Aerodynamics of Kites: How does a kite fly?

The lines keep a kite in its position (or move it), while an alrstream (the wind) is flowing by. Looking at a kite from the side, its shape is similar to the wing of an airplane.

The alrstream approaching the front tube’s leading edge is divided into two parts, one flowing on the upper, the other flowing on the lower side.

Venturi effect

According to Venturi, the air on the top and the bottom will take the same amount of time to reach the profi|e’s trailing edge. With the profile being arched like a wing, the airstream on the top has a longer way to
go compared to the one on the bottom. Since it still reaches the end at the same time, it therefore has to be faster than the stream on the bottom.

Bernou||i’s law

States that the static pressure in any current reduces with its speed increasing (and vice versa).

With the difference in alrstream speed between the top and the bottom of our profile, this leads to a higher pressure at the bottom and lower pressure on top (pulling it up). This lift allows a kite to fly, while the lines enable the rider to control the direction it flies in.

The kite’s pull

By steering a kite, the approaching airstream gets faster. The further the kite travels in one go, the more it accelerates and the more power it generates. The further downwind, the more projected area of the kite is facing the wind, and the more force it creates Ieeward.

Maximum force is generated by: wind + kite’s flying speed.

Stalling = kite’s inability to fly

If a kite’s lift is less than its weight, the kite will inevitably fall out of the sky. This can either happen due to a steering mistake, or certain wind conditions. There are two basic scenarios:

Frontstall

During a frontstall the kite will fall onto its front (front
tube) out of the sky. This happens mostly due to gusts
or pilot’s mistakes: the kite shoots too far windward in
the wind window, the alrstream is cut off, and the kite
falls.

To catch the kite again, the alrstream needs to be
recovered. React quickly to prevent the lines falling onto
you or the kite stalling into them.

Backstall

During a backstall the kite stalls via its trailing edge Ieeward. This happens when the kite’s angle of attack is too big (the kite is over sheeted): there is too much difference in pressure between the top and the bottom of
the profile and the airstream is cut off.

To recover the kite, it needs a smaller angle of attack:

  • Depower the kite (push the bar away).
  • Move the kite windward to create an airstream.
  • Pull the front lines rapidly and, if necessary, repeatedly.

TIPS

  • Move windward rapidly to recover the kite.
  • Do not keep the kite right in the zenith, but rather a bit to the side, so it can recover more quickly in case of a frontstall
  • Should the kite frontstall in the zenith try to steer it
    aggressively to one side
  • Be careful: When the kite recovers, it accelerates and generates a lot of power!

Leave a Reply

Your email address will not be published. Required fields are marked *