The framework is now ready for soldering together. It is essential that the wire and soldering bit must be perfectly clean. Apply a little killed spirits of salt to the parts to be soldered, and then place a piece of solder in position and touch with the hot soldering bit. Care must be taken to see that the wires lie close together.
When the plane is soldered together remove all the staples and clean up all the joints with a file. The joints must now be bound round tightly with fine iron wire, which must be perfectly clean. The plane must now be fastened to the board again, and all joints soldered again. When the soldering is completed the plane is once more removed from the board, straightened, the dihedral angle given, and the ribs bent to the desired camber. If the soldering has been carefully accomplished there is no fear of the joints giving way.
Fig. 65.—Swept-Back Wing
For covering planes it is far better to purchase a waterproof silk especially manufactured for the purpose than to attempt to use ordinary silk. The silk varies in weight from 1 oz. to 1½ oz. per square yard. When cutting the silk about ½ in. must be allowed for turning over for fastening. At the curved ends of the plane slits about ½ in. apart must be cut in the edge of the silk, as shown in [Fig. 64]. Apply a thin coating of glue to the silk (use seccotine) to be turned back, and allow sufficient time for the glue to get tacky. Then stick over the plane, beginning at A ([Fig. 64]) and finishing at B. Allow time for the glue to set, then fasten the opposite end in the same manner. Care must be taken to stretch the silk tightly, so that it is free from wrinkles. Then fasten first one side of the plane and lastly the other.
Another method of covering steel-wire planes is to lace the silk to the framework. The silk must be cut about ¼ in. larger than the framework, and the edges hemmed with a sewing machine. The silk cover when hemmed should be slightly smaller than the framework. First sew the silk roughly in position, and then carefully sew it, beginning at one end, following with the other end, and lastly the sides. The stitches should first be passed through the silk, and then round the wire at intervals of about ¼ in.
[Fig. 65] is the plan of a swept-back wire plane. The plan should be drawn full-size on a board by means of squares, the contour of the plane being contiguous in relation to the squares as that in the illustration and the method outlined above followed. The ribs should also be fitted up to the outline, being bound and soldered to the piano-wire frame. For machines above 30-in. span a third strengthening spar should be fixed in the position of the dotted line to obtain rigidity. Two central ribs should be fitted to provide a spar-attachment. The tips require to be set at a slight negative angle as at C.
CHAPTER VII
Simple Twin-Screw Monoplane
The accompanying illustrations show as simple a type of model aeroplane as it is well possible to make, excluding the now obsolete single-stick hand-launched 1—1—P1. It is thus a suitable model for beginners, flights of well over a quarter of a mile being easily obtainable.
The main spar ([see Fig. 66]) is cut from straight-grained birch, to the dimensions given, each end of it being tapered down to ³/₁₆ in. square. The propeller bar is of silver spruce, ⅜ in. by ⅛ in. in cross-section. The end of the main spar is slotted to receive the propeller bar, this latter being pinned and glued into position. The propeller bar support is similarly slotted to take the bar, a pin being driven through the two and clinched over on the under-side. [Fig. 67] clearly shows both joints. At 6 in. from one end the main spar is mortised to receive two tenons which are cut on the ends of the bar supports. These tenons should be so cut that they butt to one another in the centre of the mortise. An idea of the shape of the tenon will be gathered from [Fig. 68], a view of the joint assembled being given.