Interesting thread in Rec.av.homebuilt about using plywood to formglider

This is very similar to how the inner skins of the De-Haviland Mosquito
and I guess the Hornet were built with ply formed over a male plug.
Reading my copy of ANC-19 it describes how plywood can be moulded to
compound shapes by bag moulding or laying up veneer strips so I guess
the method is as old as the use of ply in aircraft.

Robin
In message , 10kDA
writes

The way Lockheed did it with the plywood shells of the Vega, Sirius,
Altair etc. was to break down the parabolic shape to a series of
2-dimensional segments, long and narrow for one longitudinal ply, then
short (longitudinally) and comparatively wide segments for the 90
degree ply, another long & narrow group, etc. These cut segments of
plywood were taped edge to edge at their widest points and folded
together for storage until needed in the mold. Air pressure was applied
to a shaped rubber diaphragm which expanded to form the male form of the
mold. The pressure during cure forced the plywood or veneer into a
compound curve. I tend to believe Bowlus broke down the teardrop shape
into similar plywood segments to create the molded BA shells. I
understand Bowlus was able to reduce the number of laminated framing
rings in the BA pod when he went to the molded skin. Creating these 2D
skin shapes would be fairly easy to do using a CAD program which would
most likely be able to represent a curved parabolic surface as a series
of equal "facets" with single curvature, joined edge to edge like a
molded canoe. Yes, I'm working on it - My project will be a scaled down
Loughead S-1 biplane, a Jack Northrop design. If it works out I'll try a
Bowlus BA shell. As far as scarfed rings, been there, done that, it
works out very nicely too.

10kDA

Wrote:
wrote:-
As I understand it, Bowlus made the first Baby Albatross with scarfed
skins (12" rings), he then carved a wood plug and made left and right
concrete female molds, followed by 2 concrete male plugs. The veneer
sections would then be fitted and placed in the mold (3 ply), don't
know if heat was applied, but everything was glued up and then the
concrete plug was lowered into the female form. After curing the two
halves were joined. Howley Bowlus was doing with wood, what we would
all see 25 years later in our fiberglass sailplanes.
JJ

Bob Kuykendall wrote:--
Longitudanally?-

Yes, longitudinal planks.--

To do one glider , it would make the most sense to do as was done on
serial #1-3 which is to use scarfed segments. Those were as pretty as
the later ones and would not require any special tooling.
The molded pods used 2 plys of poplar with external ply of mohogany.
To
do this requires not only the mold, but a whole series of patterns for
the laminations so they fit properly together.
I have one of the "California" Babys that had the pod replaced by a
steel tube inner frame with fiberglass shell which appears to have
been
pulled from an original pod. Not sure whether I'll restore that way or
do original inner structure and use shell with veneered exterior. Will
have to wait till I have more time to devote to it.
Nice to see that someone is seriously interested in thi wonderful old
glider.
UH--
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10kDA

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Robin Birch