Fiberglass cloth weight vs 'finished' weight

I was perusing the composite matierals in the Aircraft Spruce
catalog pages and noted that the fiberglass (and other ) cloths
are characterized by a unit weight, like 5.8 oz/square yard.
My naive assumption is that the cloth as purchased would,
on average, weigh 5.8 oz /square yd.

But some of the descriptions include a 'finished weight' which
is slightly different from the 'other' (nominal?) weight.

The weight of the final product after being impregnated with
resin and cured will vary with material and technique, but if
I assume an average specific gravity of about two for epoxy
fiberglass and use the nominal thickness of the cloth I compute
a weight of the resultant fiberglass sheet that is about twice
the 'finished weight'. So I'm assuming that 'finished' weight
does not refer to weight of a one square yard sheet of fiberglass
made from that cloth with epoxy or polyester resin.

So, can anyone enlighten me on what they do mean?

By 'finished' weight do they mean the actual average weight
as opposed to a nominal (rounded) value used to characterize
the cloth?

--

FF

Doesn't fg cloth have a "finish" applied to the fabric to facitlitate the
wetting of the fabric? Pat

Fred the Red Shirt wrote:
I was perusing the composite matierals in the Aircraft Spruce
catalog pages and noted that the fiberglass (and other ) cloths
are characterized by a unit weight, like 5.8 oz/square yard.
My naive assumption is that the cloth as purchased would,
on average, weigh 5.8 oz /square yd.

But some of the descriptions include a 'finished weight' which
is slightly different from the 'other' (nominal?) weight.

The weight of the final product after being impregnated with
resin and cured will vary with material and technique, but if
I assume an average specific gravity of about two for epoxy
fiberglass and use the nominal thickness of the cloth I compute
a weight of the resultant fiberglass sheet that is about twice
the 'finished weight'. So I'm assuming that 'finished' weight
does not refer to weight of a one square yard sheet of fiberglass
made from that cloth with epoxy or polyester resin.

So, can anyone enlighten me on what they do mean?

By 'finished' weight do they mean the actual average weight
as opposed to a nominal (rounded) value used to characterize
the cloth?

--

FF

No straight forward answer to that one Fred.
Way too many variables.

Biggest one is technique.

50:50 resin to glass is pretty tough to do by hand without
vacuum bagging and all that.
Even then, I thing 60:40 is abut the best I've seem.

Maybe using resin infusion process you could get 50:50.
I've heard claims of 30:70 - but never seen it myself.

Maybe some of the composite fellers can answer better.

Richard

patrick mitchel wrote:

Doesn't fg cloth have a "finish" applied to the fabric to facitlitate the
wetting of the fabric? Pat


Volan, IIRC

On Mar 18, 5:07 pm, cavelamb himself wrote:
patrick mitchel wrote:
Doesn't fg cloth have a "finish" applied to the fabric to facitlitate the
wetting of the fabric? Pat

Volan, IIRC

Aha!

I bet that's it.

Thanks.

--

FF

On Mar 18, 10:24*am, Fred the Red Shirt
wrote:

But some of the descriptions include a 'finished weight' which
is slightly different from the 'other' (nominal?) weight.

It's like this: weight is an imperfect measure of mass, since it
introduces as a variable the gravitational pull of the Earth. Which,
as everyone knows, varies depending on ones location and altitude and
other factors. To cancel out these factors, the catalogs generally
specify a standard location at which the weight is valid. In this
case, the location seems to be Finland.

But seriously, I'm as mystified as you are.

As regards the weights of fiberglass parts, I've generally had good
luck just doubling the total cloth weight. That's generally what I do
to figure out how much resin to mix - I just take the cloth, weigh it,
and mix that much epoxy. It comes out a bit high for vacuum bagged
parts, and a bit low for soupy tooling layups, but generally puts me
in the ballpark.

Thanks, Bob K.

On Mar 18, 5:33 pm, Bob Kuykendall wrote:
On Mar 18, 10:24 am, Fred the Red Shirt
wrote:

But some of the descriptions include a 'finished weight' which
is slightly different from the 'other' (nominal?) weight.

...

But seriously, I'm as mystified as you are.

I think Mr MItchel has the answer, finishes are described on these
pages:

http://www.fiberglasssupply.com/Prod...s_fabrics.html

http://www.thayercraft.com/


As regards the weights of fiberglass parts, I've generally had good
luck just doubling the total cloth weight. That's generally what I do
to figure out how much resin to mix - I just take the cloth, weigh it,
and mix that much epoxy. It comes out a bit high for vacuum bagged
parts, and a bit low for soupy tooling layups, but generally puts me
in the ballpark.


Yes, my estimate was about 2.1 times the cloth weight, but that
assumed the fill was level with the weave on both sides. An inside
surface could be left a bit 'waffly;'

---

FF

See http://www.eng-tips.com/viewthread.cfm?qid=103139

On Mar 19, 5:15 pm, "
wrote:
See http://www.eng-tips.com/viewthread.cfm?qid=103139

Thanks.

While we're discussing this, any idea as to what unit weight
is typical for 1.7 oz dacron finished with latex paint?

Would the same weight of paint also seal the heavier cloths?
(My guess would be 'almost').

--

FF

On Mar 20, 12:12*pm, Fred the Red Shirt
wrote:
On Mar 19, 5:15 pm, "
wrote:

See * * * *http://www.eng-tips.com/viewthread.cfm?qid=103139

Thanks.

While we're discussing this, any idea as to what unit weight
is typical for 1.7 oz dacron finished with latex paint?

Would the same weight of paint also seal the heavier cloths?
(My guess would be 'almost').

I've been wondering the same thing. Its on my list of experiments for
this summer. Octave Chanute used a baloon fabric that I believe was
silk impregnated with latex.

I conducted a few interesting (and historical) experiments using 2.3
oz cotton a few years ago. In one of Wilbur Wright's 1899 letters to
Octave Chanute, he asks about several things including a source for
spruce and the type of dope used on Chanute's gliders (1896-97)
stating that "hitherto we have used shellac". Based on the date of the
letter, this would have referred to the Wrights' experiments with the
1899 kite. Wilbur's purpose in asking for materials soruces appears to
have been for the 1900 glider. As we know from the notebooks, the
Wrights did not dope the wings of the 1900-1908 machines. Why not?
Good question! Here's what I found:

Assuming a 3-pound cut, I used 7 coats of orange shellac to fill the
weave (might be a little less for them since their fabric was about
1.8 oz.) That roughly trippled the weight of the fabric alone. By my
rough calculations, this would have equated to an additional 8 pounds
for the 1902 glider (317 sq, ft total surface). Considering the lift
limitations of their technology and the ultra-slow launch speeds, the
gains from ruduced porisity (sp?) did not equal the loss from the
added weight.

Unfortunately, that means that early Wright machines are made from
great expances of unshrunk cotton just waiting for that passing cloud
to turn them into giant parallelograms. (Yep, it happened, but not to
me thank God.)

Harry Frey