Yesterday's news showed a helicopter on the ground.It started to vibrate and it shook itself to pieces !! It looked so funny .The comment was it had to do something with resonance with the ground ??? Could one of you explain that to us non-helicopter types ?
Very simply; with three bladed helicopters, it's when an oscillation starts between the fuselage, the blades and the ground. It can shake the helicopter apart, the fix is to lift it back in the air again to stop it before it's too late.
If anyone is interested, I still have that BRIDGE for sale ????????????????????????????????????????????????????????????????????????????????????????????????????????.
Posts: 1096 | Location: UNITED STATES of AMERTCA | Registered: 29 June 2007
Dave got the jest of it, its something that can occur in articulated rotor systems. Or as Capt Dave said three bladed helicopters. I seen video and all I can say is that the pilot had a real bad day. The vibration starts when the rotor blades get knocked out of alignment. A hard landing and a bad shocks is usually how this occurs, the fix is lift off into a hover, and the vibration will dissipate. What happened here was either he rolled power back to flight Idle and could not go into a hover or something else occurred. Either way its not often you get to see a helicopter shake its self apart. I fly mostly Bell 206's its an underslung rotor system the rotor blades flap as a unit while in an articulated rotor system the rotor blade flap independently of each other during the rotation around the rotor mast. At the tip of the rotor blades the tip speed is around 400 mph. What happens is that a pitch change link or a droop stop could have failed, and well there is nothing much you can do about it. Its a heck of a thing to watch.
Posts: 1070 | Location: East Haddam, CT | Registered: 16 July 2000
To add to what George just said, it's a serious enough problem that the US Army covers it extensively in it's manuals and they also no longer will purchase any three bladed helicopters (they are phasing out the one's that are left or upgrading to four bladed versions). It was a bigger problem with wheel equipped aircraft that it is with skids, but as the video you mentioned showed, it can happen to skid equipped versions also.
Originally posted by ztreh: If anyone is interested, I still have that BRIDGE for sale ????????????????????????????????????????????????????????????????????????????????????????????????????????.
Originally posted by ztreh: If anyone is interested, I still have that BRIDGE for sale ????????????????????????????????????????????????????????????????????????????????????????????????????????.
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