BID weave pattern

[ColinB]

Are most of you using plain weave or 2x2 twill?

 

 

2x2 has less of a crimp between the weaves and would appear to be the superior choice

 

 

whats the general opinion on this?

[TMann]

 

whats the general opinion on this?

To use what is called out in the plans.

Hexcel 7715 & 7725

[ColinB]

To use what is called out in the plans.

Hexcel 7715 & 7725

 

and 7715 is plain

 

and 7725 is 2x2 twill

 

from reading the hexcel site

[TMann]

and 7715 is plain

 

and 7725 is 2x2 twill

 

from reading the hexcel site

Good .... sounds like you've got it.

[Kent Ashton]

and 7715 is plain

 

and 7725 is 2x2 twill

 

from reading the hexcel site

Sounds like some confusion here

Check the ACS catalog, p. 30

7715 is Unidirectional - All the fiber go one direction except for small fibers to hold the cloth together. You could call it a plain weave but the cross fibers don't do anything. it's always called "UNI"

 

7725 is Bi-directional (BID), a twill weave, i.e., a modified over-and-under weave. Used because it drapes better than a plain over-and-under weave.

[ColinB]

thanks that clears that up then

[argoldman]

This probably goes without saying----

 

 

Each glass weave has specific strength characteristics and were chosen by the designer((s) to achieve specific goals.

 

Do not interchange them, or substitute them without proper knowledge in things glass fiber.

 

Rich

[ColinB]

Im not using glass

 

im using prepreg carbon, so i will be substituting materials

however the info on the hexcel material has helped me a great deal, thanks

[TMann]

Im not using glass

 

im using prepreg carbon, so i will be substituting materials

however the info on the hexcel material has helped me a great deal, thanks

Yes, the hexcell site has all the spec sheets.

The Berkut used the CF 716 UNI in place of the 7715 glass for the wing skins in a slightly different layup schedule.

716 is prepreg.

 

Une of the downside of CF is that you can't hide the antenna under the skin.

[mak790]

716 is prepreg.

Isn't it carbon uni fibre? Not prepreg.

http://www.hexcel.com/www.hexcel.com/Fabrics_DataSheets/716.pdf

http://www.aircraftspruce.com/catalog/cmpages/unicarbongraphite.php

in a slightly different layup schedule.

I've heard about 3 carbon BID layers insted of two 7725. What did they use in place of the 7725? Was it 282 or 284?

[TMann]

I've heard about 3 carbon BID layers insted of two 7725.

They don't use 7725 on the wings. Only UNI.

[mak790]

They don't use 7725 on the wings.

I know they don't/didn't use 7725, but I thought that they replaced glass BID 7725 with Carbon BID 282.

Only UNI.

So I understand they used 3 layers of UNI, first at 45deg, second at 0deg, and third at -45deg. Do you remember exact order?

[ColinB]

the first ply is 30degrees from center line

the second ply is in opposite bias

the 3rd ply is span wise

 

 

this is for the moldless berkut wing

 

this is in uni carbon

[mak790]

Thanks Colin,

 

I completely forgot, about 2-3 years ago there was a discussion at Canaraviation forum about the Berkut wings Layup, Richard Rilley said that fabric was laid at 30 and -30 deg, unfortunately he remowed all his post there, and because he passed away last December I can't ask him about it. I remeber that he said also, that the Berkut had 8 layers of fabric in the shear web, not 6 like the Long Ez. That's all what I remember.

 

Seb

[mak790]

 

I've heard about 3 carbon BID layers insted of two 7725. What did they use in place of the 7725? Was it 282 or 284?

Wow I just checked my Long Ez plans, I haven't seen them for 6-8 months. I'm not into Long Ez any more. Seems that, there is only UNI in the wings, I'm wondering where is that 7725 come from, hmm

[longez360]

Are most of you using plain weave or 2x2 twill?

 

 

2x2 has less of a crimp between the weaves and would appear to be the superior choice

 

 

whats the general opinion on this?

I used 2x2 twill 12k tow carbon on some parts. Yes, the crimp is less. I used some non-crimp material with veil as well, but I used very different resin and cure cycle.

 

My suggestion is stick with plans materials for structure unless you are ready to commit to enough testing that would substantiate it's inclusion. Generate allowables, or bridge test to show equivalence. Not sure that's worth the effort.