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Rotorcraft Flying Menu >Helicopter
Flight Controls > Collective Pitch Control
Note: In this chapter, it
is assumed that the helicopter has a counterclockwise main rotor
blade rotation as viewed from above. If flying a helicopter
with a clockwise rota-tion, you will need to reverse left and
right references, particularly in the areas of rotor blade pitch
change, anti-torque pedal movement, and tail rotor thrust.
There are four basic controls used during flight.
They are the collective pitch control, the throttle, the cyclic
pitch control, and the antitorque pedals.
COLLECTIVE PITCH CONTROL
The collective pitch control, located on the
left side of the pilot’s seat, changes the pitch angle
of all main rotor blades simultaneously, or collectively, as
the name implies. As the collective pitch control is raised,
there is a simultaneous and equal increase in pitch angle of
all main rotor blades; as it is lowered, there is a simul-taneous
and equal decrease in pitch angle. This is done through a series
of mechanical linkages and the amount of movement in the collective
lever determines the amount of blade pitch change. [Figure 4-1]
An adjustable friction control helps prevent inadvertent collective
pitch movement.
Figure 4-1. Raising the collective
pitch control increases the pitch angle the same amount on all
blades.
Changing the pitch angle on the blades changes
the angle of attack on each blade. With a change in angle of
attack comes a change in drag, which affects the speed or r.p.m.
of the main rotor. As the pitch angle increases, angle of attack
increases, drag increases, and rotor r.p.m. decreases. Decreasing
pitch angle decreases both angle of attack and drag, while rotor
r.p.m. increases. In order to maintain a constant rotor r.p.m.,
which is essential in helicopter operations, a proportionate
change in power is required to com-pensate for the change in
drag. This is accomplished with the throttle control or a correlator
and/or gover-nor, which automatically adjusts engine power.
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