Kiteforum.com

TomW wrote: ↑

Wed Jul 18, 2018 3:04 pm

I was thinking about this. purely emperical.
Lets say the kite has 60kg pulling force in normal riding with some speed. during a jump it has more pull, say 120kg pull- I know , I know this is all wrong, but dont know any physics.

so lets say im loaded to do a jump, 120kg on center lines. CL accidentally releases and snaps up to bar that i am holding. My simplistic thinking that is like 120 kg on the center of the bar. Its hitting it sharply, but the bar is probably released from your grip and moving in relation to the hit- so the " bar ends " are not fixed.

With this thinking- if i can stand on the bar and bounce a bit- it should be strong enough...

Thoughts ?

Intuitively I would say if you can stand on it and bounce a bit you have it over dimensioned.

Your 60kg pulling force is probably overestimated during riding as you are moving with the kite. I guess it is about right during a waterstart. The 120kg must be underestimated.

A quick calculation (hope I remember and apply formulas of high school physics correctly).
80kg rider is 800N
Assuming a 8 meter jump and apex reached in 1 second is acceleration of 8m/sec.
Work would be 800N x 8m/s = 6400N is 640kg..
If you reach apex in 2 sec. or just jump 4m it would be half..
If you release powerline anchor point (qr) the force on the bar should imho be calculated as the mass of the QR times the speed of the QR in direction of the bar center hole as the QR accelerates putting 6400N in a an object of 250 gram is 2,5N.. would cause it to fly in the direction of your bar with 50 m/sec (150km/h)

All of this energy could be released in a single point (the hole in the bar) causing it to break...
If it hits your bar in stead of your hand you ar lucky.....
A bit of foam in between might minimize the damage...

This concern about breaking during sudden QR release isn’t a concern for me. It’s unlikely and the bar will be pulled out of your fingers anyway.

So what weight on the bar center, as test? 12,5 kg?

Jyoder wrote: ↑

Thu Jul 19, 2018 11:44 am

This concern about breaking during sudden QR release isn’t a concern for me. It’s unlikely and the bar will be pulled out of your fingers anyway.

Yes, but that Cl is accelerating and smashing against the bar center.
I still want to test it...
I don’t want to be 1km offshore in sideshore wind, in Brazil with no one to rescue me, and have bar snap in half.

I used my franken bar today for 2hrs. I really like the simplicity and lightweight. Plus my hobby store Eva grip is super comfy.

Discovered that instead of having hard plastic ball at Base and top stop it would be good with a rubber cushion.. Softer. Im going to 3D print some soft ones tomorrow at work.

What about coarse cork instead of EVA foam? Wonder if that would work.

phuqit wrote: ↑

Sun Jul 22, 2018 12:55 pm

What about coarse cork instead of EVA foam? Wonder if that would work.

Cork would make a really nice grip. It's used in fishing rods extensively. I tried to find some.
You would need 2mm thick or about and wrap it around just like eva.
It would look nice. Not sure how long it would last.

I checked, there's Cork sheets 1-2-3 mm thick.

Another way would be to laminate some ash wood ( used in baseball bats). The bar ends could be integrated. cut out on bandsaw, shape it, Cork grip. Cork leader covers, Be a work of art!

haare wrote: ↑

Sat Jul 14, 2018 5:54 am

I will use epoxy to glue the parts and I used epoxy also to smoothen the center hole.
edges reinforced with graffiti rod and carbon tube 20x22.
https://www.ebay.com/itm/Carbon-Stirrin ... 2749.l2649

Can you explain how you use the Graphite rod? I read about graphite mixing sticks, but I do not understand how you are using it.

thx

SalmonSlayer wrote: ↑

Tue Jul 24, 2018 4:17 pm

haare wrote: ↑

Sat Jul 14, 2018 5:54 am

I will use epoxy to glue the parts and I used epoxy also to smoothen the center hole.
edges reinforced with graffiti rod and carbon tube 20x22.
https://www.ebay.com/itm/Carbon-Stirrin ... 2749.l2649

Can you explain how you use the Graphite rod? I read about graphite mixing sticks, but I do not understand how you are using it.

thx

Don't know yet. I was planning to just use it as filler and finish the surface with epoxy. I think it can handle heat when drilling. Or I hope so. Other option is nylon rod but that might be difficult to drill big holes (it will melt)

haare wrote: ↑

Tue Jul 24, 2018 6:55 pm

Other option is nylon rod but that might be difficult to drill big holes (it will melt)

I think I would run water on the hole while drilling the nylon if melting is an issue.


Thx again for your response

Paul