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Mast Building Method

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kitexpert
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Re: Mast Building Method

Postby kitexpert » Thu Oct 20, 2016 9:06 pm

Why not just wrap carbon around the core, which might be some light weight material like paulownia or even foam? Using UD straight and at 45 degrees should be effective, perhaps one layer of weave for the surface, for aesthetics if not else. Carbon weave tube is perhaps the best solution, but more expensive than using fabrics.

If some structural complications is wanted I would divide the core in three parts, wrap them individually in carbon and then glue them together in vacuum. Then more layers of carbon on top, so three hollow beams side by side would be a core. Brokite uses that kind of method in their carbon twintips.

Simplest way to add stiffness is of course to add thickness to the mast. Thickness (and chord) can be bigger near the board, there added stiffness is needed and increased drag does not matter.

I don't see why a carbon rod should be at LE. I-beam is also structurally suspicious if it is made thin parts. Hollow beam is much better in that respect and for sure easier to make.

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Re: Mast Building Method

Postby plummet » Thu Oct 20, 2016 9:37 pm

kitexpert wrote: I don't see why a carbon rod should be at LE.
If manually shaping it will make for an easier transition and wont expose the core when shaping the mast.
Also it will provide impact resistance if the mast is hits something. There would be less likelyhood of core being exposed.

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foam-n-fibre
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Re: Mast Building Method

Postby foam-n-fibre » Thu Oct 20, 2016 11:31 pm

For the mast I did I started with corecell and ran it through a table saw cutting halfway through, at what is the thickest part of the foil. I filled it with uni carbon pretty tight and then once cured, cut the other side and did the same on the other side, so I had a single piece with a stringer through it, but never had to cut it apart fully, so it was perfectly aligned. I then did lots of very shallow cuts with a ripping fence to get the foil roughed in.

In the end I ended up with a mast which is adequately stiff but not overly stiff. It seems to me that my stringer doesn't really have any fibres going the right way for shear in the core. If I was going to do this again, I think I would wrap a square strip of corecell in biax carbon, and then bond to it foam on either side which will get mostly shaped away in creating the front and back of the foil. This would gave a box section in the middle where it is thick, and basically 2 stringers. Keep in ind that there is so much carbon added that even if you have the perfect foil shape in your core, your final laminated shape might end up a bit different. Or, if you have a mold, then the outer shape might end up perfect, regardless of the less than perfect core.

I built my fuselage hollow and water tight in the areas not highly loaded. My mast and fuselage are so light compared to the aluminum ones i see at the beach. Everyone envies my light setup!

Oh yes, and wings with corecell inside so far seem plenty stiff, no need to make them heavy either. It's the mast that really requires to the technology.

Damn, apologies to revhed for calling the strut a mast all the way through this. Strut is what it should be!

Peter

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Re: Mast Building Method

Postby Bigdog » Fri Oct 21, 2016 1:07 am

How are you doing riding your wing?

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Re: Mast Building Method

Postby revhed » Fri Oct 21, 2016 7:55 am

I, we have built numerous STRUTS over the years and will share a few thoughts.
My very first shit marine laminate wood core "C" copy about 15 cm with a hodge podge of carbon in all directions and not vac sacked that is about 2 cm thick is still flying fine VERY heavy and SLOW but stiff in both twist and lengthwise,built 2010.
P3020007.JPG
P3020007.JPG (113.33 KiB) Viewed 1622 times
Note the hardware bought alu fuse that now L funny and other use :o
Using a factory made very dense carbon plate 1.1 cm and .7 I pain stakenly built (shaped) 2 T bars using this as the only material.
PC010005.JPG
PC010005.JPG (124.46 KiB) Viewed 1622 times
STRUT is 1.1 and board plate is .7 note heating curing method
PC010006.JPG
PC010006.JPG (135.39 KiB) Viewed 1622 times
Used Strut through plate into board for more connection strength.
PC010010.JPG
PC010010.JPG (120.87 KiB) Viewed 1622 times
Same concept for STRUT to fuse conection
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300px-Mortise_and_tenon_joint.svg.png (5.75 KiB) Viewed 1622 times
y.JPG
Easy to see factory layers of the carbon on the sides of the fuse.
P1010001.3.JPG
Built 2012
Flew well for years with NO sea bottom contact and one day BANG!!
c.JPG
I was lucky to find it after searching days with mask and snorkel and in the end a close friend found on his S U P.
Repaired using very special glue as primer to try to combat mechanical connection.
So far so good, but learned 2 things SO hard to get good solid connection after parts fully cured EVEN if well textured and clean, and this carbon plate while very dense and strong in all directions is almost like glass in that it feels "brittle" if I choose the correct word?
Sorry need to go and find that if I try to save it will not accept photos so will continue latter .....
R H

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Re: Mast Building Method

Postby downunder » Fri Oct 21, 2016 9:29 am

foam-n-fibre wrote:.
.
.
This would gave a box section in the middle where it is thick, and basically 2 stringers.
.
.
.

Peter
Basically, that is the idea. As said, I am only 59-61kgs, do not want anything heavier than 4-4.5 kg. All together if possible. Yes, the fuselage is hollow, and the second wing will be as well.


kitexpert,
no problem with a core wrapping. For bending that is. But, I've built my samples and for torsion it is not enough. Torsion is the biggest problem as I see it. We can definitely wrap with more 45 degrees carbon but 1 layer each side is not enough from my tests.

My tests also proved that carbon inside the core IS important for torsion. Samples showing more torsion in just 10 -15 degrees carbon orientation difference, ie 45 degrees and 60 degrees is providing a different results (as we know).

Yes, a carbon tube is fine but again, not so for torsion. There is no 45 degrees carbon tube that I can find. The carbon rounded rod on LE is great and would make a perfect outline. Also, a rod protruding slightly from a mast into the fuselage is great leverage and possible mounting mechanism. Imagine the possibilities - something similar to RH squarish plug (click system ie. with only one bolt :)

RH,
will build a new mold and document.

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Re: Mast Building Method

Postby revhed » Fri Oct 21, 2016 12:10 pm

downunder wrote: RH,
will build a new mold and document.
Thanks tons! We have made molds but always nice to see how others do it, photos would be great.
One method used is simply plaster in a rectangle box a couple cms more than desired STRUT and pull a Convex template thru the level plaster at the correct moment of its setting using the sides as a depth guide.
R H

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foam-n-fibre
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Re: Mast Building Method

Postby foam-n-fibre » Fri Oct 21, 2016 12:46 pm

Downunder, the difference in what I described is that with a box type tube of biax the fibres of the carbon are better aligned to support shear (sliding of one side up or down compared to other side as strut flexes). Also I think having those fibres wrap onto the skin is helpful. Having said that, I think what you are planning should work fine. I also agree that carbon between layers of foam might stiffen it, but the same carbon added to the outside would be even better. Sometimes people will use a thin layer of fibreglass in a bond between foam layers, mostly because it holds a nice thickness of resin for good bonding.

Bigdog - so far so good on the foil. The project got stalled through the summer, but I've had I think 5 days on it with the kite now this fall. I floundered a bit for 10 or 15 minutes then was getting flights and by day 2 I was getting long flights. Still no transitions yet, but that will come. Maybe not this year the way the cold temps are hitting now, but we'll see. Have you caught the bug yet?

Peter

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Re: Mast Building Method

Postby Bigdog » Fri Oct 21, 2016 2:43 pm

I haven't jumped on the bandwagon yet. Probably will give it a go next summer and borrow a board first to see if I get the bug ;)

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Re: Mast Building Method

Postby faklord » Fri Oct 21, 2016 2:50 pm

DU
"There is no 45 degrees carbon tube that I can find"
My french isnt that great but there are a few products on this page
http://www.carbonetube.net/produits.php ... 7b2977e7be
that say "Construction : Fibre unidirectionnelle + tressage interne 45°, resine epoxy."
Maybe the likes of RH can confirm the meaning?


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