Helicopter Flight Information
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Helicopter Flight Information |
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The Flywheel EffectSome time ago I was on an Ag job with some friends of mine. We were flying a total of 9 helicopters on the morning of my arrival, but only 8 by that evening. Unfortunately, a very good friend of mine found himself rolled over in an irrigation ditch in the afternoon; the helicopter was a total loss, but he only had skinned knuckles out of the ordeal. He had made a very simple mistake that resulted in the accident. Actually, as with all accidents, he had made a series of mistakes which culminated in the accident. But this was his first Ag job, and he had minimal training at best. His series of mistakes began with a right turn into a downwind with insufficient altitude to recover. Well, many would say that a right turn takes less power so that should have worked. The fact of the matter is however, that it takes a much more aggressive pedal input to stop a turn than it does to execute the turn, therefore as was the case with my friend, when he came in with that strong left pedal, the main rotor rpm drooped, and he of course lost lift without the altitude cushion he needed. As he began to sink, he also began to milk the collective. He hit the ground rather hard with forward motion and slid off of a dirt road into an irrigation ditch. I have always maintained that milking the collective will not work. I have encountered some argument in that regard, but I say unjustified. Just do the math, it can not work better or quicker than a simple reduction of the collective. There were a couple of things he could have done if he had had the knowledge that this would occur. He was in a piston aircraft so he could have led with throttle immediately prior to the left pedal application which would have eliminated the rpm droop (this is even very effective in the Robinsons which have an excellent governor, but that which can not keep up with aggressive pedal application in a high powered situation). He could have climbed just a little bit higher in the turn, which would have given him more altitude to make a low powered dive back into the field. He could have kept the collective down while maintaining level flight and just let the aircraft settle slowly into the field as it built rotor rpm. Why does this happen? Don't ever forget the Flywheel Effect! True in all helicopters, but especially so if you are flying a piston powered helicopter. An abrupt left pedal input will get its power from the main rotor where a tremendous amount of energy is stored. You can experiment with this safely in a hover, but don't be overly aggressive. With a fixed collective setting into the wind and in a calm wind situation, notice that when you input left pedal, the helicopter will settle. When you input right pedal the helicopter will ascend. In the Robinson's, with the governor on, you will notice the delay in the governor application, and the corresponding droop or increase in the main rotor rpm. Don't get to aggressive with this practice, but toy with it a little bit. You can easily see why you may need to lead with throttle control even though there is a very good governor in the Robinson's. The throttle issues is not relative in turbines since the throttle is always full-open. You can still have rotor droop, you just have to be aware of it and fly accordingly.
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