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Custom Kiteboard Full Carbon

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kostantin
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Re: Custom Kiteboard Full Carbon

Postby kostantin » Sat Jan 13, 2018 10:33 am

Greetings

I ordered by mistake some years ago 0/90° carbon. Both mold injecetd boards broke within 2 week period.
I learned this lesson well.

When you look on a glider wing, 90% of the outer/inner shell is made out of biax carbon. Every thing that is not able to flex under heavy load, breaks.
I have been working as a service and repair guy for gliders a long time.

Same story on thing windmills.

Biggest part of the mill is biax, in the root area its UD glas and biax.
I worked in a huge windmill company for decades, repaired miles and miles on fibers all coleurs.
I would not start any expensive experiments on the layer directions if you are not 100% what you are doing.

I stick on my previous statement, the board is facing delemination left and right of the pads. There you have the biggest forces.

tks

Kosta

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rynhardt
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Re: Custom Kiteboard Full Carbon

Postby rynhardt » Sat Jan 13, 2018 12:03 pm

kostantin wrote:
Sat Jan 13, 2018 10:33 am

I ordered by mistake some years ago 0/90° carbon. Both mold injecetd boards broke within 2 week period.
I learned this lesson well.
Your experience may be unique.
It's possible some other variables may have been at play other than the layup direction and weave type.

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Re: Custom Kiteboard Full Carbon

Postby Grkite » Sat Jan 13, 2018 12:45 pm

Kalispera Kosta,

First of all Everything Brakes if you exceed the limits !

Now if its a matter of use OR construction OR design....its another matter. Still I wonder how you conclude that it will brake when you really dont know the glass that is inside?

And ok you see in the inner sides of the pads-midsection cracks and...delamination?

Cracks? There is no crack(s) ..Under the carbon black sheets during thermopressing they may produce....how do I know? .I know because after finishing I stand on her...jumbing....waiting to hear something..she was so flexy and nothing happened....

Delamination? I will tell you what you see and if you want you believe it. When bought the carbon ...they fold it..and didnt roll it!!! BIG mistake. This produced some kind of distortion of the straight and perpendicular lines of the square carbon fiber..adding the laying up of the fabric with epoxy and puting her under high pressure added to that look ...Belive it or not...this is what you see and for that reason I say. The lesson learnt is to avoid using this kind of weave....:)

Now This board if it brakes will be in the tips landing badly from a loop....maybe...maybe not...:) Or this board may delaminate if you leave her in the sun for days...maybe?

Thank you for your interest as I learn aswell through it. :)

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downunder
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Re: Custom Kiteboard Full Carbon

Postby downunder » Sun Jan 14, 2018 4:06 am

Grkite wrote:
Fri Jan 12, 2018 7:56 pm

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.
Ok, I still don't get it, how did you embed this graphics? Printed on a rice paper? Tell us more :)

The problem with epoxy rails is UV. I have a PU samples stored and can show you how rails look on my board after 3 years compared to samples. Very light change. Also, epoxy is much more brittle than PU, so it can't survive if the board is dropped on the concrete from ie 40 cm. Depending where it drops of course. I'm talking tips.

Is your rocker table adjustable? I see a lot of effort in making a table but my idea was to spent minimum and gain maximum :) So, simple perspex sheet, 5-6mm thick is my rocker table. Nothing more. Stored behind the door.

When making a core, the wood strips are not glued all together. The core is glued all together when glassing the top. That makes less springback possible in my experience since only wood strips are forced to bend, not the complete core (how is it said, "together we are stronger" - so loose strips are not that strong!). The more strips you have, the less springback you get. It is that simple. Less strips is easier to work with.

Full carbon on top is, well, a waste. FG is way better coz you can leave the board on the Sun (as I did this morning). Carbon on the contrary, you can bake an egg on, the temperature is exceeding epoxy TG (an assumption for a picky readers ;), and might delam. The FG will never delam coz the Sun is going through a FG, like through the glass. Than it hits a wood, which is an isolator. UV might affect epoxy tho, but, not the TG. Temperature is TG related, hence we don't see the Airbus planes black, that would be an disaster.

Cheers

D.

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Re: Custom Kiteboard Full Carbon

Postby rynhardt » Sun Jan 14, 2018 9:36 am

downunder wrote:
Sun Jan 14, 2018 4:06 am

Full carbon on top is, well, a waste. FG is way better coz you can leave the board on the Sun (as I did this morning). Carbon on the contrary, you can bake an egg on, the temperature is exceeding epoxy TG (an assumption for a picky readers ;), and might delam. The FG will never delam coz the Sun is going through a FG, like through the glass. Than it hits a wood, which is an isolator. UV might affect epoxy tho, but, not the TG. Temperature is TG related, hence we don't see the Airbus planes black, that would be an disaster.
Well, no. Carbon on top is very effective especially right in the middle where the board bends upwards.

If you use a resin with a low glass transition temp, it's simple enough to paint it a light colour.
Alternatively use a high TG resin and follow the post cure schedule.

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Re: Custom Kiteboard Full Carbon

Postby Grkite » Sun Jan 14, 2018 11:28 am

I have tried a lot of diffrent mediums for graphics. The most of them produce air...or the ink/(inkjet printer) blurred them due to colour reaction. I spent so much time trying to figure out what is right for my process and easy as i have quite high temperature in thermopress. It is plastic transparencies that I print on them. Is so simple as difficulte because you know you have to prepare the top glossy surface to avoid of delamination and some other factors..but still are specific issues on my application. I will finnally use printing on polyester fabric...in the end as I just figure out ,,,:)

For rails I may use ABS/TPU (I have it waiting), when used it was great in shaping it without any bubbles.....but issue in applying it...so diffucult ..But yes the next next next one will be yellow abs...:) Now the issue of rails is really a matter of epoxy resin and mixture and application....I have good results after checking different fillers..prepring well the surface of the outline channel...having good conditions...preparing the epoxy mix carefuly...and thinking how to have as less/little bubbles as possibble....You know these...I am sure :)

Yes the adjustable rocker table took me some time...is just from steel as the wooden ones...Big issue adjusting it.,,I mean a lot of screws! I had to use steel under such pressure! :)

Yes I will checkk that in next order..probably one third less...there are other reasons aswell for less strips...now I have 5 pawlonias...waiting...and havinf solved the springback..I even enjoying her stretcing her tips...so no prob...

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downunder
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Re: Custom Kiteboard Full Carbon

Postby downunder » Sun Jan 14, 2018 1:49 pm

rynhardt wrote:
Sun Jan 14, 2018 9:36 am
downunder wrote:
Sun Jan 14, 2018 4:06 am

Full carbon on top is, well, a waste. FG is way better coz you can leave the board on the Sun (as I did this morning). Carbon on the contrary, you can bake an egg on, the temperature is exceeding epoxy TG (an assumption for a picky readers ;), and might delam. The FG will never delam coz the Sun is going through a FG, like through the glass. Than it hits a wood, which is an isolator. UV might affect epoxy tho, but, not the TG. Temperature is TG related, hence we don't see the Airbus planes black, that would be an disaster.
Well, no. Carbon on top is very effective especially right in the middle where the board bends upwards.

If you use a resin with a low glass transition temp, it's simple enough to paint it a light colour.
Alternatively use a high TG resin and follow the post cure schedule.
Ha ha, you are a hard man to convince. But I do not need to, have a look in here:

http://kiteforum.com/viewtopic.php?f=1& ... 1&start=30

"Fibreglass twintips that have too much flex bend to much and produce a negative rocker line between the footstraps."

The stiffer the board in the middle, the less possible to produce a negative rocker. But, I push my back foot heel and lift my front foot toes when riding, lets say this is a torsion. Plus, as I mentioned, we have a 1/3-1/4 board above water, so the board moment diagram is shifting from the middle.

With wood cores, the wood is pre tensioned for rocker, FG (or CF) is also tensioned and it's really hard to produce a negative rocker....

We know the theory rynhardt, but this is a DIY, not all can afford/use PID's and specialty epoxies :) I am all for minimum effort/expense and max gain. For me, that's the mantra of DIY.

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Re: Custom Kiteboard Full Carbon

Postby Grkite » Sun Jan 14, 2018 2:19 pm

The one that I am now finishing has two strips on top with glass and carbon with glass under.
She is quite thin in the middle and really I have to add probable more heavy glass. The two carbo strips on the top with glass ...makine her flexy and strong.
For sure the best would be to able to cut the carbon sheet in shapes and put carbon where you really want to...but this is difficult to ptimize and actually to cut the carbon in stange shapes is very difficult...

With all yous discussion , I still believe carbon glass bottom and glass and carbon stiprs top will be the next one....What I would like to add in your discussion is you always have to consider the size/shape of the board..the weight of the fabrics...and the rider. Offcourse you know from FE analysis where are the areas to consider....

Finnally a question relevant to lamination ... I come across that the materials used in bottom should be the same in top....is this true? Why? Is this really a fundamental rule of lamination?.
Is there a reason due to epoxy behaviour?

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Re: Custom Kiteboard Full Carbon

Postby downunder » Sun Jan 14, 2018 3:17 pm

yes, this is fundamental and it's called symmetrical lamination as opposed to asymmetrical. However, I am not doing it coz not interested in perfection.
No, not epoxy. But wood core shrinking/expanding with different lams on top/bottom.

In reality, I would drop all carbon, since not needed for DIY boards with wood. Ie FS Radical board has none carbon, Toby is riding it, this is proving the board ;)

Of course, full carbon boards have a place.

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rynhardt
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Re: Custom Kiteboard Full Carbon

Postby rynhardt » Mon Jan 15, 2018 9:01 am

downunder wrote:
Sun Jan 14, 2018 1:49 pm

"Fibreglass twintips that have too much flex bend to much and produce a negative rocker line between the footstraps."

The stiffer the board in the middle, the less possible to produce a negative rocker. But, I push my back foot heel and lift my front foot toes when riding, lets say this is a torsion. Plus, as I mentioned, we have a 1/3-1/4 board above water, so the board moment diagram is shifting from the middle.

With wood cores, the wood is pre tensioned for rocker, FG (or CF) is also tensioned and it's really hard to produce a negative rocker....
I think we might be saying the same thing, but I'm focusing on the forces experienced by the board, not on the construction.
The reason a bendy board can produce a negative rocker line between the footstraps is because the water pressure bends the board upwards.

Now how the builder decides to prevent this is where the construction comes in, i.e. core type, thickness, reinforcement etc. And there are a multitude of ways to do this which may all be perfectly valid as long as the end result is achieved.


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