control is a mechanical linkage used to change the pitch of the main rotor blades. Pitch change is
accomplished at a specific point in the plane of rotation to tilt the main rotor disc. Most of the
helicopters now in the Army inventory have hydraulic assistance in addition to the mechanical linkage.
The collective pitch is the control that changes the pitch of all the main rotor blades equally and
simultaneously. The antitorque pedals are used to adjust the pitch in the antitorque rotor blades to
compensate for main rotor torque. Torque is explained in paragraph 3.5.
3.4. VELOCITY
A helicopter's main rotor blades must move through the air at a relatively high speed to produce
enough lift to raise the helicopter and keep it in the air. The main rotor can turn at the required takeoff
speed while the antitorque rotor holds the fuselage speed at zero.
The helicopter can fly forward, backward, or sideward as the pilot desires. It can also remain
stationary in the air (hover) with the main rotor blades developing the lift to support the helicopter.
3.5. TORQUE
The torque problem is related to helicopters of single-main-rotor design. The reason for this is that
as the helicopter's main rotor turns in one direction, the fuselage tends to turn in the opposite direction.
This effect is based on Newton's third law which states "To every action there is an opposite and equal
reaction." The torque problem on single-rotor helicopters is counteracted and controlled by an
antitorque (tail) rotor, discussed in paragraph 3.6.
On tandem rotor helicopters the main rotors turn in opposite directions and thereby eliminate the
torque effect.
3.6. ANTITORQUE ROTOR
Figure 3.4 shows the direction of travel for a main rotor, the direction of torque for the fuselage, and
the location of an antitorque (tail) rotor.
An antitorque rotor located on the end of a tail boom extension provides compensation for torque in
the single-main-rotor helicopter. The tail rotor, driven by the engine at a constant speed, produces thrust
in a horizontal plane opposite to the torque reaction developed by the main rotor.
21
Previous Page
