What exactly is ground resonance?

Muff3n

Muff3n

Well-Known Member
Hey guys,

I and some of the guys from the hanger at work were watching some helicopter ground resonance videos on youtube (yeah..working real hard right?). I always been an airplane guy have never really seen ground resonance, then I watched that military video where it shook that chinook so bad it ripped the back rotor completely off. I was just going to ask some of you helo guys (or airplane guys if you know the answer) what exactly causes ground resonance? What is the phenomona that is occurring?

Here is the video for you guys that don't know about ground resonance and how it can make a helicopter absolutely shake itself apart.

[video=youtube;RihcJR0zvfM]http://www.youtube.com/watch?v=RihcJR0zvfM[/video]

Thanks for the feedback.
 
Generally, things like a hard landing or such can induce ground reasonance. A hard landing can cause a "ripple" of shock to propogate from the landing gear or skids and up into the rotor system, throwing the system off balance. Its only common in its pure form in rotor systems with three or more blades that are fully articulated, or otherwise utilize lead-lag in each blade, allowing the blades to "hunt" and maintain a flight balance. A shock into the rotor system can cause the lead-lag in the blades to become unbalanced and get worse, almost in a dynamic instability sense. The easiest way to alleviate this is to put power into the rotor system and lift off into a hover, thus forcing the rotor system back into balance by inducing load. Note that two-bladed "teetering" or rigid rotor systems, such as the UH-1 or OH-58, aren't susceptible to this phenomena, as their blades are rigid and don't utilize lead-lag systems in each blade.

p.s.- get a job.....
 
I know that our old helicopter at the flight school, one of our pilots got into ground resonance but managed to save it, however it needed new blades after that.
 
poser765 said:
Way too many things like this that blow my mind and make me never want to fly a helicopter
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haha I'm the exact opposite. It's things like this that make me want to fly helicopters. Not that I would ever want to experience something like ground resonance, but the fact that it's a possibility makes it sound like you need to respect helicopters that much more each time you fly them. I'd love to learn how to fly rotor.
 
MikeD said:
Don't know what you're missing....
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I don't know, my friend. I took one of those 15 dollar 5 minute helicopter rides at the airshow once...hated it. I just felt way to unnatural, and that made me nervous. Nothin but love for ya if that's your thing though.
 
poser765 said:
I don't know, my friend. I took one of those 15 dollar 5 minute helicopter rides at the airshow once...hated it. I just felt way to unnatural, and that made me nervous. Nothin but love for ya if that's your thing though.
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So you do know what you're missing then! The cool thing is, at least you tried it and then determined that you didn't like it. That's fair and respectable. Alot of people claim not to like things like this, without ever having tried it or given it a shot. You did, and it wasn't for you. Thats all good, partner! :)
 
MikeD said:
So you do know what you're missing then! The cool thing is, at least you tried it and then determined that you didn't like it. That's fair and respectable. Alot of people claim not to like things like this, without ever having tried it or given it a shot. You did, and it wasn't for you. Thats all good, partner! :)
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Which do you prefer? Fixed wing or whirly-birds?

Which have you found most challenging?
 
beasly said:
Which do you prefer? Fixed wing or whirly-birds?

Which have you found most challenging?
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Helicopters and Helicopters.

That having been said, it was the WAY we flew and WHERE we flew that made it both preferable and challenging. In the military, I flew fixed-wing too and prefer helicopters. Also, I've flown civilian helicopter, although rewarding to say the least, it wasn't as challenging nor preferable to military flying.

All is lost now anyway as it's been a little over a year since I've flown one. :mad:
TurboProp and TurboJet for me now.......
 
poser765 said:
I don't know, my friend. I took one of those 15 dollar 5 minute helicopter rides at the airshow once...hated it. I just felt way to unnatural, and that made me nervous. Nothin but love for ya if that's your thing though.
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I love choppers, would love to add a rotorcraft rating to my certificate some day. Probably one of the most fun flights I've ever been on was a helicopter tour on the island of Kauai. We flew a Hughes 500 with the doors off. Flying over Waimea canyon and the Na Pali coast with no doors = awesome.

Plus, the takeoff sensation in a helicopter is pretty strange, yet neat at the same time; it's like being in an elevator.
 
Apophis said:
Plus, the takeoff sensation in a helicopter is pretty strange, yet neat at the same time; it's like being in an elevator.
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Yeah I agree. I've only done a couple flights in a Schweitzer, but it was with one of the guys from our airport who was a Huey pilot in Vietnam, so to say it was an awesome experience to fly with him, doesn't even begin to describe it. We did a lesson on hovering and a little bit of pattern. Probably the most fun I've had in an aircraft. I'd LOVE to get my rating
 
I enjoyed my experience on my one and only helicopter ride. It's just an awesome sensation!
 
I love helicopters. Got to ride in a Customs UH-1 about thirty years ago. That was a real kick because my father was engineer responsible for evaluating the UH-1 and the HH-43 for the Air Force contract back in the late '50s when we were stationed at Wright-Patterson.

His recommendation was for the UH-1, but Congress forced the Air Force to go with the Kaman.
 
RDoug said:
I love helicopters. Got to ride in a Customs UH-1 about thirty years ago. That was a real kick because my father was engineer responsible for evaluating the UH-1 and the HH-43 for the Air Force contract back in the late '50s when we were stationed at Wright-Patterson.

His recommendation was for the UH-1, but Congress forced the Air Force to go with the Kaman.
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Funny thing is, they ended up using both.

And the CBP UH-1s are still in full frontline service.
 
MikeD said:
Funny thing is, they ended up using both.

And the CBP UH-1s are still in full frontline service.
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Yeah. Ain't that a kick. The only time I ever recall seeing an Air Force Huskie is action was when we were stationed at Kadena. There was one up over the field anytime there was an ongoing SR-71 operation—launch or recovery. They were using it as a rescue craft. Never thought that boded very well for expectations on SR-71 safety. Funny thing is, when I worked in the tower at Mildenhall for a couple of months while Lakenheath redid the runway in preparation for the F-4D-to-F-111F transition, they never put up a rescue chopper during SR-71 ops.
 
RDoug said:
Yeah. Ain't that a kick. The only time I ever recall seeing an Air Force Huskie is action was when we were stationed at Kadena. There was one up over the field anytime there was an ongoing SR-71 operation—launch or recovery. They were using it as a rescue craft. Never thought that boded very well for expectations on SR-71 safety. Funny thing is, when I worked in the tower at Mildenhall for a couple of months while Lakenheath redid the runway in preparation for the F-4D-to-F-111F transition, they never put up a rescue chopper during SR-71 ops.
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Yes, the old -43s used to be the base rescue birds with the Fire Suppression kit (a mobile firefighting kit) as a sling load, and a crew of a pilot and two crash-rescue firefighters. The AF did away with the concept in the early '80s?

Interesting thing about the -43s in ''Nam; although they were base rescue birds, they did get a good few Combat rescues of downed pilots, when the normal CSAR HH-3/HH-53s weren't available.
 
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