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

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

Postby tkaraszewski » Fri Mar 13, 2020 1:39 am

We've had several discussions about light wind foiling on here in the past. People make various claims as to how light of wind they can kite in, on which kite or foil, etc. Some of these seem more believable to me than others. One thing that's almost universal though, is that nobody actually has measurements. People will quote "5" or "7" or "10" knots of wind, but they never seem to have a chart of recorded wind speeds to compare against.

So, being the engineer that I am, I'm going to re-visit this topic with my own actual data, because I like to have conversations about numbers that can support those numbers.

Here's a recording of a track of today's very short kite session:

Image
* Ignore the heart rate data, it is not accurate, it's recorded with a heart rate monitor above a wetsuit.

You can see that I did two tacks out before I dropped the kite around the location of the blue dot. I then had a swim/drift back to the beach. You can also see a pink arrow added to the graph. This points to the location of a professional wind meter, 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:

Image


I added a pink line to this graph just after 12:00PM, at the time I started my session. You can see that as I went out, the wind was averaging ~10 knots, with gusts to ~12 and lulls to ~7-8 knots. Note that these graphs are over five minutes, and the gust/lull/average (red/blue/green) measurements show the highest, lowest, and average windspeeds during that five minute interval. I felt like this was "comfortably foilable" but definitely underpowered. As a comparison, this is a track I recorded the other day on the same kite:

Image

You can see not only much better tack angles, but that I am actually tacking, as compared to the top track, where I am gybing because I felt lacking the power needed to complete a tack. This second track was recorded in wind averaging about 15-18 knots.

So, it seems I was able to foil OK, but underpowered, in winds averaging 10 knots, and lulling to ~8 or so. You can see that a few minutes later, there's a big lull, where the average wind drops to 8 and the lulls drop to 4.

I think once the wind drops below about 8 or maybe 9 knots for more than a few seconds, I have trouble maintaining speed. I did fall and spend some time in the water but was unable to waterstart, but could keep the kite flying. I eventually dropped (and relaunched) the kite (several times) and at these low wind speeds, once it's wet, it is even harder to keep it flying and moving.

Based on this data, the lightest wind I'd say I can foil in is 10 knots. Maybe 9, if the wind is *super steady* with no lulls. This was done on a Flysurfer Soul 10m, and a Moses 683S wing. I am curious if I would have been able to stay out until 1:00PM, making it through the lulls until the wind began to drop to 0, if I'd had, say, a Soul 15. I don't have a kite that big though, so I can't share my experience.

Anyway, I hope someone found this data-based post on light wind foiling interesting.

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

Postby kiteykitekite » Fri Mar 13, 2020 2:05 am

3-4knots is about the practical limit of kiting now. If you want to get there you need, either a bigger/lighter/more efficient kite and or a bigger/more efficient hydrofoil. Regis is attempting something more extreme viewtopic.php?f=196&t=2405687 but the outcome is not certain. Personally I don't see much to be gained below 3knots but it is interesting. Kites that can fly below 1 knot will certainly be useful, at least for wave riding.

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

Postby OzBungy » Fri Mar 13, 2020 2:25 am

I am not sure how practical it is to quantify how light the wind is. I doubt if you can accurately measure the wind you are kiting in.

You have the natural variability of the wind and turbulence at ground level. Compression zones. Even the turbulence off your hand makes a difference. Possibly the biggest effect is wind gradient. You can have an extra 5 knots 10-20m above you.

A matrix of wind meters on 20m poles spread along the water's edge might do it. You'd need data logging to record the immediate wind speed at frequent intervals to get an idea of what is really happening.

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

Postby bragnouff » Fri Mar 13, 2020 3:13 am

Anything related to riding on a river is gonna be tainted with whatever flow you have. I believe it's not uncommon to have +/- 2kts once you take current into account. So no point being too picky about actual data.

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

Postby Trent hink » Fri Mar 13, 2020 5:04 am

kiteykitekite wrote:
Fri Mar 13, 2020 2:05 am
3-4knots is about the practical limit of kiting now. If you want to get there you need, either a bigger/lighter/more efficient kite and or a bigger/more efficient hydrofoil. Regis is attempting something more extreme viewtopic.php?f=196&t=2405687 but the outcome is not certain. Personally I don't see much to be gained below 3knots but it is interesting. Kites that can fly below 1 knot will certainly be useful, at least for wave riding.

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

Postby OzBungy » 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.

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

Postby joriws » Fri Mar 13, 2020 9:08 am

To really make measurement what is conclusive.. How much wind does Turbine 17m, Nitro 16m and other big LEIs to fly properly? How much that big LEI barely stays up but cannot be steered towards the zenith? That is the "anemometer" at kite level proving the wind speed at level where my kite also is, no magical inversion layers or gradient. Only some forest "buffer" wind reduction which also affect my kite as I deliberately kited close to guys to compare kite power 1:1 as well as possible. Is LEI flight limit measured this way at kite level about 8kn? I don't know what Turbines require to fly, but I don't believe door-TT and 6kn winds either with my 110kg weight with all gear PFD, weitsuit, helmet, helmetcam etc.

Here I ride *door twintip* in such winds described above. If you cannot do the same with hydrofoil, maybe there is still some skill to be improved or power-engine aka kite to be swapped to better aka more efficient one. Today's race kites like FS Sonics are much improved from FS Speed4 lotus what I used on the video. So even my TT-wind range has gone down with same 15m2 kite size I use as LW kite. When looking at Regis' videos and how foil kite is behaving in the air, very sluggish but he still rides, so wind must be even less than on my video.


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

Postby tomtom » Fri Mar 13, 2020 12:09 pm

Agree, only reliable measurement for low wind is describe how known kite fly on zenith, f.e. it was stable on zenith - or it backstall or needed to be flown actively

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

Postby Peter_Frank » Fri Mar 13, 2020 3:33 pm

Nice tkaraszewski, always better with weather station data, as handheld meters are useless in this very respect about how low you can go (but to good use for the individual).

Having said that, I have to say even the "much better" weather station data with average winds and calibrated stations, are not fully the thruth either.

They are at 10 m height yes, and most often in very free areas just at the coastline.

BUT, as an example - we got one (out of many, but you learn to know these) that show the wind correctly most of the time.
Then in a very specific wind direction South to SouthSouthWest, there is a very small 1 or 2 meter high crest a bit away from the otherwise free wind meter, and at a specific windstrength, above 10 m/s, there comes a rotor, so it shows way to little.
It could be 15 m/s just next to, where we ride with our smallest kites 4-5 m2 now, and meter is only showing 9 m/s.
If the direction changes a bit, then it might jump up to 15 m/s which is more correct.

The opposite can also happen, in two other specific wind directions, wind passes around along a ridge far away, accelerates, and ends up on the wind meter - so in light winds it quite often show too much, say 5 m/s when there is around 3 m/s only.
Same can happen if it is somewhat close to an "end" of a ridge, with passes around instead of over, at the ends, and accelerates to much more than the real wind a bit further out.

Goes without saying, they can often show too little, in wind directions where obstackles behind or in front influences.


Then you have the validation of how well calibrated they are, might be a bit off.
In general though, it seems they (ours, can not speak for others) are often calibrated and my experience having put many wind meters up in several locations, is they are pretty accurate, also over time and use and weather.

The major error in wind stations is as said, other obstacles that changes the wind at the very measuring point, and not the meter itself, in my experience the last 41 years with sailing and flying.
Have been working with calibration and accuracy for 35 years, and find it interesting so always observe and deduct, to understand.


Besides this, we have a couple of other factors, even more important.

Wind gradient, mostly when riding with long lines it matters hugely. Not THAT often it makes a lot of difference though, here, with normal lines.
The 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, when winther there is more power in the wind. Not a drastic change though, but some.

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:


Current matters of course, but off topic as you have to measure the wind relative to the current, so you can have both more relative wind, or less, or the same (even in strong current), depending on direction.


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".

8) Peter

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cglazier
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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 5:07 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:


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