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Scorpion Power Scorpion Power
HelicopterAerial Photography and Video › Flying Bowling Ball
12-02-2007 09:44 PM  9 years agoPost 21
eric_b

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Denver, CO, USA

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Yes, the vibs will disappear once you leave the ground, unless the "new" structure has a resonant frequency that's the same as the vibration present (engine, tail rotor, main rotor vibs, typically in descending order).

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12-02-2007 11:54 PM  9 years agoPost 22
bill the greek

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Greece

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Interesting post. Eric thanks for info about Ground Resonance.
I read a post about this effect long time ago and the only i have in my notepad is
Ground resonance happens in helicopters with lead-lag hinges. It occurs only on the ground. It starts when the blades "bunch up" on one side of the rotor disc where they generate an unbalanced centrifical force that gets in phase with the natural frequency of the aircraft rocking on it's landing gear.
If i found the link i will post it.

edit:
I found it
here is a good info and here

BIll

Vasilis

Nobody is Perfect but who want to be Nobody...

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12-03-2007 03:41 AM  9 years agoPost 23
eyeinsky

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Fall River, Nova Scotia, Canada

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Nice ball should make your machine more reliable in the condition that we have seen you operate in. Let us know how it works out.

eric
Good video I got this from my text book.
Ground resonance is a self-excited vibration that can happen when the helicopter is on the ground, which may manifest slowly and gradually build up or appear very rapidly. It is caused by one blade leading and one blade lagging at the point of contact with the ground. The feed back from the landing gear especially if on uneven ground can start this condition. This can damage the helicopter if not corrected. The best thing to do if this condition occurs is lift off the as fast as possible it will correct its self immediately.

I have seen this, at the time I reduced power she sure rattled on the ground. Next time I will take off.

Hard job competing with gravity.

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12-03-2007 04:00 AM  9 years agoPost 24
trackhead

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utah

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Let us know how it works out.
Flew it this evening for the first time. Plenty of power, no weight concerns at all.

I'll have some new footage from it in the next week or two.

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12-03-2007 04:22 AM  9 years agoPost 25
FLAP

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Michigan

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On the visability issue, I just picked up 3 meter glider flying last year and spent some time reading on this topic. According to the glider guys, the tops of the planes are generally light colored and the bottom is usually a darker color, as mine is red. With spending time in the range of 1000-2000 feet color more or less disappers. The darker contrasting color, to the sky which appears lighter, are actually easier to see higher up.

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12-03-2007 05:52 AM  9 years agoPost 26
Spencer K

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Phoenix, Az

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did you steal that from the local news heli?

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12-08-2007 06:23 AM  9 years agoPost 27
Vortex Aerial

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Riverside Ca

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Track

Is that whole thing hard mounted to the heli frame?

Can you tell us what kind of roll stabi youll use?

Your stuff gets better by the minute man !

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12-08-2007 11:19 AM  9 years agoPost 28
gordonre

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Ireland

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Eric, very good answer above! I had the same question(s) as the other guys who asked!

Gordon

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12-08-2007 04:39 PM  9 years agoPost 29
xfc3dcd

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West Carrollton, Ohio usa

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I know this is a discussion about bowling ball technology but I thought I would share my experiences with ground resonance.

A defense contractor I was working with had installed a very tall landing gear 30" for a large gas helicopter out of PVC. By doing this it made to unit more suseptable to ground resonance. The helicopter tore itself apart on the first attempt to lift off. For a few weeks I did quite a bit of experimentation to better understand the problem. What I found is that if you "tune" the landing gears rigidity far enough away from the point that exacerbates the condition, resonance stops. On a small helicopter this could be as simple as connecting rubber bands between the two skids or conversely adding a stiffening rod. Tightening the blade grip bolts also helped.

Since this very tall gear was required to complete the project for this large gas heli, it was really a challenge to eliminate the problem. The final solution I devised was to install rubber isolators between the bottom of the frames and the struts. This totally removed the interaction between the rotating mass and the ground making resonance impossible.

Also I found that once resonance starts, it has been my experience that it is better to quickly lift off verses powering down. Powering down slows the rotation but increases the amplitude of the occilations.

Wendell
PPAP

"When things seem to be going perfectly, there is something wrong that you don't know about"

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12-08-2007 08:45 PM  9 years agoPost 30
trackhead

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utah

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My landing gear is working just fine. The ball just barely rests on the ground during landing. No worries about resonance, vibrations, or other annoying things.

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12-08-2007 11:35 PM  9 years agoPost 31
rerazor

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Mich.

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