RE: [ATM] Carbon Fiber for Spider Vanes

["Donald Good" <donald.good@comcast.net>]

If fiberglass over foam did not have lateral strength, they would not make
boat hulls out of it.  When you bump a plywood
cage against the ladder, you will probably scar the plywood but not affect
it structurally.  The CF or glass over foam will bounce back, maybe only
scratching the finish.  By the time you are hitting the fiber/foam hard
enough to crack it, you would also be putting deep gouges or holes in the
plywood.  In either case, you would need to repair it.  Fiber/foam can be
repaired to near full strength with a patch.  Structural damage to plywood
is harder to repair to full strength without replacing the entire damaged
panel/part.

Of course you would have a minimum of 2 fiber layers on each side of the
foam.  For example, an OTA (tube) might have 2 fiber cloth (twill weave)
layers on the inside oriented at 45 degrees to each other (one straight, one
at 45 degrees), then the foam (choosing a foam density and thickness that
can be bent into a tube without crushing), then another 2 fiber layers on
the outside oriented at 45 degrees to each other.  If you are really worried
about toughness, you might consider making the outer layer a fiber/Kevlar
hybrid.  2 layers is still very thin.
Don


> -----Original Message-----
> From: atm-bounces@atmlist.net 
> [mailto:atm-bounces@atmlist.net] On Behalf Of Douglas S Angle
> Sent: Wednesday, April 06, 2005 11:06 AM
> To: atm@atmlist.net
> Subject: RE: [ATM] Carbon Fiber for Spider Vanes
> 

> 
> I've been following this thread with some interest, and have 
> considered fiberglass/foam occasionally, but haven't actually 
> used it yet.  One thing I that holds me back is concern about 
> lateral strength.  For example, if I made upper cage rings 
> from carbon and foam, I understand that I can build them 
> stiffer and lighter than plywood, and they should perform 
> well in use.  Now what happens when I'm setting up and bump 
> the cage against the ladder.  Plywood takes a pretty good hit 
> without damage, and a fair amount of damage without losing 
> strength.  If I have a thin composite layer over foam, I 
> would think that it will damage easily, and that this would 
> have a big effect on the overall strength.  Do I end up 
> destroying the whole piece because of a small hit?  Would I 
> be better using glass instead of carbon, and making the 
> laminations thicker anyway?
> 
> Thanks,
> -Doug

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