CHAPTER X
Collapsible Monoplane
The difficulty of carrying a fairly large model to a convenient flying ground prevents many would-be makers taking a practical interest in model flying. The necessity of overcoming this difficulty has resulted in several excellent designs, one of the best being the monoplane designed and constructed by Mr. A. B. Clark, the secretary of the South-Eastern Model Aero Club. When this model monoplane was built the objects aimed at were extreme reliability and easy conveyance to and from the flying grounds situated some distance away.
The model is fitted with a chassis to enable it to start off good ground under its own power; but this starting-gear is so constructed that the whole model will pack up flat and make a convenient parcel. In fact, the complete model will easily go into a cardboard box measuring 2 ft. 10 in. by 1 ft. 2 in.
Referring to the accompanying illustrations, Fig. 96 shows the plan view of the complete machine, Fig. 97 a side view, and Fig. 98 a front view. The body (fuselage) is made of two pieces of silver spruce, 3 ft. 6 in. long, ⅜ in. deep, and ³/₁₆ in. thick. These gradually taper towards each end, where they measure ¼ in. by ³/₁₆ in. Two distance pieces of bamboo are shaped to streamline form and placed at equal distances along the fuselage; the front piece is 2⅜ in., the other 2 in. These pieces should be pointed at the ends, and fit in a slot made in the side lengths, as indicated at A (Fig. 99), and then bound very tightly with glued narrow silk tape or ribbon, as indicated at B. This is the neatest and also the strongest method of making joints for model aeroplane frames. The ends of the two long lengths should be bound together with strong thread and carefully glued.
The tail (used in place of the familiar elevator) is built on to the rear end of the fuselage, and is composed of two pieces of yellow bamboo, 9¾ in. by ⁵/₁₆ in by ⅛ in., tapering to ⅛ in. square at the end to which the propeller bearings are attached. These bearings are made of No. 18 or No. 20 s.w.g. piano wire, and their shape is clearly shown in Fig. 100. The bearings are bound to the inner edge of the wood with glued thread or fine flower wire. The wide ends of the bamboo lengths are held over a bunsen (the blue flame of an incandescent burner is very suitable), and bent to the angle shown in Fig. 96. The trailing edge of the tail is made of No. 26 s.w.g. piano wire, or a G banjo string. The wire is taken right through the end of the fuselage, a small hole being carefully drilled ½ in. from the end. A bead of solder should be run on the wire on both sides of the hole, to prevent movement in a lateral direction, and the two ends are taken through the bearings and bound to the bamboo with fine wire, leaving sufficient to form hooks for the two bracing wires to be afterwards attached. The whole of this tail framework is covered with proofed silk on both sides, thus forming an approximate streamline surface, which has proved remarkably efficient. Two triangular pieces of silk should be cut out, just large enough to give sufficient overlap. They should be attached with fish glue, and stretched as tightly as possible.
Fig. 96
Fig. 97
Fig. 98
Fig. 99
Fig. 100
Fig. 101
Figs. 96 to 101.—Arrangement and Details
of Collapsible Monoplane
At the other end of the fuselage is attached the hooks for the elastic, and the wire forming them is also utilised as a protector. The whole construction is made from a 10½-in. length of No. 18 s.w.g. piano wire, reinforced with a strip of thin bamboo, bent to shape over a blue flame and bound with silk tape. The part is shown unbound in Fig. 101, and Fig. 102 shows an alternative protector; but it is not so effective.
The main plane is made of bamboo and piano wire of No. 18 s.w.g., and measures 2 ft. 10 in. by 6¼ in. The leading edge is of bamboo 3 ft. 2 in. long, ³/₁₆ in. wide, tapering to ⅛ in. at the ends, with a uniform thickness of ⅛ in. When planed down the length should be heated over a blue flame, and bent to the shape shown in Fig. 96, the outside of the bamboo being kept on the outside of the curve. The trailing edge should now be attached to the ends of the leading edge, a length of ½ in. being bent up at each end of the wire, and securely bound to the bamboo. The ribs should now be cut from the same gauge wire. The ends should be bent out at an angle so that they may be bound to the leading and trailing edges, as shown in Fig. 103; the projecting ends should be about ⅜ in.
Fig. 102
Fig. 103
Fig. 104
Fig. 105
Fig. 106
Fig. 107
Fig. 108
Fig. 109
Figs. 102 to 109. Details of Collapsible Monoplane
The two centre ribs are shaped as shown in Fig. 104. It will be seen that the leading edge is raised ¼ in. above the fuselage, and the rear edge is level with it. The ends of the ribs are fitted into small holes drilled in the top of the fuselage, and kept in position by means of small metal clips, as shown in Figs. 105 and 106. Four of the clips are required, and they may be easily made from thin tinplate and soldered. The ribs should be soldered to the trailing edge so as to make them secure. The framework should be covered with proofed silk, and neatly glued on all edges.
Fig. 110.—Rear Skid
Fig. 111
Fig. 112
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.