any math/science people?

[TommyDuotone]

Just really curious if wind power is a linear function or an exponential function. In other words, is the change in power from 20-25 mph of wind(+ 5 change) more significant than a change in power from 15-20 mph (also a +5 change). It seems exponential to me. any info?

[Mr_Weetabix]

The force that is exerted on you by your kite is proportional to airspeed squared.

I think that the "feel" is largely subjective, and depends to an extent on the kite you're flying. If you're in the middle of your wind range and you get hit by an extra 5 knots, you'll absorb it without too much effort, whereas an extra 5 knots when you're already at your top end can feel much more significant.

[OzBungy]

http://www.vindselskab.dk/en/tour/wres/enrspeed.htm

[edt]

Just really curious if wind power is a linear function or an exponential function. In other words, is the change in power from 20-25 mph of wind(+ 5 change) more significant than a change in power from 15-20 mph (also a +5 change). It seems exponential to me. any info?

wind strength is proportional to velocity squared.

(25^2-20^2)/(20^2-15^2) = 1.3

The difference is 1.3 times stronger at the higher wind speed

[alexrider]

The use of the word "power" in the kite jargon is misleading.
Adequate words include strength, lift, force, pull.
Power is force times velocity of the object the force is applied to.
You can talk about the power required to lug a rider (a function of his velocity and the kite's pull opposing his drag, put briefly); but then you'd be using horsepower or kilowatts as units of measure, and not Newton or kilogram force.

[edt]

The use of the word "power" in the kite jargon is misleading.
Adequate words include strength, lift, force, pull.
Power is force times velocity of the . . .

When we say "power" (P) in kiteboarding it is not a technical term, because the technical term for power P=Fv, F=.5kv^2, where "force" (F) is also a technical term, so power varies as the cube of velocity and of course these are differential equations, but .don't worry about all that stuff, what you need to know is that when you think about how strong the wind is, and what size your kite is, the strength of the wind varies as the square of velocity.

Don't sweat the technical terms, just remember velocity squared. I knew what the original question was about, doesn't matter if he used the word "power" and didn't know its technical meaning.

[oldkiter]

So going from 15mph to 20mph the wind is 1.8 times stronger (apx) - and going from 15mph to 25mph the wind is 2.8 times stronger (apx)?????

Does downsizing the kite REALLY make a difference other than the obvious of being to handle the increased wind? In other words, is one taking advantage of the full increase of wind "strength"? Everything else being equal?

[edt]

So going from 15mph to 20mph the wind is 1.8 times stronger (apx) - and going from 15mph to 25mph the wind is 2.8 times stronger (apx)?????

Does downsizing the kite REALLY make a difference other than the obvious of being to handle the increased wind? In other words, is one taking advantage of the full increase of wind "strength"? Everything else being equal?

I don't understand your question. Of course, in addition to the quantitative difference there is a qualitative one.

So If you are on a 10 meter in 15mph to get the same power from the wind in 25mph wind you will want to be on a 3.5 meter kite. But not all things are equal, you haven't changed the PSI of your kite, you are still running dyneema lines, your weight is the same, you might scale the board a bit, I guess a good example is how people talk about an ant being able to lift 20 times its body weight, but it's not because the ant is 20 times stronger than a human. The muscle tissue of an ant within an order of magnitude the same strong as the muscle tissue of a person. But muscle strength scales as the square of the surface area while volume scales as a cube. If you actually just increased the ant to the size of a human it would not be able to lift 20 times it's body weight, in fact, it would be instantly crushed, and only be able to lift a few ounces worth of weight.

So yeah, while the wind strength does scale as the square of the wind velocity, not all things are equal, you have drag on the lines, turbulence, all kinds of things going on, so there are some qualitative differences you notice at difference wind speeds, kites really do behave differently at different speeds, and it's not just downsizing that matters.

What I'm saying is that all things are "not equal" but using the square of the velocity of the wind speed is a good starting point.

[oldkiter]

Thanks edt.

So does it follow that - approximately - when moving from a 10m at 15mph to a 3.5m at 25mph that the rider will be going approximately the same speed or jumping approximately the same height? And that is why if one were to go instead to say a 8m kite at 25mph one would jump higher or go faster?

Just looking for the relationship.

[edt]

Thanks edt.

So does it follow that - approximately - when moving from a 10m at 15mph to a 3.5m at 25mph that the rider will be going approximately the same speed or jumping approximately the same height? And that is why if one were to go instead to say a 8m kite at 25mph one would jump higher or go faster?

Just looking for the relationship.

The 3.5m and 10m will not go the same speed because the friction of the water is different at the two different velocities, and the 3.5m might jump higher, the reason being that when you launch in the air, you drift downwind so the kite has less speed relative to the wind than when you are riding. Now the 10m kite is indeed 2.8 times larger, but because wind resistance also obeys the v^2 law, while riding at a static speed, both kites will have about the same drag. However, when you launch the curve you have for both kites will be slightly different, and here well . . . not sure.

The physics of kiting could be boiled down to a single equation, doing some first order approximations, if all you are looking for is jump height and want to solve with pencil and paper, though if I were going to solve it, I would set up a bunch of differential equations and iterate a computational solution.

I think the best answer might be "Go ask some dudes how to boost big air," since the equations are a bit difficult.