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Number 21 was the name of the aroplane Gustave Whitehead first flew with on August 14, 1901. The longest flight was 60 meters (200 feet) above ground and lasted for 2.5 kilometers (1.5 miles). Number 21 was a monoplane powered by a 20 hp engine. It achieved takeoff speed by using the engine to power the wheels, as in an automobile; upon takeoff, power was switched to the propeller.
For the number 21, see twenty-one.
