Dual-Rotor Helicopter Control Principles

Control principle of dual-rotor helicopter with tandem arrangement of the lifting rotors. Longitudinal control of the helicopter is achieved by
deflecting the stick fore and aft. This leads to cyclic change of the pitch of the lifting rotors, as a result of which the axes of the cones-of-rotation are tilted forward or backward, i. e., in the direction of the stick (Figure 108). In addition to the cyclic variation of the pitch there is a differential change of the collective pitch, in which the thrust of one rotor is increased while that of the other is decreased.

If the stick is deflected forward, the axes of the cones-of- rotation of the lifting rotors are tilted forward. The collective pitch of the front rotor is reduced and that of the aft rotor is increased. As the thrust force vectors tilt, there is a change of the thrust force arms relative to the helicopter transverse axis. The result is the creation of a diving moment equal to the difference of the thrust moments of the front and rear rotors.

Under the influence of this moment the helicopter nose will drop, increasing the flight speed. If the stick is moved aft, a climbing moment is created and the helicopter nose will rise, reducing the flight speed.

Lateral control of the helicopter is achieved by deflecting the stick to the right and left. This leads to simultaneous identical change of the cyclic pitch of the front and rear lifting rotors. A lateral control moment appears which then causes rotation of the helicopter around the longitudinal axis.

Directional control, or control of helicopter rotation around the vertical axis, is accomplished with the aid of the directional control pedals. Deflection of the pedals leads to differential change of the cyclic pitch of the lifting rotors. The axes of the cones-of-rotation deflect in opposite directions, forming the directional control moment as a result of side forces. If the right pedal is pushed, the coning axis of the front rotor is deflected to the left. The side components of the lifting rotor thrust forces create a pair, whose moment turns the helicopter to the right.

Control principle of the dual-rotor helicopter with side-by-side lifting rotors. The control stick is moved fore and aft for longitudinal control, and this causes the same change of the cyclic pitch of the lifting rotors and deflection of the axes of the cones-of-revolution in the direction of stick displacement. This creates a longitudinal control moment (just as in the case of the single-rotor helicopter).

Lateral control is accomplished by deflecting the stick to the right or left. This deflection leads to differential change of the collective pitch of the lifting rotors. If the stick is moved to the right, the collective pitch of the right rotor is reduced and that of the left rotor is increased. Change of the collective pitch causes change of the thrust forces. The difference of the thrust forces of the right and left lifting rotors leads to the creation of a lateral moment which then causes a bank to the right.

The helicopter with side-by-side arrangement of the lifting rotors has an auxiliary wing which gives the helicopter lateral stability.

Directional control of the helicopter is accomplished by the control moment which is created by differential change of the cyclic pitch and tilting of the axes of the cones-of-rotation in opposite directions: forward and

backward. If the right pedal is pushed, the axis of the cone-of-rotation of the right rotor is deflected aft while that of the left is deflected forward. The horizontal components of the thrust forces create the directional control moment which causes rotation of the helicopter to the right.

Control principle of dual-rotor helicopter with coaxial rotors. Longi­tudinal and lateral control is accomplished similarly to the control of the single-rotor helicopter, i. e., by cyclic change of the pitch of the upper and lower lifting rotors. When the stick is deflected, the axes of the cones-of – rotation deflect in the same direction as the stick, creating the longitudinal or lateral control moment.

Directional control is accomplished by deflection of the pedals, which leads to differential change of the collective pitch of the lifting rotors.

This does not cause any change of the overall thrust, but leads to a change of the reactive moments of the lifting rotors and the helicopter turns in the direction of the action of the larger reactive moment.

Control of the vertical displacement of all helicopters is the same.

When the collective-throttle lever is moved up, the collective pitch of all the lifting rotors is increased, which leads to increase of the thrust and upward displacement of the helicopter. If the collective-throttle lever is fixed, the collective pitch is reduced, the thrust force decreases, and the helicopter transitions into descent.