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Mast Building Method

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faklord
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Re: Mast Building Method

Postby faklord » Sat Dec 31, 2016 4:00 pm

"Might not loose it since a wood core2 - i maybe wrong but i thought the moses fuse was Al?

"..my feeling was footstraps already are not far enough forward." - One would hope that the footstrap locations on a standard production board + foil would be correct?
but a 50mm shift is pretty significant. Also, if anything, a shorter mast is going to require your weight to be moved forward. (You can think of this as the drag from the foil x strut length is partially countered by center of mass acting on distance behind the strut. Reduce the strut length and center of mass needs to move forward)

"Making strut plate to board longer moves bolt position relative to strut, perhaps putting more stress on the plate." Agreed but it is easy to make the plate as stiff and strong as you like..just make it a bit thicker and increase carbon skin thickness..very little compromise here? There should be no impact on the stresses applied to the board.

"What do you think of just angling the strut back?" I can see two potential drawbacks to this, though I suspect these are both more theoretical than realistic:
1) an increased chance of ventilation/cavitation being drawn down to the fuse and causing issues with the stab wing.
2) the increased bending moment in supporting the riders weight will tend to cause a torsional stress in the strut. possibly leading to an instability (humming strut?)..this may be hard to visualize - try holding something like a thin plastic ruler fixed at one end then apply a force to the edge at the other..it will give way by a twisting motion?

Your strut to plate connection is looking much better.
I would wrap extra carbon round the strut to increase the skin thickness at the ends & where the barrel nuts are. make sure the barrel nuts engage with the carbon skin, rather that just the core material. Then ad a final layer to cover the barrel nuts.

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Re: Mast Building Method

Postby TomW » Sun Jan 01, 2017 12:19 pm

The Moses fuselage is aluminum. Strut is cf.

This is off topic: Footstrap placement. I measured and took pics of my T40 board and interesting is that the mast attachment plate is not the same as online drawings.
Dimensions are not 100% clear on Moses drawing how far rear strap holes are from tail.
But one thing is different: my rear strap holes are positioned 50 mm forward of of the plate compared to drawing, Or the plate is positioned 50 mm forward on the board, which appears to be the case.
I'll have to start another thread on this topic.

Ok, I'll adjust plate to strut position and keep strut vertical. Beef up the plate

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Re: Mast Building Method

Postby downunder » Mon Jan 02, 2017 3:46 am

Cont...

My first strut-O-mast build with a stringers wasn't successful. Under the vac the wood strips moved position and the stringers ended not vertical enough.

Got myself clamps this time. Was reluctant to buy them for years, need no more tools, but...

Clamped:
0659.JPG
Tomorrow, if everything ok, I can profile the strut.

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Re: Mast Building Method

Postby downunder » Tue Jan 03, 2017 1:31 pm

As promised,

today profiled the strut, took me 2hrs. Notice little carbon stringers:) I can tell already, this is very very hard to bend. It's got 4 carbon tow 10mm which sort of created an semi I-Beam. That was the idea.
IMG_0665.resized.JPG
To speed the sanding process, the oldie but goldie hand tool is great. See the excess tow carbon near the carbon stringer. The 'stringer's are 100cm long, 10x2mm, and the strutOmast will be around 90cm. I am planing to 'embed' this carbon rods into the fuselage and possibly into the board. Will see.
IMG_0667.resized.JPG
Copying an ALU profile (WIP):

IMG_0669.resized.JPG
Hoping to wrap it in carbon tomorrow, last day of holidays.

D.

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Re: Mast Building Method

Postby TomW » Thu Jan 05, 2017 2:41 pm

That thing is not going to flex much sideways, but dont forget the torsion. Discussion above says we should use Biax for torsion.
Be interesting to know what flex is with "5kg, 80cm out test" is on your shaped mast without external lams. Then measure torsion.

Ordered M6 SS inserts from these guys- https://www.anchorinserts.co.uk they sell in small quantities.
My un-shaped and un-reinforced uni-D abachi ply strut blank flexed 70mm with 5kg on the end 75cm out from base.

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Re: Mast Building Method

Postby downunder » Fri Jan 06, 2017 2:11 am

Hi Tom,

thanks for the link.

Not sure about the plain biax tho. Twill weave might be better.

About the inserts, would it be better to use a barrel nuts? This was discussed many times, a lot of guys are using it (ie for cross threading) :

http://www.wsurf.eu/fins-spare-parts/

I am thinking about it but will probably fix the mast permanently to the fuselage/board plug. But you're building a removable mast :)

D.

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Re: Mast Building Method

Postby TomW » Fri Jan 06, 2017 3:49 pm

D, Thanks for the link, didn't know where to get them.
I ordered the anchor inserts. Seems like both would work fine.
Yes, I need to fit my strut to the Moses fuselage.

If the strut works, and I learn to ride the thing this summer, it might be fun to make an entire foil or wings.
Cheers.

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Re: Mast Building Method

Postby plummet » Fri Jan 06, 2017 6:56 pm

downunder wrote:

IMG_0669.resized.JPG

Hoping to wrap it in carbon tomorrow, last day of holidays.

D.
Could be the photo, but it looks like the trailing third of could do with more tapering

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Re: Mast Building Method

Postby GrantL » Sat Jan 14, 2017 5:38 am

From my experience in carbon fiber prepreg and infusion you can't think of the bending and torsional stiffness like steel. An I beam in carbon won't work very well.
Any layup of a long slender part like a mast must have a combination of 70% uni at 0deg to the long axis, and double bias 30% at +/- 45deg.
Remembering the threads only work in tension.

The pic of a time trial bike frame and handlebar I built which uses this ratio 70/30%
Sections vary in thickness 2mm to 3mm and hollow. But you have a reasonable cross section.
One of the problems of a mast section compared to a bike is that the sections are extremely slender. If you make a section which is hollow or has a core of some type you will never be able to produce the stiffness that you think you should get.
Also if you use a mould to make a mast all of your laminate layers are sitting in a curve dish shape, not actually linear. This applies to the double bias laminate
. Just my experience shared
Attachments
bike 1.jpg
Example of prepreg, hollow sections.

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Re: Mast Building Method

Postby downunder » Sat Jan 14, 2017 3:38 pm

^

You've built this? You really need to get into building a HF asap :)


My 'motto' is to build optimally, feasibly and light. No molds, no infusion, prepreg and stuff...

This carbon rods already made a mast stiff in bending. Wrapping it in carbon will hopefully stiff it for torsion.
I could 'thread' some carbon in cross section but that would be overkill) In reality, I think, to make it stiff for torsion, one should try that ( a construction high crane is good example with cross section beams for exactly that). But this is difficult to implement on a mast.

"70% uni at 0deg to the long axis, and double bias 30% at +/- 45deg." - for sure, that was the plan anyway. The million $ question is how much is optimal for the rider weight. That is - my weight.

Cheers


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