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Bank attitude control is controlling the angle made by
the lateral tilt of the rotor and the natural horizon, or,
the movement of the helicopter about its longitudinal
axis. After interpreting the helicopter’s bank instruments
(attitude indicator, heading indicator, and turn
indicator), cyclic control adjustments are made to attain
the desired bank attitude.
Power control is the application of collective pitch with
corresponding throttle control, where applicable. In
straight-and-level flight, changes of collective pitch are
made to correct for altitude deviations if the error is
more than 100 feet, or the airspeed is off by more than
10 knots. If the error is less than that amount, use a
slight cyclic climb or descent.
In order to fly a helicopter by reference to the
instruments, you should know the approximate
power settings required for your particular helicopter
in various load configurations and flight conditions.
Trim, in helicopters, refers to the use of the cyclic centering
button, if the helicopter is so equipped, to relieve all
possible cyclic pressures. Trim also refers to the use of
pedal adjustment to center the ball of the turn indicator.
Pedal trim is required during all power changes.
The proper adjustment of collective pitch and cyclic
friction helps you relax during instrument flight.
Friction should be adjusted to minimize overcontrolling
and to prevent creeping, but not applied to such a
degree that control movement is limited. In addition,
many helicopters equipped for instrument flight contain
stability augmentation systems or an autopilot to
help relieve pilot workload.
STRAIGHT-AND-LEVEL FLIGHT
Straight-and-level unaccelerated flight consists of
maintaining the desired altitude, heading, airspeed, and
pedal trim.
PITCH CONTROL
The pitch attitude of a helicopter is the angular relation
of its longitudinal axis and the natural horizon. If available,
the attitude indicator is used to establish the
desired pitch attitude. In level flight, pitch attitude
varies with airspeed and center of gravity. At a constant
altitude and a stabilized airspeed, the pitch attitude is
approximately level. [Figure 12-11]
PPITITCCHH C COONNTTRROOLL
Figure 12-11. The flight instruments for pitch control are the airspeed indicator, attitude indicator, altimeter, and vertical
speed indicator.
12-8
ATTITUDE INDICATOR
The attitude indicator gives a direct indication of the
pitch attitude of the helicopter. In visual flight, you
attain the desired pitch attitude by using the cyclic to
raise and lower the nose of the helicopter in relation to
the natural horizon. During instrument flight, you follow
exactly the same procedure in raising or lowering
the miniature aircraft in relation to the horizon bar.
You may note some delay between control application
and resultant instrument change. This is the normal
control lag in the helicopter and should not be confused
with instrument lag. The attitude indicator may show
small misrepresentations of pitch attitude during
maneuvers involving acceleration, deceleration, or
turns. This precession error can be detected quickly by
cross-checking the other pitch instruments.
If the miniature aircraft is properly adjusted on the
ground, it may not require readjustment in flight. If the
miniature aircraft is not on the horizon bar after leveloff
at normal cruising airspeed, adjust it as necessary
while maintaining level flight with the other pitch
instruments. Once the miniature aircraft has been
adjusted in level flight at normal cruising airspeed,
leave it unchanged so it will give an accurate picture of
pitch 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 12-12] If a further change 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 you
have made the correction, cross-check the other pitch
instruments to determine whether the pitch attitude
change is sufficient. If more 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.
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