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Mast/Strut Fiber Angles

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foam-n-fibre
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Mast/Strut Fiber Angles

Postby foam-n-fibre » Tue Dec 12, 2017 7:07 pm

OK, time for another theoretical question. What is the best angles for the fibers to run on a mast/strut? On the one I built, I used unidirectional carbon (0 degrees) and also some biax at +45 and -45 degrees. Obviously 0 degrees (top to bottom) is best for bending. Is 45 degrees the best for torsional rigidity? I looked online and found some stuff, but much deals with shafts, which might be a different beast compared to what is closer to a flat plate. I wonder if a shallower angle is better on a foil which is closer to a flat plate and only loaded in torsion at each end. I'm sitting here holding a ruler and twisting it back and forth... Has anyone ever looked into what the best angle is for our application?

Thanks,
Peter

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Re: Mast/Strut Fiber Angles

Postby tegirinenashi » Tue Dec 12, 2017 10:55 pm

Does it has to be 2 layers? If more than two, then evenly splitting the angle seems to be the most natural choice, say 0, 30, and 60 degrees.

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Re: Mast/Strut Fiber Angles

Postby foam-n-fibre » Wed Dec 13, 2017 12:01 am

When I refer to +45 and -45, I mean that the cloth is woven that way, with fibers on both diagonals and none parallel with the roll (it's woven with very thin tracers along the 0 axis to hold the cloth together better). But you are right, it is possible to lay cloth on a diagonal at a shallower angle. That's basically what I'm wondering, if I should buy the 45 degree biaxial cloth again, or whether an angled strip of unidirectional, or even regular 0/90 degree weave laid at varying angles is better. Of course if you use 0/90 cloth at a shallow angle half of the fibers will be perpendicular to the desired angle, which might make it less worth the trouble of doing that.

Peter

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Re: Mast/Strut Fiber Angles

Postby bacon2109 » Wed Dec 13, 2017 12:29 am

been writing to long, some answer were posted;

@ tegirinenashi;
for a mast , a DIY build, to reach a fair stiffness and torsion, you put 2 to 3 mm wall tickness of fibre carbon on each side.

1st answer (post)
I've searched info on "structural composite beam".
find somewhere , on the net; 0/-30/+30/-60/+60

In regard of the application, you can vary the type of carbon fiber also; tensile strenght/modulus of the fibre , some experts say's

My next mast should be ,
a Sandwich type of mast. 2 type of carbon fiber; HT and UHM (or better if possible to find in small quantity).
standart fiber (HT) in the core (UD) with layers at ; 0/-30/+30/-60/+60, for 7... 8 mm in tickness
The shell with UHM , 2....2.5 mm wall tickness, same orientation.
for a maximun tickness under 13 mm

I am almost certain that with such an assembly I can go down under 11mm, 12mm without problem for the lower part (fuselage side).
board side may go up to 20mm.... meanging that the mast start from the board thicker, size down after 30...35 cm or more,
the part of the mast that is out of the water most of the time.
---flex and torsion stiffness increase on shorter beam---
I didn't figure out yet, how to build it.....

2nd answer
all goes with your suppliers, what he have and can get.
I work with UD, i dont see a real gain in using biax or more.. since i'm with 6K

Not a expert, just giving idea from a home builder

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Re: Mast/Strut Fiber Angles

Postby downunder » Wed Dec 13, 2017 1:58 am

bacon2109 wrote:
Wed Dec 13, 2017 12:29 am
been writing to long, some answer were posted;

@ tegirinenashi;
for a mast , a DIY build, to reach a fair stiffness and torsion, you put 2 to 3 mm wall tickness of fibre carbon on each side.
If using about 200g/m^2 cloth, 1mm thick carbon is 5 layers. 3mm carbon would be 15 layers.

15 layers each side is overkill for DIY, particularly with 6k. This are 30 layers, take or leave, with 60-90 mins pot time for the normal person wrapping a mast. So, not a pro:) If one is really skilled, maybe, just maybe less than 60min to wrap it. That is a huge stress for DIY builder who never attempted to build something similar.

What you're missing completely from the picture is a stringer. Stringer will replace heaps of carbon needed for bending strength.

Also, 30-60 is not a torsional strength. 45 is. No matter how it bends you can't get wrong with 45. The guys who build the moth HF will tell you more 45, the better. I did splat 2 layers each site if remember well. All together 4 layers each side, so less than 1mm. Strong as. Two carbon stringers.

Uni can't be used for 45 (or any angle) simply because it's impossible to align it properly. Remember, the epoxy pot life is your enemy - not what theoretically one can do. So you need to go with biax, plus with woven carbon for non 45 angle if you wish.

To put it simply, all of this is replaced by prepreg. One can do whatever with a prepreg since no epoxy pot life to worry about.

As I see it DIY is a compromise. As an engineer, building a bridge is a compromise too. Actually, everything is. So we're optimising for our application, time and money.



D.

PS

---flex and torsion stiffness increase on shorter beam--- No. The structural property is the same. What's different is the amount of stress or a leverage on shorter/longer mast.

Also, building an asymmetric mast (thinner in the middle), creates wrinkles on carbon. It would be enormously difficult for one off DIY builder to manage this.

Hm...A lot covered. Good luck.

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Re: Mast/Strut Fiber Angles

Postby plummet » Wed Dec 13, 2017 7:45 am

Yep. I ran uni-on the angle from corner to corner of mast. Maybe 10 deg?

Essentially when laying up carbon you want to run the fibers in the direction you want the stiffness. With a mast you want stiffness in many directions. 45/45 is not that effective because each individual strand does not span much width of the mast.

I say run fibers 0,15,45,60. That will cover many of your bases for torsional and lateral stiffness.

Hey down under. Have you done the mast stiffness test? I'm interested to see how it compares to mine.
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Re: Mast/Strut Fiber Angles

Postby downunder » Wed Dec 13, 2017 7:56 am

plummet wrote:
Wed Dec 13, 2017 7:45 am
Yep. I ran uni-on the angle from corner to corner of mast. Maybe 10 deg?
This means it's not wrapped, correct? Because very hard to go 'around' mast LE with Uni. Not impossible, but hard.

I still need to make a plug, so no. No tests for now. Also, I'm building for 60kg rider, and you are 80-90 :)

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Re: Mast/Strut Fiber Angles

Postby plummet » Wed Dec 13, 2017 8:10 am

downunder wrote:
Wed Dec 13, 2017 7:56 am
plummet wrote:
Wed Dec 13, 2017 7:45 am
Yep. I ran uni-on the angle from corner to corner of mast. Maybe 10 deg?
This means it's not wrapped, correct? Because very hard to go 'around' mast LE with Uni. Not impossible, but hard.

I still need to make a plug, so no. No tests for now. Also, I'm building for 60kg rider, and you are 80-90 :)
77kg to be exact!... no wrapping of that layer. But I did wrap the 45 layers.

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Re: Mast/Strut Fiber Angles

Postby foam-n-fibre » Wed Dec 13, 2017 1:11 pm

Thanks for the replies. I'm not too clear on why we would run fibres at an angle as much as 60 degrees though. My thinking was that 45 was too steep of an angle to be ideal, and that less than 45 might be better. Is there someone that can explain why 60 might be good? It might just be that we can substitute 30 and 60 with a simple 45 biax. I might consider running some of my uni at a shallower angle, but sounds like a fair bit of wasted material unless I can find a use for a bunch of triangles.

Peter

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Re: Mast/Strut Fiber Angles

Postby bacon2109 » Wed Dec 13, 2017 1:40 pm

My build info (in french) for me at 90Kg;
http://kitefoil.forumactif.org/t3854-j- ... r-bien-sur
with images, mast wrap by hand 0/+45/-45, had to remove a twist after epoxy cure, a bad day sanding CF, to not scrap it, i rewrap it.
1 good 0/+45/-45 layer, mast end up to be 1000x138x15mm.
Yes , if you look at the finish mast, the wrap is not easy, under vaccum.

result of the 5Kg test
- 5Kg @ 80 cm ; flexion of 15mm +/- 1mm
- 5Kg @ 50 cm ; torsion of 1 degree

that is why i'm going to go 0/+30/-30/+60/-60, to increase all strenght, with a mould
since it was made with standart carbon fiber (HT) .....
i like the idea of 0/15/45/60 layers


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