foil kite for 8-12 knots again

[dave1986]

Interesting - we know it is like that (apart from the higher value at lower speeds), and how "cheese" winds affect us regarding feeling stable but no power.
Also how surface roughness is a factor for wind farms wind gradient assumptions/calculations.

But how is this turbulence measured???

Simply based on loss of efficiency of wings at a given windspeed, or can it be measured in a different way?

Peter

Turbulence intensity is calculated from measured wind data from an anemometer mast. It is the standard deviation of the wind speed divided by the average wind speed over some time period, typically 10 minutes. If the wind fluctuations are large and rapid, then the turbulence intensity will be high.

[rnelias]

Wind temperature is also very important due to density and inertia.

8 knots @ 15 Celsius will give us more power than @ 30 Celsius.

We had nice low wind winter sessions here on our local spot

[abel]

Also the land and building scape has significant influence.
Air waves bouncing on buildings or cliffs can create "black holes" spots up to few hundreds of meters from shore.
For the techies, those are kind of 'standing waves" like when kayaking in streams.
If you get inside them, in light winds, then high probability to swim in.

[Regis-de-giens]

Interesting post.
Another déterminant parametrer is the wind gradient (so the difference of wind between thé mesure at 2m above ground , like for a personal handy anemometer, or rider "feeling", and wind at kite height , say 10-20 meters elevation. This différence can vary a lot between sites (nature of soil, topology). Here is an example of very high gradient of wind , making believe that there is almost no wind (ground) , while consistant wind (about 9-10 knot according to the heavy rider of the video ...)

[Flyboy]

Interesting post.
Another déterminant parametrer is the wind gradient (so the difference of wind between thé mesure at 2m above ground , like for a personal handy anemometer, or rider "feeling", and wind at kite height , say 10-20 meters elevation. This différence can vary a lot between sites (nature of soil, topology). Here is an example of very high gradient of wind , making believe that there is almost no wind (ground) , while consistant wind (about 9-10 knot according to the heavy rider of the video ...)

That's pretty crazy! An obvious assist from the music though!

Better than all the discussion about what kind of kite though is ... to have an extra 2 or 3 knots of wind. A solid 10/11 knots & you don't need to worry about fancy light wind foil kites at all.

[bitxopalo]

Here is an example of very high gradient of wind , making believe that there is almost no wind (ground) , while consistant wind (about 9-10 knot...

But in that video, what is the origin of the gradient? It seems a lake and the other side is far far away... So the wind can not find any obstacles or ground roughness.

Also have doubt with the effect of air temperature, in fact cold air is a bit more dense, but has significantly less viscosity which produce a decrement on the reynolds number that makes the airfoil works worse. That is, needs more speed to generate the same lift.

I have no studies in that way... but I have the opposite feeling than @rnelias, I have more pull with warm temperatures than with cold ones.... anyone else?

[Regis-de-giens]

I am also not sure about "obvious" impact of temperature and never noticed a general rule about a noticeable différence when i tried to ride in marginal winds for décades.... Humidity can impact and humidity maximum rate also depends on temperature, so...

I trust more the impact of gradient, and gradient may change on a given site, by température of air, but also water, soil for thermic profiles, humidity, History of wind.

For this video in particular, and the reason of gradient, i had no firm explanations of it when i asked the rider but the phenomena is common on this site in canada . The hypotheses given is a light ascendant wind coming from water just above the lake surface, that C
would "maintain" the main air flow of wind at a significant height . That sounds reasonnable, like a thermal "Pump" of hot air used by paragliders to gain altitude that would provide a renewed air cushion with lower wind at lake surface.

This very old video of flysurfer was similar and i have been told it was on the same magical-marketing lake.

(this "questionnable " vidéo made me dream and buy my first foil kite years ago... A bit decept when i learned it was spot soecific ...)

[bitxopalo]

Luckily your deception turned into enthusiasm

The gradient explanation fit with the first video , the rider tries to keep the kite high, but does not fit with the flysurfer video, sometimes the kite is just touching the water (min 2:45) and the kite keep flying great. So there must be wind

Maybe is something in the water... like small seaweeds...take a look


In this case small seaweeds keep the water flat as a mirror

Another one, in this case is more a "soup"... Salt, weed etc..

[tsuneo]

weight of the kite is important in this wind

[Peter_Frank]

Arent we off the OP topic 8-12 knots now (again)?

But IMO temperature is quite easy to feel as a difference powerwise.

Humidity means nothing whatsoever, as only 1-2 % difference from 0 % to 99.9 % relative humidity in terms of density (and the dry air gives you the most power as the atomic weight is higher)

Whereas going from 0° til 30° air means around 10 % difference in density (lift).

BUT, as most of us ride where the temperature slowly increases or decreases, we will not notice this difference in reality.
Only if you travel between two opposites, you might feel this difference very distinct.

Around here, and I believe in most countries with frontal systems, we usually have more gusty wind in the wintertime, so not only is the density higher so the wind hits "harder" - but when combined with winter gusts it feels even more different than soft smooth gutless summerwind

Which can trick us a lot, so we conclude based on the wrong facts.

But the warmer the air, and the more moisture - the less power you get with a given kitesize.

Humidity can not be felt as less than 1 % difference around 20° and only 1.5 % at 30°.

Peter

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