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HelicopterMain Discussion › Full power on a tied up Heli ??? healthy ???
10-20-2004 07:51 PM  13 years agoPost 21
BC Don

rrElite Veteran

Calgary, AB Canada

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Rays Helecopter book talks about "tieing" down. IN his example, he locks the Heli onto the top of a step ladder so it is up about 6 feet in the air. The picture is "really cute", shows this guy reaching up, wearing some old helmet from the 60s as a safety device.

Got Money? Send it to me, I'm a Heli Addict.

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10-20-2004 07:53 PM  13 years agoPost 22
sixeven

rrApprentice

Ft. Myers Florida

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corey11,

I'm not so sure about that. In full scale your right...but in our scale the head speed is high enough to get into the higher harmonics.

Either way, ground resonance is not the major concern as I mentioned earlier.

SiXeVeN

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10-20-2004 07:57 PM  13 years agoPost 23
corey11

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Bay Area, California

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true...the head speed might change it...but ive hit helis on the ground prety hard and no ressonance....i dont believe it can because when ground ressonance happens, the blades go out of phase with each other..and since we run a average of 1700rpm's compared to real helis which are usually no more than 400rpm's the rpm on our helis get them back in phase rather quickly. So i still believe full scale, and rc helis with 2 bladed rotor heads can not get ground ressonance....

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10-20-2004 08:06 PM  13 years agoPost 24
gigi

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Port-au-Prince,​Haiti

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It would indeed be nice...

... to arrive at halfway decent settings prior to being at the field.

I once spent a half-an-hour trying out a new Super-Tiger carb on my O.S. .50 SX-H. Spool up, too rich, spool down, close the needle a quarter click, repeat. Of course, it would either conk out, or fizz out, or just plain toy with me the whole time. It's now sitting on my bench, grand total number of flights on it: .05 (hopping off the ground, that is...)

'Gotta admit, it's simpler to setup plank engines.

As far as 2-bladed helis not getting into ground resonnance, I don't know what it was that started shaking the daylights out of my Raptor 50v2, but I sure the hell won't ever run it tied down like that again. Besides, those 4 little screws that hold the landing skids to the frame probably aren't up to the task of resisting the pull of the rotor anyway. Wouldn't one look stupid if the skids stayed put while the rest of the heli flew away, most likely to crash hard at high speed against a house or a tree? No thanks, I'll suffer through flight-testing, thank you very much.

Say, Galifrey, what's "FBDO" mean?

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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10-20-2004 08:17 PM  13 years agoPost 25
sixeven

rrApprentice

Ft. Myers Florida

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corey11

Yeah, you may be right. It's hard to say....

It is likely related to the unfortunate combination of the right headspeed with the right airfoil shape and the right blade mass to produce the those building harmonics. Even more so if your blades are slightly out of balance or mis-pitched.

The quicker the head speed the higher you can go into the multiple order harmonics and the greater chance for acheiving a vibratory amplitude that could be damaging. That is why 3, 4, & 5 bladed helis have more resonnance trouble as they are already in a higher frequency (assuming the head speed is the same).

Just like the woman who can belt out a vocal tone that can break glass.

Very curious question though! It would be fun to do some experiments with it....Just not with my heli

SiXeVeN

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10-20-2004 08:32 PM  13 years agoPost 26
vinrx7

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Americas finest city

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seems like most of the accidents happen while the heli is tied down or clamped to something. something always goes wrong. fly, land and tune. no better way.

STUPID TREE!!!

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HelicopterMain Discussion › Full power on a tied up Heli ??? healthy ???
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