PPRuNe Forums - View Single Post - Helicopter down outside Leicester City Football Club
Old 10th Dec 2018, 19:03
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ShyTorque

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Originally Posted by m25
hoistop, I think this is a good question. The AAIB report on page 5 states that this nut was "found to have a torque load significantly higher than the required assembly value".

In addition, on page 7, paragraph 2 "the increased torque load on the castellated nut that remained on the spider end of the shaft is consistent with rotation of the tail rotor actuator control shaft"

Are they saying the jammed bearing would tighten the nut? If the rotor is turning anti-clockwise, the bearing jams and the thread is clockwise it does not seem to make sense. Or does it mean it could have tightened on impact?
I think it's likely that as the right hand duplex bearing began to seize, the nut on the left side came under a loosening torque but was initially held firm by the resistance of the split pin, as per the design intention and it began to rotate clockwise in the pin carrier. No doubt the locking wire would break at this point. The continued rotation of the shaft simultaneously caused a tightening torque on the starboard nut. When the starboard nut could be tightened no more, the port nut, still rapidly rotating as it was not designed to do, friction welded to the carrier, the split pin then came under sufficient torque to be sheared off, allowing the nut to instantly be unwound off the thread on the end of its shaft, at which point the controls no longer responded to the pilot's input.
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