To see the air lift such weights astonishes most people, because in the quiet of our rooms we move through the air without an effort, and it even fails to support the lightest and downiest feather. But give the air enough motion and it will lift anything made by man. In the terrific wind of a tornado houses are lifted and burst like egg-shells. Even locomotives are not too heavy for such winds to lift. A locomotive is said to have been lifted in a tornado at St. Louis and carried fifteen feet. At Blue Hill we find that the kites in a wind that blows 10 miles an hour lift about two ounces for each square foot of surface; in a 25-mile wind they lifted about a pound for each square foot; and in a 40-mile wind, nearly three pounds for each square foot.
FIG. 1.
The recent interest in kites has brought about a great improvement in their forms. The Malays discovered that a diamond-shaped kite constructed with two sticks could be made steady in the wind, and could fly without a tail if the cross-sticks were bent backward and tied with a cord so as to hold them in the shape of a bow. A writer in the American Boys' Handy-Book calls a kite of this form a Dutch kite, indicating that it has been flown for a long time in Holland. Mr. W. A. Eddy, of New Jersey, is one of the first persons who have attempted to improve the kite for scientific use. He did this by making a kite with the bowed cross-sticks longer and nearer the top than they are in the Malay or the Dutch kite. Mr. Eddy's kite is illustrated in Fig. 1.
FIGS. 2, 3, 4.
To make a kite of this kind five feet tall the sticks should be about ½ by 3/8 inch cross-section if only two sticks are to be used; but if they are to be strengthened by cross-sticks, as is done at Blue Hill, they should be about ¾-inch wide and ¼-inch thick. These sticks can easily be sawed out of a board of the proper thickness. A B and C D should each be 60 inches in length. C E should be 18 per cent. of C D; that is, in a five-foot kite A B should cross C D 10.8 inches below the top of C D. O is the centre of gravity, or the point where the kite balances when supported on the finger. It is placed about 35 per cent. of the distance from C to D. In the simplest form of construction A B is bent backward like a cross-bow (see Fig. 2), and tied so that the deepest part of the bow is about one-tenth of the length of A B. The lower part of the kite should be strung first, and the eye should not be trusted to make A D and B D equal. The distance should be carefully measured, because the success of the kite depends on the exactness of these proportions. In bending A B great care is required to make the bend on one side of the point of junction at E exactly symmetrical with the other bend. The slight bagging inward of the covering of the triangle A E D should be equal to the bagging of B E D. If the kite flies sidewise, owing to inequality in the two sides, it can be partly remedied by tying half-ounce or quarter-ounce weights at A or B. If A should swing too far to the left, tie the weight at B. If B should swing too far to the right, tie the weight at A. The hanger should be tied in front of the kite at E and D, and when pulled sidewise should extend nearly to B, and have a loop or ring tied in it an inch or two inches below B for the kite line. To make Eddy's kite strong and trustworthy, a more complex method of building it, adopted by Mr. Fergusson at Blue Hill, is as follows:
FIG. 5.
A drawing of the actual size of the kite is made on a floor or a table, and four screws are driven into the positions occupied by the corners, leaving the heads projecting about a quarter-inch. The cloth covering is then stretched over the floor or table, and tacked down several inches outside of the edge of the kite, as outlined by the screws. A piece of cord for the edge is then passed around the outside of the screws, drawn tight, and tied at the top by a square bow-knot. A knot is also made just below each of the corners at the sides so that when the cover is transferred from the floor to the sticks the knot will prevent the ends of the cross-sticks from slipping downward, because that is the cause of most of the trouble due to bad balancing. The cover is then pasted to the cord, a lap of about one inch being sufficient, and the cord is left bare at each corner where it passes over the screws. It is well first to wet with water the part of the cloth which is to be pasted, and the paste should be rubbed into every part of the cloth, and a smooth seam should be made. The cover should not be removed from the screws until perfectly dry. While it is drying, the kite-frame can be made. The upright stick is made of two flat sticks fastened at right angles to each other, so as to form a T; that is, they have that appearance when looked at endwise. (See bottom of Fig. 4.) The two sticks are glued to each other, and then firmly lashed. For the cross-stick A B two sticks set at an angle to each other are used instead of a single bowed stick. The method of making the angle joint is shown in Figs. 3 and 4. In a piece of square brass tubing, B, is cut a slot, into which fits the upright stick, C D. The tubing is then bent around the upright stick, C D, to the angle desired; a piece of wood, E, is fitted to the angle, and the whole is firmly lashed together. The ends A and B of the two arms of the cross-stick are driven into the ends of the tubing and strengthened by a brace, F. The frame is then ready for the cover, and the proportions are the same as those of the kite with two sticks. The ends of the sticks are notched to receive the loops of cord left at the corners of the cover, and the cover is slipped over the frame with the knots at A and B beneath the ends of the stick. The cord in the cover should then be lashed to the sticks, except at C (Fig. 1), and coated with glue, in order to prevent the cover from drawing away from the corners. The cord at C is left free to permit adjusting the tension of cover and string by retying when necessary. These kites will fly without a tail, but they are much steadier and better if flown with a tail, like the one invented by Mr. Archibald. This tail does not act by its weight, since it should weigh only one or two ounces, but by the pressure of the wind on it. It is made of two or three cloth cones joined to each other and to the end of the kite at D (Fig. 1) by a fine cord. The front of each cone is made of a wire ring, stiff enough to hold its shape, and two cross-braces of wire, or two cross-strings, as shown in Fig. 5. The tail string is tied to the braces in the centre of the ring, and passes down through the end of the cone, and several feet beyond it, where a second cone may be attached. To make the kite lift well, and to fly it in wet weather, it is best to cover the cloth and sticks with varnish which is mixed with rubber to make it elastic, as suggested by Dr. Stanton. The following proportions are used at Blue Hill: Pure rubber, shredded, 2 ounces; bisulphide of carbon, 2 to 4 pounds. When the rubber is dissolved, this solution is mixed with spar-varnish in the proportion of 2 pounds of the solution to 1 pound of varnish, and thinned with turpentine. Apply a small quantity at a time, evenly distributed, and give two or three coats.