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Author Topic: Question regarding the direction of ripstop "grain"  (Read 1754 times)
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Ladelnutts
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« on: July 19, 2009, 08:39 PM »

I have a question regarding the direction that the grain within ripstop should run. For the sake of discussion, it seems that on higher end kites such as Prisms & Bensons, that the ripstop grain is perpedicular to the individual sail panels.  On my Flying Wings Alpha+ there is no rhyme or reason to the grain of the ripstop.  I would imagine that the Alpha+ uses the fabric in whatever manner yields the most pieces from a yard of fabric.  All that being said, is a kite sail built with the ripstop grain perpendicular to the panel stronger than one built with the hodge podge method?  Or is the grain pattern on these higher end kites more for aesthetics?

Any info appreciated. 
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fidelio
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« Reply #1 on: July 20, 2009, 12:59 AM »

it's called bias and, to my knowledge, every woven fabric so far has it. what it means is under stress the fabric will stretch or deform more in one direction than it will if the same force is applied in the other direction.

this applies to the construction of kites where the maker wishes to eliminate or reduce stretching of the fabric in a certain direction.

on more finely made kites the orientation of the fabric bias is most definitely intentional.

generally speaking on more well made kites you'll find the ripstop pattern of the fabric aligned with the direction of stress. if you were to look along the spine of the kite the boxes will be aligned with it, and along the leading edge they'll also be aligned, but where these two pieces of fabric meet you will have the boxes at an angle to each other.

you can see exactly this principle, in the picture below.


thanks to skippy for posting this picture elsewhere on the forums.
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Fdeli
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« Reply #2 on: July 20, 2009, 01:07 AM »

by virtue of the fact this process creates more waste, it increases the cost of the production.
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chilese
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« Reply #3 on: July 20, 2009, 01:45 AM »

It has been years and I am doing this from memory.

There are 3 major stretch directions in material of this type.

1 Least stretch: The major axis or roll direction of the material.
2 Mid stretch: The minor axis or perpendicular to the roll direction.
3 Most stretch: 45 to both axis. This assumes the major and minor axis are perpendicular to each other.

One axis is the weave, the other axis is the roving (rove?), but I don't remember which is which. I am open to correction as it's been several years since I did any work in Hi-Mod stuff.

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inewham
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« Reply #4 on: July 20, 2009, 02:37 AM »

Warp - along the roll
Weft - across
Bias - 45deg.

The warp is the direction of least stretch so it usually gets aligned with the trailing edge, spine etc. BUT... Polyester fabrics are usually sufficiently low stretch in all directions that cheaper kites get away with aligning to minimise wastage.

Even on stretchy fabrics, sometimes people used to align the bias with the leading edge to create a little billow just behind the LE as the fabric stretches.
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Ladelnutts
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« Reply #5 on: July 20, 2009, 09:29 AM »

Thanks to all of you for the information!   Kiss
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mikenchico
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« Reply #6 on: July 20, 2009, 01:29 PM »

good info given already so I'll just mention: if your looking at building something an important factor to take into consideration is that both sides of the kite mirror each other. The grain of the fabric should run the same way on the right side panel and the left side panel. Even though Poly fabrics have very little stretch even on the 'Bias' and you'll get decent results without being consumed with the grain having to run this or that, you still want both wings of the kite to stretch and react the same.

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« Reply #7 on: July 20, 2009, 02:47 PM »

To reply to the OP:

It is unprofessional to align panels with a different bias regardless of fabric usage (this is a serious PITA to a kite maker!). I'd love to cut a certain panel at a funny angle to save some fabric, but you need to be consistent across the board.

I have a simple rule, pay attention to tension.

If it is a Spine-based panel then it should be perpendicular to the spine.
If it is a LE-based panel then it should be perpendicular to the Leading Edge.

Both areas are under tension and the fabric's bias (in my case Icarex), should align with that grid. It is stronger and more consistent in this configuration.

Anything in-between is set accordingly, but 45 degrees is usually good enough.

There's no magical rocket-science involved here, just use your common sense. Radial lines from nose-to-tail-to-TE-to-LE will give you a a good basis to work from.

You can deviate a little for the sake of material-usage, just not so much that it becomes blatentley obvious that you've done so, for the sake of yourself and your stock. That's when you risk negative feedback from buyers. You know, it'll just look rubbish compared to.....'X' kite maker!

Mark
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Ladelnutts
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« Reply #8 on: July 21, 2009, 05:50 PM »

Thanks everyone for the great information.  I have only made kites for myself so I have the flexibility to deviate from the rules a bit for the sake of using the material in an efficient way. 
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