“During the war, black walnut and mahogany were practically the only species used for propellers. Since the available supply of these species in the U.S. was not sufficient to keep up the necessary production, other species had to be substituted. The U.S. Forest Products Laboratory at Madison, Wis., was able to suggest several native woods which appeared suitable for propellers. Quarter-sawn white oak combat propellers were put into production and other native species, such as birch and maple, were used on training planes, but not for combat propellers. At the present time almost all propellers are made up with hide glue. It is not water proof, and under extreme conditions of humidity the joints may open.”
—Scientific American, September 1919
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