Translating Tendency

Translating Tendency

In the Rotorcraft Flying Handbook also called "Drift"; but it won't drift if you don't let it! I haven't figured out why they have it written that way because if it is drifting, the pilot is failing. Though it would indeed drift if you didn't compensate for the tendency. Translating Tendency is the tendency of the helicopter to drift in the direction of tail rotor thrust.

Translating tendency is overcome by the pilot through cyclic inputs. Although most helicopters have a couple of degrees of mast tilt which is not to counter this drift because it won't, but rather to center the cyclic in consideration of where the pilot will position the cyclic in compensation. If the mast were not tilted to the left, the pilot would have the cyclic displaced to the left in high power conditions and would therefore have significantly less left cyclic available. If you think about it, proper technique prior to lifting the helicopter into the hover is control centering, not control position anticipation. Those who input out of neutral or center (control leading) will exceed needed control input in another aircraft which is different or rigged differently. I see this all the time by pilots who have been flying one particular aircraft. Control position is often different when flying different aircraft sometimes even of the same model, most noticeably when a weight and balance change has occurred.

An important issue regarding translating tendency are the issues encountered during departure from a hover and approach to a hover. I was sitting in on a class recently where an instructor was discussing these issues with his student. Although the instructor was partially correct, he was also partially incorrect. The instructor had stated that when on approach, the helicopter leads to the right due to tail rotor thrust.

This is only partially correct because the helicopter begins drifting to the right early in the approach, which the average student will not promptly correct for, if at all. The drift is caused by gyroscopic precessional effect on the main rotor, not due to translating tendency. Translating tendency does not come into play until the termination of the approach to hover when the collective is increased significantly to terminate the approach and left pedal is applied to counter the increase in torque. When this occurs, the drift is much more significant and the student will not correct the issue largely because he/she did not anticipated these actions.

When departing from a hover, if properly executed, the helicopter power should remain stable. The power applied should be at or nearly at hover power. Consequently, the amount of pedal applied will not change significantly until after passing through Effective Translational Lift when a slight decrease in power transitioning to departure power is accomplished. This decrease in power is usually about 10 percent less than hover power was.