Aeronautics: For Sale: Autogiros

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At takeoff, the rotor is started turning by a self-starter, a clutch device which draws 10 h. p. from the engine. In a few seconds the blades are turning 120 r. p. m. and the autogiro may begin to rise with a run of between 10 ft. and 100 ft. In full forward flight the rotor provides about 80% of the lift; in vertical descent, practically 100%. The autogiro need not drop vertically, may approach a landing in a normal airplane glide.

Important feature of the rotor is the freedom of each blade to move, by hinges, up and down or laterally during rotation. At rest, the blades droop downward at a slight angle. Light cables keep them from collapsing entirely. In flight the upward pressure of air might be expected to shoot the blades upward like the ribs of an umbrella turned inside out by the wind, but centrifugal force holds them firmly, lending them a strength far exceeding the strength of their own materials. But all four blades cannot behave in the same manner at the same time while the autogiro is flying at 100 m. p. h. The advancing blade, having the forward speed of the ship added to its own rotational speed, would have a tendency to lift, like any airplane wing, throwing the craft off balance. The receding blade, losing forward speed, would contribute to the same effect by drooping. Hence, the hinging allows the blades to work up and down freely without tipping the machine. Until that principle of "articulation" was worked out and applied by Senor de la Cierva in 1923, after four years of labor, his autogiros would scuttle along the ground, but they would not fly.