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attitude at all times.
When making initial pitch attitude corrections to maintain
altitude, the changes of attitude should be small and smoothly
applied. The initial movement of the horizon bar should not
exceed one bar width high or low. [Figure 6-3] If a further
adjustment is required, an additional correction of one-half bar
normally corrects any deviation from the desired altitude. This
one-and-one-half bar correction is normally the maximum
pitch attitude correction from level flight attitude.
After making the correction, cross-check the other pitch
instruments to determine whether the pitch attitude change
is sufficient. If additional correction is needed to return to
altitude, or if the airspeed varies more than 10 knots from
that desired, adjust the power.
Altimeter
The altimeter gives an indirect indication of the pitch
attitude of the helicopter in straight-and-level flight. Since
the altitude should remain constant in level flight, deviation
from the desired altitude indicates a need for a change in
pitch attitude and power as necessary. When losing altitude,
raise the pitch attitude and adjust power as necessary. When
gaining altitude, lower the pitch attitude and adjust power
as necessary. Indications for power changes are explained
in the next paragraph.
The rate at which the altimeter moves helps to determine pitch
attitude. A very slow movement of the altimeter indicates
a small deviation from the desired pitch attitude, while a
6-5
fast movement of the altimeter indicates a large deviation
from the desired pitch attitude. Make any corrective action
promptly, with small control changes. Also, remember that
movement of the altimeter should always be corrected by
two distinct changes. The first is a change of attitude to stop
the altimeter movement; the second is a change of attitude to
return smoothly to the desired altitude. If altitude and airspeed
are more than 100 feet and 10 knots low, respectively, apply
power in addition to an increase of pitch attitude. If the
altitude and airspeed are high by more than 100 feet and 10
knots, reduce power and lower the pitch attitude.
There is a small lag in the movement of the altimeter;
however, for all practical purposes, consider that the altimeter
gives an immediate indication of a change, or a need for
change in pitch attitude. Since the altimeter provides the
most pertinent information regarding pitch in level flight, it
is considered primary for pitch.
Vertical Speed Indicator (VSI)
The VSI gives an indirect indication of the pitch attitude of
the helicopter and should be used in conjunction with the
other pitch instruments to attain a high degree of accuracy
and precision. The instrument indicates zero when in level
flight. Any movement of the needle from the zero position
shows a need for an immediate change in pitch attitude to
return it to zero. Always use the VSI in conjunction with
the altimeter in level flight. If a movement of the VSI is
detected, immediately use the proper corrective measures
to return it to zero. If the correction is made promptly, there
is usually little or no change in altitude. If the needle of the
VSI does not indicate zero, the altimeter indicates a gain or
loss of altitude.
The initial movement of the vertical speed needle is
instantaneous and indicates the trend of the vertical movement
of the helicopter. A period of time is necessary for the VSI to
reach its maximum point of deflection after a correction has
been made. This time element is commonly referred to as
instrument lag. The lag is directly proportional to the speed
and magnitude of the pitch change. When employing smooth
control techniques and small adjustments in pitch attitude are
made, lag is minimized, and the VSI is easy to interpret.
Overcontrolling can be minimized by first neutralizing the
controls and allowing the pitch attitude to stabilize, then
readjusting the pitch attitude by noting the indications of the
other pitch instruments.
Occasionally, the VSI may be slightly out of calibration.
This could result in the instrument indicating a slight climb
or descent even when the helicopter is in level flight. If the
instrument cannot be calibrated properly, this error must be
taken into consideration when using the VSI for pitch control.
For example, if a descent of 100 feet per minute (fpm) is the
vertical speed indication when the helicopter is in level flight,
use that indication as level flight. Any deviation from that
reading would indicate a change in attitude.
Airspeed Indicator
The airspeed indicator gives an indirect indication of
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Instrument Flying Handbook仪表飞行手册上(119)
