Most helicopters have four major pilot-operated controls: collective pitch, throttle, cyclic pitch, and antitorque pedals. Pilots use the collective pitch control, also referred to as thrust lever or collective, to simultaneously and equally alter the pitch angle of the helicopter’s main rotor blades, which controls the rate of climb or descent. Pilots operate the collective pitch control with their left hand.
Linkages and hydraulic actuators connect the thrust lever to the swash plate, a mechanical device comprising a stationary bottom part and a rotating top part. The swash plate on the main rotor mast converts the input from the pilot’s controls in the fuselage into motion of the rotating rotor hub and rotor blades. The rotor mast, also called the rotor shaft, connects the transmission to the rotor and rotates the swash plate’s top part and blades.
The simultaneous and equal increase of the pitch angle of all blades produces lift, and the helicopter starts climbing. The more the pilot raises the collective, the faster the aircraft climbs. Decreasing the pitch angle of all main blades produces less lift, and the helicopter starts descending. The more the pilot lowers the collective, the faster the descent.
Changing the pitch angle of the blades, however, also changes the drag, which impacts the main rotor’s revolutions per minute (rpm). The pitch angle and the drag are in inverse correlation with the rpm. Increasing the first two decreases the latter, and vice versa.
Maintaining a constant optimal rpm underlies helicopter operations. Thus, changes in drag mandate proportionate compensatory changes in power. The throttle control and the correlator, a mechanical connection between the collective and the engine throttle, play key roles here. Typically mounted directly to the collective, the throttle control’s primary function is to adjust engine power output.
The engine drives the main transmission, to which the main rotor and the tail rotor are connected. The gears turning in the transmission simultaneously turn the two rotors but at different speeds. Typically, the speed ratio of the main rotor and the tail rotor is 1:6, or for one complete revolution of the main rotor, the tail rotor turns six. All helicopters have an optimal rpm for producing maximum lift set by their manufacturer. The throttle setting must maintain sufficient engine power to keep the rotor speed at the desired limits.
Thanks to the collector, raising and lowering the thrust lever increases and decreases power automatically. If a helicopter lacks a correlator system or it is dysfunctional, the pilot must operate the throttle control manually with the twist grip to maintain the optimal rpm.
Pilots operate the cyclic pitch control or cyclic, which typically protrudes from the cockpit floor beneath their seat, with their right hand to move the helicopter left, right, forward, and backward. The cyclic regulates the tilt of the rotor disks against the horizon, which determines the direction of the rotor disk thrust and allows the pilot to control the helicopter’s direction.
As the pilot moves the cyclic, which is also connected to the swash plate, each linkage moves independently to tilt the swash plate’s stationary half in the direction the pilot moved the cyclic. The swash plate’s rotating half mirrors the tilt of its stationary counterpart. The pitch angle of each main blade that rotates around the helicopter also changes according to the swash plate’s tilt.
Therefore, if the pilot pushes the cyclic forward, the rotor disk also tilts forward; if the pilot pushes it to the right, the rotor disk also tilts to the right, and so on. The more the pilot moves the cyclic, the greater the disk tilts and the quicker the aircraft turns in the desired direction. If the pilot keeps the cyclic control centered, the helicopter should stay stable unless there is a strong wind.
Finally, the antitorque pedals function similarly to the collective control but work the tail rotor. Located on the cockpit floor by the pilot’s feet, the antitorque pedals control the pitch and thrust of the tail rotor blades. Without control and counteraction, a helicopter’s fuselage will rotate in the opposite direction of its main rotor blades.
Thus, most helicopters have a tail rotor or antitorque rotor, making flying possible and compensating for the torque. The pedals enable the pilot to control the tail rotor blade pitch angle, which serves two main functions, depending on whether the helicopter is in forward flight or hover. In the first case, the antitorque pedals help keep the tail in line behind the helicopter’s nose. In the second case, the pedals allow the pilot to turn the aircraft 360 degrees.
