Queues & Manches - Tails & Drogues

Les queues et les manches ont un rôle de stabilisateur directionnel. Leur résistance est l'élément essentiel de leur fonctionnement; elle peut être réduite ou augmenter à volonté, il est important de bien distinguer les effets de leur poids et ceux de la résistance au vent.

Par grand vent, les pressions exercées sur la face inférieure d'un cerf-volant peut être compensées par l'action régulatrice de la queue. Il faudra donc adapter sa longueur à la force du vent. En général, les queues sont environ 7 fois plus longues que la membrure de leur cerf-volant.

Avant l'ascension proprement dite, il est bon de procéder à une série d'essais avec des longueurs de queues différentes. Elles ne doivent ni être trop longues, ni trop courtes. Elles doivent voler gracieusement dans le ciel, en contrebalançant les mouvements du cerf-volant sans le moindre contre-coup.

Si les grands cerfs-volants n'en ont pas besoin, les cerfs-volants plats par contre ne peuvent voler sans queue. Les vents n'ont pas toujours une grande régularité. Il peut toujours arriver que leur vitesse augmente au moment même où les cerfs-volants  prennent de l'altitude. La bonne ascension dépend de la souplesse de la queue et de sa facilité à s'allonger ou à se rétracter. C'est le propre d'une manche à air qui n'est en fait qu'une pièce de tissu cylindrique dans laquelle s'engouffre le vent. Elle est généralement ouverte aux deux bouts et règle automatiquement le débit d'air en s'adaptant à la vitesse du vent. Lorsqu'elle s’incline trop, de simples tensions sur la corde suffisent pour la relever.


the loop tail simply a length of ribbon is most effective than it looks

Although a tail is theoretically inefficient in as much as it produces drag, this is what it is designed to do, and if the correct amount of drag is induced in the right place it can be turned from a negative to a positive force.

Drag should not be confused with weight. Weight is concerned with vertical forces, and drag - in this application at least - is concerned with horizontal forces. The drag factor can be increased or reduced by either lengthening or shortening the tail. The dynamic forces acting upon the kite face are offset by means of the tail. These forces increase with wind velocity and correspondingly longer tail with be needed to offset them. Although the formula of seven times, the length of the spine is a reasonable rule of thumb, the only way to assess properly the correct tail length is by a little trial and error.

A tail of ideal length should , under normal conditions, not fly two straight (too long) neither should it be excessively skittish (too short); rather it should sway gracefully and gently, literally computing - and counteracting - the movement of the kite.

So, tails help stabilize kites. Some kites do not need a tail since they are designed to be stable. That supports a saying among Japanese kite makers: " a goof kite needs no tails." Even when tails are unnecessary, they may be added for artistic or visual effect. There are many possible tail configurations: thin, thick, multiple, u-shaped, balanced, Y-shaped, twisting, drogues and combinations. Here are a few ideas:
While flat kites are solely dependent upon the drag factor of a trail to provide directional stability, other kites, normally classifiable as tailless kites - and particularly kites with a high aspect ratio - may need the extra stabilizing influence of a tail in high winds. As wind velocity tends to increase with height, maximum efficiency throughout a lift would depend upon a tail capable of automatically lengthening itself - or increasing drag - with altitude.

In fact this effect is produced by the drogue or wind cup. The drogue, a conical sleeve open at both ends, acts as an extremely efficient self-regulating tail.

It functions in much the same way as a funnel used for pouring liquid, in as much as when the input is slightly greater than the output the liquid gradually builds up until it overflows. So the drogue is capable of modifying the air flow and, even when spilling air, is producing maximum relative drag. The drogue governs the directional stability of a kite in a somewhat different manner from the normal tail. As a length of hanging string may be straightened either by smoothing it through its length or, more efficiently, by pulling at its end, so the later applies to the drogue effect, which is more than simple leverage; and just as longer levers are used for heavier weights, so longer drogue towing lines are used for heavier kites.
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