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HomeAircraftHelicopterCentury Radikal G20-30 N640 Hawk Predator › predator head build, grips not free
01-12-2010 02:38 AM  8 years agoPost 1
flyinfriend

rrApprentice

North American continent

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Hi,

I'm building a Century gasser predator and I can not get the grips to rotate freely. I have built 3 other helis in the past and the grips have always been completely free moving. I removed two of the three shims (Century says to use 1-3 depending on what works) that go on the feathering shaft on the yoke side and when I tighten the bolts on the feathering shaft the grips loose their free play. They aren't stuck by any means, they just aren't free like my other helis. I have ensured that the thrust bearings are in the correct order with the large id closer to the main shaft. If anyone has any suggestions I would really appreciate it as I am at a standstill in this build.

Thank you,

Tom

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01-12-2010 08:29 PM  8 years agoPost 2
jackheli

rrProfessor

Vancouver - Canada

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If you pull the grips outwards do they loosen up? That is what is going to happen in flight with the blades attached.

If they do run freely in that condition I wouldn't worry: the setup will sit in as you break in the helicopter.

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

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01-13-2010 02:39 AM  8 years agoPost 3
flyinfriend

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North American continent

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Hi jackheli,

If I pull the grips out they seem to smooth out. Turning them slowly without pulling out they almost feel slighlty notchy.

When you tighten the end bolts in the feathering shaft do they go flush against the shaft ends or do they tighten against the thrust bearing and compress the bearing stack before going tight? My outer thrust bearing race is about flush with the grip bearing case or maybe a very slight hair above. I have used a socket wrench to ensure the radial bearing and shim are seated all the way in. I am at a loss here. My other 3 helis i have built all had grips that dropped under there own weight.

Thank you,

Tom

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01-13-2010 03:52 AM  8 years agoPost 4
Billme

rrElite Veteran

MS

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You do have a little drag on these heads, but like Jack said under load, they smooth out...
the washer should stop against the spindle..You may want to check you have the radial bearings seated good..Take something and give them a punch to make sure. Make sure your dampeners are seated as well..

Are you 4 runner?

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01-13-2010 12:33 PM  8 years agoPost 5
flyinfriend

rrApprentice

North American continent

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Hi Bill,

No, I'm not 4runner. I did use a socket to tap the radial bearing and inner washer/shim down into the cup. The outer race of the thrust bearing sits above the spindle end so that is causing the end bolt/washer to tighten against the bearing stack before hitting the end of the spindle. It almost seems like the spindle is too short but I measured it at 94.17mm and someone else on another forum measured theirs and got 94 too so I'm pretty sure that's not the case. I will tap a little harder in trying to seat the radial bearing and shim. I just don't want to damage the bearing. Should the outer race of the thrust bearing sit just below the cup of the grip? Mine is slightly higher.

Thank you for all the help,

Tom

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01-13-2010 04:50 PM  8 years agoPost 6
imnxtc

rrVeteran

BC.Canada

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Like Jack said, if they are smooth when you pull the grips out by hand then all is fine.

In static form the dampers will preload such thet the spacers rub slightly against the outer part of the race and feel notchy, but under the loading in flight (the blade grips are pulled outward) they rotate smoothly.

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01-13-2010 06:43 PM  8 years agoPost 7
jackheli

rrProfessor

Vancouver - Canada

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My other 3 helis i have built all had grips that dropped under there own weight.
yes, but that just means the dampers are not as compressed on those other helis as they are on the pred grips, that's all...

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

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01-14-2010 02:49 PM  8 years agoPost 8
flyinfriend

rrApprentice

North American continent

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Hi,

Thank you all for your helpful replies. I am continuing on with my build. I made sure the radials and thin inner shim are seated and the dampers are seated in the hub. I used one small shim and the large one against the dampers and I'll leave it at that. The grips turn without binding but don't 'spin' completely lose and pulling them out and turning does feel perfectly smooth and easy. So I think I'm good to go.

Thanks again for all the advice.

Tom

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