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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 2:47 pm 
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ok for the danger problem. So now, what about the height ?

Let's take a classic: Cab switch 7m in 30 kts and 9m in 25 kts, that's their respective official upper wind range, as per cab's website.

What makes you jump:
- rider's speed
- edging hard before jump
- throwing the kite back and above before jump
- good synchro of the previous 2 params for a more vertical pull
- kite pull to stop you straight and initiate the pendulum

1. rider's speed will be slightly higher with the 7m
2. kite pull: 30*30*7 > 25*25*9, slight advantage to the 7m
3. I think it is quite straigthforward that a (much) faster moving kite will allow for a much better synchro. It also allows you to initiate a jump in less time, allowing you to spot the right bump within a flash when riding in the chop for example. Very hard with a bigger kite ...

Well, that's IMHO the theory which explains why smaller kites jump higher. In practice I can say I do jump much higher with my 7m than my 9m.


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 3:00 pm 
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there is only so much kinetic energy when you jump, The key is how little loss there is when you convert that kinetic energy into height. Suppose the wind speed is 35 knots, you are going 25 knots on a reach and boost, apparent wind is 43 knots that's the kinetic energy you'll be using, g is 10 m/s^2, 43 knots is 22 m/s, 1/2 mv^2 = mgh, h=1/2 v^2/g, = 1/2 18^2/10 = 24 meters or 80 feet that is your maximum height when the wind is 35 knots if you get a nice ramp so you don't lose much energy on the pop, and if you have an efficient kite. It doesn't matter what size kite you have what matters is how efficient the kite is, and how good your technique is, though if your kite is too small you won't be able to convert all the kinetic energy to height and end up skimming the water. There are plenty of problems with this model, doesn't take into account energy stored in the lines drag of the kites or sining the kite during the jump to generate additional apparent wind, but it is the best one we have right now


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 3:23 pm 
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edt wrote:
there is only so much kinetic energy when you jump, The key is how little loss there is when you convert that kinetic energy into height. Suppose the wind speed is 35 knots, you are going 25 knots on a reach and boost, apparent wind is 43 knots that's the kinetic energy you'll be using, g is 10 m/s^2, 43 knots is 22 m/s, 1/2 mv^2 = mgh, h=1/2 v^2/g, = 1/2 18^2/10 = 24 meters or 80 feet that is your maximum height when the wind is 35 knots if you get a nice ramp so you don't lose much energy on the pop, and if you have an efficient kite. It doesn't matter what size kite you have what matters is how efficient the kite is, and how good your technique is, though if your kite is too small you won't be able to convert all the kinetic energy to height and end up skimming the water. There are plenty of problems with this model, doesn't take into account energy stored in the lines drag of the kites or sining the kite during the jump to generate additional apparent wind, but it is the best one we have right now


Could you explain how the apparent wind speed is related to 1/2mv²=mgh, where "v" is quite clearly the rider's speed ?

edit: I got it, I don't know why you are using apparent wind but you are obviously wrong: take the example of you riding close hauled at 1 knot, 35 knots apparent wind speed. You sure about your formula ?


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 3:41 pm 
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Too much mathematics for me...lets meet at the beach ;-)


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 3:42 pm 
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romkite wrote:
edt wrote:
there is only so much kinetic energy when you jump, The key is how little loss there is when you convert that kinetic energy into height. Suppose the wind speed is 35 knots, you are going 25 knots on a reach and boost, apparent wind is 43 knots that's the kinetic energy you'll be using, g is 10 m/s^2, 43 knots is 22 m/s, 1/2 mv^2 = mgh, h=1/2 v^2/g, = 1/2 18^2/10 = 24 meters or 80 feet that is your maximum height when the wind is 35 knots if you get a nice ramp so you don't lose much energy on the pop, and if you have an efficient kite. It doesn't matter what size kite you have what matters is how efficient the kite is, and how good your technique is, though if your kite is too small you won't be able to convert all the kinetic energy to height and end up skimming the water. There are plenty of problems with this model, doesn't take into account energy stored in the lines drag of the kites or sining the kite during the jump to generate additional apparent wind, but it is the best one we have right now


Could you explain how the apparent wind speed is related to 1/2mv²=mgh, where "v" is quite clearly the rider's speed ?


just think about it. Try some thought experiments. Think about how high a rider will jump if he is strapped to a car going 20 mph down the highway and lets go in a wind speed of 0. then think about what if he is strapped to the same car going 20mph but now there is wind and it is blowing 20 mph in the same direction as the car, then think about what if he is going 20mph but now the car is driving into the wind. This is not rigorous but thought experiments like this let you see why you measure v in respect to the wind and not the ocean or the land. Think also about how high you jump if you just do a standing still jump compared to building up some apparent wind.

toby you jump high not because of your large kite but because of your excellent technique.


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 5:34 pm 
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In the same wind the kiter that can hold down the biggest kite can theoretically jump the highest if he has the technique to convert all that power to jumping height.


So in your example Toby, comparing a 9m against your 18m with your technique is not fair. That 9m will not be super-lit in 25kn, the high-end will be when the wind is gusting 40kn and in that wind a 9m will definitely jump higher than anyone can do on a 18m in 25kn. Period.


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 5:54 pm 
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Another fish nibbling at the bate.....


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 6:15 pm 
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evan wrote:
In the same wind the kiter that can hold down the biggest kite can theoretically jump the highest if he has the technique to convert all that power to jumping height.


So in your example Toby, comparing a 9m against your 18m with your technique is not fair. That 9m will not be super-lit in 25kn, the high-end will be when the wind is gusting 40kn and in that wind a 9m will definitely jump higher than anyone can do on a 18m in 25kn. Period.


Actually evan according to theory all kites jump the same high. Because it is not torque which is used to jump but kinetic energy.

so yes, if you have an 18 meter out it will pull twice as much as a 9 meter kite, you will feel it in your arms legs and abs so yes the pull is there. But that pull is not what is used to jump it is the conversion of horizontal kinetic energy into potential (or vertical) height.

I know it seems a little bit weird that even tho the 18 pulls like a monster truck it would not jump any higher than a 9 meter but that's what the math says.

And toby could outjump us all on a 9 or an 18, I don't think the kite size matters he has excellent jumping technique.

You can be so overpowered that when you jump you will actually catch and ride thermals on your kite, if you do that your jump height is pretty much unlimited, and here yes, it matters that you have a big enough kite to catch lift to ride a thermal because you are using it like a wing. I call it getting on the elevator.


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 6:54 pm 
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edt wrote:
evan wrote:
In the same wind the kiter that can hold down the biggest kite can theoretically jump the highest if he has the technique to convert all that power to jumping height.


So in your example Toby, comparing a 9m against your 18m with your technique is not fair. That 9m will not be super-lit in 25kn, the high-end will be when the wind is gusting 40kn and in that wind a 9m will definitely jump higher than anyone can do on a 18m in 25kn. Period.


Actually evan according to theory all kites jump the same high. Because it is not torque which is used to jump but kinetic energy.

so yes, if you have an 18 meter out it will pull twice as much as a 9 meter kite, you will feel it in your arms legs and abs so yes the pull is there. But that pull is not what is used to jump it is the conversion of horizontal kinetic energy into potential (or vertical) height.

I know it seems a little bit weird that even tho the 18 pulls like a monster truck it would not jump any higher than a 9 meter but that's what the math says.

And toby could outjump us all on a 9 or an 18, I don't think the kite size matters he has excellent jumping technique.

You can be so overpowered that when you jump you will actually catch and ride thermals on your kite, if you do that your jump height is pretty much unlimited, and here yes, it matters that you have a big enough kite to catch lift to ride a thermal because you are using it like a wing. I call it getting on the elevator.


The jumping may need to be studied a bit to figure in all the factors...

But once in the air, the bigger kite will "fly", or as many say "drift" longer.

Regards,


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 Post subject: Re: Small kites jump higher? Nope!
PostPosted: Fri Nov 08, 2013 8:32 pm 
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sure, hangtime is something different!

I have a friend of mine here, he loves his new Rally 12...he was former worldcupper, so let's see one day in 20-25 knots who gets higher. Interesting for sure ;-)


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