Helicopter Flight Information
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Helicopter Flight Information This domain is for sale. #1 in all relative searches, 12,000 views per month averaging 400 views per day! |
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Translating Tendency In the Rotorcraft Flying Handbook also poorly called 'Drift' A student I was recently talking with didn't recognize right away what I was talking about when I inquired to him about translating tendency, as I queried him more, he said, "oh, you mean drift". I explained to him that I was inquiring as to his knowledge of translating tendency and he stated that in the rotorcraft flying handbook they called it drift. It is somewhat disappointing that an FAA publication would include informal terms or slang if you will, in its reference to aerodynamic terms. Why don't we just start calling 'Vortex Ring State', 'Sink'; 'Effective Translational Lift', 'Blowback', etc? The fact is that Translating Tendency is the tendency of the helicopter to drift in the direction of tail rotor thrust. Any student should understand what the technical aerodynamic terms are, and the he/she should be able to describe them in detail when asked about them specifically. Translating tendency is overcome by pilot cyclic inputs. Although most helicopters have a couple of degrees of mast tilt which is not to counter this drift, 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. Imagine landing on a slope, left skid upslope, in this condition. 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, which is poor technique) will exceed needed control input in another aircraft which is different. I see this all the time by pilots who have been flying one aircraft. Control position is often different when flying different aircraft even of the same model of aircraft, 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 incorrect because the helicopter begins drifting to the right early in the approach, and the average student will not correct this. The drift is caused by gyroscopic influence 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 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 has 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 quite insignificant because it should be less than 10 percent lower than hover power.
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