ROTORCRAFT FLYING HANDBOOK1(24)

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influences manifold pressure; therefore, each is considered
to be a secondary control of the other’s function.
Both the tachometer (r.p.m. indicator) and the manifold
pressure gauge must be analyzed to determine which
control to use. Figure 4-3 illustrates this relationship.
CORRELATOR / GOVERNOR
A correlator is a mechanical connection between the
collective lever and the engine throttle. When the collective
lever is raised, power is automatically increased
and when lowered, power is decreased. This system
maintains r.p.m. close to the desired value, but still
requires adjustment of the throttle for fine tuning.
A governor is a sensing device that senses rotor and
engine r.p.m. and makes the necessary adjustments in
order to keep rotor r.p.m. constant. In normal operations,
once the rotor r.p.m. is set, the governor keeps the r.p.m.
constant, and there is no need to make any throttle adjustments.
Governors are common on all turbine helicopters
and used on some piston powered helicopters.
Some helicopters do not have correlators or governors
and require coordination of all collective and throttle
movements. When the collective is raised, the throttle
must be increased; when the collective is lowered, the
throttle must be decreased. As with any aircraft control,
large adjustments of either collective pitch or throttle
should be avoided. All corrections should be made
through the use of smooth pressure.
CYCLIC PITCH CONTROL
The cyclic pitch control tilts the main rotor disc by
changing the pitch angle of the rotor blades in their
cycle of rotation. When the main rotor disc is tilted, the
horizontal component of lift moves the helicopter in
the direction of tilt. [Figure 4-4]
Figure 4-2. A twist grip throttle is usually mounted on the end
of the collective lever. Some turbine helicopters have the
throttles mounted on the overhead panel or on the floor in
the cockpit.
If

Manifold

Pressure

is
and

R.P.M.

is
Solution
Low
Low
Low
High Low
High
High
High
Increasing the throttle increases manifold

pressure and r.p.m.
Lowering the collective pitch decreases

manifold pressure and increases r.p.m.
Raising the collective pitch increases

manifold pressure and decreases r.p.m.
Reducing the throttle decreases manifold

pressure and r.p.m.
Figure 4-3. Relationship between manifold pressure, r.p.m.,
collective, and throttle.
Figure 4-4. The cyclic pitch control may be mounted vertically
between the pilot’s knees or on a teetering bar from a
single cyclic located in the center of the helicopter. The cyclic
can pivot in all directions.
4-3
The rotor disc tilts in the direction that pressure is applied
to the cyclic pitch control. If the cyclic is moved forward,
the rotor disc tilts forward; if the cyclic is moved aft, the
disc tilts aft, and so on. Because the rotor disc acts like a
gyro, the mechanical linkages for the cyclic control rods
are rigged in such a way that they decrease the pitch angle
of the rotor blade approximately 90° before it reaches the
direction of cyclic displacement, and increase the pitch
angle of the rotor blade approximately 90° after it passes
the direction of displacement. An increase in pitch angle
increases angle of attack; a decrease in pitch angle
decreases angle of attack. For example, if the cyclic is
moved forward, the angle of attack decreases as the rotor
blade passes the right side of the helicopter and increases
on the left side. This results in maximum downward
deflection of the rotor blade in front of the helicopter and
maximum upward deflection behind it, causing the rotor
disc to tilt forward.
ANTITORQUE PEDALS
The antitorque pedals, located on the cabin floor by the
pilot’s feet, control the pitch, and therefore the thrust,
of the tail rotor blades. [Figure 4-5] . The main purpose
of the tail rotor is to counteract the torque effect of the
main rotor. Since torque varies with changes in power,
the tail rotor thrust must also be varied. The pedals are
connected to the pitch change mechanism on the tail
rotor gearbox and allow the pitch angle on the tail rotor
blades to be increased or decreased.
HEADING CONTROL
Besides counteracting torque of the main rotor, the tail
rotor is also used to control the heading of the helicopter
while hovering or when making hovering turns. Hovering
turns are commonly referred to as “pedal turns.”
In forward flight, the antitorque pedals are not used to
　
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