egroups.com:


BA-100 wrote:

My question is, would it be possible to laminate your own shell using

vacuum bagging?
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Yes. But with a bit of fore-thought. My first effort at vacuum
bagging leading-edge skins ended up crushing my mold :-)

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Seems to me even the wettest veneers would split if you
tried to force them into or around a male or female mold.

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Forming a compound curve, the plywood is usually HOT as well as wet,
and is remarkably plastic.

A standard technique in the repair of such structures offers a bit of
insight into fabricating such a hull from scratch. The general
procedure is as follows:

A mold is taken from the opposite side of the structure. (The
assumption here is for a symmetrical form). The mold is usually made
of plaster, stiffened with burlap or jute fiber and is a few inches
larger than the section to be replaced.

The plaster mold is used create a pair of re-enforced concrete molds,
much thicker than the plaster mold and usually in a frame of welded
steel angle-iron that has been previously drilled for bolts.

The concrete is wet-cured for about a week then air-dried in a warm
hangar for about ten days.

The plywood or veneer is boiled or steamed then laid into the mold,
which has been pre-heated to about 170*. If veneer, the usually
adhesive is a urea-formaldehyde type such as Weldwood 'Plastic Resin'
or resorcinol (the concrete mold must be protected). The upper part of
the mold is put in place and drawn down with bolts. The closed mold is
then returned to the oven or hot box and allowed to cure for 24 hours.

The resulting part is then scarfed to match the area to be repaired.

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The point often overlooked is that this method may also be used for
scratch-building the entire pod. This is because the pod is
symmetrical. Other than the nose, which is usually carved from balsa,
you need only five or six molds to duplicate a longitudinal SLICE from
the pod. The builder simply makes eight copies of each panel then
scarfs them onto a frame.

It should also be apparent that this method works even better using
composite materials and vacuum-bagging, since you need only a few
pounds per square inch to cause the fiber & resin to conform to the
shape of the female mold (the male part is not required). Prior to
WWII there was considerable effort devoted to composite structures
including a few that actually flew (circa 1940) but they tended to be
heavier than their aluminum counterparts. I know the glider people,
but here (ie, Sandy Eggo) and Santa Monica had considerable success
using linen fabric, balsa cores and urea-formaldehyde 'resins.'



Yipes. Getting complicated. Here was my plan:
Get a couple of 4x8 sheets of the thinnest stuff I could get, and lay them
over a male mold soaking wet but cold with a bit of ammonia thrown in for
good measure. Get a good coating of glue on the sheets and slip the whole
lot into the vac-bag. I-m pretty sure the original came in two halves, but
now you have me thinking it might be do-able if it was quartered
longitudanally.
just to give you all another look at one of these contraptions,
http://www.museumofflight.org/collec...lay.html?ID=32
as you can see, this one is also made of segmented, scarfed cones, but most
were made of two halved sides.
(at least i think they were halved, I have an original assembly manual for
one and that's the way the kit came)
unrealistic?