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Here's a jumping question - fatty vs skinny

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Kamikuza
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Here's a jumping question - fatty vs skinny

Postby Kamikuza » Tue May 07, 2013 2:21 pm

Let's say the wind is constant... two riders of different weight - for sake of argument, 50kg and 100kg. Both riders are powered to the same extent, on 7m and 13m kites respectively.

Or something like that - you know what I'm getting at... fatty is holding down a bigger kite than skinny can in the same wind.

Who jumps higher? :jump:

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Re: Here's a jumping question - fatty vs skinny

Postby darippah » Tue May 07, 2013 2:27 pm

Kamikuza wrote:Let's say the wind is constant... two riders of different weight - for sake of argument, 50kg and 100kg. Both riders are powered to the same extent, on 7m and 13m kites respectively.

Or something like that - you know what I'm getting at... fatty is holding down a bigger kite than skinny can in the same wind.

Who jumps higher? :jump:


IMHO definitely smaller guy on smaller kite. He has the same power, and he has a quicker kite which equals height

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Re: Here's a jumping question - fatty vs skinny

Postby jespin4845 » Tue May 07, 2013 3:15 pm

speed, but also a guy that has strength and able to hold down the power till the last second, so a small fragile guy won't do so well compared to a heavier guy with some strength

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Re: Here's a jumping question - fatty vs skinny

Postby edt » Tue May 07, 2013 4:49 pm

if you set potential energy = to kinetic energy you get this equation

mgh = 1/2 mv^2

You have to remember v is not your velocity but your velocity in relation to wind speed this is why it's possible to do a beach jump start.

The 'm' or mass of the rider drops out of this equation so all you are left with is velocity.

In general a skinny rider jumps higher not because he weighs less but because he is more fit and can hold down more power relative to his size, but it's not the weight of the rider it's how fast he can go. someone like Rob Douglas who weighs somewhere around 220 pounds is incredibly fit for his weight and can go really fast, he would be able to outjump everyone if he liked doing that instead of his speed runs.

The problem with just building up a ton of speed to jump high is that at the top end most of us loose a bit of control because it's so difficult to hold it all down. So our highest jumps don't come from our fastest runs flat out, but our fastest runs in the highest wind speeds, with a big enough kite so you can convert that energy from kinetic to potential where we still have great control.

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Re: Here's a jumping question - fatty vs skinny

Postby L0KI » Tue May 07, 2013 7:00 pm

In practical terms, the fatty's don't jump high.
One kid (23) on our local crew who is 6' 4 and 220 pounds, boosts fantastic, but he does not qualify as a fatty, he is young, strong and fit.
Our local 245 and 265 guys don't get the height.
I think the strong middle weights (Langeree) seems to do best for max boost.

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Re: Here's a jumping question - fatty vs skinny

Postby plummet » Tue May 07, 2013 7:17 pm

I think we need to consider 2 forms of velocity in edt equation. the velocity of the rider... ground speed and the velocity of the kite. The smaller kite can turn faster and be sent faster backward and create more aprarent wind speed when sending. thus the smaller bloke with the smaller kite should go higher.

but in reality I see no difference on the beach.

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Re: Here's a jumping question - fatty vs skinny

Postby edt » Tue May 07, 2013 10:30 pm

if you crank out some numbers, you'll get heights like this (assuming you are kiting where there is quite a bit of chop so your maximum speed is somewhere around 18 knots and you are kiting at 90 degrees to wind direction so v = sqrt(wind^2 + 18)

If your top speed is faster than 18 knots, adjust the height to be higher according to the formula.

wind speed knots . . . . height in meters (feet)
20 9 (30)
25 12(40)
30 16(51)
35 21(66)
40 26(82)
45 31(100)
50 37(121)

As you see, the theoretical limit of height seems to be a bit higher than our actual jumps. You are suggesting that the theoretical limit be even more because a smaller kite can sine the wind for more apparent speed.

it seems though that a bigger kite is better because it is more efficient and the equation I posted above is sufficient, and to get more height you just need to do 2 things 1) more velocity and 2) more efficiency.

If you look at weight lifting competitions it seems the strongest humans pound for pound are the lightest ones as they can snatch 3x their body weight but the heaviest olympic lifters can only snatch 2x their body weight but even so that range from 2x to 3x goes from 56kg all the way up to 105kg so for kiters I think this difference in fitness over body size doesn't matter much.

In kiting there is such a range of fitness and skill level it doesn't matter how large you are.

I don't think being actually large makes as much difference in humans as it does in sailboats, because the difference between a 5 foot person and a 7 foot person is just not that much, and besides we plane so we don't have to worry about the hull speed that sailboats worry about.

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Re: Here's a jumping question - fatty vs skinny

Postby L0KI » Tue May 07, 2013 11:12 pm

edt wrote:In kiting there is such a range of fitness and skill level it doesn't matter how large you are.
I guess you really have to define the term fatty.
My buddy who is 265 lbs is very strong, but he will never do as many chin ups as a thin or medium weight guy.
I know chins ups do not equate to kiting, but it shows that his body weight to strength ratio is very different than the rest of us.
He has a much harder time jibing a kite surfboard or windsurf rig, than a thinner man.
It's harder for him to hop up to stand on a surfboard, the gut is in the way.
I have also not seen the same level of success with timing, coordination and flexibility for take off and landing his jumps while he is carrying a beach ball under his shirt.
And he has been kiting far longer than the whole rest of the crew here.

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Re: Here's a jumping question - fatty vs skinny

Postby Kite2Heaven » Wed May 08, 2013 2:15 am

Hmmm big numbers n equations - my statts.. 1/2 fat :)

In reality 'on flat water' speed has nothing to do with jump height. There comes a point where you cannot stomp the board from risk of spinnout - resulting in suttle distance jumps. Fatboy Slim and Not enough donuts both reach the same speed/water resistance equation before losing there stomp carve edge.
Add in a ramp - to easy - but wind Velosity is now coupled with wind drag on the 13 - tradjectory angles change also.
Long story short - Kamy dude, put that Donut back in the box lol !

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Re: Here's a jumping question - fatty vs skinny

Postby lander » Wed May 08, 2013 12:13 pm

I believe Dr. Frank can give you the correct explanation, but buttom line is, that if the two persons has same technique, speed etc - the height of the jump will be the same


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