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Ground Resonance Vid

S

selmacf7

Registered User
Question: it's caused by a shift in CG as a result of some outside force acting on the helo (like rough landing or wind gust I guess). The shift is a result of lead/lag joints on the blades (dyssemetry of lift, if I can remember what VERY little erau taught me about helos). Is there a way to solve the problem once it begins aside from taking off again? Seems that full autos could be a pretty dangerous concept should they not go 100% in a fully articulated system.

Also, looking at the video from the side (http://www.heli-chair.com/videos_pu...ound_resonance/Ground_Resonance_Side_View.mpg) how come the forward blade doesn't seem to resonate? In dual rotor systems I would assume it would be easily possible for one of the rotor systems to become resonant, but shouldn't the other eventually go as well?

Think helo aero is some of the cooler stuff out there... I'd love to fly those things.
 
Gatordev

Gatordev

Well-Known Member
pilot
Site Admin
Contributor
erautreetopflyr said:
Also, looking at the video from the side (http://www.heli-chair.com/videos_pu...ound_resonance/Ground_Resonance_Side_View.mpg) how come the forward blade doesn't seem to resonate? In dual rotor systems I would assume it would be easily possible for one of the rotor systems to become resonant, but shouldn't the other eventually go as well?
Click to expand...

Not necessarily, as each disc is operating in it's own world and has it's own CG. I'm not a dual rotor guy, so I don't know the intricacies of the system, but for example, when you FCF single disc systems, you're finding the center CG and adjusting it. I'm sure one disc would affect the other overall, through the transmission or airframe, but they each have their own physics. For example, I landed one time w/ a stuck right wheel brake. It caused some massive vibration, to include the instrument console to move in a way I wouldn't have thought possible. Sure the vibe was sent through the airframe from the main mount, but not all of the airframe was vibrating at the same rate. I know this is a bit different from ground resonance, but you get the idea.

Interesting to see the video from the side, thanks for the link. You can see one of the blades make contact w/ the front blade (puff of smoke) before it really starts to spin down. Guess that blade was leading (or lagging) enough that the space wasn't enough.
 
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