Figs. 75 to 77.—Another Simple Monoplane Design
Some details are also given of a similar design, the difference being that the former machine is built for distance, whilst the latter ([ see Fig. 75]) is built for duration. The main spar is of spruce ⅜ in. × ¼ in. in cross-section and of the length shown in [Fig. 75]. The main plane, as with the previous machine dealt with, is adjusted by means of the tin clips and extending centre-rib; a plan of the outrigger is also given in [Fig. 76]. The main plane has a dihedral angle of 1½ in. A is a side elevation of the elevator, showing its angle of incidence in relation to the spar, and [Fig. 77] a perspective sketch of the elevator. An idea of a model of this type flying can be gathered from [Fig. 78].
Fig. 78.—Finished Model
CHAPTER VIII
Simple Twin-screw Biplane
According to the type formula, the machine illustrated on [p. 63] is of the 1-2-p2 type, which signifies that it has two superposed main supporting surfaces and twin screws, and that it flies with the small plane leading. The writer, in testing the model from which the drawings were made, found that 300 yards were easily obtainable at every flight at an altitude of 40 ft. or so. Although its construction is slightly more complicated than a monoplane, this is amply compensated for by its majestic appearance in the air.
The central spar is hollow, and measures 36 in. by ⅜ in. by ⁵/₁₆ in. [Fig. 79] shows a cross-section of it. Spruce was used for this, a groove ⅛ in. by ⁹/₃₂ in. being ploughed in the spruce, and a ³/₃₂-in. strip being glued over the open side. The spar should be tapered off from a point 12 in. from the front end to ¼ in. by ¼ in., to give additional strength.
The propeller bar is mortised into one end of the central spar, and is stayed from a point 6 in. from the rear end to ½ in. in from each end of the propeller bar, to which projection the bearings, cut from sheet brass, are lashed. These latter are shown in [Fig. 80]. To the front of the spar are bound two hooks, formed from one continuous length of wire. These embrace the rubber, and should be covered with valve tubing.
Four birch struts should next be cut, ¼ in. by ¹/₁₆ in. in section and 7 in. long, to support the main aerofoils on the spar. They should fit over the spar in the position shown, small blocks uniting them top and bottom, and should be so fixed that their upper ends are 3 in. off the spar. Notches are to be cut in them 2¼ in. below the spar, to form a convenient fixing for the lower main plane. [Fig. 81] clearly shows the struts united to one of the blocks; the saw cuts or notches will also be apparent from this.
A cane skid is bound to the lower blocks, and to the spar at the position indicated in [Fig. 82]. A half-section of a round cane is quite suitable for this purpose.