[Auburntsts]

OK,
Silly question of the day. Once I cut a section of BID cloth off the roll on a 45 deg bias, how should I orient the subsequent layups that I cut out. Like #1, #2, or it doesn't matter. Thanks!

 

[Danny7]

I'd keep the bias at 45 all the time. the cloth is stronger, both thread directions are holding something. if you cut a long skinny strip with threads oriented 90 and 180 degrees the threads running parallel aren't doing very much if your fabric is covering and bridging a joint.

what are you working on? are you cutting long skinny strips? (like 1-2 inches wide, a foot+ long)

 

[osxuser]

Layups are to be alternated 45? then 0? then 45?. I would always have a odd number, with 45? on the two outside layers. Either 3, 5 or 7 ply layups.

 

[Auburntsts]

Layups are to be alternated 45? then 0? then 45?. I would always have a odd number, with 45? on the two outside layers. Either 3, 5 or 7 ply layups.

So to make sure I understand the orientation using my example, for a 3-ply layup you recommend I cut plys 1 and 3 like my #1 and ply 2 like my #2. Is that right?

 

[gpiney]

Always like #1. The ONLY orientation is like #1. I've done Hundreds of layups. After the initial corner cut, All subsequent cuts off the roll are properly oriented. Layups are not done 45-0-45. They are all 45.

 

[Danny7]

So to make sure I understand the orientation using my example, for a 3-ply layup you recommend I cut plys 1 and 3 like my #1 and ply 2 like my #2. Is that right?

what are you working on? cessna (columbia) and lancair don't do any of the 45-0-45 layups for long skinny bid tapes. all on the 45, all the time.

edit- i've also done hundreds of layups, in the lancair factory. from 2 layers to 12 or 16 (I forget, but it is the reinforcement for the IV foot peg, and it is really (no really) thick) but that is composite based planes, and that is why i tried to give an explanation for having fibers run 45 all the time instead of 90 and 180 (or zero if you want to look at it that way). That is why i've asked what you are working on. how many layers do you think you will lay down on this part you are doing?

i don't see much explanation for WHY to do a 45-0-45 style.

 

[Auburntsts]

I'm slowwwwwly working my RV-10 emp fairings, but my question was just general recommended how-to rather then aimed at a specific layup. I had assumed that my #1 example was the way to go, where I keep the layup edges parallel or perpendicular to the 45 bias. It made the most sense to me, but figured I'd ask those with experience before I unecesssarily screwed something up. Thanks for the replys!

 

[Danny7]

I'm slowwwwwly working my RV-10 emp fairings, but my question was just general recommended how-to rather then aimed at a specific layup. I had assumed that my #1 example was the way to go, where I keep the layup edges parallel or perpendicular to the 45 bia. It made the most sense to me, but figured I'd ask those with experience before I unecesssarily screwed something up. Thanks for the replys!

sweet. in general, always 45

 

[jsharkey]

Depends where you want the strength

0 deg strips - along the length of the roll - are strongest in tension and compression

90 deg strips - across the width of the roll - are slightly less strong in tension and compression because the "fill" fibers in a woven cloth tend to be less straight than the "warp" fibers - not a significant factor for non-structural fiberglass but carbon drawings often specify a required warp fiber direction - a bit like grain direction for critical metal parts

45 deg strips are strongest in shear - they also drape and form into and around corners more easily - the down side of this is that they can also be a bit "squirrelly" to handle, especially if you pre wet them on the table.

45 deg strips can make less efficient use of the material

Cleats and other shear carrying brackets and angles tend to be 45 deg

If you want to mimic a metal's strength in all directions over a big surface - e.g. a cover plate or cowling - it is common to mix 0 deg and 45 deg plies - be careful to make the plies symmetric about the mid plane though if you don't want a potato chip!

For obvious tension or compression members like wing spar caps or struts it is most efficient to use rovings of straight fibers with a minimum amount of 90 or 45 fabric to stop the laminate splitting and to help tie it to the spar web and/or skin

For the windshield strip on my -6 tip-up I mixed zeros and 45s - but I don't think it matters

 

[Danny7]

45 deg strips are strongest in shear - they also drape and form into and around corners more easily - the down side of this is that they can also be a bit "squirrelly" to handle, especially if you pre wet them on the table.

45 deg strips can make less efficient use of the material

if you wet them on a table, use film plastic to sandwich them. this way you can also roll out any bubbles and excess resin. cut the whole thing with rotary cutter, and you've got perfect edges, easy to handle even when 3-4 feet long strips.

 

[az_gila]

WEST System epoxies...

if you wet them on a table, use film plastic to sandwich them. this way you can also roll out any bubbles and excess resin. cut the whole thing with rotary cutter, and you've got perfect edges, easy to handle even when 3-4 feet long strips.

...sell a two layer 45 degree orientation tape that works well for small applications - saves cutting and messy edges...

http://www.westmarine.com/1/1/27459-727-episize-biaxial-tape-4-x-10-roll-from-west-system.html

 

[osxuser]

i don't see much explanation for WHY to do a 45-0-45 style.

If you want to mimic a metal's strength in all directions over a big surface - e.g. a cover plate or cowling - it is common to mix 0 deg and 45 deg plies - be careful to make the plies symmetric about the mid plane though if you don't want a potato chip!
...
For the windshield strip on my -6 tip-up I mixed zeros and 45s - but I don't think it matters

To make it strong in shear, compression, and tension. Not particularly important for fairings, but if something is worth doing, it's worth doing right. I'm not a composites expert, I've never worked in a factory making plastic airplanes.... but just because Cessna does it a certain way only means they've figured out that it's acceptable. I don't know what they use for fairings, but I am absolutely sure for anything structural, they have a precise schedule for layups to assure proper strength in the proper directions... Lacking a way to determine how strong it needs to be in any given direction, I choose to make it universally strong in all directions.

 

[Danny7]

To make it strong in shear, compression, and tension. Not particularly important for fairings, but if something is worth doing, it's worth doing right. I'm not a composites expert, I've never worked in a factory making plastic airplanes.... but just because Cessna does it a certain way only means they've figured out that it's acceptable. I don't know what they use for fairings, but I am absolutely sure for anything structural, they have a precise schedule for layups to assure proper strength in the proper directions... Lacking a way to determine how strong it needs to be in any given direction, I choose to make it universally strong in all directions.

how will changing the bias orientation affect the shear strength, or for that matter compression? the way i think of composites on a metal airplane working, they primarily work in tension, until you use them in cored applications like seen on cowls. I doubt anyone is going to ask how to do that with a thread at VAF (making a cored composite anything) doesn't seem like anyone is going to make something thick enough to have a significant compressive strength.

is the shear you mention the different layers of fabric sliding against each other? how would changing the bias affect that?

 

[jsharkey]

It's shear in the plane of the fabric - i.e. parallelogramming, skew wiffing or kitty wampusing - etc.

You are correct the layup schedule has little effect on interlaminar or ply to ply shear.

 

[f1rocket]

OK,
Silly question of the day. Once I cut a section of BID cloth off the roll on a 45 deg bias, how should I orient the subsequent layups that I cut out. Like #1, #2, or it doesn't matter. Thanks!

For anything on an RV that is fiberglass, the strand orientation is , in all practicality, irrelevant. I can't think of a single fiberglass part that is load bearing outside of normal air pressure flows. It is best to cut your cloth 45 degrees to the selvage because this gives the strip the most strength and the most flexibility to flow around edges, etc. When cut 90 degrees or 0 degrees to the selvage, the cloth does not want to bend around corners without creating an air pocket underneath the cloth.

I wouldn't worry too much about it. If you want to change the orientation between layers, it won't hurt anything so go for it, but it's not needed for purposes of strength. Most of the stuff I see people do with fiberglass violates many of rules you should follow when building a glass airplane anyway, but since our glass is all cosmetic, it's not worth making it a big deal. Having built a Long-EZ (with the emphasis on Long, as in long time), you are schooled in the Rutan epoxy glassing techniques. As other posters have pointed out, in those airplanes strand orientation if critical because they are the load bearing structures. you must pay very close attention to number of plies, type of cloth (BID or UNI), orientation, epoxy ratio, temperature, etc. I just don't see the need for that level of intensity on our parts unless you really want to do so.

 

[vonjet]

and

If it isn't structual then it probably wont matter too much what orientation it is. Say, if your building a glove box or something. However, I try to stick with the 45 orientation on all my layups even if just making something for fun. Its easy, correct and probably looks nicer too.