Читать книгу Building and Flying an Aeroplane. A practical handbook covering the design, construction, and operation of aeroplanes and gliders онлайн

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To prevent the ribs from splitting open at the ends, they are protected by light steel ferrules, shown in Fig. 15. When received in the rough-sawed condition from the mill, the ribs must be tapered at the ends with a plane or spoke shave to fit these ferrules, and the sharp edges should be rounded off. In doing this, it must be remembered that the upper surface of the small ribs gives the curvature to the cloth surface, so that any tapering must be done on the lower side. The main ribs may be tapered from both sides, as it is the center line, or crack between the third and fourth laminations, that determines the curve. Every inch along this line A-inch holes are to be drilled for the lacing, Fig. 15.

The ferrules for the front ends of the small ribs are light 1/2-inch seamless steel tubing; they may be flattened to the proper shape in a vise without heating and are drilled with a 1/8-inch hole. They are driven tight on to the tapered ends of the ribs and fastened in place with a small screw. The rear-end ferrules are 1/2-inch lengths of 3/8-inch tubing, driven on and drilled with a 1/32-inch hole for the rear-edge wire. The rear ferrules of the main ribs may be the same 1/2-inch tubing used for the front of the small ribs; they should be cut off so that their ends will come in the same line as the holes in the ends of the small ribs. If the quick-demountable plan be followed, the second main rib from each end may be left long and drilled with a hole like the small ribs. The front ferrules of the main ribs should be 3/4-inch tubing of heavier gauge, drilled with a 1/4-inch hole. The finished ribs are sandpapered smooth and shellaced or coated with spar varnish. The latter is much more expensive and slower in drying but has the great advantage of being weather-proof and will protect the glue cracks from moisture. The ferrules may be painted with black enamel.