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Shear web spar in many part or spar cap in section -choosing option

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opcod

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Aug 28, 2010
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Canada
Hi

I'm posting in regard of the shear web for spar. I haven't find much info on earlier post so here is a tricky question, i do think.

Some glider used rooving or uni tape. So let say the spar cap is the black box of a ridiculous 90ply uni tape.

In the option 1: the foam core (pink block) is wrapped in fiberglass (blue.)
And web are made in C shape to be bond on top of the glassed foam.

flange opt1.jpg

Option 2 : the web are made into a c-Channel mold (green ) and the 2 are bond with a foam core in between at same time.

So after that, the spar cap is bond on each side.

flange opt2.JPG

Base on those 2 option, which one is the best design ? I'd do think the option 2 is way too heavy and don't give much used...


Option 3, will it be better to just build up 2 full C-channel and bond them together with the spar cap imbedded into it ? And with foam at inside..

flange opt3-1.JPG flange opt3-assy.JPG


Option 4 : with foam at outside in between the 2 C made with spar.

flange opt4.JPG


And on spar cap, is it be better to be in 1 strip instead of 2 as option 3 and 4 ?.. Like some SCH glider as :
glider spar.JPG


Many thanks
 

StarJar

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I think your 3 & 4 are getting close, and then use a single strip. Otherwise you have individual strips carrying different loads, of hard to determine values.
Good luck.
 

BoKu

Pundit
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I suspect you might be overthinking this. Have a look at the ways Marske describes:

Graphlite Carbon Rod by Jim Marske

We use a single encapsulation wrap for most of the spar, with a few reinforcements at the inboard end.

Also, it is pretty hard to get good compressive strength with hand-laid uni tapes. That's one of the things the Graphlite pultrusions do really well.

Thanks, Bob K.
 

opcod

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Aug 28, 2010
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Canada
Hi

I had plan to infused a spar cap, so it should give good ratio, but of course lower than Graphlite.
I do know some said the rod need to be interleave if a stack of 2 are used.
But the only rod from Marske is of 0.092 x 0.22 in size. It's look quite pretty small to work with many of those... is it ?

Is there larger rectangular rod available to used ?
I think larger can help handling and I could go with that option more easily if it's available without cut in coil too.

Thanks again
 

BoKu

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...I had plan to infused a spar cap, so it should give good ratio, but of course lower than Graphlite.
Test some coupons, and see what they go to.

...I do know some said the rod need to be interleave if a stack of 2 are used...
I've never heard that, and my spar design was reviewed by Marske himself. I would check the credentials of this "some," and see if they actually have any practical experience that bears on the topic at hand. In theory, theory and practice are the same. In practice, they're not.

...But the only rod from Marske is of 0.092 x 0.22 in size...
That doesn't sound right, though I haven't talked with Jim in a while.

...It's look quite pretty small to work with many of those... is it ?...
Hmmm... Let's see... When my choices are many fussy plies of uni tape that might or might not go to 60ksi in compression, or some unitary sticks that I just drop into their trenches to get a pretty much guaranteed 250ksi in compression, I think I will continue to use the sticks, even though I don't press the stuff much above about 90ksi @ 8g.

...Is there larger rectangular rod available to used ? I think larger can help handling and I could go with that option more easily if it's available without cut in coil too.
There are larger rectangles available. The hitch is that they won't want to coil anything with a minor width greater than 1/8" (~3mm). Anything more than that, and the energy stored within the coil represents a substantial risk to shippers and handlers in case it gets loose.

I think that there are military contractors using massive cross-section pultrusions, but they are paying through the nose for custom runs of custom profiles, and don't seem to mind that it is also rather expensive to ship. The rest of us abide by the compromises required to get the material at more economical rates.

Thanks, Bob K.
 

wsimpso1

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Spar construction involves four major things...

Each cap has to be pretty much solid - yeah, dense unidirectional material in the caps. If you are determined to lay it up, do some test pieces and check the compressive strength, then design for that;

The shear web has to connect the caps together - The shear webs have to lap over onto the caps. If it does not go to the caps, it is not part of the shear web;

The spar has to come out of the mold.

So, how you do it is really up to you.

My spar caps are made from Uni tape that is laid up in a simple mold, brushed and squeegeed down wet, and results in close to minimum epoxy content without even vacuum bagging, and they test at higher strength than the book value of 70 ksi. My webs have both been UNI cloth wet open layup and 18 oz BIAX vacuum bagged. They are lighter vacuum bagged in a mold, but some shapes would not come out of a mold. I have built on a table with the caps jigged in place, then insert foam core and layup most of the shear web, finish by removing from the table, invert it, and layup a shear web around the outside.

Jim Marske's methods work. Lost of airplanes with graphite rod caps made Jim's way.

Billski
 

autoreply

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I do know some said the rod need to be interleave if a stack of 2 are used.
There is a point where you need to interleave the shear web in the rods. That's certainly above what you mention. Do the math, keep a thin spar cap, or interleave for safety if it's a thick spar cap.


There are larger rectangles available. The hitch is that they won't want to coil anything with a minor width greater than 1/8" (~3mm). Anything more than that, and the energy stored within the coil represents a substantial risk to shippers and handlers in case it gets loose.
By minor you mean thickness right?

Generally you don't want to coil it below a diameter of 1 promille of the thickness. (so 1 meter for 1 mm thick). Increase that by a factor of 5 for HM fibers.


DPP will do a lot of custom stuff with their stock mandrels, including infinite pultrusions:
vDijk Pultrusion Products (DPP) - dpp-pultrusion
 
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