Fig. 86
Fig. 87
Fig. 88
Figs. 86 to 88.—Details of Biplane
The last, and perhaps the most important, unit of the model should be made—the propellers. Cut a pair of blanks, as shown in [Fig. 88], to shape from ¹/₁₆-in. birch to form the propellers. Strips of tinfoil are wrapped round their centres, to which the spindles are soldered. Bend the blades at the dotted lines under a jet of steam from a kettle, making them to revolve in opposite directions. They rotate on steel-cupped washers placed on the spindles.
Motive power is supplied from eight strands per side of ¼-in. strip rubber well lubricated with soft soap emulsified with water. These skeins will stand 650 turns each, which number should be gradually worked up to on new rubber, and not applied at the first flight. A perspective view of the finished model is given in [Fig. 89].
Flying the Model.—Having selected a large open space clear of trees, give about 100 turns on the propellers in order to adjust the elevator. If the model points its nose in the air it is elevated too much. If the model flies too low it is not elevated enough. In each case it requires adjustment until the precise position is arrived at. The elevator should never be at a greater angle than 8° or less than 5°. If the machine still flies too low with the elevator at 5° the main planes will have to be moved forward slightly; but the exact position is only found by experiment. If it flies too high with the elevator at 5° the planes will have to be put back.
