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for by pedal pressure, the ball remains in the
center. To center the ball, level the helicopter laterally
by reference to the other bank instruments, then center
the ball with pedal trim. Torque correction pressures
vary as you make power changes. Always check the
ball following such changes.
COMMON ERRORS DURING STRAIGHT-ANDLEVEL
FLIGHT
1. Failure to maintain altitude.
2. Failure to maintain heading.
3. Overcontrolling pitch and bank during corrections.
4. Failure to maintain proper pedal trim.
5. Failure to cross-check all available instruments.
30°
0°
60°
90°
Figure 12-14. The banking scale at the top of the attitude indicator
indicates varying degrees of bank. In this example, the
helicopter is banked a little over 10° to the right.
12-11
POWER CONTROL DURING STRAIGHT-ANDLEVEL
FLIGHT
Establishing specific power settings is accomplished
through collective pitch adjustments and throttle
control, where necessary. For reciprocating powered
helicopters, power indications are observed on the
manifold pressure gauge. For turbine powered helicopters,
power is observed on the torque gauge. (Since most
IFR certified helicopters are turbine powered, this
discussion concentrates on this type of helicopter.)
At any given airspeed, a specific power setting determines
whether the helicopter is in level flight, in a
climb, or in a descent. For example, cruising airspeed
maintained with cruising power results in level flight.
If you increase the power setting and hold the airspeed
constant, the helicopter climbs. Conversely, if you
decrease power and hold the airspeed constant, the helicopter
descends. As a rule of thumb, in a turbine-engine
powered helicopter, a 10 to 15 percent change in the
torque value required to maintain level flight results in a
climb or descent of approximately 500 f.p.m., if the airspeed
remains the same.
If the altitude is held constant, power determines the
airspeed. For example, at a constant altitude, cruising
power results in cruising airspeed. Any deviation from
the cruising power setting results in a change of airspeed.
When power is added to increase airspeed, the
nose of the helicopter pitches up and yaws to the right
in a helicopter with a counterclockwise main rotor
blade rotation. When power is reduced to decrease airspeed,
the nose pitches down and yaws to the left. The
yawing effect is most pronounced in single-rotor helicopters,
and is absent in helicopters with counter-rotating
rotors. To counteract the yawing tendency of the helicopter,
apply pedal trim during power changes.
To maintain a constant altitude and airspeed in level
flight, coordinate pitch attitude and power control. The
relationship between altitude and airspeed determines
the need for a change in power and/or pitch attitude. If
the altitude is constant and the airspeed is high or low,
change the power to obtain the desired airspeed.
During the change in power, make an accurate interpretation
of the altimeter; then counteract any deviation
from the desired altitude by an appropriate change
of pitch attitude. If the altitude is low and the airspeed
is high, or vice versa, a change in pitch attitude alone
may return the helicopter to the proper altitude and airspeed.
If both airspeed and altitude are low, or if both
are high, a change in both power and pitch attitude is
necessary.
To make power control easy when changing airspeed, it
is necessary to know the approximate power settings for
the various airspeeds that will be flown. When the airspeed
is to be changed any appreciable amount, adjust
the torque so that it is approximately five percent over or
under that setting necessary to maintain the new airspeed.
As the power approaches the desired setting, include the
torque meter in the cross-check to determine when the
proper adjustment has been accomplished. As the airspeed
is changing, adjust the pitch attitude to maintain a
constant altitude. A constant heading should be maintained
throughout the change. As the desired airspeed is
approached, adjust power to the new cruising power setting
and further adjust pitch attitude to maintain altitude.
Overpowering and underpowering torque approximately
five percent results in a change of airspeed at a moderate
rate, which allows ample time to adjust pitch and bank
smoothly. The instrument indications for straight-andlevel
flight at normal cruise, and during the transition
from normal cruise to slow cruise are illustrated in figures
12-15 and 12-16 on the next page. After the airspeed
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ROTORCRAFT FLYING HANDBOOK2(24)
