Re: ? Problems with CF Spider;Was Re: [ATM] Thin Titanium Spiders & Diffraction Spikes

["matt" <mariusrf@bellsouth.net>]

Rod, thin carbon laminates that need to withstand other than tension are
frequently using an outer layer of aramid (kevlar) or glass , against
puncture and abrasion.

Foam cored composites are a great solution when one designs for optimizing
strength to weight and stiffness to weight, unfortunately spiders aren't in
this category, they're thickness to strength and thickness to stiffness
optimized , or should be . There are some incredibly strong aramid and
carbon fibers that exceed steel and are used in sailboat rigging, in
replacing stainless steel cable . These new ropes are lighter and stronger
than the older style stainless steel standing rigging . Except that they
don't replace rod rigging yet , meaning that whenever cross section rather
than weight is the issue, they're not better than solid metal.

I had some time ago considered tinkering with a carbon spider but was not
able to come up with a practical laminate schedule that would yield any
significant advantage over a metal spider. Probably the spider is the worst
place in the whole scope to put carbon fiber composites. The mirror cell ,
truss tubes , upper cage or solid OTA tube are all better composite
candidates than the spider . I'd rather cut titanium or steel and then
forget about it than replace damaged composite all the time. No repair is
possible that would maintain structural integrity *and* the same thickness .

If I absolutely had to do a carbon spider, its laminating schedule must be
correlated with the spider attachment points , both at the outer end and at
the secondary holder end . Unidirectional carbon along the effort lines
sandwiched between thin kevlar skins sounds good, but I don't see how it
could easily be made 0.020" thin .

best regards,
matt tudor



-----Original Message-----
From: Rod Shea <RodShea@comcast.net>
To: atm@atmlist.net <atm@atmlist.net>
Date: Monday, November 15, 2004 7:38 PM
Subject: Re: ? Problems with CF Spider;Was Re: [ATM] Thin Titanium Spiders &
Diffraction Spikes


>Matt,
>
>I have a sinking feeling you are right about a CF spider.  I do notice the
>only ones I have ever seen were ~ 1/8" thick, with a foam core, used to
>raise the sec assembly above the plane of a single ring spider.  I never
>figured this thickness was worth the optical cost.
>
>Do you have any thoughts on my plans to put a layer of Kevlar BID in the
>vanes, and to angle the UNI CF plies similar to the angles in a wire
spider?
>
>Thanks,
>
>Rod
>


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