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Re: Viewports gobbed on with silicon
Gary, Thanks for the references, I'll see if I can't get a copy. I agree
that you shouldn't re-invent the wheel, but my design is a little radical
and is going to require some re-engineering. The only thing I don't like
about acrylic is that it has an Izod impact resistance of 0.5 ft-lb/in
compared to polycarbonate which has an Izod impact number of ~ 15.0
Otherwise, the basic plastics are very similar in strength and mechanical
properties. One of the problems with poly besides it's UV stability
(yellowing) is that it requires a higher temperature to process than
acrylic. Because of this, you have to "dry" it and minimize the absorbed
moisture before forming. Since my canopy is going to be 1/2 inch to 3/4 inch
thick, I'm going to have to form it myself. It would be easier if I used
acrylic, but I'd feel a lot safer with poly. It's overall strength is about
20 % higher than acrylic in most categories (Tensile, elongation,yield,
compressive, flexural). One of my major concerns is adequate sealing of the
canopy to the inner hull. I essentially have a biplanar (two planes) sealing
problem. Unlike a hatch cover and gasket, which seal on one plane, I will
have to insure that the pressure and loading of the canopy seals a "V" type
of configuration. Ahhhh.. I know, lots of work, but hey, that's half the fun
of building this thing. Thanks again for the help.
Suds
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