The second general division has more than ordinary interest these days, as out of this group has been developed the most important of the air ship inventions. The latest air ships are kites of large dimensions, combining compound box and plain kites with the addition of propelling apparatus.
Reference to Plate IV should convince one that there is ample opportunity for variety in this class, too, the square or rectangular being perhaps the most familiar. The square kite is only square in cross section. It consists of a light framework of four long sticks, one in each corner, running lengthwise, and four short ones used as braces. Two bands of paper or cloth surround the kite, one at each end, with an open space between them. It is necessary to have these open spaces as air vents. The band and space enclosed is called a cell. The braces are fitted in about half the depth of the cell. The brace should be cut to fit the corner piece, as shown in Fig. K. The winding is to prevent splitting when the kite is suddenly wrenched by a whirl of wind. A good size for the long sticks is 3/16 x 1/2 x 34 inches set diagonally in the corner as shown in Fig. K. The braces should be just long enough between notches to necessitate their being sprung into place. Shallow notches should be cut in the long sticks to receive the braces. The covering we will suppose to be of cloth, the kite to be 16 inches square. It will require a strip 64 inches long plus 1 inch for seam. The two edges should have a 1/2 inch hem, and the cell should be 9 inches wide; so to allow for the two hems, the strip would need to be 10 inches. If paper is used, it should be turned back like a hem and pasted down with a string inside to give strength to the edge. The cloth or paper should be glued fast to the outside edge of the long sticks. We start with two sticks first as shown in Fig. L, when dry the two sticks can be brought together, and the other two glued as shown in Fig. M. This gives an even spacing that otherwise would be hard to get. Such a kite can be rolled into small space and is very serviceable. It is easy to see that directions cannot be given for all the box kite class, but many articles have been writen on this phase of the subject, and by reference to the bibliography, no great difficulty should be encountered.
The triangular box kite can be compounded to quite an extent, but the tetrahedral has been developed by Dr. Bell until it can be made of any size, which is not true of other box. kites. Some of the aeroplanes have a number of square cells in a series, with a number of adjustable planes for guiding purposes.h1
The making of box kites requires more real construction, and their lifting power is greater.