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standard rate turn, the helicopter turns 45° in 30 seconds.
Timed turns can be used if the heading indicator becomes
inoperative.
Prior to performing timed turns, the turn coordinator should
be calibrated to determine the accuracy of its indications.
To do this, establish a standard rate turn by referring to the
turn-and-slip indicator. Then, as the sweep second hand of
the clock passes a cardinal point (12, 3, 6, or 9), check the
heading on the heading indicator. While holding the indicated
rate of turn constant, note the heading changes at 10-second
intervals. If the helicopter turns more or less than 30° in
that interval, a smaller or larger deflection of the needle is
necessary to produce a standard rate turn. After the turnand-
slip indicator has been calibrated during turns in each
direction, note the corrected deflections, if any, and apply
them during all timed turns.
Use the same cross-check and control technique in making
timed turns that is used to make turns to a predetermined
heading, but substitute the clock for the heading indicator.
The needle of the turn-and-slip indicator is primary for bank
control, the altimeter is primary for pitch control, and the
airspeed indicator is primary for power control. Begin 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 changes in heading; then begin
the roll-out when the computed number of seconds has
elapsed. If the roll-in and roll-out rates are the same, the time
taken during entry and recovery need not be considered in
the time computation.
If practicing timed turns with a full instrument panel, check
the heading indicator for the accuracy of the turns. If executing
turns without the heading indicator, use the magnetic compass
at the completion of the turn to check turn accuracy, taking
compass deviation errors into consideration.
Change of Airspeed in Turns
Changing airspeed in turns is an effective maneuver for
increasing proficiency in all three basic instrument skills.
Since the maneuver involves simultaneous changes in all
components of control, proper execution requires a rapid
cross-check and interpretation, as well as smooth control.
Proficiency in the maneuver also contributes to confidence in
the instruments during attitude and power changes involved
in more complex maneuvers.
Pitch and power control techniques are the same as those
used during airspeed changes in straight-and-level flight.
As discussed previously, the angle of bank necessary for a
given rate of turn is proportional to the true airspeed. Since
the turns are executed at standard rate, the angle of bank
must be varied in direct proportion to the airspeed change in
order to maintain a constant rate of turn. During a reduction
of airspeed, decrease the angle of bank and increase the pitch
attitude to maintain altitude and a standard rate turn.
6-15
Altimeter and turn indicator readings should remain constant
throughout the turn. The altimeter is primary for pitch control,
and the turn needle is primary for bank control. Manifold
pressure is primary for power control while the airspeed is
changing. As the airspeed approaches the new indication, the
airspeed indicator becomes primary for power control.
Two methods of changing airspeed in turns may be used.
In the first method, airspeed is changed after the turn is
established. In the second method, the airspeed change
is initiated simultaneously with the turn entry. The first
method is easier, but regardless of the method used, the rate
of cross-check must be increased as power is reduced. As
the helicopter decelerates, check the altimeter and VSI for
needed pitch changes, and the bank instruments for needed
bank changes. If the needle of the turn-and-slip indicator
shows a deviation from the desired deflection, change the
bank. Adjust pitch attitude to maintain altitude. When the
airspeed approaches that desired, the airspeed indicator
becomes primary for power control. Adjust the power to
maintain the desired airspeed. Use pedal trim to ensure the
maneuver is coordinated.
Until control technique is very smooth, frequently crosscheck
the attitude indicator to keep from overcontrolling
and to provide approximate bank angles appropriate for the
changing airspeeds.
Compass Turns
The use of gyroscopic heading indicators makes heading
control very easy. However, if the heading indicator fails
or the helicopter is not equipped with one, use the magnetic
compass for heading reference. When making compass-only
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Instrument Flying Handbook仪表飞行手册下(4)
