style of Glass Fabrics

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Albert80

Member
Joined
Jun 30, 2009
Messages
11
Location
Bologna, Italy
Hi Guys,
I have one questions...I know that there are many type of glass fabrics like S2-Glass E-Glass etc... that are the most used for airplane costruction. I have found (by RUTAN) the following E-Glass:
E-Glass style 7715 UNIDIRECTIONAL
E-Glass style 7725 BIDIRECTIONAL
My question is what are the difference between this two and the E-Glass syle 7781? The other two are one UNI (used for exemple for cap-spar) the otherone is BID (used for exemple for web-spar) and I know how it be used but I don't understand what kind of fibre is style 7781! is a UNI or BID and when and for what is used?

Thanks for you help
Albert
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,308
Location
Saline Michigan
IIRC it is poor man's BID. It is same weight and weave, drapes nicely for compound curves, and surface treated for epoxy. 7725 was made to Rutan specs while 7781 is not, but it is pretty much the same thing at less cost.

A long time ago, there was technical article in Sport Aviation about general use fabrics in substitution for RAF fabrics.

I am sure that anybody with more specific info will chime in.

Billski
 

kent Ashton

Well-Known Member
Joined
Aug 15, 2008
Messages
727
Location
Concord, NC
The Rutan BID 7725 is a 4-harness (crowsfoot) weave and 7781 is an 8-harness weave.
Weaves - Fiberglass Warehouse
I've tried using 7781 on cowls and it is nice cloth but 7781 is a tighter, finer weave. For me, it does not conform to curves as easily and harder to straighten and wetout and tends to retain dime-sized air bubbles that don't want to work out easily (using Saf-T-Poxy). The Rutan BID is just a little easier to use.
 
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