[Illustration: Fig. 51. Kite details]
The cellular kite is made in several forms. The rectangular box variety
is perhaps the most common, and with the bridle attached is shown in
Fig. 51. The standard dimensions are: length _a b_ 79 inches, width
_a c_ 78 inches, depth of cell _c d_ 32 inches, and width of cloth
covering _c e_ 25 inches. A very convenient size is obtained by
dividing approximately by two, making length and width 40 inches each,
and depth 16 inches.
Mr. H. H. Clayton, of the Blue Hill Observatory, has patented one
form of this kite known as the "Blue Hill Naval Box Kite," so the
amateur must confine his use of it to experimenting. Other forms of
cells which have been used are shown at 2 3 4 5. These all possess
the advantage--that each plane is a lifting surface, whereas in the
rectangular form the vertical planes have only a rudder action, tending
to hold the kite parallel with the wind.
When launching a box kite, the assistant stands in front of and under
it, while with the Malay he stands behind it and lets go at a given
word. About a hundred yards of line should be run out before launching,
and only a few steps backward by the boy at the string should be
necessary. Running is only required when the line out is insufficient.
[Illustration: Fig. 52. The tetrahedral kite]
The tetrahedral form invented by Dr. Graham Bell is unique and
interesting. Based on the geometrical figure, it has a remarkable
strength of frame, and possesses a surprising lifting power. The
principal difficulty in the construction is in fastening the sticks,
as three of them meet at every point. The frame consists of six pieces
of equal length. Drill a 1/32-inch hole in each end of all the pieces,
about 1/4 inch from the end. Place the pieces on the floor as shown
at 1. Pass a piece of soft iron or brass wire through the three holes
at _a_ and bind lightly. Do the same at angles _b_ and _c_. Now raise
loose ends _d e f_ until they meet over the centre, as at 2. Join with
wire and tighten all the joints with a pair of pliers. (Fig. 52.)
Each face of the frame is an equilateral triangle, and the covering is
to be on only two sides, as shown at 3. The shape of the piece to be
cut is shown at 4. This forms a single cell, and the large sizes are
broken up into many small tetrahedral cells. The line may be tied at
_c_ or _d_.
The designing of fancy figure kites is a fascinating occupation,
but unless certain fixed principles are kept in mind may end in
much experimenting and many disappointments. The question of
steadiness or stability seems to be summed up in the mathematical
expression--"dihedral angle."
A kite having a stiff, flat surface presented to the wind will often
cut up queer antics, while the same frame covered with a more flexible
covering will fly beautifully. The reason is that the flexible covering
will be bowed back by the wind, forming an approximate "dihedral angle."
In the triangular box and tetrahedral kites this bowing back is not so
necessary, because the dihedral angle is provided in the construction.
In these kites, when a sudden gust of wind presses harder on one side
than on the other, the first side is pressed back, reducing the
resistance, and the other side is brought forward until both sides
receive equal pressure, or the kite is in equilibrium, facing the wind;
and the shifting of the breeze is constantly provided for. The bowing
back of the covering of an Eddy kite takes care of sudden changes in
the same way. Double Malay kites or two tetrahedral kites, fastened
together, tandem fashion, will be found stable, especially if the rear
one be slightly smaller than the forward one. (Fig. 53.)
[Illustration: Fig. 53. Double kites]
Geometrical forms like the hexagon, six-pointed star, and even the
circle are used, but these generally require a tail.
A butterfly design may be used, provided the body is designed as a keel
and the two wings are tilted backward to provide the required angle.
In some of the Chinese kites, in the form of insects, the wings have
split bamboo frames, flexible enough to bend backward and provide the
necessary stability. A flexible lower end on the frame also has a good
balancing effect.