Re: [RCSE] C/F Boom Molding Question

[Jon Stone]

David,

The key is to get the CF oriented lengthwise to the boom, to get the maximum
bending stiffness.  But UNI-CF alone will give the boom very little
tortional stiffness.  Having the FG at +/- 45 accomplishes this.  The
tortional stiffness is needed when side loads get applied to the tail.
(i.e. when a TLG gets launched).

Having the CF +/- 45, as you suggest will give you a very tortionally stiff
boom, but it be less resistant to bending.  According to a book I have, the
45 CF matrix has a modulus approx. 1/5th to 1/8th the strength in the
0-degree direction along the boom, as UNI-CF does.

In short, if you want a boom that won't twist, go with the 45.  If you want
a boom that won't bend, go with UNI.

Jon Stone


- Original Message -
From: David A. Enete [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Sent: Sunday, July 08, 2001 3:14 PM
Subject: Re: [RCSE] C/F Boom Molding Question


  I would like to mold a thin walled 1 OD Carbon Fiber Tube.
 I am going to make a male plug and a two piece mold.
 
 This seems like an extremely labor-intensive way to make a tube.
 I suggest John O'Sullivan's Rollfuz method:

 Why not just use a mandrel and CF braided tubing?  Wax your mandrel
 (euphemism) or use a protective barrier.  Slip the CF braided tube
 over the mandrel.  Wet it out and extract as much excess resin as
 needed.  Then just cover the whole layup with heat-shrink tubing and
 shrink it.

 That should give you 45-degree fiber orientation, a very nice outer
 surface, and no need for mold building or bagging.  Or am I missing
 some important fact?

 - David
 [EMAIL PROTECTED]

 North Atlanta Soaring Association
 http://atlantasoaring.org/

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Re: [RCSE] C/F Boom Molding Question

[Mark Drela]

Why not just use a mandrel and CF braided tubing?
That should give you 45-degree fiber orientation, 
a very nice outer surface, and no need for mold building 
or bagging.  Or am I missing some important fact?

This is ideal for a torque tube, but not a tailboom.
The 45 degree tube will have only 15% of the bending stiffness
and even less bending strangth as a unidirectional tube 
of the same weight. 

One compromise solution is to use an oversize braided tubing
like the 1.5 circumference stuff from CST.  When stretched
out to neck it down to the 1 mandrel, it will have roughly
30 degree fibers.  This will have 40% of the bending
stiffness of the uni tube.

- Mark
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Re: [RCSE] C/F Boom Molding Question

[David A. Enete]

I am molding a 40 x 1od long tube, I am not sure if a condom will stretch
that much, I know I push them to the limits...  8-) Kidding

My wife is a health educator who worked through college as a 
sexuality educator, and I can tell you personally that most modern 
condoms (latex) will easily stretch to 40x1.  And, you can also put 
one over a collegiate-size football.

- David
[EMAIL PROTECTED]

North Atlanta Soaring Association
http://atlantasoaring.org/

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