airplane dope question from a boat builder
Dan Miller
Hi-
I have a question for the airplane builders; crossposting to
rec.boats.building for interested boat builders, especially
those restoring Penn Yans.
I build and restore wood canoes, and one of my current
projects is a 1946 Penn Yan canoe. Penn Yan was involved
with the aircraft industry during WWII, I believe with
Curtis Airplane, and they used airplane technology in
their boatbuilding. I am considering doing a true restoration
of the canoe using the airplane dopes as in the original, and have
some questions.
The basic procedure, which I got from PY 'historian' Dan Sutherland,
is:
cover with very light (tablecloth weight) canvas
- 1 coat clear butyrate dope mixed with 4oz fungicide paste
- 3-4 coats nitrate dope
- 1 coat non-taughtening nitrate dope
- 3-4 coats Rand-O-Fill (has aluminum for uv protection)
I understand the basic roles of the products; the fungicide
helps prevent mildew, the nitrate shrinks the canvas, the
non-taughtening nitrate halts the shrinking process, and the
aluminum protects against UV.
My questions are:
What is the functional difference between butyrate and nitrate
dopes?
Based on this schedule of application, who much of the weave
of the cloth can I expect to be filled?
Can I finsih with my usual marine enamels (Interlux or Pettit), or
would it be better to use something like Ranthane (will be durable
in a freshwater environemnt - typical canoe usage)?
Are their drastic differences between different manufacturers
dope products, say Randolph and Certified Coatings? Are their
cheaper sources than Aircraft Spruce?
How does one apply dopes? with a natural or synthetic bristle
brush, foam pad, or otherwise?
Is there anything else I should be aware of that I haven't brought
up due to inexperience with the material?
If there is sufficient interest, I shall summerize to the
appropraite newsgroups and deposit a copy at the Wooden Canoe
Heritage Association website (http://www.wcha.org)
Thanks much for any and all help.
Cheers,
Dan
--
Daniel Miller
dmi...@gcg.com
Independent Boatbuilder and Small Craft History Enthusiast
So many boats, so little time....
John R. Johnson
It looks like you have been doing some research, Dan.
I will try to answer your questions. By the way, I also
do canoes!
On Fri, 18 Oct 1996, Dan Miller wrote:
> Hi-
>
> I have a question for the airplane builders; crossposting to
> rec.boats.building for interested boat builders, especially
> those restoring Penn Yans.
>
> I build and restore wood canoes, and one of my current
> projects is a 1946 Penn Yan canoe. Penn Yan was involved
> with the aircraft industry during WWII, I believe with
> Curtis Airplane, and they used airplane technology in
> their boatbuilding. I am considering doing a true restoration
> of the canoe using the airplane dopes as in the original, and have
> some questions.
>
> The basic procedure, which I got from PY 'historian' Dan Sutherland,
> is:
> cover with very light (tablecloth weight) canvas
Aircraft Cotton. It is a tightweave cotton fabric, tablecloth weight.
I would add the following steps ....
1. Tack the fabric snugly over the canoe, with tacks along the edges
only. Sew any seams made to conform to compound curves with a
curved needle, heavy cotton thread ( rug and carpet thread works well )
and a "baseball" stitch.
2. Wet the cotton with water and set it out in the sun to shrink. Water
will shrink the fabric. Nitrate dope will shrink a little, but most
of the shrinkage in a Grade A Cotton covering job comes from the water
shrink. This can be repeated several times until it is taut and not
just snug. Then proceed with dope.
> - 1 coat clear butyrate dope mixed with 4oz fungicide paste
I would use clear nitrate, not butyrate. See difference note below!
> - 3-4 coats nitrate dope
After the second coat apply cotton tape with dope over seams for protection.
> - 1 coat non-taughtening nitrate dope
I would use butyrate dope here. The Rand-O-Fill is fine. You can make
your own "Rand-O-Fill" by mixing aluminum powder into clear butyrate dope.
> - 3-4 coats Rand-O-Fill (has aluminum for uv protection)
>
The aluminum also acts as a filler and rapidly fills the weave in the
cloth. Wet sand the aluminum to a slick surface. Becareful where there
are bumps or stitches underneath the dope film because it is easy to sand
through the dope film into the fabric underneath. You do NOT want to do
that!
Apply aluminum fill coats sanding after every couple of coats until you
are happy with the surface and you have a good aluminum film for uv
protection.
Then finish with two coats of your finish color in pigmented butyrate dope.
When it is thoroughly dry, you can rub out the color coat with rubbing
compound to bring up a nice shine.
Do NOT cover with Ranthane. Ranthane or any enamel is a NON-reversible
finish. Dope is a reversible finish. You can always soften the dope
with a little dope thinner, and bond patches in like they were part of the
original job. A little more dope on top, and a little rub out and the
patches become invisible. To patch enamel or urethane over dope requires
removing every trace of the foreign unreversible finish before patching.
Also, enamels use a thinner that tends to remove the plasticizer from
dope and embrittle it, causing cracking that lets water penetrate the
finish!
> I understand the basic roles of the products; the fungicide
> helps prevent mildew, the nitrate shrinks the canvas, the
> non-taughtening nitrate halts the shrinking process, and the
> aluminum protects against UV.
>
> My questions are:
>
> What is the functional difference between butyrate and nitrate
> dopes?
Nitrate is Cellulose Acetate Nitrate, butyrate is a butyl base.
The Nitrate is MUCH more flammable. Cellulose Aceate Nitrate and
cotton approximates "guncotton" in flammability. Butyrate is much
less flammable and should be used for the outside coats.
Nitrate dope is much "stickier" than butyrate and will make a better
bond with the wood and fabric than the butyrate will. Butyrate bonds
alright to nitrate because the thinners are somewhat compatible.
Both provide some tautening, neither provide much!
>
> Based on this schedule of application, who much of the weave
> of the cloth can I expect to be filled?
You can apply aluminum fill coats until all the weave is filled.
>
> Can I finsih with my usual marine enamels (Interlux or Pettit), or
> would it be better to use something like Ranthane (will be durable
> in a freshwater environemnt - typical canoe usage)?
See above about patching!
>
> Are their drastic differences between different manufacturers
> dope products, say Randolph and Certified Coatings? Are their
> cheaper sources than Aircraft Spruce?
The biggest difference is a small variation in percent of solids!
There are many cheaper sources than Aircraft Spruce, IMHO.
>
> How does one apply dopes? with a natural or synthetic bristle
> brush, foam pad, or otherwise?
Use a natural bristle brush or a spray gun. The first coats should always
be brushed. You can let it harden in the brush and it doesn't hurt a
thing. When you dip the brush into fresh dope, it will immediately start
to dissolve and resoften the old dope. It is reversible! The thinners
used will immediately dissolve synthetic applicators and brushes. I
remember a "doping party" where the host provided everyone with cheap nylon
brushes! He was appalled when he saw the large thick black streaks in the
clear dope coat caused by the brushes dissolving into the dope!
>
> Is there anything else I should be aware of that I haven't brought
> up due to inexperience with the material?
It is best if there is a minimum delay between coats to avoid contamination.
Each additional coat will soften the previous one and merge into the previous
coat thickening it and filling the weave. If you wait more than a few
hours between coats, I would precede the next coat with a wipedown with
a tack rag dampened with nitrate dope thinner. Nitrate thinner will dissolve
almost everything. I use it to remove hardened enamel from my spray
equipment!
Be aware, this is the aircraft procedure for applying fabric over a steel
tube structure. With a canoe you are applying fabric over a wooden
structure that is essentially a complete support. When working with
wooden aircraft we often apply fabric over wood. Many antique aircraft
were built this way. I have only found ONE way to make good adhesion
between cotton fabric and the wooden structure underneath. I always use
this modified procedure for covering wooden skinned structures with
fabric.
Before applying the fabric to the wood, mix up a thin mixture, milk thick
instead of heavy cream thick, of Weldwood or Casco resin wood glue.
Brush this over all of the wood to be covered, wet the fabric and stretch
it into the wet glue. Then brush the fabric with the thin glue mixture
and rub it smooth with your bare hands to get the glue mixture well
through the fabric. Let it dry overnight at least. Then proceed as
above with the dope process. When done in this way I have NEVER had the
fabric separate from the structure.
John
Tim Hewitt
John R. Johnson wrote:
[clip - lots of GREAT stuff on doping aircraft]
> Be aware, this is the aircraft procedure for applying fabric over a steel
> tube structure. With a canoe you are applying fabric over a wooden
> structure that is essentially a complete support. When working with
> wooden aircraft we often apply fabric over wood. Many antique aircraft
> were built this way. I have only found ONE way to make good adhesion
> between cotton fabric and the wooden structure underneath. I always use
> this modified procedure for covering wooden skinned structures with
> fabric.
>
> Before applying the fabric to the wood, mix up a thin mixture, milk thick
> instead of heavy cream thick, of Weldwood or Casco resin wood glue.
> Brush this over all of the wood to be covered, wet the fabric and stretch
> it into the wet glue. Then brush the fabric with the thin glue mixture
> and rub it smooth with your bare hands to get the glue mixture well
> through the fabric. Let it dry overnight at least. Then proceed as
> above with the dope process. When done in this way I have NEVER had the
> fabric separate from the structure.
I don't believe you want to do these steps in a canoe. You do NOT want
the canvas to adhere to the wood - quite the contrary - the canoe hull
wants to "float" inside the doped canvas skin. The canvas should only be
attached at the gunwales and stems, and not to the planking. I would
probably oil the wood before applying the canvas to ensure that the dope
does NOT stick to the wood.
-Tim
--
Tim Hewitt - President, Downeast Chapter
Wooden Canoe Heritage Association, Ltd
http://www.wcha.org
Bruce A. Frank
Dan Miller <dmi...@gcg.com> wrote:
>Hi-
>
>I have a question for the airplane builders; crossposting to
>rec.boats.building for interested boat builders, especially
>those restoring Penn Yans.
>
>I build and restore wood canoes, and one of my current
>projects is a 1946 Penn Yan canoe. Penn Yan was involved
>with the aircraft industry during WWII, I believe with
>Curtis Airplane, and they used airplane technology in
>their boatbuilding. I am considering doing a true restoration
>of the canoe using the airplane dopes as in the original, and have
>some questions.
>
>The basic procedure, which I got from PY 'historian' Dan Sutherland,
>is:
>cover with very light (tablecloth weight) canvas
>
>helps prevent mildew, the nitrate shrinks the canvas, the
>non-taughtening nitrate halts the shrinking process, and the
>aluminum protects against UV.
>
>My questions are:
>
>What is the functional difference between butyrate and nitrate
>dopes?
>
>of the cloth can I expect to be filled?
>
>would it be better to use something like Ranthane (will be durable
>in a freshwater environemnt - typical canoe usage)?
>
>dope products, say Randolph and Certified Coatings? Are their
>cheaper sources than Aircraft Spruce?
>
>brush, foam pad, or otherwise?
>
>up due to inexperience with the material?
>
>appropraite newsgroups and deposit a copy at the Wooden Canoe
>Heritage Association website (http://www.wcha.org)
>
>Thanks much for any and all help.
>
>Cheers,
>Dan
>--
>Daniel Miller
>dmi...@gcg.com
>Independent Boatbuilder and Small Craft History Enthusiast
>So many boats, so little time....
Butyrate was developed to reduce the flamability, Nitrate adheres(sp?)
better to polyester fabric, that is why it is used as the first coat.
Either will work very well on cotton canvas. If you are using polyester
fabric you do not need the fungicide.
A brush is used for first coat to carry enough wet dope to saturate the
fabric. On polyester, dope bond is strictly mechanical, it wraps around
the strands and its strength to itself through the weave holds it to the
fabric. Subsequent coats should be sprayed if you want a good looking
finish. Brushing can be done but the dope must be thinned with retarder
to allow flow time for the dope to self level- brush marks to smooth out.
I would not mix brands. Urathane is more durable to uv exposure but if
you do not need a "wet look" finish it is not necessary unless the boat
is left out for weeks on end. In that case you might consider a 100%
urathane process.
I am not familiar with this boat. If the fabric is fastened over an open
frame work rather than over a wood surface do not use marine or any other
kind of enamel. Flexing of the fabric will crack it.
Bruce A. Frank
Bruce A. Frank
<Before applying the fabric to the wood, mix up a thin mixture, milk
<thick
<instead of heavy cream thick, of Weldwood or Casco resin wood glue.
<Brush this over all of the wood to be covered, wet the fabric and
<stretch
<it into the wet glue. Then brush the fabric with the thin glue mixture
<and rub it smooth with your bare hands to get the glue mixture well
<through the fabric. Let it dry overnight at least. Then proceed as
<above with the dope process. When done in this way I have NEVER had the
<fabric separate from the structure.
You could also precoat the wood with several layers of nitrate dope. Then
thin the first coat of dope on top of the fabric to soften and help bond
to the dope on the wood underneath.
Bruce A. Frank
brian whatcott
In article <326794...@gcg.com>, dmi...@gcg.com says...
>
>Hi-
>
>I have a question for the airplane builders; crossposting to
>rec.boats.building for interested boat builders, especially
>those restoring Penn Yans.
>
>I build and restore wood canoes, and one of my current
>Daniel Miller
This is not the answer you're looking for but I hope, a helpful
suggestion or two.
When I built a canvas canoe I was not impressed with the longevity of
the material (stored outdoors).
People often choose proprietary polyester material brands in the 1.8
oz range on up, for aircraft these days.
It's important to stick with the scheduled adhesives and coating with
this type material, as we found when cherished designer Wittman died.
And this material is still subject to UV degradation - hence the
aluminum filler.
Though I'm sure you will receive worthy responses from this newsgroup,
the people who will REALLY resonate with your desires are the
rec.aviation.restoration group who have often discussed the 'authentic'
coatings and materials.
Regards
brian whatcott <in...@intellisys.net>
Altus OK
Dan Miller
Some one suggested I post my question to this newsgroup as well.
Apologies to those who may have seen it in rec.aviation.homebuilt.
Also to those in rec.boats.building, but I wanted interested
folks to be sure to see any follow-ups.