Re: Re: Carbon fiber cloth for Treger's vp prop hub?

From: <themaxout_at_aol.com>
Date: Sun, 9 Jan 2011 11:44:26 EST

I'll chip in my 2 cents.
 
Pre-preg in "pre-impregnated" cloth or fiber. It's a product that has the
appropriate amount of matrix (adhesive) like a temperature cure epoxy
impregnated. My experience with it is a woven cloth and parallel laid up fiber.
 
The use is to save time when doing large surface layups like panels or
wound layups. However, because of that, it has to be "debulked" every so
often as the layers typically aren't wound or wrapped perfectly.
, usually by vacuum bagging. Then, the layup is cured in an autclave (for
temp control) at a starting temp and a soak at that temp, and then,
depending on the actual matrix, a process gradient of temp/soak/increase/soak,
etc. Maintaining a uniform temp thru the layup is the key for a good final
product.
 
For modeling purposes, dry fibers have only tension capability. We add
epoxy or some other adhesive...cellulose...dopes, etc. as the "matrix." In a
previous post, the matrix gives the fiber layup strength in shear by
virtue of the matrix' mechanical strength. Epoxies...usually about 10,000
-20,000 psi. Using a fiber that is .005 and ignoring the "roundness" this
translates to a strength of about (.005x10,000) = 50 # / inch.
 
A small number, but calculate the load on an F1D and you don't need much
strength.
 
The beauty of composites, or should I say advantage is strength to weight.
 For ref, a normal carbon fiber / matrix composite density is about 65% of
aluminum, or .065#/in-3.
 
And all this relies on the "adhesive" strength bonding the fiber to the
balsa. Since the fiber tension modulus is right up there with steel and
balsa is very low, a single .005 fiber top and bottom of a .1 sq balsa (prop
spar root?) would increase it's bending strength about 3x for a weight
increase of say .01% (napkin calc's)?
 
The skill in using a reinforcement fiber is probably the biggest
issue...amounts are really small! And some of this discussion was centering around
micrograms(!?). Indoor builder skills amaze me...my fingers are too fat.
 
 
Go to "themmmclub.com" - "tech articles" - structures design article and at
 the end is a short dissertation for the lay person.
 
 
Rick Pangell
Editor of "The Max-Out" Newsletter of
The Magnificent Mountain Men FF Club of Colorado

 
In a message dated 1/9/2011 6:52:59 A.M. Mountain Standard Time,
nickaikman_at_hotmail.com writes:

Hi Phedon,

Re: 'Maybe you can define for me what really is prepreg. To my knowledge
it is TOW containing a resin that has to be heated to 100 degrees in order
for it to cure.'

I think that's correct.

'If I am right then it is inferior.'

Inferior to what? And, for what reason?

If it works well on the F1D components we're dealing with, it can't be
inferior.

Nick.



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Received on Sun Jan 09 2011 - 08:46:26 CET