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Message-Id: <4.1.19981231131115.0092f960@mail1.abac.com>
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Date: Thu, 31 Dec 1998 13:31:07 -0800
To: <lancair.list@olsusa.com>
From: Buchanan & Newcomer <bnn@abac.com>
Subject: Fixing phenolic
In-Reply-To: <19981227055153.AAA14144@truman.olsusa.com>
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At 09:51 PM 12/26/98 , you wrote:
>Does anyone know if it's possible to "fix" drilling mistakes in phenolic by
>filling the holes with flox and drilling new ones?  The previous owner
>drilled the GM4 main attach plates 0.42" too close to the fus on the pilot
>side and I would like to fix this. If this is too risky I would have to hack
>out the piece and add in a new one.
>
>Pine Pienaar

Pine,
	Sorry about the late response. I've been away from the world for a while.
It's already been recommended that you replace the phenolic block, but I
don't know the difficulty involved so I'll offer some alternatives.

1. Be wary of using "flox" as a structural material. Depending on what you
use as filler you can get tension strengths between 3% and 25% of the
parent material. Compression strengths will be between 10% and 25% of the
parent. (All assuming the parent is well made quasi-isotropic
fiberglass/epoxy.)

2. Fill the original hole with a very close fitting phenolic plug bedded in
high strength adhesive, a la' Hysol. Cover both sides of the plug with
enough layers of glass to mimic the original skin laminate. Re-drill. Pro:
Minimum work. Con: Questionable fatigue life. It's possible that the plug
could come loose and/or disintegrate if it's too small and too highly
loaded. Also, you may have to apply glass to the outside skin, which will
be unsightly unless rebated via extended tapers.

3. Drill a hole large enough to eliminate the old hole and to drill the new
hole in the center of the replacement bushing. Then do 2, above. Make sure
you have at least 2/3 of the bushing diameter outside the bushing in parent
material. Pro: Much more stable than option 2. Con: Large hole sometimes
too difficult to fit.

4. Same as 3 except use a metal bushing with large overlapping washers
inside and out. Pro: Substantially easier than 2 or 3. Con: Possibly
unsightly. Very low strength perpendicular to the skin. (Assumes the only
load is in the plane of the skin.)

5. Buy a new kit. Start over at the beginning. <G>


Guy Buchanan 
Buchanan & Newcomer

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