The longitudinal curve on the camber can be regulated by the original tension given to it, and by the manner of its fixing to the main framework. Suitable wire projections or loops should be bound to it by wire, and these fastened to the main framework by binding with thin rubber cord, a very useful method of fastening, since it acts as an excellent shock absorber, and "gives" when required, and yet possesses quite sufficient practical rigidity.
§ 9. Flexible joints are an advantage in a biplane; these can be made by fixing wire hooks and eyes to the ends of the "struts," and holding them in position by binding with silk or thread. Rigidity is obtained by use of steel wire stays or thin silk cord.
Fig. 49b.—Mr. T.W.K. Clarke's 1 oz. Model.
Showing the position of C. of G., or point of support.
§ 10. Owing to the extra weight and difficulties of construction on so small a scale it is not desirable to use "double surface" aerofoils except on large size power-driven models.
§ 11. It is a good plan not to have the rod or tube carrying the rubber motor connected with the outrigger carrying the elevator, because the torque of the rubber tends to twist the carrying framework, and interferes with the proper and correct action of the elevator. If it be so connected the rod must be stayed with piano wire, both longitudinally (to overcome the pull which we know is very great), and also laterally, to overcome the torque.
Fig. 49c.—A Large Model Aeroplane.
Shown without rubber or propellers. Designed and constructed by the writer. As a test it was fitted with two 14 in. propellers revolving in the same direction, and made some excellent flights under these conditions, rolling slightly across the wind, but otherwise keeping quite steady. Total weight, 1½ lb.; length, 6 ft.; span of main aerofoil, 5 ft. Constructed of bamboo, cane, and steel wire. Front skids steel wire. Back skids cane. Aerofoil covering nainsook.
§ 12. Some builders place the rubber motor above the rod, or bow frame carrying the aerofoils, etc., the idea being that the pull of the rubber distorts the frame in such a manner as to "lift" the elevator, and so cause the machine to rise rapidly in the air. This it does; but the model naturally drops badly at the finish and spoils the effect. It is not a principle that should be copied.
