The plywood monocoque car guy

I know I haven't posted in here in about forever, and I'm (sadly) no
further along in this project than the "gathered most materials, still
doing last-minute-design" stage, but I need to ask a couple plywood
questions:

First, I'm guessing that marine plywood was used in the construction
of the Marcos line of cars because it was the best laminate wood
material available at the time (early '60s). The car I'm building will
be very much like the Marcos, in that it will be a multiple "stressed
box" semi-monocoque structure bonded at the sills and front and rear
bulkheads to the open-cockpit fiberglass body I'm using. In the year
2008, is there a another grade of plywood besides "marine" that will
do as well? The entire 1/2" ply bottom of the car will be epoxy-sealed
against moisture and rubberized for noise absorption.

Second, when you guys build (built?) monocoque small aircraft
structures of the stringer/skin/bulkhead type, what thicknesses of
plywood do you typically use?

Thanks for your kind tolerance!

Bart

On Apr 18, 10:15 am, Bart wrote:

...Second, when you guys build (built?) monocoque small aircraft
structures of the stringer/skin/bulkhead type, what thicknesses of
plywood do you typically use?

Well, "monocoque ... structures of the stringer/skin/bulkhead type" is
kind of an oxymoron. Technically speaking, monocoque structures are
stressed-skin shells that, because of their stiffness and shape,
require no internal structure. However, such structures are somewhat
problematic when it comes to buckling and crippling, so the more
common implementation is "semi-monocoque" in which the skin still does
the heavy lifting, but is stiffened with internal structure that helps
it hold its shape. I think that's the kind of thing you're talking
about.

Anyhow, semantics and minutiae aside, have a look at the Web site for
the Sequoia Falco, a homebuilt kit based on a certificated Italian
speedster from the mid-1950s:

http://www.seqair.com

The builder's photos are very interesting and informative. Also, the
skunkworks articles have a lot of good info:

http://www.seqair.com/skunkworks/skunkworks.html

Construction Note 61008-1 shows that most of the fuselage skins are
2mm or 2.5mm, and the cockpit interior skins are 1mm - waaaay thinner
than I'd like between me and other motor vehicles.

As another reference point, the Bowers Fly Baby uses 1/8" (about
3.2mm) plywood for the sides of it's fuselage.

Thanks, and good luck

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

"Bart" wrote in message
...
I know I haven't posted in here in about forever, and I'm (sadly) no
further along in this project than the "gathered most materials, still
doing last-minute-design" stage, but I need to ask a couple plywood
questions:

First, I'm guessing that marine plywood was used in the construction
of the Marcos line of cars because it was the best laminate wood
material available at the time (early '60s). The car I'm building will
be very much like the Marcos, in that it will be a multiple "stressed
box" semi-monocoque structure bonded at the sills and front and rear
bulkheads to the open-cockpit fiberglass body I'm using. In the year
2008, is there a another grade of plywood besides "marine" that will
do as well? The entire 1/2" ply bottom of the car will be epoxy-sealed
against moisture and rubberized for noise absorption.

Second, when you guys build (built?) monocoque small aircraft
structures of the stringer/skin/bulkhead type, what thicknesses of
plywood do you typically use?

Thanks for your kind tolerance!

Bart

Knowing that this subject is a little OT for this group, I took a couple of
extra minutes to don my trusty old asbestos suit. ;-)

I admit that I have long been intrigued by the Marcos wooden cars, and that
I did covet one in my youth. However, I am not at all sure of exactly what
grade, thickness, or ply count of plywood was actually used in their
construction--and I strongly advise that you find out for sure before
attempting to proceed. Even if it was "marine plywood", which I think that
I may have heard at some point, I believe that the term "marine" only
specifies that the glue between the plies is not water soluble; so an
acceptable grade of plywood may not be as close as your nearest "Borg".

I was curious enough to take a quick look, but did not find any usefull
specifications. However, here a couple of Marcos Owners Club links:
http://www.marcos-oc.com/
http://www.clubmarcos.net/Links.aspx

BTW, I've always wondered what they did to keep the nearest portions of the
wood work safe from the heat of the exhaust--and, of course, my curiosity
remains unsatisfied.

Peter

"Peter Dohm" wrote

Even if it was "marine plywood", which I think that I may have heard at some
point, I believe that the term "marine" only specifies that the glue between
the plies is not water soluble; so an acceptable grade of plywood may not be
as close as your nearest "Borg".

Marine plywood also has a higher quality standard for the inner plys, with a
higher standard of species allowed in the interior plys allowed, and no voids
allowed, although they are allowed to have plug repairs in the inner plys, as I
recall.

The glue in marine plywood does have to be waterproof, but more significantly,
remain strong while submerged in water for some specified period of time.

I don't believe that marine would have been specified for the glue content, most
likely. It is probably specified because of the higher guarantees of strength
and consistency.

Any plywood meant for construction that bears an "X" in the name has waterproof
glue, but it will have voids and repairs allowed, varying with the grade. CDX
is a common structural grade of plywood that has plugs on the C side, and filled
repairs on the D side, with the most knots and defects allowed in commonly
obtained grades.

Any plywood the bears a B or A grade will also have waterproof glue, unless it
bears an interior marking in addition.
--
Jim in NC

"Morgans" wrote in message
...

"Peter Dohm" wrote

Even if it was "marine plywood", which I think that I may have heard at
some point, I believe that the term "marine" only specifies that the glue
between the plies is not water soluble; so an acceptable grade of plywood
may not be as close as your nearest "Borg".

Marine plywood also has a higher quality standard for the inner plys, with
a higher standard of species allowed in the interior plys allowed, and no
voids allowed, although they are allowed to have plug repairs in the inner
plys, as I recall.

The glue in marine plywood does have to be waterproof, but more
significantly, remain strong while submerged in water for some specified
period of time.

I don't believe that marine would have been specified for the glue
content, most likely. It is probably specified because of the higher
guarantees of strength and consistency.

Any plywood meant for construction that bears an "X" in the name has
waterproof glue, but it will have voids and repairs allowed, varying with
the grade. CDX is a common structural grade of plywood that has plugs on
the C side, and filled repairs on the D side, with the most knots and
defects allowed in commonly obtained grades.

Any plywood the bears a B or A grade will also have waterproof glue,
unless it bears an interior marking in addition.
--
Jim in NC
Thanks for that. I had considered adding "ping Jim Morgan".

Peter

"Peter Dohm" wrote

Thanks for that. I had considered adding "ping Jim Morgan".

You're welcome. Glad to be of help.

There may me some minor nits to pick in my description of the various factors
and such, but I think it hits the major factors in enough detail to get the
general idea.

Thing is, I don't often deal with the more strange types of plywood, unless they
deal with house construction, or cabinet making.

I have one other plywood trivia ditty that I though might be relatively unknown
to most folks, and might be of interest.

There exists a type of plywood that is strangely bendable, in one direction,
only. The other direction is as strong as normal plywood. You can buy a 4' x
8' sheet, rolled up so that it is 4' tall, in a circle (cylinder, to be more
precise) with a diameter of perhaps 28".

Yep, you heard me right! And that was a roll of plywood with around 1/2"
thickness!

From what I recall, it is made by having the outer plys grain running straight
across the 4' width, and the interior plys perhaps only 5 degrees (or so) off of
that alignment; just enough off to keep the layers bound together.

The application I used it for was for one of those fancy bay window roofs that
have a fairly deep bend in the roof structure, and hips (kinda' like a ridge on
an slope) going to a point at the top of each of the sections, then covered with
copper. I was working for a framing subcontractor at the time, and he turned me
on to this type of plywood; available only from "boutique" plywood distributors.

For those looking for unusual plywood, I suggest you do some looking in your
local yellow pages (hopefully in a relatively large population area) under
plywood, and see if you can find a place that advertises a specialty of stocking
unusual types and grades of plywood. There are more plywood types under the
sun, than you can imagine, and I can imagine a LOT ! g
--
Jim in NC

"Morgans" wrote in message
...
snip
For those looking for unusual plywood, I suggest you do some looking in
your local yellow pages (hopefully in a relatively large population area)
under plywood, and see if you can find a place that advertises a specialty
of stocking unusual types and grades of plywood. There are more plywood
types under the sun, than you can imagine, and I can imagine a LOT ! g

Jim ..........

The place in Tacoma where I bought most of the Finnish Birch plywood for the
Emeraude also stocks molded plywood. This is intended for use in rolling
over cardboard with knives imbedded in the wood. The cardboard is cut into
the various shapes, such as for folding into boxes or packing. The plywood
half-cylinders are about 3/4" thick and are not bendable - they're
structural. Real pretty stuff, too with birch outer layers.

They advertise in Sport Aviation. Beside almost all thicknesses of Finnish
Birch for aviation (.5 mm, 1.0 mm, 1.5, 2.0, 2.5, 3.0, etc.) they sell
Italian Poplar bending plywood. Ideal for making single curve windshield
molds, for instance. I was lucky to have a supplier like this only a
half-hour drive away. When you add in the fact that the principal wholesaler
of aircraft spruce in the nation is also in Tacoma, this is an ideal place
to build a wooden airplane, boat, or organ.

Rich S.

On Fri, 18 Apr 2008 22:18:56 -0700, "Rich S."
wrote:

"Morgans" wrote in message
...
snip
For those looking for unusual plywood, I suggest you do some looking in
your local yellow pages (hopefully in a relatively large population area)
under plywood, and see if you can find a place that advertises a specialty
of stocking unusual types and grades of plywood. There are more plywood
types under the sun, than you can imagine, and I can imagine a LOT ! g

Jim ..........

The place in Tacoma where I bought most of the Finnish Birch plywood for the
Emeraude also stocks molded plywood. This is intended for use in rolling
over cardboard with knives imbedded in the wood. The cardboard is cut into
the various shapes, such as for folding into boxes or packing. The plywood
half-cylinders are about 3/4" thick and are not bendable - they're
structural. Real pretty stuff, too with birch outer layers.

They advertise in Sport Aviation. Beside almost all thicknesses of Finnish
Birch for aviation (.5 mm, 1.0 mm, 1.5, 2.0, 2.5, 3.0, etc.) they sell
Italian Poplar bending plywood. Ideal for making single curve windshield
molds, for instance. I was lucky to have a supplier like this only a
half-hour drive away. When you add in the fact that the principal wholesaler
of aircraft spruce in the nation is also in Tacoma, this is an ideal place
to build a wooden airplane, boat, or organ.

Rich S.

Isn't aircraft ply made with the plies on a 45 degree bias for
bending?
** Posted from http://www.teranews.com **

In article ,
clare at snyder dot ontario dot canada wrote:

On Fri, 18 Apr 2008 22:18:56 -0700, "Rich S."
wrote:

"Morgans" wrote in message
...
snip
For those looking for unusual plywood, I suggest you do some looking in
your local yellow pages (hopefully in a relatively large population area)
under plywood, and see if you can find a place that advertises a specialty
of stocking unusual types and grades of plywood. There are more plywood
types under the sun, than you can imagine, and I can imagine a LOT ! g

Jim ..........

The place in Tacoma where I bought most of the Finnish Birch plywood for the
Emeraude also stocks molded plywood. This is intended for use in rolling
over cardboard with knives imbedded in the wood. The cardboard is cut into
the various shapes, such as for folding into boxes or packing. The plywood
half-cylinders are about 3/4" thick and are not bendable - they're
structural. Real pretty stuff, too with birch outer layers.

They advertise in Sport Aviation. Beside almost all thicknesses of Finnish
Birch for aviation (.5 mm, 1.0 mm, 1.5, 2.0, 2.5, 3.0, etc.) they sell
Italian Poplar bending plywood. Ideal for making single curve windshield
molds, for instance. I was lucky to have a supplier like this only a
half-hour drive away. When you add in the fact that the principal wholesaler
of aircraft spruce in the nation is also in Tacoma, this is an ideal place
to build a wooden airplane, boat, or organ.

Rich S.

Isn't aircraft ply made with the plies on a 45 degree bias for
bending?
** Posted from http://www.teranews.com **

Some is 45; others are 90 -- you can specify when ordering.

--
Remove _'s from email address to talk to me.

On Apr 19, 8:26 pm, Orval Fairbairn
wrote:

Isn't aircraft ply made with the plies on a 45 degree bias for
bending?
** Posted fromhttp://www.teranews.com**

Some is 45; others are 90 -- you can specify when ordering.

I think it's the face plies that are either 90 or 45 to the cut
edges, and the core plies are at 90 degrees to the face plies. I
haven't seen plywood with the cores at 45 to the faces.
45 degree faces are for places where the design calls for
angled grain across some structure (like a box spar) to closely align
with the stress forces, while avoiding so much waste.

Baltic birch (or Finnish birch, if you prefer) will bend most
readily across the face grain (grain 90 degrees to the bend line) if
it's dampened. I used to spray water on the faces and run a hot
clothes iron across it, turning that water to steam and driving it in.
Doesn't hurt the resorcinol ply glue. I once cut a 3/4" wide strip of
1.5mm ply, face grain running the long way, steamed it, and wrapped it
around a pencil spiral-fashion without it buckling or breaking. Tied
it that way and when it was dry it pretty much held that shape.
Trying to bend it with the grain (grain parallel to the bend
line) will usually fracture the core plies, since it's pretty hard to
get moisture that deep.

Dan