Revolution mixing was commonly used before the advent of heading hold gyros. As collective pitch is increased, the increased drag on the main rotor requires that the throttle be increased to maintain the head speed. The increase in throttle increases the torque reaction, requiring tail rotor thrust to be increased to maintain the helicopter's heading.
When using a rate mode gyro, this corrective signal must be generated by the pilot, either by increasing rudder inputs when raising collective, or by setting up a revolution mix on the transmitter to correlate rudder to throttle automatically. A revoultion mix would rarely be a precise match to the changing torque, so the pilot would still have to fine tune the heading with the rudder control as power was added and removed.
With the advent of heading hold gyros, revolution mixing was rendered obsolete. A heading hold gyro (in heading hold mode) would see any revolution mix input as a request to yaw and would do so, regardless of any changes in rotor torque.
- Practical Theories, by Colin Mill.
Share your opinion