E. P. Warner
The idea of using a propeller rotating about a vertical shaft to give lift and to sustain a weight by balancing it directly with the thrust is almost as old a the screw propeller itself, and the elements of the theory of the action of a lifting propeller have been understood for at least fifteen years. Unfortunately, however, the printed discussion of this theory are almost all in French, German, or Italian, and those which are available in English are mostly contained in advanced treatises which are not likely to fall into the hands of the casual student. It is felt, therefore, that a broad survey of the problem will be of use in making clear the nature of some of the obstacles which have prevented any helicopter from reaching the stage of practical usefulness as yet and may lead to a saving of some of the time and money which are constantly being squandered on attempts to demonstrate anew facts which are already perfectly well understood without in the least striking at the root of the problem.
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