, descents, and standard rate
turns are combined. For practice, simultaneously turn and
start the climb or descent. The primary and supporting
instruments for a stabilized constant airspeed left climbing
turn are illustrated in Figure 6-15. The level off from a
climbing or descending turn is the same as the level off from
a straight climb or descent. To return to straight-and-level
flight, stop the turn and then level off, or level off and then
stop the turn, or simultaneously level off and stop the turn.
During climbing and descending turns, keep the ball of the
turn indicator centered with pedal trim.
Common Errors During Turns
1. Failure to maintain desired turn rate
2. Failure to maintain altitude in level turns
3. Failure to maintain desired airspeed
4. Variation in the rate of entry and recovery
5. Failure to use proper lead in turns to a heading
6. Failure to properly compute time during timed turns
7. Failure to use proper leads and lags during the compass
turns
8. Improper use of power
9. Failure to use proper pedal trim
6-16
Figure 6-15. Flight Instrument Indications for a Stabilized Left Climbing Turn at a Constant Airspeed.
Unusual Attitudes
Any maneuver not required for normal helicopter instrument
flight is an unusual attitude and may be caused by any one
or combination of factors such as turbulence, disorientation,
instrument failure, confusion, preoccupation with flight deck
duties, carelessness in cross-checking, errors in instrument
interpretation, or lack of proficiency in aircraft control. Due
to the instability characteristics of the helicopter, unusual
attitudes can be extremely critical. As soon as an unusual
attitude is detected, make a recovery to straight-and-level
flight as soon as possible with a minimum loss of altitude.
To recover from an unusual attitude, a pilot should correct
bank-and-pitch attitude and adjust power as necessary. All
components are changed almost simultaneously, with little
lead of one over the other. A pilot must be able to perform
this task with and without the attitude indicator. If the
helicopter is in a climbing or descending turn, adjust bank,
pitch, and power. The bank attitude should be corrected
by referring to the turn-and-slip indicator and attitude
indicator. Pitch attitude should be corrected by reference to
the altimeter, airspeed indicator, VSI, and attitude indicator.
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Instrument Flying Handbook仪表飞行手册下(5)
