Theory of flight part 6 – Apparent wind and window’s edge

Now let’s debunk one of the most common clichés among beginner and intermediate kiters.
Certainly from beginners you will be found in this situation: In the water, you start to glide planning with your board: at a certain point (because at the moment it does not matter) we can no longer properly load the upwind edge of the table and we begin to accelerate downwind and immediately we see the kite move back in the window while the traction continues to increase and we have the impression that it is no longer possible to bring the kite back to the window’s edge (whose position we mentally identified on the ground when we did take off the kite or in the water just before leaving) and you have the doubt to make a mistake,  feeling the traction growing too much and we fear that the kite is running away in power zone.
Most of the times I have asked for explanations of this phenomenon, I have heard myself answer that “you have to bring the kite back to the window: make it move forward and you will see that it will pull less and you will be able to control it”.
In reality the increase in traction is not due to the fact that the kite is flying in power zone, but, as we have shown previously, it is a consequence of the apparent wind: in practice the kite is already at the edge of the window, only our reference is the flight window we identified on the ground.
As mentioned at the beginning, it must be remembered that it is impossible for the kite to be ‘stationary’ in power zone, it tends naturally and inevitably to reach the window edge: if we want to keep it, we must force it by turning it and countering its natural tendency to get out of it , but we are riding, with the kite standing against our body and the table.

So what actually happens?
We try to illustrate the situation, taking up the scheme used to illustrate the concept of apparent wind and superimposing the outline of a flight window.
The design shows how the entire flight window rotates around us, leading to a “backward” of the window edge, with an angle that is greater the greater the speed of the table compared to that of natural wind.
This angle has the same width as that formed by the apparent wind vector with respect to that of natural wind.


natural sense kitesurf

In our example the window edge moves back 45 ° and we find, with respect to the position of the kiter, in what we could already consider almost power zone if we were still: here is therefore explained the illusion of the kite that, even though still, “ … it pulls too much because it flies in power zone and I can’t bring it to the window … “, as we often hear.
This also explains why, when you fall and stop abruptly, the kite jerks forward: in practice, it happens that, by immediately ceasing the effect of the apparent wind, the flight window rotates around us and the window edge advances , all in a fraction of a second.
The same thing happens when you brake sharply with the board, perhaps to avoid an obstacle, the kite advances quickly: many kiters believe that this advance is caused directly by our action on the bar but it is not.
How many times have you heard “if you have to stop quickly you have to bring the kite to the edge of the window”?
This is impossible because the kite is ALREADY on board the window: we are not the ones who, acting in who knows what way on the boom, bring the kite from the power zone to the edge, but it is the very edge that advances due to the rotation of the whole window of flight, induced by our slowing down obtained through a greater friction of the board.
The kite does nothing but “adjust” to the new situation, quickly reaching the new position of equilibrium.
Therefore, contrary to what many believe, the progress of the kite is not the cause of the slowdown, but a consequence.

Source: Geppy Piloni – Teoria e pratica del kitesurf 

By achim Theory