compound curves in plywood

I'm considering building a replica of a 30's glider that was originally
built in two halves, like a plastic model, but with pressed plywood halves.
Duplicating this has been outside the reach of a homebuilder without some
sort of press, and any made since have either been made out of fiberglass
or segments of scarfed plywood as were the prototypes. Here's a pic of one
here. The fuselage on the production originals was, as I say, made of
molded plywood in two halves and assembled over formers and stringers.
some of you might be familiar with the Bowlus Baby albatross.

http://www.fiddlersgreen.net/AC/airc.../info/info.htm

My question is, would it be possible to laminate your own shell using
vacuum bagging? Seems to me even the wettest veneers would split if you
tried to force them into or around a male or female mold. to date, the only
sort of manipulation I've done with ply is to wrap 1/16 leading edge pieces
over a hot pipe. I just don't see how Hawley Bowlus got the compound
curves..


Any insights?

Earlier, BA-100 wrote:

My question is, would it be possible to laminate
your own shell using vacuum bagging? Seems to me
even the wettest veneers would split if you tried
to force them into or around a male or female mold.

Well, it's pretty easy to try it and see. Get some strips of thin
veneers (I'm thinking 1/64" to 1/32" or so) and try it out. For a test
part you can use any compound curved surface of about the curvature of
your porposed surface. I'd be inclined to try it out using VW beetle
(the old ones) fenders or roof sections from a junkyard. That'll give
you both internal and external test curve surfaces. If you can make
that work, it should give you enough experience and confidence to
proceed.

There are still folks around who know exactly how Bowlus made his
fuselage pods, it shouldn't be too hard to explore that. I believe that
Jeff Byard even has photos of the Bowlus tooling. There are also a
multitude of photos of the Lockheed Vega tools that used (I belive)
concrete molds and pressurized rubber bladders.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

Luthiers commonly steam wood and form it over jigs, clamps hold it in place
until it drys out. May be the same kind of construction used to build this
sailplane. Just a thought and maybe something to check out.

Patrick
student SPL
aircraft structural mech

"Bob Kuykendall"
egroups.com:

Earlier, BA-100 wrote:

My question is, would it be possible to laminate
your own shell using vacuum bagging? Seems to me
even the wettest veneers would split if you tried
to force them into or around a male or female mold.

Well, it's pretty easy to try it and see. Get some strips of thin
veneers (I'm thinking 1/64" to 1/32" or so) and try it out. For a test
part you can use any compound curved surface of about the curvature of
your porposed surface. I'd be inclined to try it out using VW beetle
(the old ones) fenders or roof sections from a junkyard. That'll give
you both internal and external test curve surfaces. If you can make
that work, it should give you enough experience and confidence to
proceed.

Sounds like a plan! I've located a place that sells bags for vacuum forming
that would certainly be big enough and I think Icould get an old compressor
to do the honors if I mess it around enough.

There are still folks around who know exactly how Bowlus made his
fuselage pods, it shouldn't be too hard to explore that. I believe that
Jeff Byard even has photos of the Bowlus tooling. There are also a
multitude of photos of the Lockheed Vega tools that used (I belive)
concrete molds and pressurized rubber bladders.

Thanks, and best regards to all

Yes, that's right, that's exactly how Bowlus did it. I did a lot of
research on it years ago when i started the project the first time around,
(even talked to the funder of a lot of Hawley Bowlus' creations, Steven
DuPont) but making a molded pod was pretty much out of the question at the
time. the preferable option was to do like they did with the protottypes
and pretty much every other glider of the period and make a series of
scarfed rings (why did i think this would be less work?) but when I found
out about vacuum bagging, I saw it as a possible way around this. A male
mold would be the easiest to build of course. I figure a series of ply
formers, filled in with foam and sanded to shape, then maybe a layer of
resin and voila, a half a fuselage. Has the aded advantage of being easily
replicated left and right.
If that didn't work, I suppose I could use that as a plug to make a female
mold out of concrete. (yipes, what would I do with it afterewards? ) and
use vacuum bagging on that.
Might actually give it a try...

"W P Dixon"
:

Luthiers commonly steam wood and form it over jigs, clamps hold it in
place until it drys out. May be the same kind of construction used to
build this sailplane. Just a thought and maybe something to check out.


Yes, I've done this in fact. Have a guitar and a violin under my belt, but
no compound curves. Most flattop guitars have a small radius which is
compound, but nothing like what I'm talking about (a complete teardrop)
This sort of technology realy died out when fibreglass hit the scene,
though i'm sure there are some masters still around.Most likely source of
info are boatbuilders, of course, but their curves wouldn't even appraoch
the radius I'm talking about.....

I would guess that the construction techniques used
were similar to those used in boatbuilding.

http://www.albacore.org/USA/members/...g_albacore.asp
http://www.boats.com/content/default...contentid=1184
http://www.albacore.org/USA/members/...g_albacore.asp
May help.

There is a remarkable wooden flying boat hull in the RAF Museum
at Hendon that was built in the early 1920s. It has a 'moulded'
hull which appears to have been constructed using boatbuilding
techniques of the time.

http://www.rafmuseum.org.uk/supermarine-southampton.htm

With its varnished finish it is simply stunning to
look at.

egroups.com:

I would guess that the construction techniques used
were similar to those used in boatbuilding.

http://www.albacore.org/USA/members/...g_albacore.asp
http://www.boats.com/content/default...contentid=1184
http://www.albacore.org/USA/members/...g_albacore.asp
May help.

There is a remarkable wooden flying boat hull in the RAF Museum
at Hendon that was built in the early 1920s. It has a 'moulded'
hull which appears to have been constructed using boatbuilding
techniques of the time.

http://www.rafmuseum.org.uk/supermarine-southampton.htm

With its varnished finish it is simply stunning to
look at.



All good stuff, but not what I realy need to know. Rummaging around, I
found this, which is a bit enlightening..
http://personal.eunet.fi/pp/gsahv/torture/torture.htm

BA-100 wrote:

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

vacuum bagging?

I would do some googling on "cold molding" and boatbuilding. Very
common method for building hulls. It's also how the SPruce Goose and
Mosquito bombers were built. You'd find...

http://www.nwmarinedesign.com/coldmold.htm

You can build up a structure as strong as fiberglass but lighter with
this technology.

http://www.glen-l.com/weblettr/weble....html#notebook

BA-100 wrote:

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

vacuum bagging?

I would do some googling on "cold molding" and boatbuilding. Very
common method for building hulls. It's also how the SPruce Goose and
Mosquito bombers were built. You'd find...

http://www.nwmarinedesign.com/coldmold.htm

You can build up a structure as strong as fiberglass but lighter with
this technology.

http://www.glen-l.com/weblettr/weble....html#notebook

In article .com,
wrote:

I would guess that the construction techniques used
were similar to those used in boatbuilding.

http://www.albacore.org/USA/members/...g_albacore.asp
http://www.boats.com/content/default...contentid=1184
http://www.albacore.org/USA/members/...g_albacore.asp
May help.

There is a remarkable wooden flying boat hull in the RAF Museum
at Hendon that was built in the early 1920s. It has a 'moulded'
hull which appears to have been constructed using boatbuilding
techniques of the time.

http://www.rafmuseum.org.uk/supermarine-southampton.htm

With its varnished finish it is simply stunning to
look at.

Is everyone forgetting the deHavilland Mosquito? Constructed almost
entirely of cold-moulded plywood.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."