Science: Contradictory Screws

Like one of the fastest airplanes that ever flew,† the two-man Japanese submarines which attacked Pearl Harbor had contrarotating propellers —two tandem screws placed close together, turning in opposite directions. Blades on the second screw are pitched counter to those of the other screw so that both thrust in the same direction. Such devices for U.S. warplanes were announced last week to be "in the developmental stage" by Curtiss-Wright, United Aircraft, other plane builders.

Purpose of this mechanism in planes (and submarines) is to overcome torque or sideways twist created when 1) the air's...

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