Figs. 111 and 112.—Details of Screw
The chassis is shown by [Fig. 107], No. 18 gauge piano wire being used for the framing, and an ordinary cycle spoke for the axle. Figs. [108] and [109] show the flexible joints of the chassis, which folds up flat when the hooks at C ([Fig. 107]) are withdrawn.
The wheels are 2 in. in diameter, and are rubber tyred, the ends of the spoke being burred over to keep them in position.
The rear skid is shown in [Fig. 110], and is made of No. 18 gauge piano wire. A single length is used, being bent to shape, passed through the end of the fuselage, and held to its work by the projecting end D, which fits in a hole in the under-side of one of the pieces of wood. When not in use the skid may be folded flat.
The two propellers are of the simple bentwood type, 10 in. in diameter and 1 ft. 8 in. pitch. They are made of ¹/₁₆-in. birch in the usual way. The shape of the blades is shown in [Fig. 111], and the angle at which the blades are bent is shown in [Fig. 112]. Six strands of strip rubber should be attached to each propeller, ordinary soft soap being used as a lubricant.
CHAPTER XI
Tractor Monoplane
Some of the competitions arranged by the Kite and Model Aeroplane Association have been for duration models of a minimum weight of 1 lb., capable of rising from the ground under their own power, carrying a dead weight of a quarter of their own total weight. Such a model is that here illustrated and described. It has flown repeatedly for thirty-eight seconds after rising from the ground, while its hand-launched duration is about half a minute, by no means a small accomplishment for a 16-oz. model. It will be seen that it has somewhat larger dimensions than the ordinary rubber-driven model.
The top main spar is of spruce, 4 ft. 6 in. long and ½ in. by ¼ in. in cross-section, the bottom one being 2 in. longer and ¼ in. by ³/₁₆ in. in section. The bottom member is to be bent by steam approximately to the shape shown in the side view of the machine ([Fig. 113]), and then fitted to make a clean butt joint to the top spar B [(Fig. 114]). Bearings for the two ⅝-in. gears, details of which are shown in [Fig. 115], are bent to shape from No. 20 gauge sheet-brass, a lug being left projecting to engage with the bottom member of the fuselage. The holes for the shafts should be drilled so that the gears make a fairly tight mesh. The spindles are to be of No. 16 gauge piano wire, on to which the gears are to be soldered. The propeller shaft is continued forward of the bearing for 1½ in., and is bent back at an angle (as shown in detail at A in [Fig. 116]) to grip tightly in the propeller boss. The gears are kept central between the two bearings by means of pieces of brass tubing, which are slipped on the spindles at each side of the bearing and soldered in position.
Fig. 113.—Side Elevation