FLYING   THERMAL UPDRAFT WINDS

 Wind occurrence

 

When flying kite in thermal updraft winds, it is scary for many kiters, and even worse for the kapers.

These winds occur when the main wind is not so strong, less than 6 m/s and weather is sunny and warm. The thermal updraft winds can easily reach more than 10 m/s upward speed. In fact, each time there is an updraft wind, there is also a downward wind in the surrounding area. So, it is expected that later the kite could suddenly go down.

 

These are possible solutions

  Kite behaviour

 

The kite will go flying at a high angle line, eventually reaching the vertical. I have experienced a few times the line going more than 90°.

It can be observed in some occasions that the kite is hovering and moving as following the whirl of the updraft. When the updraft vanishes, there is no more lift. All the weight of the line is forward the sail aerodynamic center. It can incline the kite, nose diving. Then the kite starts to go down like a glider.

Or if there is enough wind, the kite will fly backward, and loose height.

 

Compensating operations

There are several actions that will help.

The first is to release anchoring if any, and have the line and the reel in hands.

The second is to not stay vertically under the kite, but move aside. It is very important that when rewinding, the kite is not over your head.

Then, watch carefully the kite, and as soon as the line is getting loose, rewind it. Now you will face one of the two following cases:

If the kite is going backward giving the line less angle, let it go, only maintain the line not too loose. As soon as the line angle becomes normal, about 60°, it is possible to rewind faster to maintain the kite if the wind is not enough.

If the kite is gliding against the wind, let it go, walk aside as fast and as far as you can, releasing line, and to such distance that there is now a sufficient angle between the kite gliding direction and the kite line. 30° is fine but 15° can be sufficient. At that time, rewind as fast as possible, run backward if possible. Now the kite will rotate and its nose will come towards you. It is now possible to control it depending on your rewinding efficiency.

Recommended kites

Most of the time, kites for light winds have large sail areas, are light, and have less drag. So, they fly at higher line angle.

It is not recommended to have kites flying normally at more than 60° line angle. The lack of drag will bring the kite too vertically. It will not fly backward downwind when updraft wind will cease. So modification of kite to increase the drag will be an advantage, not a drawback.

Increase the drag can be some fuzzy tail, or windsocks, or drogues, or floating trailing edges, or some kind of sleeve fins sewn on the kite. The very effective and reliable item that I know is the trailing sail made of small triangular pieces of cloth sewn together by their tips. See the delta page.

Recommended line

Of course, the lightest line will be more performing and will avoid or refrain the kite dive gliding forward as well as it will let it going down slower.

However, because the updraft wind can be very strong, it is important to know well the maximum pull of the kite and get the better line for it.

Moreover, a line with less stretching is preferred, allowing a better feeling to the wind variations, and giving a better response of the kite to the sollicitations of the kiter.

 

ANTI  UPDRAFT  BRIDLE

The principle of this bridle is to bring the weight of the line backward, closer to the sail aerodynamic center, easing the kite to keep its flying attack angle and to go backward when wind decreases.

The bridle is set as usual. An additional strand A-B is set from the center of the bridle to the back of the kite. It comprises a rubber which is stretched when the kite is flying normally, and is pulled back when the tension on the line decreases, especially if the kite is floating horizontally and the line hangs vertically underneath.

When nosing up the kite stops to float in the air and goes backward in the wind.

Wind back the line just keeping it straight until the kite starts to fly again normally.

 

Fabrication

 

Use a tubular rubber for fishing.

Its length and diameter are set depending on the kite. A rubber 6 to 8 mm in diameter and 20 to 30 cm long is usually OK.

 

To each end insert a pin pushed in by force until twice the diameter.

Set the additional strand AB so that in normal flight the bridle is fully stretched to its total length.