Fiberglass orientation...

[GuinnessGuy74]

OK, I know there is no such thing as a stupid question but....

 

I am planning on starting Chapter 4 soon. I know questions should be limited until you start, as most answers become apparent when actually working on the part, but this is more of a general build question.

 

I do realize the difference between BID and UNI and when each is used. However, I don't understand why UNI is sometimes laid out two plys at 45 degrees (seatback for example). Wouldn't two plys of BID cut on the 45 bias be the same thing?

 

Please know, I am not QUESTIONING the design, just trying to understand the reasoning. I mostly see UNI laid along the one direction, where strength is needed in that direction.

 

Can anyone shed some light on this for me?

 

Jim

[Marc Zeitlin]

However, I don't understand why UNI is sometimes laid out two plys at 45 degrees (seatback for example). Wouldn't two plys of BID cut on the 45 bias be the same thing?

It would be, IF each of the directions of glass in the BID was as thick as a single ply of UNI, and if they weren't interwoven. Two plies of UNI is stronger than one ply of BID, and two plies of BID weighs more than two plies of UNI. Sometimes, what you suggest would be OK, depending upon the needs, but sometimes, crossing UNI gives a better fit to the strength/stiffness requirements of a particular layup than does BID.

[GuinnessGuy74]

IF each of the directions of glass in the BID was as thick as a single ply of UNI

That is exactly what I needed. I wasn't thinking clearly. I was focused more on orientation...

 

Thanks Marc, makes sense to me now...

 

Jim