A Canvas Roof?

Anything to do with mechanical, construction etc

Postby jagular7 » Fri Jun 09, 2006 8:39 am

Lots of questions coming....

When you 'dope' the cloth, is the protection just on the outside of the fabric surface? Or is the fabric itself protected, thus meaning the string of the fabric absorbs the 'dope'? (Going down to the micro-scale of the material)

In your explanation of the airplane, IIRC there is an inner frame with outer cloth that tightly fits across the frame. With the fabric condensing on the frame, not only does this add structure and stability to the frame, but the 'string gaps' in the fabric become lesser. With the gaps lesser, the airflow is limited to go across the fabric rather than through it. Same with water.

My understanding of your canvas use was to use a lightweight frame, interior lined wood paneling, and a fabric exterior. No mention of insulation or treatment of the lightweight frame or the backside of the interior paneling (I'll assume the floor would be treated).

In building a TD, most use solid sides so side insulation is none or it's added to the inside of the exterior wall before the interior panel is installed. If there is a frame for the sides, insulation is placed between the frame rails and secured to one of the inner or outer walls. For the top of the TD, most have crossmembers, insulation between the crossmembers, interior paneling, and an exterior panel that is aluminum or wood that is thin enough to bend to the curves of the top configuration.

With the insulation, not only is the temperature somewhat controlled, so is the noise. When doping the canvas, and the effect on the canvas is to shrink, does this add a R-value of insulation to the fabric? I would tend to think so.

Here's a thought, have separate sub-frames for floor, walls, top, front, back, etc., canvas the separate sub-frames, then assemble the TD? You encompass the frame on both sides with the fabric. Edge trim could hide the assembly screws/bolts. That would be cool.....
Mike
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Postby GPW » Thu Jun 15, 2006 8:25 am

Being an old airplane guys , I'd like to comment on the fabric Dope thing ... This is all merely a tent on a frame ... Structure is basically provided by the framework ... The taught fabric does contribute to it's stifness , but is not considered in the stress/loads part of the design .... Doping the fabric , does keep the wind out and preserve the fabric, by encapsulating the fibers , but does little else , soundwise or else .... R value ???? Hahahahaha , ever go up in a old biplane to a reasonable altitude... Bring a good jacket and blanket Dude !!!!
I saw on an old movie , the back of a stagecoach , sliding hatch thingie', canvas with battens , appeared to slide between two opposing rails ... looked easy and fairly waterproof ... mostly easy , and with a few fixed crossmembers and the rails running above it , you could make a convertible TD...

:thinking: :roll:
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Re: A Canvas Roof?

Postby Laredo » Sat Jun 17, 2006 12:10 am

angib wrote:
Witch wrote:If paint wouldn't work, are there any other options to adhereing canvas to wood?

As this message had rung a bell when I read it, coming across the 1950 Mechanix Illustrated boat plans book (bought by my father, I hasten to add) in the chaos of my study, I've looked up what they call for. A couple of plans say:

- "6oz canvas bedded in canvas cement, turned over the edges and fastened with copper tacks" - this is a boat with a small cabin, so about teardrop-sized.

- "Cover with 10oz canvas bedded in marine glue" - from a bigger 'cabin cruiser'.

So that's not a big help, but they do all talk of fixing the canvas down with glue (and then painting it), not with paint.

And is it worth mentioning for anyone confused that this thread has been talking, simultaneously, about two entirely different ideas?

1) Using canvas (or other fabric) as a waterproofing layer over a solid (typically wood) base.

2) Using fabric* stretched over an open framework. The fabric is then stiffened and made waterprooof by coating it. Traditionally this was done by doping it (which had the major advantage that the dope shrank the material, pulling it drum-tight) and then paiting it with enamel paint. The modern equivalent is to coat/impregnate the fabric with epoxy resin to make it stiff.

*For aircraft this was always 'Egyptian Cotton' - I don't think the nationality of the cotton mattered much to how the plane flew, it was just that they produced the best in the world.

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Ok, no hijack -- Andrew, do you remember a movie about a group of prisoners / WWII POWS scaping from, I think someplace in Eastern Europe, by building an aeroplane, the wings' canvas of which they 'doped' with whatever their breakfast gruel was, watered down many times and coated over and over and over? I think the 'canvas' was actually either long underwear or overcoats, cut down and patched in...

Cannot for the life of me remember the name of the film or the names of any of the lead actors, but the youngster (a minor part IIRC) who flew the thing was the subject of an instant crush. It was on TV in about 1968 in the US... and that'd've probably been a first-run TV showing, maybe CBS.
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Re: A Canvas Roof?

Postby Nitetimes » Sat Jun 17, 2006 12:34 am

Laredo wrote:
Ok, no hijack -- Andrew, do you remember a movie about a group of prisoners / WWII POWS scaping from, I think someplace in Eastern Europe, by building an aeroplane, the wings' canvas of which they 'doped' with whatever their breakfast gruel was, watered down many times and coated over and over and over? I think the 'canvas' was actually either long underwear or overcoats, cut down and patched in...

Cannot for the life of me remember the name of the film or the names of any of the lead actors, but the youngster (a minor part IIRC) who flew the thing was the subject of an instant crush. It was on TV in about 1968 in the US... and that'd've probably been a first-run TV showing, maybe CBS.


I'd say it was

"The Birdmen"

This movie's not bad for a TV movie, but it's interesting to note it's historical basis. Colditz Castle was 'Supermax'; the German repository for Allied 'Escape Experts'. Every prisoner in residence had at least one close-to-successful escape attempt from another facility under his belt.

Colditz had the distinction of being the only German POW camp where the guards outnumbered the prisoners. Even so, successful escapes were made.

The most daring plan involved the building of the glider in this movie.

It was actually built, but never used. They were ready to go a month or two before the end of the war, but all prisoners were ordered through the intelligence network by London to sit tight because the Germans had begun shooting escapees. The Colditz gang decided to follow their orders and save the glider to be used in case the Germans starting murdering prisoners and a quick, sure way was needed to get someone 'over the wire' to alert the oncoming Allied forces.

The camp was liberated without incident and the glider was shown around for a few weeks as a morale booster to repatriates of other camps. It was then boosted back up into the attic, but disappeared over the winter of 1945-46; probably destroyed by Russian officers billetted there and used as firewood against the unusually severe winter.

For more info read P.R. Reid's "ESCAPE FROM COLDITZ".
Rich


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Postby angib » Sat Jun 17, 2006 7:21 am

Isn't it interesting how things go round in circles? I don't know anything much about the Colditz glider but there is a link - my Dad spent five and a half years as a PoW in Germany in WW2, part of it in Spangenberg castle (Offlag IX) which looks much like Colditz:

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Postby Laredo » Sat Jun 17, 2006 4:52 pm

wow, Angib.
Good on your dad, getting back okay.

Nitetimes, was Burt Lancaster in the one you're talking about?
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