From: N295VV@aol.com
Message-ID: <e6.fb4476d.27887764@aol.com>
Date: Sat, 6 Jan 2001 08:28:04 EST
Subject: Re: Laying up Multiple Bids
To: lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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It is my opinion that laying up more than 3 layers of bid at one time, i.e., 
6, 8, or 10 bid in one sandwich, is false economy of one's time.

In multiple bid layers, the strength is only as good as the attachment of the 
first layer.

If the multiple bid layer is so thick that it resists the conformation of the 
parts being joined,  the result may be that the most important lower layers 
pull away from the surfaces and leave bubbles that can't be seen,  and most 
certainly can't be worked out if they were seen.

Bubbles of any size are death to a bond.  They must be absent.

Even if bubbles don't appear under the first layer,  there may be a tendency 
for the heavy multiple layer to move away from the contours and wick in epoxy 
under the first layer to allow the movement.

A thick layer of epoxy is almost as bad as bubbles.  Epoxy by itself has no 
strength.  The strength comes in the bonded matrix of fiber glass with the 
epoxy.  Thus, when the first layer is separated from the contour of the parts 
being bonded by a thick layer of epoxy which was not worked out, the result 
is a very poor joint.

So, how do you avoid bubbles and thick epoxy layers in your multiple thick 
bid buildups?

Simple--you build up the layers 2 or 3 bids at a time, working out the 
bubbles and pushing the layers into the contours with a stiff brush.

Yes, it is two or three or four times as much work.  But, when you are going 
250+ kts and input some drastic control movement sometime, your 8 bid layup 
has the strength of 8 bids, not the strength of 1 bid, and your plane is not 
going to come apart.

The extra care and time is well worth the extra effort.

David Jones, Pecatonica, Illinois
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Please send your photos and drawings to marvkaye@olsusa.com.
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