[TowerTalk] Carbon Fiber Tubing

[Roger (K8RI)]

> Before everyone falls in love with carbon fiber, look at this
> chart (see URL below).  Carbon is only 10% stronger than plain
> vanilla fiberglass (E-glass) and it's 25% less strong than
> S-glass.  It is 3/4 of the weight of 'glass, big deal.

When used in a composite such as carbon fiber over (inside and out) a foam 
core and then a layer of Kevlar and finally two layers of fiberglass and 
Vinylester Resin you can end up with substantial weight savings and strength 
increase BUT this is really viable only where weight saving (as in the 
horizontal stab on an airplane) is essential and price is no object. Even 
then it's usually a last resort. OTOH there are complete aircraft 
constructed out of the carbon fiber, foam core, glass and Kevlar composites. 
These are highly specialized aircraft where light weight and strength are 
essential. If you've watched the "Red Bull" air races, I think you will find 
most of the competing aircraft use this type of construction.
Used to replace the tower sections used for a boom on a 75 or even 40 meter 
Yagi  the weight savings could be substantial, BUT it would add a new 
dimension to the word expensive when talking about antennas.

Typically using carbon fiber for major structural components in an antenna 
is not practical just due to the extreme cost. Also building a foam core 
composite in a long tube brings up some interesting mechanical issues. They 
are not insurmountable, but just add more expense and construction time. 
Without going into a long explanation you just don't start with a carbon 
fiber lay-up, followed by the foam which is then covered by more layers of 
carbon fiber as there are bonding issues.
> The only redeeming characteristic is *stiffness* (modulus).
> Three times as stiff.  This is very useful in your golf club

This is why it's normally used in conjunction with other materials.
> or tennis racket.  For antennas, I would think it is only
> important for Titanex style DXpedition type verticals.

It'd be great in long booms as well where sag is a consideration. Just think 
of a boom for a 75 meter Yagi that only weighs a few hundred pounds compared 
to a couple thousand when using tower sections. Of course we're talking a 
boom that costs as much as a new 4 passenger airplane too. <:-)) After all 
that you still have UV deterioration to worry about

Roger (K8RI)


>
> Rick N6RK
>
> Tod -ID wrote:
>> Some links
>>
>> Comparison of properties of carbon fiber tubing and other types of
>> material
>> used to make tubing [e.g. 6063-T6 Al].
>> http://www.carbonfibertubeshop.com/tube%20properties.html
>>
>> Link to tubing pricing and some specifications. It appears that a five
>> foot
>> length of 2" diameter, 0.060 " wall tubing will weigh 1.25 pounds and 
>> cost
>>
>