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How high is it possible to jump with a kite ?

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Peter_Frank
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How high is it possible to jump with a kite ?

Postby Peter_Frank » Mon Jun 14, 2010 6:28 pm

Hi all ! (warning - THEORY coming up !)

This question has been asked numerous times, maybe disguised in different words.

How high can you jump ?

Of course we have to look away from "not normal" conditions as updrafts, thermals, extreme wind gusts or shear winds :naughty:

Would like to show how the physics are regarding this, as there are SO many wrong conclusions around regarding jumps.

First of all, let us explain the simple basics.

A kitesurfer travels at a certain speed across the water, approximately perpendicular to the wind.
So, the apparent wind hitting the kite is the square root of the squared speed plus the squared wind speed.
Thats known of course.

This speed determines the kitesurfers kinetic energy (its "total" energy when moving across the water) :thumb:

In theory, if you jump and you redirect ALL your speed into height, meaning you get to the apex of your jump with absolutely zero speed relative to the wind (not really possible maybe, but almost), you convert all your kinetic (speed) energy to potential (height) energy 8)

These are the simple basics - and here the "mass" of the kitesurfer pays no role at all - meaning, whether you are light or heavy, you can jump the same height, all other being equal :D


Okay, when redirecting the kite, you have some "loss" of course.
If we neglect this loss, and say it is about the same (it is not, smaller kites are way more efficient, I know), and assume some typical kite sizes and max halfwind speeds in different winds, the numbers and results will be like this :

Image

As in very light wind, we assume you dont reach the same max speed, but over 10m/s you should have reached your max half wind speed IMO.


So if we plot this as a graph (the thick line is the "smoothed" curve like it actuallly might be).
Where it is max height with a given typical kite size, relative to your max height with a 10m2 kite, so we can somewhat eliminate the "loss" we dont really know the size of :

Image


The same, just compared to wind speed in meters per second

Image


And in knots

Image


Hope this clears out some of the "mystery" and why it does not really help to pick bigger kites, regarding jump height (only regarding hangtime !)

Some think that the bigger kite you choose, the higher you jump - this is NOT true :o
If you have a kite that "fits", you will jump the max, because of the best compromise between power and perfect control and the least loss.


---------------------------






AND, regarding hangtime - suddenly we have the theoretical max height, versus the kite size.
As hangtime is for sure directly proportional to the jump height AND kite surface, we can make a really interesting graph based on above numbers, which shows the relative hangtime, compared to a 10m2 in 10m/s:

Image

This is in fact no surprise to most of us, as we all know that big kites in low wind can not jump high, so even if they "float" longer, the hangtime is not good.
And really small kites in nukin winds, will jump REALLY high, but will drop fast like a rock too - so not max hangtime here either.

The answer is somewhere in between :thumb:

My (theoretical only !) graph shows max hangtime most often will occur around 12-13m/s and the kite size that fits here (or one size bigger preferably) - but of course it can be shifted up and down according to rider weight, AND some of the losses has not been taking into account.

The bigger kite you can use, still able to jump the same height, the more hangtime.
But if too big, you dont jump as high, and maybe dont gain anything in hangtime either, and have a lower jump and less agility and less fun and control :(

Just had some spare minutes here, so could not resist calculating on this :thumb:

Really interesting in fact 8)

Kindly, Peter Frank
Last edited by Peter_Frank on Tue Mar 24, 2015 11:16 pm, edited 1 time in total.

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Re: How high is it possible to jump with a kite ?

Postby Toby » Mon Jun 14, 2010 6:36 pm

wow, no wind in Denmark ? Or who did this? Nice!

But I don't see anyone jumping 6m in 10 knots...the rest is possible!

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Re: How high is it possible to jump with a kite ?

Postby Peter_Frank » Mon Jun 14, 2010 6:53 pm

Toby wrote:wow, no wind in Denmark ? Or who did this? Nice!

But I don't see anyone jumping 6m in 10 knots...the rest is possible!
Lots of wind here - we are "hammered" the good way after a weekend with 5 and 7m2 kites and big waves :P

Didnt take long to make these here this afternoon (thats what I work with daily...)

No, the 6m jumps in 10knots, not being possible in real life, is because of the loss in the big kites :o

And of course assumed you have a raceboard for the strong apparent wind and high jumps to be "likely" in 10 knots - but above this, a "normal" TT for jumping :thumb:

Remember - it is the max theoretical height if no loss - will never be possible to reach these values if conditions are "normal" :naughty:

But when the wind is gusty, and you get shear winds and maybe local updrafts, you can go even higher of course - we all know that 8)


Just thought it could be interesting for others to see some of the physics behind :idea:

:D Peter

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Re: How high is it possible to jump with a kite ?

Postby tolvsbo » Mon Jun 14, 2010 7:01 pm

....and if you fly the kite actively , like looping it, can you influence height and hangtime ???

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Re: How high is it possible to jump with a kite ?

Postby FredBGG » Mon Jun 14, 2010 7:03 pm

Humungus jumpus :o :thumb:


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Re: How high is it possible to jump with a kite ?

Postby JS » Tue Jun 15, 2010 6:03 am

tolvsbo wrote:....and if you fly the kite actively , like looping it, can you influence height and hangtime ???
No, not in steady wind. However, looping a kite like a helicopter while jumping can keep you moving downwind in step with the rising side of a rotor (turbulent air phenomenon). Such circumstances can result in crazy hang time, including a 20+ second jump widely circulated on video.

Here's a piece I wrote on the subject 3 years ago:
http://www.kiteboardbc.com/index.php?pr ... ,_Hangtime

Cheers,
James

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Re: How high is it possible to jump with a kite ?

Postby JS » Tue Jun 15, 2010 6:22 am

Peter_Frank wrote:...In theory, if you jump and you redirect ALL your speed into height, meaning you get to the apex of your jump with absolutely zero speed relative to the wind (not really possible maybe, but almost), you convert all your kinetic (speed) energy to potential (height) energy)...
Yes, it is possible. As long as your lines are in tension, your kite will maintain near constant airspeed. But you, the kiter, can time your jump so that you are swinging below the kite in synchronization with the moving airmass, as you reach the apex of your jump. In so doing, you will have converted all of your kinetic energy to potential energy, net of losses. If you get it exactly right, you could theoretically blow gentle smoke rings while at the apex. You can't practically convert the kite's kinetic energy though, but fortunately the kite's mass is rather insignificant compared to yours (and therefore its kinetic energy).

Here's a piece I wrote a few years ago, fundamentally stating the content of your post:
http://www.kiteboardbc.com/index.php?pr=Biggest_Jumps

Best regards,
James

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Re: How high is it possible to jump with a kite ?

Postby funalex » Tue Jun 15, 2010 9:12 am

humungus jumpusus plus :wink: :


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Re: How high is it possible to jump with a kite ?

Postby knuthansen » Tue Jun 15, 2010 8:12 pm

@Peter:
How did you calculate the rider's speed in the first table?

Great topic, I reckon it should be possible to jump quite a bit higher in the future than today, already because there is no serious effort spend on it these days.
The skilled riders rather do unhooked stuff or megaloops than practicing big air, and even for the average boosting joe, there is a lot of uncertainty what works best: Kite (bow vs c,..), board (narrow vs freestyle, big fins etc.)

As for the kite size: The key for me is to load up the lines as hard as possible, and therefore I send the kite from pretty low. If I can't hold the edge properly when bringing the kite up and gain too much speed, that's the sign for me that I am too overpowered.

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Re: How high is it possible to jump with a kite ?

Postby Windrider » Wed Jun 16, 2010 7:09 am

knuthansen wrote: ... Great topic, I reckon it should be possible to jump quite a bit higher in the future than today...
Assuming Moore's Law, the height of kite jumping should double about every two years, and kites should cost half as much and perform twice as good every 18 months or so! What a future to look forward to! Of course, in two years, the kites will require water cooling systems because they'll over heat in the sun, and end up becoming multi-canopied all in one frame. Gonna get strange!


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