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HomeAircraftHelicopterCentury Radikal G20-30 N640 Hawk Predator › Why my Raven Spun outa control
10-15-2005 01:14 AM  12 years agoPost 1
BC Don

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Calgary, AB Canada

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Finally got the tail section apart. I posted earlier that during a hover I lost all control of the tail and when Picked up what was left found that I could turn the main shaft without the tail turning.

After disassembling it, I found that the rear bevel gears for the tail were destroyed. They are ground down so that they don't mesh anymore. Plus, it almost looks like the main bevel gear heated up enough to cause the plastic to migrate outwards a bit. I also found that the "pin" holding the tail rotor bevel gear was partially out.

So, the question is "WHAT CAUSED THIS"? Did the pin coming partially out cause things to go out of balance which in turn caused the melt down or was there something else? Note that prior to the crash I was doing some hovering tests and when I gave full collective I'd get a small amount of Heli piroette (not enough tail rotor force) - I figured it was gyro which is why I landed, increased the gyro rate and tried again (resulting in total loss of control).

All suggestions appreciated. Should I go with the metal bevel gears now that I have to order more or was this some kind of anomoly? Note that I had lots of lithium grease in the tail section, same as in my Hawks.

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

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10-15-2005 01:31 AM  12 years agoPost 2
jackheli

rrProfessor

Vancouver - Canada

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Are you sure the tail didn't strike the ground prior to the crash?

How about any hits to the tail section during transportation?

Just to get those two possibilities out of the way...

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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10-15-2005 01:40 AM  12 years agoPost 3
BC Don

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Calgary, AB Canada

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Yes, the tail had hit the ground in an earlier crash so that certainly could have contributed to things. Suppose it could have partially stripped the gears and then the force exerted on them as I attempted max vertical did the rest. Although I'm not sure of that.

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

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10-15-2005 01:42 AM  12 years agoPost 4
perfesser zero

rrKey Veteran

Dublin, VA., USA

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BC Don...
How "partially" was it out? I had one back out on me too, but I was fortunate to catch it in time. No gear damage either. Set screw in shaft backed out and let the pin drift out to the outer case. In your case maybe it caught on some part of the case and stopped the gears turning causing "tooth decay" and maybe the melting part too. I'm just guessing here because in my case everything worked in my favor and not Century's!!!

I don't know if the metal gears are the answer or not and don't know if they will even fit, but you could try them. Having to much grease might be worse than to little. BTW, were you using a lithium or synthetic grease? Petroleum based grease is supposed to be detrimental to the plastic gears. You obviously would not have this problem with metal gears.

Later...

Tiger 50 - OS 50SX-H
Hawk Sport - OS 37SZ-H
Raptor 30 - OS 37SZ-H
JR 10X/R950S

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10-15-2005 01:53 AM  12 years agoPost 5
BC Don

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Calgary, AB Canada

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PZ, when I first checked it didn't seem like it was out far enough to catch on anything, I'll have to recheck. It seemed to be at a point where the pin had moved to a point where it was still in the gear and in the rod but not in the other side of the gear. I was able to easily push the pin back in. So yes, the set screw wasn't holding it in.

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

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10-15-2005 02:04 AM  12 years agoPost 6
jackheli

rrProfessor

Vancouver - Canada

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If the pin fell off it could have locked on of the shafts, which would strip the teeth of both gears. Friction of a stopped gear against a spinning one could be responsible for the melting...

Check this thread:http://www.runryder.com/t202804p1

It's easy to find an excuse to do wrong. Hard is not to find an excuse to do right.

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10-15-2005 02:56 AM  12 years agoPost 7
trevorz

rrApprentice

Calgary, Alberta Canada

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When you reassemble tail gears, before putting the pin in, run the set screw all the way through and back out again. This will ensure there is no burr on the inside of it preventing the set screw from grabbing firmly on the pin.

If you hit the tail, or this pin did come out and locked, it could definately explain the stripped gears.

Personally, I think the delrin are simpler, and if you do have a problem they will be the ones to strip out. If you had metal gears in there, then the force would have been applied somewhere else, possibly stripping the main gear. Much harder and more expensive to replace.

Trevor,

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10-15-2005 07:02 PM  12 years agoPost 8
BC Don

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Calgary, AB Canada

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Main gear has a couple of missing teeth as well so this crash got both the tail rotor bevel gears and the main gear. However, after reading various posts I suspect that an earlier crash started the damage and if I had taken a few minutes to take apart the tail I would have seen the damage then and not be waiting for parts now.

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

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10-16-2005 12:33 AM  12 years agoPost 9
genovia

rrElite Veteran

N UR NECK OF DA WOODS

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My Raven spoon out of control......................... I saved it, once on the bench I noticed, that I did not push the tail boom far enough to properly set my SS toqure tube into the coupler. I've witness the same thing on a Minature.... Poorly built.

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