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Revisiting the "how low can you go" (light wind) discussion, but with actual data.

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby jyka » Fri Mar 13, 2020 5:21 pm

This is a good video:


Experienced kiters with good gear, and the limit seems to be around 4.5 knots.

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby cglazier » Fri Mar 13, 2020 5:35 pm

Nice video jyka.
I believe that the usual wind threshold in big races (where all the riders have 18m to 21m kites) is 6 knots of wind as measured by hand on the committee boat (on the race course). Below that, the race is not started.

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby tkaraszewski » Fri Mar 13, 2020 5:48 pm

cglazier wrote:
Fri Mar 13, 2020 5:07 pm
tkaraszewski wrote:
Fri Mar 13, 2020 1:39 am
..that recorded the following graph. Being so close to the area I was kiting, and professional equipment, this is about as good quality of wind data as most of us are likely to be able to get:
Interesting topic tkaraszewski. But it looks like you are using data from the Weatherflow Event Site sensor. The actual wind on parts of the Columbia river varies greatly from this. There is often twice as much wind near the middle of the river as where you launched at the Event site.

:roll:
Yes, but you can see from the GPS track exactly where I was kiting, which was kiting right in front of the sensor. This is similar to the comment above about current. Yes, in general, the current affects the wind on the river, but the current affects the wind very little to the immediate west of the sandbar (where I'm kiting on this map), because the sandbar blocks the main current flow and actually creates a small eddy effect here. At no point on this track was I farther than about 1/2 mile from the wind sensor itself, and never out in the main current flow to the north of the sandbar.

You can see the wind data from the hatchery sensor here:
Image

For the same time period, just past noon, the wind at the hatchery is very similar to that at the event site. Yes, sometimes it's twice as windy 2.5 miles up the river at this sensor, but it was not yesterday, the wind was fairly consistent across the river when this was recorded.

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby Regis-de-giens » Fri Mar 13, 2020 7:06 pm

Peter_Frank wrote:
Fri Mar 13, 2020 3:33 pm
Short version is:
Weather stations are a lot better yes, especially average wind, but not to be trusted either.
Handheld are mostly pretty useless for how low you can go, although often fine for an indication for the individual knowing "how to".
200% agree and not comparable to handy anemo at 2m height, sometimes twice lower wind due to gradient...

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby PullStrings » Fri Mar 13, 2020 7:41 pm

Peter_Frank wrote:
Fri Mar 13, 2020 3:33 pm
in my experience the last 41 years with sailing and flying.

so always observe and deduct, to understand.

other factors, even more important.

most classic is that there is wind a bit up 10 to 20 meters, and then you can have almost glassy water surface, so you can ride, but if you drop the kite, you can hardly drift ashore as no wind - happens quite often with this "close to zero" wind at the surface, but easy to ride when you keep the kite up.

Air temperature matters a bit

IMO by far the most important thing is "wind quality".

You can have gusty wind where easy to feel, and it can have a bit less power than average measured wind.
But you can also have "mini" imperfections, small bubbles in the wind you can not feel in any way, I call it "cheese wind".
These can make 4 to 5 m/s wind almost unrideable, eventhough it feels smooth and good.

The direct opposite is silky smooth perfect wind.
In this wind it can be possible to ride in 3 m/s wind only, with same gear where you could hardly ride in 4-5 m/s.
It just feels good riding in this :rollgrin:

8) Peter
:thumb:

nice post

in my experience the last 55 years with sailing windsurfing landboarding kitesurfing

air temperature versus water temperature appears quite significant as far as power in kite during the late winter and spring

that is when you hear of all those records of low wind numbers for riding...but like you said...observe and deduct the reason why it is

warm light air traveling over much colder water will bring a denser silky smooth wind packing more punch

yes gradient too plays a good part

I like your cheese wind description ….as in swiss cheese with full of holes....solid cheddar cheese wind is so much more fun

in the dead of summer with hot air traveling over warm water you usually only get thin air in the kite and no low light wind speed data bragging

about once a year during summer a hot light wind sideshore for several days will create an upwelling in the ocean

this makes the ocean surface temperature drop sometimes up to 8C /14F and create magical powerful really light wind session

with the wind light wind remaining sideshore to side side-onshore there will be no sign of wind on the water or even from the trees

trying to measure the very light wind speed with machine does not work in many cases...but your gut knows

with experience we know how much there is or what type of wind it is by feel and we should probably still put a kite up to test

sometimes the wind will be sucker type and other times you get a big surprise and a wow session
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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby knotwindy » Sat Mar 14, 2020 12:17 am

Just curious. Know anyone that has tried, on a NO wind day, to fly a kite off the back of a pickup to see how slow they can go before the kite says ‘f off, your done’ ?

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby kiteykitekite » Sat Mar 14, 2020 1:37 am

It has been done. You can also run or walk with a kite. A flying kite can need as little as 1 knot. There has also been repeated flyings of kites with weather stations right next to them, with hand held meters and held at kite height. Lightwind is not new, there has been kites that could go in very light wind for a long long time more than 2 decades. It has long been established the static limit for most foil kites is 5knots, ultralight 4knots and now some are lighter a bit below that. It also depends on the size of the kite, bigger ones need less wind and smaller ones more. The Beaufort scale is also very accurate if on open ocean with onshore wind. Between using the Beaufort scale and your kites behavior you can reasonably know what sort of wind you are in. 3-4knots is the limit, you can go below that but it is dubious what you can do. You can go many times the wind speed on the water, the multiple you can do over wind speed increases as the wind is lighter. I would not be surprised you could do 4 or more times the wind speed in 4knots. Large hydrofoils can lift a person from about 2knots of speed. With any forward motion they make lift and they do not need to lift you all in one go to get you going.
OzBungy wrote:
Fri Mar 13, 2020 2:25 am
Even then, to foil in 3-4 knots you're going to have to do at least double the wind speed just to move forward. That's very optimistic.
Double is easy, but as well no you do not need 3-4knots to move forward or even get out of the water.
Trent hink wrote:
Fri Mar 13, 2020 5:04 am
You have bad measurements. The practical limit is more like 5-7 knots. Handheld annenometers give bad measurements.

I have seen guys kiting in something probably around 5-6 knots. They were on race gear, they were very skilled riders, and none of the ones I've talked to said they enjoyed it.

Some people like to brag about their light wind skills. Many more people just have bad measurements.

Never forget that the power available is proportional to the velocity squared.

Take a minute to think about what that means.
No the measurements are fine. They are establish from water conditions and kite behavior and linked to accurate measurements.

Kiting is 5-7knots is ridiculously easy. You do not even need a kite to ride a hydrofoil, though a kite does help make it a lot easier :lol: . In under 5knots I will have to pump though jibes though because the kite just slacks and falls, slowly though.

Good you bring up the power is related to speed. A few things to note, a kite can go much faster than the wind, so its velocity and so power is not fixed exactly to the wind speed. The result is that it can increase power much greater than squaring. The other is that most kites on the market because they are so fat (drag) have a relatively low maximum speed. That is they will struggle beyond a point to go much faster. The effect is that their speed and so power beyond a certain point does not increase much. It creates this effect that where you can fly the kite at lower winds you can still make good power but the power and speed at higher winds is not tremendously more or does not increase as much. A sort of S curve. I think you get the most benefits as you move up wind in the lower speeds vs higher. It is hard to find data on this but kitegen has a page talking on some of this.
http://www.kitegen.com/en/2016/03/30/sp ... h-kitegen/ . Whether it agrees or not with me it is interesting. I am not sure the "kite" they use or the wind speeds at the height they flew it.

From link.
Powercurve_Comparison1.png
OzBungy wrote:
Fri Mar 13, 2020 7:17 am
To put low wind riding into context, when riding on my foil 8 knots on the GPS feels almost stationary. I need to be going 12 knots to feel that I am riding comfortably.

So that means in 4 knots you're going to be riding at 2-3 times wind speed. Before that happens you're going to have done some kind of water start with no additional apparent wind and relying on the drag from your board and foil for line tension.
So I think it is quite possible to ride more that 12knots in 4knots wind. The kite can as well generate apparent wind in spite of any rider speed, it flies on strings. A hydrofoil or anything will start generating lift at any speed, so you can use the wing and board to make lift before you are fully or at all out of the water. Before a hydrofoil I used to ride boards like skimboards underwater like a hydrofoil. They would do this are very low speed like under 1knot could lift you out of the water. On some large hydrofoils you can ride comfortably from 4-5knots water speed or even a bit less.
Peter_Frank wrote: IMO by far the most important thing is "wind quality".
Definitely. It is harder to adapt as the wind changes. Lighter wind can require a much finer touch and feel. Foil kites in particular can lose power in big changes because of their inertia and easy stall. One thing though light wind does tend to be smoother and have less gradient. Lower wind speed is lower entropy. Heat also increases entropy so colder air is lower entropy.

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby cglazier » Sat Mar 14, 2020 2:30 am

kiteykitekite wrote:
Sat Mar 14, 2020 1:37 am
a kite can go much faster than the wind, so its velocity and so power is not fixed exactly to the wind speed. The result is that it can increase power much greater than squaring.
huh????? :roll:

The wind generates power which is proportional to the square of the wind speed. The apparent wind at the kite is often greater but it is only what is felt by the kite.

For example a wind turbine in 10 knots of wind will rotate so the wind speed at the tip of its blades is far greater.. but the turbine still only generates power related to the 10 knots of wind.

Another example: If apparent wind generated power then when I was kiting fast and entered into a no wind area then my apparent wind would generate power to keep me going.. but it doesn't of course.

:!: CG

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Re: Revisiting the "how low can you go" (light wind) discussion, but with actual data.

Postby kiteykitekite » Sat Mar 14, 2020 3:21 am

So if you look at that link http://www.kitegen.com/en/2016/03/30/sp ... h-kitegen/ it goes into this in depth. Which is why a kite can harness more power than something fixed like a wind turbine. Yes a wind turbine moves but not as much as a kite can. The explanation, from skimming it, is the area of air that a kite disturbs is greater.

So it is easy to demonstrate this or feel this. Given that kite power is pull, by flying a kite you can increase the pull or power. So just because you have apparent wind does not mean that the apparent wind is not connected to the wind. Unless you are running or riding a wave or sitting on the back of a moving car or bike generating your own wind then the apparent wind you have is reliant on the actually wind. So the system you use to generate pull is reliant of at least some wind to kitesurf in most instances. You can say ride a wave and fly a kite "upwind" of you, because the wind can switch directions. That is the most extreme example though.

So yes you are correct the power is related to the wind, but how you harness it changes that. The optimal for light wind would be the fastest kite you could make. Kite designers have completely missed that boat by designing the slowest kites you could imagine for light wind. At the basis of their(and our) problem is a misunderstanding of the principles. Be they the physics or the uses of the gear. It's why we have chickenloops everywhere.


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