Re: How to build a bar? Just the rod/pole item ~60cm. Anyone done it?
Posted: Thu Jul 19, 2018 10:25 am
Intuitively I would say if you can stand on it and bounce a bit you have it over dimensioned.TomW wrote: ↑Wed Jul 18, 2018 3:04 pmI 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...
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...