Differential Pitch Control
For helicopters with contra-rotating rotors, helicopter control requires interaction between the two rotors. A helicopter with tandem rotors uses differential collective pitch to change the pitch attitude of the aircraft. To pitch nose down and accelerate forward, the collective pitch on the front rotor is decreased and the collective pitch on the rear rotor is increased proportionally. Conversely, the synchropter and transverse-mounted rotor helicopters use differential collective pitch to affect the roll of the aircraft. All of these configurations use differential cyclic pitch to control movement about the yaw axis, tilting the rotors in opposite directions to cause the aircraft to spin in the direction of the tilted rotors.
Read more about this topic: Helicopter Flight Controls
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