Old 11th Oct 2018, 17:44
  #27 (permalink)  
Join Date: Nov 2010
Location: Earth
Posts: 609
Originally Posted by widgeon View Post

At the very start of my Career I worked at Westlands at Yeovil on composites development.
We built a prototype tailboom for the scout from all Unidirectional High Modulus Carbon fibre ( there was not any woven product available in the mid 70's).
I witnessed the destructive test and I will never forget the load crack when it failed , to call it an explosive failure was an understatement.There were bits of tailboom all over the hangar. If I am not mistaken it exceeded design load by quite a factor .
I would suspect that the machine laid tape would be interleaved with woven fabric on any new blade , especially at the root .

Sounds like matrix failure of early epoxy non-toughened resins! I've heard a lot of stories like this from that era. Nowadays, the usage of elastomer toughened resin systems makes a matrix failure like that a bit less dramatic.

There is off-axis-laid tape in the design of the similar but smaller S-97 and X2 blades to create the required torsional stiffness, for example, but it is all still unidirectional tape with no fabric.

If you were using AFP to fabricate a SB1 blade, then the addition of broadgood fabric plies would negate the advantages of using an automated tape laying system as you would have to repeatedly stop the process. I imagine the additional bulk of fabric with the weft fibers could also cause overall weight challenges, since the warp direction is inherently softer from being woven and would require more plies to achieve the same stiffness.

Based on the patent applications for V280 blades, they appear to be made entirely of fabric material, though the design requirements of a proprotor are entirely different. Hopefully the SB1 blade patent shows up soon so we can see whats going on inside!
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