# Question for BoKu

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#### RSD

##### Well-Known Member
Hi BoKu,

Did any of these fabrics look like the one you mentioned that you are using in your glider cockpits?

A

B

C

#### BoKu

##### Pundit
HBA Supporter
I don't remember if I've used any of those particular weaves, but they all look similar to what I've use. In general, the weave of a cloth has a relatively small effect on its strength or stiffness. The big driver there is mass (weight per unit area). I think what we've generally used is about 6oz/yd^2, maybe an ounce or so more or less. We use a ply on the inside surface of the fuselage shell in the cockpit, and also on the expose surfaces of the cockpit longerons and canopy rail closeouts.

We've lately started using a clear gelcoat product from Fiberglass Supply on some of the "aesthetic carbon" parts we make for the racing jets. Going forward, we will probably start using it on the molded cockpit parts so that the hybrid fibers aren't right there on the surface where any bit of sanding turns them into hateful fur patches.

Thanks, Bob K.

#### RSD

##### Well-Known Member
I don't remember if I've used any of those particular weaves, but they all look similar to what I've use. In general, the weave of a cloth has a relatively small effect on its strength or stiffness. The big driver there is mass (weight per unit area). I think what we've generally used is about 6oz/yd^2, maybe an ounce or so more or less. We use a ply on the inside surface of the fuselage shell in the cockpit, and also on the expose surfaces of the cockpit longerons and canopy rail closeouts.

We've lately started using a clear gelcoat product from Fiberglass Supply on some of the "aesthetic carbon" parts we make for the racing jets. Going forward, we will probably start using it on the molded cockpit parts so that the hybrid fibers aren't right there on the surface where any bit of sanding turns them into hateful fur patches.

Thanks, Bob K.
Cheers Bob - very informative.

#### BoKu

##### Pundit
HBA Supporter
...In general, the weave of a cloth has a relatively small effect on its strength or stiffness...
Correcting myself here: That's generally true for weaves with the same mass of fiber on both the warp and weft. But where there is a substantial difference between the two (for example in a unidirectional like 7715 fiberglass), the strength and stiffness will be much greater in one direction than the other. I've been bitten hard by this with fabrics that look uniform to the casual glance, but actually have like 80/20 fiber distribution when examined closely. Since glass and epoxy have slightly different thermal coefficients, that's a good way of unintentionally making large thermometers.

--Bob K.

#### RSD

##### Well-Known Member
Correcting myself here: That's generally true for weaves with the same mass of fiber on both the warp and weft. But where there is a substantial difference between the two (for example in a unidirectional like 7715 fiberglass), the strength and stiffness will be much greater in one direction than the other. I've been bitten hard by this with fabrics that look uniform to the casual glance, but actually have like 80/20 fiber distribution when examined closely. Since glass and epoxy have slightly different thermal coefficients, that's a good way of unintentionally making large thermometers.

--Bob K.
Also very informative - many thanks Bob.

FYI I have just stumbled across an interesting 3:1 CF/K - the one in the bottom right of the picture -

#### BoKu

##### Pundit
HBA Supporter
Also very informative - many thanks Bob.

FYI I have just stumbled across an interesting 3:1 CF/K - the one in the bottom right of the picture - View attachment 89532
Be careful with that one and the one right above it; request a sample before you commit to using a lot of it. It looks like the kevlar fibers are only in one direction. If so, whatever good it does after the carbon starts breaking, it'll only do in one direction.

--Bob K.

#### RSD

##### Well-Known Member
Be careful with that one and the one right above it; request a sample before you commit to using a lot of it. It looks like the kevlar fibers are only in one direction. If so, whatever good it does after the carbon starts breaking, it'll only do in one direction.

--Bob K.
I will ask them to send me a better photo - I tried zooming in but it was too pixellated to see anything. Certainly the one above as you pointed out only has the kevlar going in one direction.

#### RSD

##### Well-Known Member
Better photo they sent me - I think the kevlar goes in both directions

#### wktaylor

##### Well-Known Member
RSD... what are the weave design #s for these various fabrics?

Caution... Kevlar has a known tendency for moisture absorption along the fibers... which can cause the composite to swell and affect the epoxy [matrix] strength... not to mention gain weight.

#### Lendo

##### Well-Known Member
RSD,
Is that RED in the Red and Black photo also Kevlar?
George

#### RSD

##### Well-Known Member
RSD... what are the weave design #s for these various fabrics?
I didn't ask for the weave designs for the other fabrics unfortunately but I can find out for you.

Caution... Kevlar has a known tendency for moisture absorption along the fibers... which can cause the composite to swell and affect the epoxy [matrix] strength... not to mention gain weight.
Many thanks for the heads up on that - wasn't aware of that! Will try to put some measures in place to stop that being a problem hopefully!

#### RSD

##### Well-Known Member
RSD,
Is that RED in the Red and Black photo also Kevlar?
George
Hi George,

I believe so - as far as I am aware all of the photos are of various carbon fibre/kevlar fabrics that they have, and they do seem very reputable to deal with.

#### RSD

##### Well-Known Member
Missed it amongst others, no I didn't pay 2$/m shipping. It was flat rate to about 30lbs. Don't know what Canadian/us/Aussie$ is these days. I think they hit me about 35$up to 10kg. They didn't calculate it per metre, but that's just what it worked out to when I was seeing what the all in costs were per metre.$35 for 10 kilos might explain the delivery time - its on that slow boat from China! Australian \$ has fallen a bit lately due to suffering from the fallout of the various trade wars, currently one Canadian buys 1.1 Aussie.

#### RSD

##### Well-Known Member
Just a quick update - my carbon fibre cloth and carbon fibre / kevlar hybrid cloth arrived from China yesterday so shipping took exactly 7 days. Haven't opened the package yet to see what it is like but I'm confident that it will be good quality.