A forum dedicated to Hydrofoil riders
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- Kiting since: 2008
- Local Beach: North Sea (NL)
- Favorite Beaches: Wijk aan Zee (NL)
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tomtom wrote: ↑
Wed Mar 04, 2020 1:23 pm
Its simple not true about more and more downwind - you very quickly loose pressure this way as soon as your direct downwind VMG start approach real wind speed - which ALWAYS is your only source of energy.
As soon as you loose this power gradient between your kite and wind you are done. No ammount of dragless kite help you.
The trick is to gradually point more and more downwind and gaining more and more board speed at the same time. So the apparent wind is getting stronger and stronger. The kite does not fall out of the sky. The windspeed becomes almost irrelevant because the board speed surpasses the wind speed by a factor of 3 or 4 if the rider has the capabilities.
However, I´m lightyears away from such skills. But I regularly see the foil pros doing this. It works.
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The point is, no relevant closed sailing system works because of apparent wind. The DTW generates apparent wind because it has a rotor. The apparent wind on the foil is created by the sum of the rotation and vehicle movement. The concept that is not easily explained, imho, is that the energy input can only be from the existing wind but the forces involved at any given instant of time have to be analysed by including the accumulation effects of the craft's acceleration-velocity. It becomes easy to make the intellectual mistake,imho, that this is bringing something or driving the system.
Not that it matters from a kiting or sailing point of view. When riding or sailing it is the art of continuously exploiting the actual flow over the aerofoil at each instant that maximizes the potential of the wind. Of course, the actual flow is the summation of the real and apparent wind.
Regards Herman - my last roll off the dice on this one?
PS The rotation of the DTW aerofoil is akin to the dive of the kite and the vehicles speed is akin to a riders board speed!
Conservation of energy and moment retain rather than bring anything may be a helpful way of looking at it!!!
The presentation also explains how a sailing craft can tack downwind faster than the wind and touches on the importance of a good lift to drag ratio in order to achieve that. Explained with the appropriate apparent wind vector diagram.
Last edited by Herman
on Sun Mar 08, 2020 8:33 am, edited 4 times in total.
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- Kiting since: 1999
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Apparent wind will always bring a big smile on your face !
I've been told several times that I make my own wind !
And i'm not talking about eating too many beans !
Always enjoyed going fast on a beam or broad reach
In my youth it was riding with a Tornado catamaran
Later on it was with a speed needle windsurf
Then moved to a beach with hard pack sand
Went fast on wheels with a Norblanc Speedsail windsurf
Then more on wheels using Terra board with kites
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