Page 1 of 3

Custom Kiteboard Full Carbon

Posted: Sat Jan 06, 2018 1:08 pm
by Grkite
Core Pawlonia And light for 140 x 42!!
Made more for speeding up than looping high high....:)
Finished in 2017.10!

Re: Custom Kiteboard Full Carbon

Posted: Sun Jan 07, 2018 12:54 pm
by kostantin
Kalimera,

your board will break. You have been using 90° carbon. This prevents the board from flexing. Watching your board picture closely, you have allready two broken areas left and right of the pads. Pad view to the middle of the board.

Have a look on the bridge picture. Everything that is flexing is using 45° Only bridges with bow cables do not follow this.



Image

tks

Kosta

Re: Custom Kiteboard Full Carbon

Posted: Sun Jan 07, 2018 3:37 pm
by Grkite
kalimera,

Thanks for the info...have a nice year :)
I have to say that there is no crack!...:)What you see is the carbon not so straight at these points. Time will show..offcourse...still The flex was quite nice ,

There is also glass ,,is not only carbon...

Still thank very much!

Re: Custom Kiteboard Full Carbon

Posted: Sun Jan 07, 2018 3:44 pm
by jumptheshark
Then why post as full carbon?

Re: Custom Kiteboard Full Carbon and glass

Posted: Sun Jan 07, 2018 7:17 pm
by Grkite
Both sides have carbon and glass. Sorry if misled you...

Re: Custom Kiteboard Full Carbon

Posted: Fri Jan 12, 2018 8:04 am
by downunder
Hi

good stuff. I like it. For the next one , I think you might use heaps less wood strips which makes it easier.

2.2kg is very good. However you can make it even more light with using some light FG. Carbon on top has absolutely no function, and contrary to Kosta's comment, it does not add much to stiffness.

This is because on board top carbon is compressed when you load the board. You would need carbon on bottom to be tensioned. That adds to stiffness.
Of course, carbon on top still works as a "rocker keeper" but other than that nothing more. So, use lighter FG and prebend your core.

See: http://kiteforum.com/viewtopic.php?f=107&t=2387451

The carbon is mostly cosmetic. This board I'm using 99% of my time, has like 300 sessions. So, no. It wont break.

I also covered SS inserts with a veneer. This is better because I did pull one insert (well, the bolt rusted so needed to take it out), and with no veneer under I would drill through the board. But veneer prevented this and viola! Invisible fix.

D.
12430154.jpg
12430154.jpg (14.1 KiB) Viewed 1188 times

PS

Tell us more about it! how did you do the rails and finish? I love the stickers! Can I have it? :) Oh, and I did sent SS inserts to Izmir, close to you.

Re: Custom Kiteboard Full Carbon

Posted: Fri Jan 12, 2018 9:07 am
by rynhardt
downunder wrote:
Fri Jan 12, 2018 8:04 am

2.2kg is very good. However you can make it even more light with using some light FG. Carbon on top has absolutely no function, and contrary to Kosta's comment, it does not add much to stiffness.

This is because on board top carbon is compressed when you load the board. You would need carbon on bottom to be tensioned. That adds to stiffness.
Of course, carbon on top still works as a "rocker keeper" but other than that nothing more. So, use lighter FG and prebend your core.
Eh? No. The middle of the board bends upwards, i.e. the top will be in tension.

For reference, here's the diagram of a simply supported beam with double overhangs, uniform load. Of course, in our case the diagram is turned upside down, but I assume that's pretty obvious.
And of course depending on speed the uniform load gets skewed towards the trailing edge, but qualitatively the diagram still applies.

Re: Custom Kiteboard Full Carbon

Posted: Fri Jan 12, 2018 4:02 pm
by downunder
No, because stiffness comes with thickness ^3, the middle of the board is way more stiff than tips, so if tips are 3mm and mid 12mm, thats way more than 1 layer of carbon is providing.

Plus, whan landing, its a console with heaps tension on bottom. None on top. The board buckle under the pads coz on compression, not tension. They also break wide open under pads on bottom by tension.

The pic is assuming uniform Ibeam, not a reinforced beam, and most boards are not uniform as you know.


Remember, we are making a reinforced ibeam with top glassing and bending wood. So the glass is always tensioned on top. Like a pre cast concrete (when concrete is put on compression, with tensioned steel).

So, yeah, its not that simple as on pic. As you said, it is not even uniform load. Depending on the edging, 1/3 of the board might be above water, so the load is really this (WIP, could not find any on the Net, so will make one for you in due course:)

The pics are also telling you that the support is fixed, non movable. Which is wrong, coz our foot is moving in straps (well maybe not in boots; ). What we have is this sign as on B!
Image

Which totally messes the diagrams when you have a dynamic, non uniform load with non fixable support. Civil engineering 1o1. We also talking hydro dynamic here which wasn't my forte on uni.

Plus, Kosta is wrong on bridges as well, the reason why bridge is 45 degrees is tensioning steel via load distribution for stability. Nothing to do with flex, but with tension. We do not want a bridge to flex, coz this creates dynamic forces, and that creates unknown vibrations. We want steel to be in equilibrium of tension, no compression, no flex, no vibrations.

Re: Custom Kiteboard Full Carbon

Posted: Fri Jan 12, 2018 7:56 pm
by Grkite
Ok.Thank you!

Still..so many different approaches..ideas and theories..I wonder what is right?...
I am sure you all know that any calculation so simple in a comblex environment will give only relative values. Yeah yeah I am a mechanical engineer.....and you need FE and CFD analysis with so many different parameters all around...so still...

Trial and error will finilize the kiteboard whatsoever. Always you have the ability to copy...that I hate and dont really do...I prefer me to design... to print to shape the core...to make the graphics ..to customize it to user/level/spot/style....and then laminate and thermopress it...and ofcourse finishing..

I spent my time making calculations..i reached a point that really needed good software and expertise in CFD,,,,and then I moved on...I had to :) In all these calculations...you always have limitations of the main three stages of the making....and these are always the a real challenge.....so building the thermopress ....deciding what is possible..finding the materials....and then perform all the stages with presition and perfection....is a real challenge...always.

For example a made a board with glass ..carbon...tpu/ptex sheets...and 1cm thick midpoint....lol....is so stiff and bit heavy...still i am sure for the right person will be the best....see:

viewtopic.php?f=107&t=2395943

It wont break ...I am 84 kg and i was jumbing in the middle to hear a crack..even in the tips..I also ride her....everything good.Now the one that you see..I really reached the limits...so light...so flexy..so beautiful...

Downunder: The stickers are not stickers..can be....took a photo of the owner and embed it in my logo...and then laminate it :) The rails is one of my main focus...I really believe they change so much the behaviour of the kiteboard ..so there are made quite carefully...with different profile..in different points....the material is epoxy..pigment..filler...:) Prebenting the core..is agood idea...but as I have set the rocker(adjustable steei rocker table) already including the springback..I woukd rather not readjust it....now! Thank you.

Re: Custom Kiteboard Full Carbon

Posted: Fri Jan 12, 2018 11:30 pm
by rynhardt
downunder wrote:
Fri Jan 12, 2018 4:02 pm

So, yeah, its not that simple as on pic. As you said, it is not even uniform load. Depending on the edging, 1/3 of the board might be above water, so the load is really this (WIP, could not find any on the Net, so will make one for you in due course:)
I've made a separate topic for this. I think the discussion may be useful in its own right.

http://kiteforum.com/viewtopic.php?t=2398562&p=1002409