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Helimax Catastrophic Blade Failure, headspeed limit?

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Helimax Catastrophic Blade Failure, headspeed limit?

Old 06-05-2008, 03:18 PM
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Srfingfreak
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Default Helimax Catastrophic Blade Failure, headspeed limit?

Hello all,
I'm working on an engineering project which involves pushing a custom hub up to the 4k-5k rpm range. I'm trying to identify failure points, but I can't seem to find a way to test the blades themselves to failure without clamping the blade and yanking on it, which isn't fair to the blade since it'll collapse the blade itself. The Blade I'm working with is a HMXE4308 made out of what seems to be carbon fiber. I was wondering if any of you out there have managed to catastrophically fail a blade through spinning, pitching, or just throwing a helicopter into a tree, and what the conditions were?
Of course, if anyone knows where I could get some engineering data on the subject, that would be invaluable.

Thank you very much
Old 06-06-2008, 09:15 PM
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Teenage Pilot 14
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Default RE: Helimax Catastrophic Blade Failure, headspeed limit?

If they're CF they'll hold at least well into the 7000+ rpm range. Don't worry about a thing. If they're not CF, though, may physics have mercy on you.
Old 06-06-2008, 10:51 PM
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osterizer
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Default RE: Helimax Catastrophic Blade Failure, headspeed limit?

ORIGINAL: Teenage Pilot 13

If they're CF they'll hold at least well into the 7000+ rpm range. ....
Perhaps you could explain the basis for that statement.

Old 06-07-2008, 04:51 AM
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Default RE: Helimax Catastrophic Blade Failure, headspeed limit?

Well, I rolled my Axe into the ground in FFF the other day, damaging a bunch of small parts and requiring a head rebuild, but the wood blades are each amazingly in one piece and almost still usable! So maybe these things are tougher than we think.
Old 06-07-2008, 11:11 AM
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osterizer
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Default RE: Helimax Catastrophic Blade Failure, headspeed limit?

They are pretty tough until they hit something, but then it's kind of a crapshoot, unless it's a HBFP . I'm curious about the 7000 rpm figure. The blades I use have some pretty varied weights, and varied distribution, but most of fthem have similar construction. Given the exponential change in stress with changing weight, and my personal expectation that it's the fiber, construction and cross section of the grip root that's going to determine the blade's "speed limit," I wonder what data support that they'll all spin that fast.
Old 06-07-2008, 03:13 PM
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Default RE: Helimax Catastrophic Blade Failure, headspeed limit?

Well I went into sand out here in the AZ desert, I suspect that had a lot to do with the blades' survival.
Old 06-08-2008, 08:55 AM
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Srfingfreak
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Default RE: Helimax Catastrophic Blade Failure, headspeed limit?

In case any of you are interested, the equation for centripetal force is

Fc = m(v^2)/r

Which makes your hub radius (to the center of mass of the blade, of course) and the tip velocity some of the most important factors. The CF blades I've got seem to have a C.O.M. at approximately half their length, which is good airfoil design.

I'm glad nobody's managed to spin one of these things into breaking itself. When I break mine through stress-testing, and I will, believe me, I'll post some info about the circumstances, and some cool pics too I hope.

Thanks for the help!

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