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Helicopters.
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4
Aeronautics.
3
Inventions.
2
Aeronautical engineers.
1
Autogiro Company of America.
1
Autogiros.
1
Avro airplanes.
1
Cierva, Juan de la, 1895-1936.
1
Engineers.
1
Helicopter pilots.
1
Inventors.
1
Pitcairn, Harold F., 1897-1960.
1