The Sail Kite
This kite shows the influence of the box kite in its structure. It is in two parts; one being in the form of a triangle; the other in the form of a sail. It is designed to achieve steady flight in different weather conditions, and should be capable of attaining to a good height quickly. It is robust in construction to withstand the normal wear and tear of flying and handling. The first stage is to make the crossbars, A and B. They are formed from 1/4 in. square stripwood. A is 2 ft. 6 in. in length, and B is 1 ft. 8 in. The ends are grooved, as shown at C (Fig. 17). Next, make the two longerons, D and E. These are each 2 ft. 6 in. in length, and are cut from stripwood, 3/8 in. square. Groove them at the ends, as at C. Assemble the four pieces to form a framework. Lay the longerons on top of the crossbars, and join together with glue and 1 in. fretwork nails. Bend the ends of these over and hammer flat. Before nailing, part drill through the wood to prevent it splitting. Inject a little light machine oil into the holes as a further safeguard. See Fig. 17 for the measurements relating to the assembly of the framework. Now bind round the joints with fine string. This frame must be really firm, so that it will keep its correct shape in flight.
Proceed by making the triangular framework. A third longeron, F, which is 2 ft. 6 in. in length is cut from 1/4 in. square stripwood. Two upright struts, G and H, are also needed. Cut them from 1/4 in. square stripwood, and make them 9 7/8 in. in length. Cut a V-shaped groove at one end of each, to a depth of 1/8 in. to act as a cradle for the top longeron. Bind round the struts with strong thread just below the V-shapes. This will prevent them splitting during flight. Now smooth every part with fine sandpaper, and apply a coat of clear varnish, after which the frame pieces may be enamelled, if desired. Next, brace the sail frame. Bind round and tie a length of fine string to the right-hand end of the top crossbar, leaving a 5 in. tail where it is knotted. Take the string round the edges of the frame to form an outline for the sail. Complete the bracing by tying to the tail at the first knot. The bracing must be taut in order to provide a firm support for the sail. When you are satisfied that this has been achieved, stick strips of insulating tape over the ends of the frame. They will keep the string in place and prevent the wood from splitting.
Use cambric or very fine calico for the sail. Pin the material to a board. Lay the framework upon it, and with a soft-grade pencil, mark the shape. Add a margin of 1 in. all round. The cover may be decorated at this stage. Use fabric painting oil colours. The design should be simple and bold, for example, it might be a large centre circle or diamond-shape, with the surround edged with the same colour; or one's initials, in the form of a monogram could be painted on. When the paint is dry, cut out the cover. The method of securing the cover to its frame is as follows. Roll the material on to a 3 ft. length of 1/2 in. diameter dowelling. By doing this, the cover can be stretched evenly as it is being attached. Fasten the cover to the top of the two longerons, D and E, by means of fretwork nails. Place small cardboard strips between the material and the nail heads. Roll the cover down and fasten in the same way to the ends of the top crossbar. Next, keeping it as firmly stretched as possible, fasten at the ends of the bottom crossbar, and lastly, to the bottom ends of the longerons. A better way, instead of using nails, would be to use 1/4 in. round-headed fine brass screws, with small washers, which may be cut from tin or obtained from model-makers' shops. Drill holes part way through the wood to receive the screws, as one would also do for nails. Now fold the margin over the bracing strings and sew down. The cover may be further secured by the use of a few extra nails or screws along the crossbars. No more than two or three should be used, as too many will tend to weaken the crossbars. The result should be an evenly stretched, firmly secured and well-balanced sail.
The next stage is to complete the triangular shape. Two cloth bands, as at I (Fig. 17) are needed. Cut two pieces, 22 3/4 in. in length and 9 in. in width. Fold over 1/2 in. of the material all round, make a crease at the folds and sew down to make a hem. Now make a sharp crease along the centre of the bands, going across the width of the material. Fasten the bands at these creases to the third longeron, so that one edge of this fits into the creases. Secure the longeron in this position with glue, and a nail or screw at each end of the bands. Now attach the free ends of the bands to the ends of the longerons D and E. Use glue, and for preference 1/4 in. fine brass screws with washers. About four will be needed for each end of the covers. Instead of washers one may use thin tin strips which are 8 in. in length and 1/4 in. in width.
Take the two upright struts, G and H, and insert them between the top longeron and the crossbars. They must be a good fit, otherwise the cloth bands will be too slack. They are 9 7/8 in. in length, as has been previously stated, but it is a good thing to cut them slightly oversize, so that they can be trimmed to the length required, which may vary from the one given. As these struts are subjected to considerable strain in flight, they must be reinforced with small glued blocks, fixed in the position shown at J (Fig. 17). Both struts will need six blocks, 1 in. x 1/4 in. square. The bridle is made from stout string, 6 ft. in length. Tie it in the form of a loop to the top longeron, 4 in. from each end. In order to do this, the bands must be pierced, and they will need strengthening at these points with strips of material, glued in place. The kite line is attached to the bridle by means of a bowline knot and a reef knot, see Chapter 7, under 'Knots', for details of these. These kites do not need a tail, and balance is improved by the correct position of the line on the bridle which is found by experiment whilst flying the kite. When this has been found, the kite will climb and soar in a most satisfactory manner.