AIRCRAFT CONTROL
Controlling the helicopter is the result of accurately
interpreting the flight instruments and translating these
readings into correct control responses. Aircraft control
involves adjustment to pitch, bank, power, and trim in
order to achieve a desired flight path.
Pitch attitude control is controlling the movement of
the helicopter about its lateral axis. After interpreting
the helicopter’s pitch attitude by reference to the pitch
instruments (attitude indicator, altimeter, airspeed indi-
cator, and vertical speed indicator), cyclic control
adjustments are made to affect the desired pitch atti-
tude. In this chapter, the pitch attitudes illustrated are
approximate and will vary with different helicopters.
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 instru-
ments (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 center-
ing 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 overcontrol-
ling and to prevent creeping, but not applied to such a
degree that control movement is limited. In addition,
many helicopters equipped for instrument flight con-
tain 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 avail-
able, 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]
PITCH CONTRPITCH CONTROLOLPITCH CONTROL
Figure 12-11. The flight instruments for pitch control are the airspeed indicator, attitude indicator, altimeter, and vertical
speed indicator.
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 fol-
low 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 level-
off 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 main-
tain 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.
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 deter-
mining 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 atti-
tude. 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 infor-
mation 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.
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 atti-
tude 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 con-
sideration when using the vertical speed indicator for
pitch control. For example, if the vertical speed indica-
tor showed a descent of 100 f.p.m. when the helicopter
was in level flight, you would have to use that indica-
tion 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. A rapid change in airspeed indi-
cates 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.
Generally, a departure from the desired airspeed, due to
an inadvertent pitch attitude change, also results in a
change in altitude. For example, an increase in airspeed
due to a low pitch attitude results in a decrease in alti-
tude. A correction in the pitch attitude regains both air-
speed and altitude.
BANK CONTROL
The bank attitude of a helicopter is the angular relation
of its lateral axis and the natural horizon. To maintain a
straight course in visual flight, you must keep the
lateral axis of the helicopter level with the natural hori-
zon. Assuming the helicopter is in coordinated flight,
any deviation from a laterally level attitude produces a
turn. [Figure 12-13]
ATTITUDE INDICATOR
The attitude indicator gives a direct indication of the
bank attitude of the helicopter. For instrument flight,
BANK CONTRBANK CONTROLOLBANK CONTROL
Figure 12-13. The flight instruments used for bank control are the attitude, heading, and turn indicators.
the miniature aircraft and the horizon bar of the attitude
indicator are substituted for the actual helicopter and
the natural horizon. Any change in bank attitude of the
helicopter is indicated instantly by the miniature air-
craft. For proper interpretations of this instrument, you
should imagine being in the miniature aircraft. If the
helicopter is properly trimmed and the rotor tilts, a turn
begins. The turn can be stopped by leveling the miniature
aircraft with the horizon bar. The ball in the turn-and-slip
indicator should always be kept centered through proper
pedal trim.
The angle of bank is indicated by the pointer on the
banking scale at the top of the instrument. [Figure 12-
14] Small bank angles, which may not be seen by
observing the miniature aircraft, can easily be deter-
mined by referring to the banking scale pointer.
Pitch and bank attitudes can be determined simultane-
ously on the attitude indicator. Even though the miniature
aircraft is not level with the horizon bar, pitch attitude can
be established by observing the relative position of the
miniature aircraft and the horizon bar.
The attitude indicator may show small misrepresenta-
tions of bank attitude during maneuvers that involve
turns. This precession error can be immediately
detected by closely cross-checking the other bank
instruments during these maneuvers. Precession nor-
mally is noticed when rolling out of a turn. If, on the
completion of a turn, the miniature aircraft is level and
the helicopter is still turning, make a small change of
bank attitude to center the turn needle and stop the
movement of the heading indicator.
HEADING INDICATOR
In coordinated flight, the heading indicator gives an
indirect indication of the helicopter’s bank attitude.
When a helicopter is banked, it turns. When the lateral
axis of the helicopter is level, it flies straight.
Therefore, in coordinated flight, when the heading indi-
cator shows a constant heading, the helicopter is level
laterally. A deviation from the desired heading indi-
cates a bank in the direction the helicopter is turning.
A small angle of bank is indicated by a slow change of
heading; a large angle of bank is indicated by a rapid
change of heading. If a turn is noticed, apply opposite
cyclic until the heading indicator indicates the desired
heading, simultaneously checking that the ball is cen-
tered. When making the correction to the desired head-
ing, you should not use a bank angle greater than that
required to achieve a standard rate turn. In addition, if
the number of degrees of change is small, limit the
bank angle to the number of degrees to be turned. Bank
angles greater than these require more skill and preci-
sion in attaining the desired results. During straight-
and-level flight, the heading indicator is the primary
reference for bank control.
TURN INDICATOR
During coordinated flight, the needle of the turn-and-
slip indicator gives an indirect indication of the bank
attitude of the helicopter. When the needle is dis-
placed from the vertical position, the helicopter is
turning in the direction of the displacement. Thus, if
the needle is displaced to the left, the helicopter is
turning left. Bringing the needle back to the vertical
position with the cyclic produces straight flight. A
close observation of the needle is necessary to accu-
rately interpret small deviations from the desired
position.
Cross-check the ball of the turn-and-slip indicator to
determine that the helicopter is in coordinated flight. If
the rotor is laterally level and torque is properly com-
pensated 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-AND-
LEVEL 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.
30ϒ0ϒ
60ϒ
90ϒ
Figure 12-14. The banking scale at the top of the attitude indi-
cator indicates varying degrees of bank. In this example, the
helicopter is banked a little over 10° to the right.
POWER CONTROL DURING STRAIGHT-AND-
LEVEL 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 helicop-
ters, 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 deter-
mines 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 heli-
copter 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 air-
speed 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 air-
speed. 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 air-
speed, the nose pitches down and yaws to the left. The
yawing effect is most pronounced in single-rotor helicop-
ters, and is absent in helicopters with counter-rotating
rotors. To counteract the yawing tendency of the helicop-
ter, 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 inter-
pretation of the altimeter; then counteract any devia-
tion 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 air-
speed. 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 air-
speed 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 air-
speed is changing, adjust the pitch attitude to maintain a
constant altitude. A constant heading should be main-
tained throughout the change. As the desired airspeed is
approached, adjust power to the new cruising power set-
ting 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-and-
level flight at normal cruise, and during the transition
from normal cruise to slow cruise are illustrated in fig-
ures 12-15 and 12-16 on the next page. After the airspeed
has stabilized at slow cruise, the attitude indicator shows
an approximate level pitch attitude.
The altimeter is the primary pitch instrument during
level flight, whether flying at a constant airspeed, or
during a change in airspeed. Altitude should not change
during airspeed transitions. The heading indicator
remains the primary bank instrument. Whenever the
airspeed is changed any appreciable amount, the torque
meter is momentarily the primary instrument for power
control. When the airspeed approaches that desired, the
airspeed indicator again becomes the primary instru-
ment for power control.
The cross-check of the pitch and bank instruments to
produce straight-and-level flight should be combined
with the power control instruments. With a constant
power setting, a normal cross-check should be
satisfactory. When changing power, the speed of the
cross-check must be increased to cover the pitch and
bank instruments adequately. This is necessary to
counteract any deviations immediately.
COMMON ERRORS DURING AIRSPEED CHANGES
1. Improper use of power.
2. Overcontrolling pitch attitude.
3. Failure to maintain heading.
4. Failure to maintain altitude.
5. Improper pedal trim.
STRAIGHT CLIMBS (CONSTANT AIRSPEED
AND CONSTANT RATE)
For any power setting and load condition, there is only
one airspeed that will give the most efficient rate of
climb. To determine this, you should consult the climb
data for the type of helicopter being flown. The tech-
nique varies according to the airspeed on entry and
whether you want to make a constant airspeed or con-
stant rate climb.
ENTRY
To enter a constant airspeed climb from cruise airspeed,
when the climb speed is lower than cruise speed, simul-
taneously increase power to the climb power setting
and adjust pitch attitude to the approximate climb atti-
tude. The increase in power causes the helicopter to
start climbing and only very slight back cyclic pressure
is needed to complete the change from level to climb
attitude. The attitude indicator should be used to
accomplish the pitch change. If the transition from
level flight to a climb is smooth, the vertical speed indi-
cator shows an immediate upward trend and then stops
at a rate appropriate to the stabilized airspeed and atti-
tude. Primary and supporting instruments for climb
entry are illustrated in figure 12-17.
When the helicopter stabilizes on a constant airspeed
and attitude, the airspeed indicator becomes primary
Figure 12-16. Flight instrument indications in straight-and-level flight with airspeed decreasing.
Figure 12-15. Flight instrument indications in straight-and-level flight at normal cruise speed.
50 60 70
TORQUE
PERCENT
Supporting Pitch□
and Bank
Primary Power Primary Pitch
Supporting PitchPrimary BankSupporting Bank
Supporting□
Power
50 60 70
TORQUE
PERCENT
Primary Bank
Primary□
Power□
Initially
Primary PitchSupporting Pitch□
and Bank
Primary Power as Airspeed□
Approaches Desired Value
Supporting PitchSupporting Bank
for pitch. The torque meter continues to be primary for
power and should be monitored closely to determine if
the proper climb power setting is being maintained.
Primary and supporting instruments for a stabilized
constant airspeed climb are shown in figure 12-18.
The technique and procedures for entering a constant
rate climb are very similar to those previously
described for a constant airspeed climb. For training
purposes, a constant rate climb is entered from climb
airspeed. The rate used is the one that is appropriate for
50 60 70
TORQUE
PERCENT
□Primary Pitch□
Supporting Bank
Primary□
Power□
□
Supporting PitchPrimary BankSupporting Bank
Figure 12-17. Flight instrument indications during climb entry for a constant airspeed climb.
50 60 70
TORQUE
PERCENT
□Primary Pitch Supporting Pitch□
and Bank
Primary□
Power□
□
Supporting PitchPrimary BankSupporting Bank
Figure 12-18. Flight instrument indications in a stabilized, constant airspeed climb.