Tony,
I recently finished building the flaps for my XS, and I too decided to
correct the washout, since the jig blocks produced 0.9 degrees on one flap,
and 1.6 degrees on the other. I suspect that this might affect how straight
the airplane flies, and the adjoining ends of the cores were at different
heights and angles, so shimming was required in any case. I had to start by
sanding the mating surfaces of the inboard and outboard cores (which were
not square to the leading edge) until the leading edge came out straight.
Here's the procedure I used to set the washout to 1.4 degrees (assuming the
1.0 degree reference on page 6-2 is left over from the Classic).
1. Shim the appropriate jig block at the center joint to get the mating
surfaces to meet properly, and join the cores with the sandwich piece,
ignoring washout for the present.
2. Glue the first set of jig blocks to the core, and allow to set.
4. Divide the length of the core by 7, and make marks at this interval along
the core, to show the points where the washout should shift by 0.2 degrees.
3. Collect pieces of cardboard, stiff plastic, wood, etc. to use as shims,
varying from about .005 inch to .040 inch or more, every .005 inch or so.
Use these for shims between the bench and the jig blocks to get the trailing
edge perfectly straight. (I needed up to .085 inch total thickness.)
4. Check the angle of the top surface with a digital level at each of the
marks on the core, and shim the leading edge at these points to get the
washout to progress as required. Obviously, you have to start at the point
which needs to be lowest on the leading edge, as it cannot be shimmed
further downward, though the location of this point may not be obvious at
first.
5. "When you are happy with the cores' alignment" (to quote the manual's
description of the foregoing procedure), glue the blocks (and shims) to the
bench, and lay up the first side. I kept a lot of sand bags on top of the
cores throughout the alignment procedure, as slight changes in pressure
cause significant variations in angle readings.
6. Because the other side of the flap is not flat, it is easier to first
align the other set of jig blocks on the bench without the flap core in
place. The "flat" surface of my jig blocks was actually slightly convex, so
I had to sand it a bit to get the digital level to rest on the leading and
trailing edges everywhere, in order to get consistent angle readings.
7. Following the earlier procedure, glue the jig blocks to the bench, after
the leading and trailing edges have been shimmed straight, and the washout
is a uniform 1.4 degrees. Glue the flap cores to the jig blocks, and do the
layup.
Expect to repeat this process when you get to the ailerons, though it's a
bit easier, since they have flat areas on both top and bottom surfaces.
Lacking a digital level, I suppose one could try to use the procedure in the
manual for checking the washout of the ailerons, but I don't think you could
get the washout distributed evenly along the length. Mine varied
dramatically, even twisting back in the wrong direction in one place.
Dave DeFord
Builder #A135
-----Original Message-----
From: Tony Renshaw <renshaw@ozemail.com.au>
Date: Wednesday, June 02, 1999 3:45 AM
Subject: CAD dimension request
>Andy,
>Can you please have a look at your CAD and supply me with angles of the
>bottom skin at the root, 5mm rib,and tip please? I noticed my angular
>difference between root and tip of my first flap is 0.7 degree. When
>measuring my second flap I noticed my root block appears to have no washout
>cut into it and all the angular difference appears to be in the outboard
>block. I am setting it up so it matches the first one and figure I should
>be able to make up a couple of timber jigs to attach to this first skin, if
>I know the dimensions, so that when I invert them onto my bench for the
>second layup I will be able to jig exactly the correct washout. (I know the
>washout is hard to measure when the datum is the top of the 1st skin.)
>The plan is to have jigs precut and lay them onto peel ply at the root,
>mid, and tip location ontop of peel ply as the first skin is layed up. I
>figure I can then invert them and bond the jigs to the benchtop to get the
>correct twist. I should add that my flaps are not at all similar off the
>bench, which is why I wish such advice.
>Thanks Andy, and I hope you can help.
>Reg
>Tony Renshaw
>Reg
>Tony Renshaw
>Builder No.236
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