Spar cap material

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BBerson

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I think somewhat below yield tension. Each ribbon would need to be pulled individually. They pulled the cables on the Tacoma Narrows suspension bridge with dozens of hydraulic rams.
 

BBerson

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canardlover

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What about using a roll of chopper gun roving for the spar caps? Gun Roving
This is exactly how Velocity spars are made using S-Glass roving in a mold then layers of Biaxial cloth laid last in the mold for the shear web. The Traxial glass wing skin is bonded to the outside surface of the spar cap thus imparting some protection against lateral failure of the resin matrix encapsulating the glass fiber tow under heavy structural loading.

Jeff
 

cblink.007

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Then look for compatable S-glass roving. The Aircraft Spruce tape is E-glass same as chopper gun roving.
As long as I can access mechanical properties data by way of due diligence, all good! I'm just averse to using any resin or glass without proper data!
 

BBerson

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As long as I can access mechanical properties data by way of due diligence, all good! I'm just averse to using any resin or glass without proper data!
The Wicks 12" tape is listed as S-glass. So of course it costs more. Do the plans call for S or E?
 

cblink.007

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The Wicks 12" tape is listed as S-glass. So of course it costs more. Do the plans call for S or E?
I am not the one building, but my background with Long EZ's has me understanding that S-glass tapes are used for the spar caps...
 

Marc Zeitlin

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I am not the one building, but my background with Long EZ's has me understanding that S-glass tapes are used for the spar caps...
Nope. E-glass on the VE, LE, COZY, E-Racer, etc. See:

 

BBerson

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My guess is that Rutan and other designers may have chosen the economical E-glass because ultimate strength is secondary to deflection with fiberglass.
(the extra cap thickness needed for low deflection at design load gives an ultimate strength like 12g)
 

Lendo

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TFF, I have considered this myself, in Carbon rods they immerse the Carbon Tow in Resin as it moves to a die under tension, one to remove excess resin and 2 to maintain all the filaments in the desired direction. I would suggest just as much tension to do those two things. A bit of trial and error would identify the desired outcome. I'm hoping to test this in the future, but different sized Tow might make the tension different.
Hope that helps.
George
 

TFF

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Once the material is wetted out and straightened, how in the tooling does it stay that way?
Something like carbon rods probably have a 400 m long building for the process. One off layup is a little strapped for space, as you know. The only way I see is being able to clamp each layer independently, but in mass, and apply tension. It really comes down to what is needed; a few psi required, or does it really requires a lot more?
 

cblink.007

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Lendo

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TFF, in regards to Tooling- ever hear of Bobbins, their stainless steel inserts where the Glass or Carbon is wrapped while maintaining some tension, some pins would also do but the Bobbins have a hole in them for mounting in structures - if desired.
There is probably a number of ways of doing this for varied applications. I'm still struggling with Spar and Landing gear for the easiest best (strongest) and lightest way.
George
 

wsimpso1

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What about using a roll of chopper gun roving for the spar caps? Gun Roving
Gotta be a sarcastic comment, designed to get ol' Billski revved up. Grin.

Spar caps see a huge fraction of their loads as tension and compression along the long axis of the cap. Unidirectional composites are just about ideal for this purpose as max strength and max stiffness is aligned the long way in the laminate.

E-glass uni tape and epoxy, properly laminated makes a uni directional composite with a min strength of above 70 kpsi and min elastic modulus of 4.4 Mpsi. You can easily exceed 70% fiber volume in open laminates of this tape. This is far superior to all other laminates likely in E-glass, and a straightforward manner for laminating and assembling spars. It also has a long history of producing sturdy long lived structures.

Chopper gun work loses all directionality in the laminate, much of the length of the fibers are spent in picking up load rather than being loaded, fiber fractions tend to be low, tends to have fatigue strength at an even lower fraction than with the unitape mentioned above, and this method is almost universally used with polyester resins. The result is a laminate that will do well to reach strength of 15 kpsi and modulus of 1.8 Mpsi. The result of this is that you will need on the order of six to eight times the cross section area as an equivalent uni-tape layup with huge weight penalty. While you might succeed in redesigning the structure to fit inside the wing and have adequate strength and stiffness, hardpoints for connection to the rest of the bird will be - at absolute best case - problematic to design and execute.

Going further, the Long-EZ has its spar caps built on cores made of polystyrene foam that is completely soluable in the typical resins used in chopper gun work. Any failure to completely protect the cores from the resin or its vapors will destroy the cores...

What if you replaced the plans built spar with caps made using a chopper gun? The airplane would require substantial redesign, much of its useful load would be used up in the new structure, and you may not even succeed in building it in the first place.

So we are back to "stick to the plans" unless there are both know issues and known good fixes to the known issues, then "stick to the plans including the plans for known good fixes". Those of us qualified to design, build, and test new designs may go forward this way, but it takes longer to build and fly. Much longer.

Billski
 

BJC

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Gotta be a sarcastic comment, designed to get ol' Billski revved up. Grin.
Bill, my interpretation is that the other Bill was asking about using the unidirectional glass fiber that is fed to chopper guns as a potential source of uni for spar caps. No suggestion there of chopping it.

The question that I would have is about the quality of the material.

Wrt pretensioning glass fibers to emulate pultruded rods: how would one go about doing that? Seems to me that the best that a homebuilder could do is to carefully align as many fibers as possible in a female mold before wetting with resin.


BJC
 
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