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Name: Pinnaka
Status: student
Age: N/A
Location: N/A
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Question:
On windy days I have noticed kites flying in the wind following a stable track, which looks approximately that of a number 8. Here I am referring to one stringed kite. Why this happens and what causes this?



Replies:
Pinnaka,

I have not done that trick with a kite in years! (I assume you are talking about a horizontal '8') However, it is a fairly simple trick to perform. First, it is important to understand that when the string is slack, the kite will be free to turn in its desired direction, but when it is pulled tightly it will race towards its point, with little ability to turn itself upright.

First, wait for the kite to point a bit to one side, (we will say left), and pull the string firmly for a couple of seconds. Now the kite is off to the left, compared to straight downwind. Let the string go slack, and it will try to right itself, turning well tot he right to get back downwind, maybe even tilting all the way over. Pull the string hard again, and this time it will race back to the right, continuing in its rightward twist until you let the string go slack again. Now it is off to the right from downwind, and will first turn upright, then even towards the left and over as it tries to get downwind of you again. Pull the string hard, and it will now dive off to the left.

Ryan Belscamper


The forces on a kite, especially in windy / gusty days are very irregular. When a kite pulls against its string, the force pulls it up (against gravity) and also away (against the string). The mass of the kite and string combined with your pull on the string and the lift force produced by the kite all balance more or less. If the forces are unbalanced, like if the wind shifts, the kite will move side to side or up or down relative to the string axis. If the forces are unbalanced but constant, the kite can stabilize in a circular(-ish) pattern. In your case, if the forces are always changing, the result is a "figure eight" -- which is actually a serious of overlapping circular(-ish) shapes around the string that are not quite centered due to the unbalanced lifting forces. As the kite moves around its tether (the string), it is pulled back to the center, but not exactly with the same force, so it 'orbits' around the string in the figure eight pattern.

Hope this helps,

Burr Zimmerman



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