| The United Aircraft Corporation Hamilton Standard Propellers Division of East Hartford, Connecticut (hereinafter HamStd), developed a hard aluminum alloy to be used in propeller blades on aircraft needing blades with a higher erosion resistance. In July 1939, HamStd submitted a report to Wright Field on the properties of a new propeller alloy that the Aluminum Company of America (hereinafter Alcoa) had developed. The aluminum alloy propellers generally used on airplanes up to 1939 were made of a comparatively soft mixture called the 25 ST alloy. Alcoa's new product, a hard alloy called HSP-26, was developed with a view to making a propeller of increased fatigue strength, increased ultimate tensile strength, and greater erosion resistance. It was expected that the increased ultimate tensile strength would result in a lighter propeller, and that the greater erosion resistance would serve as a safety factor against stress-raising nicks. Those properties were desirable in propellers, particularly since stresses on propellers were increasing as higher power output engines were developed. |
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