What does DCP do to the tandem rotor helicopter?

• A. Varies the amount of thrust produced by forward and aft rotor system
• B. Stabilizes the helicopter in hover
• C. Changes the rotor speed
• D. Controls tail rotor pitch

Answer: (A)

In a tandem rotor helicopter, control of pitch and yaw comes from changing how much lift each of the two main rotors produces. DCP, or differential collective pitch, adjusts the collective pitch of the forward and aft rotors in opposite directions, shifting thrust between them. That thrust imbalance creates a pitching moment (and, when used with other inputs, a yawing moment) so the helicopter can tilt forward or backward or rotate about its vertical axis. Rotor speed is kept constant by the engine/governor, and there is no tail rotor to pitch in a tandem-rotor design, so DCP isn’t about tail rotor control.