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Since the altitude should remain constant in level
flight, deviation from the desired altitude shows a need
for a change in pitch attitude, and if necessary, power.
When losing altitude, raise the pitch attitude and, if
necessary, add power. When gaining altitude, lower the
pitch attitude and, if necessary, reduce power.
The rate at which the altimeter moves helps in determining
pitch attitude. A very slow movement of the
altimeter indicates a small deviation from the desired
pitch attitude, while a 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; and the second, a change of attitude to
return smoothly to the desired altitude. If the altitude
and airspeed are more than 100 feet and 10 knots low,
respectively, apply power along with 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
The vertical speed indicator 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 vertical speed indicator in conjunction
with the altimeter in level flight. If a movement of the
vertical speed indicator 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 you do not zero the needle of the
Figure 12-12. The initial pitch correction at normal cruise is
one bar width.
12-9
vertical speed indicator immediately, the results will
show on the altimeter as 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. It must be realized that
a period of time is necessary for the vertical speed
indicator to reach its maximum point of deflection
after a correction has been made. This time element
is commonly referred to as “lag.” The lag is directly
proportional to the speed and magnitude of the pitch
change. If you employ smooth control techniques
and make small adjustments in pitch attitude, lag is
minimized, and the vertical speed indicator 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 vertical speed indicator 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 it cannot be
readjusted properly, this error must be taken into consideration
when using the vertical speed indicator for
pitch control. For example, if the vertical speed indicator
showed a descent of 100 f.p.m. when the helicopter
was in level flight, you would have to 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
helicopter pitch attitude. With a given power setting
and pitch attitude, the airspeed remains constant. If the
airspeed increases, the nose is too low and should be
raised. If the airspeed decreases, the nose is too high
and should be lowered. Arapid change in airspeed indicates
a large change in pitch attitude, and a slow change
in airspeed indicates a small change in pitch attitude.
There is very little lag in the indications of the airspeed
indicator. If, while making attitude changes, you notice
some lag between control application and change of
airspeed, it is most likely due to cyclic control lag.
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ROTORCRAFT FLYING HANDBOOK2(22)
