If, when pursuing a straight course, the aeroplane is tilted by a sideways wind (_b_), the action of the pendulum as described above restores it to an even keel, as in (_a_). Diagrams showing action of Marmonier gyroscopic pendulum.] Chapter IX. FLYING MACHINES: HOW TO BUILD. Santos-Dumont’s gift--_La Demoiselle_--Mechanical skill required--Preparatory practice--General dimensions--The frame--The motor--The main planes--The rudder-tail--The propeller--Shaping the blades--Maxim’s experience--The running gear--The controls--Scrupulous workmanship. When Santos-Dumont in 1909 gave to the world the unrestricted privilege of building monoplanes after the plans of his famous No. 20--afterward named _La Demoiselle_--he gave not only the best he knew, but as much as any one knows about the building of flying machines. Santos-Dumont has chosen the monoplane for himself because his long experience commends it above others, and _La Demoiselle_ was the crowning achievement of years spent in the construction and operation of airships of all types. In view of Santos-Dumont’s notable successes in his chosen field of activity, no one will go astray in following his advice. Of course, the possession of plans and specifications for an aeroplane does not make any man a skilled mechanic. It is well to understand at the start that a certain degree of mechanical ability is required in building a machine which will be entirely safe. Nor does the possession of a successful machine make one an aeronaut. As in the case of bicycling, there is no substitute for actual experience, while in the airship the art of balancing is of even greater importance than on the bicycle. The would-be aviator is therefore advised to put himself through a course of training of mind and body. Intelligent experimenting with some one of the models described in Chapter XI. will teach much of the action of aeroplanes in calms and when winds are blowing; and practice with an easily constructed glider (see Chapter XII.) will give experience in balancing which will be of the greatest value when one launches into the air for the first time with a power-driven machine. An expert acquaintance with gasoline motors and magnetos is a prime necessity. In short, every bit of information on the subject of flying machines and their operation cannot fail to be useful in some degree. The dimensions of the various parts of the Santos-Dumont monoplane are given on the original plans according to the metric system. In reducing these to “long measure” inches, all measurements have been given to the nearest eighth of an inch.