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Old 02-16-2012, 06:06 AM   #5326
Elburrito
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last weekend...



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Old 02-16-2012, 08:13 AM   #5327
Hedge36
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Hey, man - your Robbie's got really bad dundruff
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Old 02-16-2012, 09:59 AM   #5328
Weirdo OP
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Originally Posted by aclark79 View Post
Passed my 427 checkride today, back to being a single pilot Capt again.
Nobody else to blame!
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Old 02-17-2012, 05:37 AM   #5329
poondogger
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Great Sand Dunes National Park

Flying will never get old for me.
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Old 02-17-2012, 07:33 AM   #5330
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Flying will never get old for me.
Maan!
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Old 02-17-2012, 07:09 PM   #5331
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Flying will never get old for me.
Not jealous. Not jealous. Not jealous.
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Old 02-20-2012, 01:21 PM   #5332
MsLizVt
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Just curious ...

Hi!

My apologies if this is 205, but I don't remember seeing this video in this thread. At 43 or 44 seconds in, there's a Green Skyline Agusta. Anyone recognize it? (Weirdo?)

Enjoy,



Liz









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Old 02-24-2012, 11:15 AM   #5333
IheartmyNx
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rut ro...

new embed..

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Old 02-24-2012, 11:36 AM   #5334
Trixie
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any idea what happened? looks like it somehow became off-balance or off center.
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Old 02-24-2012, 01:25 PM   #5335
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any idea what happened? looks like it somehow became off-balance or off center.
Ground resonance.
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Old 02-24-2012, 02:48 PM   #5336
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Ground resonance.
Please explain?
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Old 02-24-2012, 02:57 PM   #5337
Jeffy
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Please explain?
I will defer to Wikipedia: http://en.wikipedia.org/wiki/Ground_resonance

Ground resonance is a hazardous condition that can occur any time the rotor of a helicopter or gyroplane is turning while the aircraft is on the ground. Similar in concept to the behavior of a washing machine when the clothes are concentrated at one point during the spin cycle, ground resonance can occur with a rotorcraft when the spacing between blades becomes irregular or the damping system, including drag hinge dampers, landing gear oleo struts, or wheel tire pressure, is operating out of limits. Ground resonance occurs at three rotor rpm bands, the first at about one-third of normal rotor speed, the second at a range including normal rotor speed, and the last in a range above normal rotor speed.

Ground resonance is precipitated by a shock to the aircraft arising from excessive motion of a rotor blade in its plane of rotation thereby moving the rotor center of gravity from the axis of rotation. Inadequate damping allows the rotor center of gravity to spiral away from the rotor axis of rotation, causing the rotor to generate unbalanced rotating moments beyond the compensating ability of the damping system. In addition to damping system malfunctions mentioned above, such blade movement can occur as a result of taxiing over rough ground with the rotor turning at a speed within a susceptible range, or takeoff/landing in which a shock occurs to one side of the landing gear.

Under extreme conditions, the initial shock can cause violent oscillations that quickly build and result in catastrophic damage of the entire airframe. In some cases, complete destruction occurs, e.g. body panels, fuel tanks, and engines are torn away, even at normal rotor speed.

Recovery is possible in some cases. If sufficient rotor RPM exists, immediate takeoff can restore rotor balance. If rotor RPM is low, complete shutdown may be sufficient.
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Old 02-24-2012, 03:35 PM   #5338
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freakin helos are for teh birds....
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Old 02-25-2012, 12:29 AM   #5339
Hay Ewe
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As the ground resonance is caused by (but not limited to) the blades not being equal distance, I wonder if that could have caused.

Looks to be an AS350 of some model (B2) and they have elastomeric heads so maybe one of (or more) of the elastomerics were flogged out and caused this?

could be totally wrong but...

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Old 02-25-2012, 12:43 AM   #5340
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I know that Huey's can go into ground resonance at idle under the right conditions - fuel load, total aircraft weight, type of surface it's sitting on, etc. When we feel a bit of vibration (you know it the first time you feel it) we pull in a bit of collective to load the rotor system and change the static and rotating dynamics such that the resonance frequency is changed and the aircraft is no longer in danger of falling to pieces. Another option is to increase rotor RPM and actually lift off for a second and then set the aircraft back down again. Sometimes a slight change in how the aircraft sits on the ground can make enough of a change.

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