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Old Feb 25, 2012, 06:49 AM
Time for me to Fly...
Mr. Wiz's Avatar
United States, MI, Fenton
Joined Jan 2000
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Question
Hard points in stabs or CF?

I'm puttin some very nice OBI tail feathers on a plane but there are no hard points on the stab. Should I drill it and make hard points or just put a strip of CF to tighten the the screw heads to?
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Old Feb 25, 2012, 06:53 AM
Team Hong Kong F3K
ThomasLee's Avatar
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I like to make hardpoints
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Old Feb 25, 2012, 07:55 AM
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Canada, ON, Puslinch
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Drill it then take a L shaped Piece of wire or something and gouge out some foam beyond the hole opening , fill back up with epoxy and then redrill the final hole.
If it has a spar drill some where other than through the spar.

You gotta put something to handle the compression of the screw. On my own personal stuff I put vertical balsa in that area before bagging.
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Old Feb 25, 2012, 08:25 AM
Time for me to Fly...
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Vertical balsa.... Hum... I think I could cut the skin off the bottom, gouge out the foam and put some vertical balsa in there with some foam safe ca. Then just sand the bottom side flush. I could then drizzle some thin ca over it just to make it a little harder. What do yo think?

They wouldn't be round but then I'm not drilling a thin piece of foam.
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Old Feb 25, 2012, 08:42 AM
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Canada, ON, Puslinch
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Go with the resin hard point. The balsa is done best before bagging the core and it also a fairly large shape to reduce a stress riser.

The supergee plan is a good reference for the balsa approach FWIW http://www.charlesriverrc.org/articl...2/sg2_tail.pdf
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Old Feb 25, 2012, 08:56 AM
Time for me to Fly...
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United States, MI, Fenton
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Resin it is.... In from the bottom an leave the top skin untouched.... Except to drill the screw hole, that is.

Thanks!
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Old Feb 25, 2012, 04:45 PM
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Bellevue WA,
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Its not to hard to drill a single hole for a 3-56 nylon screw and then gouge out the foam and not take a larger hole from the bottom.
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Old Feb 27, 2012, 08:24 PM
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Mr. Wiz:

I recommend what DLGjunkyard did: epoxy hard points.

Personally, I go in from the top with the L-shaped wire. Make the hard point about twice the diameter of the hole you intend. Cover the bottom with masking tape, so if anything leaks out, it has no where to go. I use 20-minute epoxy with micro-balloons. Other materials work well, but the mixture I use is easily drilled without fractures or chips.

You can counter-sink for flat-head screws, no sweat.

Oh, yeah: about the 20-minute epoxy. Wait at least four (4) hours before drilling. Sometimes the inside doesn't cure so fast.

Yours, Greg
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Old Feb 27, 2012, 09:36 PM
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I just cut some approx 1/4" square holes in the bottom of the stab where the hard points were to go. Then I gouged out the foam. Next I put in a mixture of 20 Min epoxy and some micro balloons. You think that's going to be OK? It seemed simple enough.
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Old Feb 27, 2012, 10:08 PM
Will fly for food
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40% to 50% micro balloons (by volume) to epoxy mix
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Old Feb 28, 2012, 07:42 AM
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Mr. Wiz:

Sounds like you're done.

Never really tighten the screws, anyway - just firm, no slop.

Yours, Greg
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