1:
If I ride full downwind, and just let the kite drift: I guess I am going just a little slower than windspeed. Riding faster than windspeed, the lines would slack.
2:
If I start looping, I am getting an extra pull and Start going faster, BUT: is the windspeed the limit to go full downwind?
I am fully aware that you can ride faster than the wind, but question is for going downwind / full downwind.
Yes in theory you can go faster than the wind downwind looping the kite The relative wind from the speed of looping the kite can easily exceed wind speed and “fill”the kite creating lift that will exceed the drag force on a kite moving downwind faster than the static wind speed
Whether this is practical on water factoring in board drag etc I’m not really sure …I feel like it is. I can definitely get tossed faster than the wind speed if I load up and loop the kite in light wind in a field.
A looping kiteboarder will kick the hell out of any sailing vessel in a downwind river race but don’t travel at “dead downwind” angles as it’s not the most efficient way to achieve vmg.
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1234567Simon (Fri Oct 22, 2021 11:34 am) • AndersP (Sat Oct 23, 2021 8:46 am)
No you cannot go faster than wind in pure downwind, even in theory, with a kite.
You Can reach a vmg (négative) greater than wind but you need to keep a minimum angle, not pure downwind.
Some wind machines Can but they all use a mechanical system that act like a kind of lever arm to still offer a sail surface hit at the rear even when you go faster than wind. This requires to rigidly drive thé sail from the water/ soul, and not actuated by the wind like for a kite loop.
A simple kite cannot provide this rigide link between the water and the wind to allow this lever arm unfortunetelly ... So kite will stop looping when you reach wind speed, like when no wind on the beach and collapse, offering no force anymore
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indeed quite complexe but now understood and well explained if you focus hours on the topic; i love it by the way.
However for a "simple system like a standard kite", it impossible because the rotation of kite is self actuated by wind itself , so it cannot pursue turning at higher speed than wind because of 0 then negative wind.
on DDWFTW machines like those videos, the rotation is actuated by the soil, hence pursued even if you reach wind and overcome it. This mechanical link with soil, combined with the calculated blade angle, offers a surface that goes a bit rearward vs the soil, in projection in wind direction; so it goes locally lower than the soil/water speed, so the wind can still push on the upwind surface of the sail like a spinacher (so still pushes sail from rear to front , like when 0 speed).
Last edited by Regis-de-giens on Thu Oct 21, 2021 11:59 pm, edited 2 times in total.
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1234567Simon (Fri Oct 22, 2021 11:34 am) • spork (Sat Oct 23, 2021 8:29 am)
in fact, the question has not a simple answer and raised a very interesting debate recently on YouTube (Veritasium's channel)...
This video is really excellent !!! thank you ; very clear and finally presents the good physics and good counter arguments of non - believers ; i strongly encourage you to listen to it.
thanks again rnelias
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rnelias (Thu Oct 21, 2021 10:07 pm) • 1234567Simon (Fri Oct 22, 2021 11:35 am) • spork (Sat Oct 23, 2021 8:28 am)
Wing foilers can go faster than true wind down wind with a help of wave & foil. Indication of that is that wing foilers pull the wing from le handle behind and the wing stays horizontal in air because there is apparent wind. Wing will hang vertical from le handle when apparent wind is zero i.e. rider going exactly true wind velocity down wind. Go faster and you are hauling the wing again. So check when wing is taken back to dual hand wield and generates power, what is the wing direction measured to waves vs power position.A long intro.
Take a look Johnny Heineken wingfoil video at YouTube. When you accept wind speed is relative you can start understanding wing foil wave runs or kite galactical/360/deadmans turn etc.
At 3:41 surf you can see the trajectory speed and how wind window behaves. Earlier on video you can see Heineken's wing going vertical.
Imo nothing prevents doing that with a kite if you can pull the kite over zero apparent wind kite flying le first but to opposite direction.
The very same can be used on kite hill glide to also downwind. You take-off speed is just higher by true wind speed when taking off tail wind. On upwind take off speed is less due to head wind. And enough airspeed (wind) airplane can take of with zero ground speed.
Or bicycle, you wonder why always headwind. Well if you ride 4m/s down wind with 10m/s bike speed you have 6m/s apparent wind speed head wind.
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