evaluating the winds - évaluer les vents

Author : Glenn Davison.  the book, “Kites in the Classroom.”
Now that you have a kite and a good place to fly it, now you need wind! The best conditions are smooth, steady winds without changes in direction or speed.

Is there enough wind?
Most kites fly when the wind speed is between 4 and 15 MPH. Choose a day to fly kites based on the wind. Don't expect the wind will fit your schedule! It is important to know your kite and to know the current conditions because some kites are designed for low winds or no wind (indoors) while others are designed for high winds. 

How can I tell if the wind is right?
Remember that the wind speed changes with altitude. Higher winds are often found at higher altitudes. Changes in wind speed are worse than changes in direction. A sudden increase in speed, called a gust, can snap a flying line that would otherwise work well. A drop in speed can quickly ground a kite and if you are not careful the kite can land on a road, in a tree or in the water.

Smooth wind - Not strong wind
Many people believe that strong winds provide ideal conditions for kites. This is not true! Wind flows in waves of varying speed and direction. That means, depending upon where you try to fly your kite, you may not find enough wind or the turbulence may be too great for your kite to fly well. Turbulence results in a bumpy flight and decreases the speed of the wind, which often hinders the launching of a kite.
Scout the lay of the land before you launch your kite. A ground obstruction blocks smooth wind from the kite. When the wind reaches an obstruction, it flows over and around it, causing turbulence on the downwind side for a considerable distance. Trees, shrubbery, a hill or a building cause turbulence far downwind by as much as seven times the height of the obstruction. If your kite is held too close, even your body could block the wind.
To find smooth wind you must find a large flat area without obstructions or fly your kite high enough to avoid turbulence.

Evaluating the wind direction
In preparation for launch you should always determine the wind direction. This will help you to choose an appropriate anchor position, launch your kite successfully and fly the kite safely. The wind direction is important because many flying locations get smooth wind from one direction and turbulent wind from another.
There are many signals that will tell you the wind direction. The obvious ones are flags, banners, weather vanes, other kites, smoke and streamers. Another method is to feel the wind on your face and hands. Turn your face in the wind till the sound of the wind is equally strong in both your ears.
Some less obvious methods include carefully watching hair, the leaves on a tree or swaying grass. Some people drop a few grains of sand or a few blades of grass to see which way they blow.

Selecting the right kite for current conditions
Judging the strength of the wind will help you to select the right kites to fly on a given day. Since the wind speed and direction may change abruptly, experienced kite fliers have a number of kites and know which ones are better suited for winds of different forces. Just the way you change your clothing to match the weather, kite fliers will switch kites to match the wind speed.

In heavier wind you might choose kites with:
  • long tails
  • extra bow, extra flex or extra dihedral
  • a small sail area or vented sails
  • higher bridle adjustment
In light wind you might choose kites with:
  • no tails
  • a lightweight frame with less dihedral
  • a large sail area
  • lower bridle adjustment
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