1931-01-01

Weight Saving by Structural Efficiency 310034

METHODS employed by the author to reduce the weight of the structural frame without sacrificing strength are described in the paper. To obtain this result the best available cross-section must be selected and the members arranged to transmit the load directly to the final supports which should lie approximately in a plane that is parallel to the load vector; also where a bending moment is caused by the loading, the support attachment should produce a moment of the same amount and of opposite sign. Avoiding secondary bending and utilizing the advantages of full continuity over supports can be secured by a simple arrangement of the frame members.
Substitution of power tools for hand tools will effect a reduction in assembly costs. Sections suitable for power assembly include closed hollow-sections, which have a high structural efficiency, as well as angles, channels, I-beams and similar shapes. These shapes and the riveting machines employed to assemble them are briefly described and illustrated, and some applications to flying-boat construction shown.
A weight of 1.10 lb. per sq. ft. for a tapered wing-section with a duralumin frame and a fabric covering, as contrasted with 1.75 lb. for metal-covered wings, was possible, according to one discusser.* Beryllium alloys, while interesting from a laboratory viewpoint, are handicapped by high cost was the author's answer to another question. Stainless steel could be only one-third as thick as duralumin for the same weight or reinforcements must be spaced three times as closely. Another speaker said that very thin Bakelite fastened directly to the wood stringers of a flying-boat hull with countersunk screws enabled the boat to slide through the water easily because of its slipperiness, and since this material does not corrode, applications of protective paint are unnecessary.

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