Re: ATM Carbon vs. Glass fiber for tube

["Jon H. Peterson" <jon@osisoft.com>]

I've built lots of structures with carbon fiber, kevlar, and glass. Here's 
my comments:

Carbon is much stiffer and stronger then glass. Kevlar is stronger than 
carbon but not as stiff, it is stiffer than glass. If you really want a 
light stiff tube, carbon would give you it. Hand layups generally reduce 
the differences material properties. Actual material properties are readily 
available for both fibers and layups--it gets fairly complex, resin, weave, 
orientation, etc. Unless you're doing detailed stress analysis the relative 
values gives the general trends.

Approximate prices from memory:
6 ounce/sq yard s-glass:        $6
6 ounce/sq yard carbon:         $26
5 ounce/sq yard kevlar:         $26


Carbon and glass are about equal to work with, except glass is easier to 
see if it is properly "wet out"--it gets clear. Kevlar is very difficult to 
work with, it's difficult to cut, gets real ugly if you sand it.

Carbon looks pretty cool. If you do a good layup, painting isn't necessary 
as long as you keep the UV exposure low--not a problem at night. Glass over 
cardboard definitely would need painting to look good.

Jon Peterson