Helicopter disintegrates on landing

[Nicola_M]

Eurocopter A Star disintegrates on landing (Video in link)

http://www.bbc.co.uk...merica-17150747

Edited February 24, 2012 by Nicola_M

[Hueyman]

Arf, again those fu***ng ground resonnance ... They should know the only escape is pull the collective and take off quickly to dissipate the vibrations, let it on the ground, letting vibration go through the ground is the best thing to destroy your Chopper ..

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[Nicola_M]

That second vid, the Squirrel, I thought that one's Dynamic Rollover.

[Simmo W]

That second one was horrid. You can see the forces throw the pilot around, making it even harder to recover.

[Hueyman]

Yes guys, the second was what we call " Dynamic Rollover ". To be short, when your Heli start to fall on a side, usually pilot tend to apply opposite side cyclic action, that's not what we should do, just take off and do a proper landing. Those accident, or not always deadly, but fatal for airframes, the fact that a big rotating system, turning fast and being heavy is to be managed properly or...

[Simmo W]

A coincidence, this just happened

http://video.msnbc.msn.com/msnbc.com/46513631/

I wonder why these occur, if basic training covers such risks? A heli version of Gottagetthere syndrome?

[Hueyman]

Yes, this is the video Nicola_M show us earlier.

Basically, you don't really can prevent it. It's a physical phenomenon related to turbine ( or piston engine ) vibration frequency, rotor vibration frequency and ground asphalt rigidity. It's caused by a unbalanced rotor, but it become unbalanced on his own, on normal operation, that rotor was perfectly balanced, but that oscillating movement just amplify the thing.

All ground resonance always happen on very Hard Surfaces which do not absorb vibration at all :

Here, the pilot didn't understand the only way to escape this hell is to take off :

This time, that pilot ( probably ex military pilot who served in Vietnam, with thousands of hours on chopper ) did the right thing, he didn't wait that the Gazelle become many spare parts, he quickly take off and the ground resonance was gone.

The only thing you can do to avoid entering into this phenomenon is to land ( or take off ) on good grass, smooth, that help absorbing vibrations. But new modern helis like EC-135 etc.. seems to have something to prevent this thing, as we can see sometimes see EC-135, 145 or those new modern heli, waiting on taxiway ( hard surface ) at idle or even at normal flight regime, without any problems.. probably something related to landing gear flexibility ( or hardness ? ) and dampers on the rotor system. On that area I don't know much, I would love to meet some Eurocopter engineer to have the right answer.

Hope to have explained a bit ;-)

Have a nice day guys !

Valentin