AVSIG: Not a Robbie... wwswsigarch.jpg (7236 bytes)

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Jeff Hartmann CIC
Top Gun


Reged: 05/18/04
Posts: 7323
Loc: Chico,CA
Not a Robbie...
      #336508 - 02/27/12 10:11 PM

http://www.bbc.co.uk/news/world-latin-america-17150747

How do you describe this Anne, other Bill?

--------------------
Jeff

nothing clever to say right now...


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Mase Taylor
Top Gun


Reged: 04/29/04
Posts: 9446
Loc: SOCAL
Re: Not a Robbie... [Re: Jeff Hartmann CIC]
      #336509 - 02/27/12 10:13 PM

Looks like some kind of harmonic problem?

--------------------
Fly The Airplane As Far Into The Crash As Possible. - Bob Hoover 1922-2016 R.I.P.


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Jeff Hartmann CIC
Top Gun


Reged: 05/18/04
Posts: 7323
Loc: Chico,CA
Re: Not a Robbie... [Re: Mase Taylor]
      #336511 - 02/27/12 10:33 PM

Have to warn the TSA about Harmonicas.

--------------------
Jeff

nothing clever to say right now...


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Ray Tackett
Top Gun


Reged: 04/30/04
Posts: 8892
Loc: Philadelphia, USA
Not a Robbie... [Re: Jeff Hartmann CIC]
      #336533 - 02/28/12 07:43 AM

Ground resonance: http://tinyurl.com/8xopthr

In my training, the instructor said a good way to get into ground resonance
is to land hard on one wheel or one end of one skid.

--------------------
Ray,

Owner, Lake Wood Be Gone

Turning quality lumber into sawdust and noise since 2013.


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Jeff Hartmann CIC
Top Gun


Reged: 05/18/04
Posts: 7323
Loc: Chico,CA
Re: Not a Robbie... [Re: Ray Tackett]
      #336534 - 02/28/12 07:54 AM

Sort of exacerbated "doyoyoyyoingggg".

Impressive.

--------------------
Jeff

nothing clever to say right now...

Edited by Jeff Hartmann (INT/SVH) (02/28/12 07:55 AM)


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Anne Umphrey (KBED)
Top Gun


Reged: 04/28/04
Posts: 12756
Loc: KBED
Re: Not a Robbie... [Re: Ray Tackett]
      #336550 - 02/28/12 09:07 AM

Excellent understandable description of the phenomenon of Ground Resonance, how to get into it, and how to get out of it.

The news clip mentioned not unlike a washing machine out of balance. Apt description. I take exception however, because the article says "while the helicopter is on a level surface." It isn't the surface the helicopter lands on, but the way it is set down. Too hard on one skid can cause it for example.

Anne

--------------------
You haven't seen a tree until you've seen its shadow from the sky.
- Amelia Earhart, 1897 - 1937


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Jeff Hartmann CIC
Top Gun


Reged: 05/18/04
Posts: 7323
Loc: Chico,CA
Re: Not a Robbie... [Re: Anne Umphrey (KBED)]
      #336553 - 02/28/12 09:12 AM

Anne, or Ray

Can you just pick it back up to get out?

Or, do you select the Delicate cycle.....

--------------------
Jeff

nothing clever to say right now...


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Bill Bridges - 9S1
Top Gun


Reged: 05/17/04
Posts: 6008
Loc: 9S1
Re: Not a Robbie... [Re: Jeff Hartmann CIC]
      #336558 - 02/28/12 10:51 AM

Quote:

http://www.bbc.co.uk/news/world-latin-america-17150747

How do you describe this Anne, other Bill?




I always thought ground resinance was related more to the blades gettin out of phase similar to what happened on the L-188. It could be a problem on the TH-55 (more than two rotor blades with lag dampeners) only when one of the oleo struts was deflated. I have never heard of it happening on Bells since they normally have only two rotor blades.

the other bill


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Stephanie Belser-2
Top Gun APC


Reged: 04/28/04
Posts: 7139
Loc: KFAM
Re: Not a Robbie... [Re: Jeff Hartmann CIC]
      #336561 - 02/28/12 11:39 AM

Quote:

Anne, or Ray

Can you just pick it back up to get out?




That's what this pilot did.


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Ray Tackett
Top Gun


Reged: 04/30/04
Posts: 8892
Loc: Philadelphia, USA
Not a Robbie... [Re: Anne Umphrey (KBED)]
      #336572 - 02/28/12 12:45 PM

When local news ran that clip, they said ground resonance was caused by the
rotor continuing to turn after landing. That should scare lots of people,
which is what they seem to want.

--------------------
Ray,

Owner, Lake Wood Be Gone

Turning quality lumber into sawdust and noise since 2013.


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Ray Tackett
Top Gun


Reged: 04/30/04
Posts: 8892
Loc: Philadelphia, USA
Not a Robbie... [Re: Jeff Hartmann CIC]
      #336574 - 02/28/12 12:45 PM

In a way, it's what tore the wings off of Lockheed Electras. You get into a
vibration mode (whirl mode on the outboard engines of the Electra) where the
engine powers the oscillation until something breaks and ends the cycle.

--------------------
Ray,

Owner, Lake Wood Be Gone

Turning quality lumber into sawdust and noise since 2013.


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Anne Umphrey (KBED)
Top Gun


Reged: 04/28/04
Posts: 12756
Loc: KBED
Re: Not a Robbie... [Re: Ray Tackett]
      #336606 - 02/28/12 04:39 PM

Or they were just clueless. The statement in the write up said that it happens while the helicopter is on a level surface or words to that effect. I'll bet that when the reporter asked the expert/pilot or whomever, he said that it could happen even on a level surface if conditions were favorable. the reporter left out the "even on " part and "conditions".

Anne

--------------------
You haven't seen a tree until you've seen its shadow from the sky.
- Amelia Earhart, 1897 - 1937


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Anne Umphrey (KBED)
Top Gun


Reged: 04/28/04
Posts: 12756
Loc: KBED
Re: Not a Robbie... [Re: Jeff Hartmann CIC]
      #336607 - 02/28/12 04:45 PM

If you have the power you can lift off the ground and that will take care of the problem. But often the helicopter is slowing down and there isn't sufficient power to lift off the ground.

If you note the one in the MacGyver incident the helicopter was at full power so he just got up off the ground and everything evened out. I'll bet his heart was beating a little faster however.
Anne

--------------------
You haven't seen a tree until you've seen its shadow from the sky.
- Amelia Earhart, 1897 - 1937


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Reams Goodloe
Top Gun


Reged: 05/07/04
Posts: 2582
Loc: Kent, Washington
Re: Not a Robbie... [Re: Stephanie Belser-2]
      #347347 - 07/17/12 06:22 PM


Take a look at the Chinook test at that same YouTube location...

- Reams-


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