Helicopter rattles apart after landing

Almost happened on a MacGyver episode... helicopter lifted off the deck, even with the door open, to fix the problem (remove helicopter contact with the surface)...

 
Google CH-47 Ground Resonance
and watch a Chinook have a mid air with itself. Only had one get close in my time flying them. Jerked it into a hover then crapped myself:). Scary feeling!
 
Rotor&Wing said:
Eurocopter claims the AS350 won't go into ground resonance.

Just blew that claim. :rolleyes:
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Eurocopter really claimed that? I watched one a few years back land and start the ground res dance. Pilot took appropriate action and got it airborne and landed again so it was a non-incident. However, after that I was told by another pilot with time in the machine that the Astar was very susceptible to ground res. I thought that was it's 'claim to fame'.
 
Laurie said:
Eurocopter really claimed that? I watched one a few years back land and start the ground res dance. Pilot took appropriate action and got it airborne and landed again so it was a non-incident. However, after that I was told by another pilot with time in the machine that the Astar was very susceptible to ground res. I thought that was it's 'claim to fame'.
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Yep, they claimed the "springs" (those things on the aft end of the skid that look like a leaf spring) would prevent ground resonance. The AS350 is one helicopter I found it hard to make good consistent touch downs.
 
Nsconductor said:
Google CH-47 Ground Resonance
and watch a Chinook have a mid air with itself. Only had one get close in my time flying them. Jerked it into a hover then crapped myself:). Scary feeling!
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Holy Crap! :yikes: I've never heard of/seen that... Unbelievable! But I've always said, "Too many moving parts; And every one of them is needed to keep them airborne."
 
How susceptible are helicopters to this? I'm no rotary-wing pilot, so I've never heard of it. Now, after seeing these videos, I wonder why they ALL don't shake apart every time?
 
Matthew said:
How susceptible are helicopters to this? I'm no rotary-wing pilot, so I've never heard of it. Now, after seeing these videos, I wonder why they ALL don't shake apart every time?
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Fully articulated rotor heads are susceptible to ground resonance.

On a 3 (or more) blade system the blades flap and feather, but they also lead and lag. As the blades accelerate they lag, when decelerating they lead. So on a 3 blade system each blade is 120 degrees apart.

On landing if a sudden shock is made it can translate into the rotor head and cause one blade to go slightly out of phase, say 120, 243 and 360. Now the main rotor shaft is "stick stirring" rather than being central as the blades rotate. This is ground resonance. To get out of it simply lift the helicopter back in flight and centrifugal force will bring the blades back to 120, 240 and 360. A way to picture this is drop a quarter on a table and watch it waller around before it stops.

To answer your question, it's not a big deal if the helicopter is maintained, the rotor head and it's dampers are maintained and the shock absorbing system on the landing gear is maintained. Of course good pilot training and recognizing the signs early and making the correction ASAP.

The AS350 uses these spring like devices on the aft of the skids to help prevent ground resonance but it does make the helicopter tricky to get a good landing.
 
Thanks for the description. I can understand how the off-kilter situation can get out of control (after watching heavy equipment walk across a factory floor.)
 
Matthew said:
I can understand how the off-kilter situation can get out of control (after watching heavy equipment walk across a factory floor.)
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..and how DNA ultra-centrifuge rotors walk right through the concrete wall of the vault they are mounted in :) .
 
Yeah - I guess I was just surprised that once the helicopter is off the ground that it stabilizes.
 
Matthew said:
Yeah - I guess I was just surprised that once the helicopter is off the ground that it stabilizes.
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It's a bit like a boat smashing itself to smithereens against a dock vs being out in the water where there's nothing to amplify the forces when it moves.
 
A relative flew Seasprites in the Navy some years ago, sometimes off bigger ships (LPH's) and sometimes they would land on smaller ships (Destroyers and Frigates), which would sometimes be assisted by a ship-mounted winch...so my questions- 1: in there more/less susceptibility to ground resonance in seaborne operations, and 2: would the winch be an amplifier or a resistor to the risk?
 
The AvWeb version of this says there were reports the helicopter was vibrating excessively in the air prior to touchdown, and that would seem to jive with the fact that you can see the pilot start to lift off into a hover again and think better of it about halfway through the video. The aircraft gets light enough on the skids to turn about 30 degrees.
 
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