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The Sikorsky R-4 is a two-seat light helicopter that was designed by Igor Sikorsky with a single, three-bladed main rotor and powered by a radial engine. The R-4 was the world's first large-scale mass-produced helicopter and the first helicopter used by the United States Army Air Forces, the United States Navy, the United States Coast Guard, and the United Kingdom's Royal Air Force and Royal Navy. In U.S. Navy and U.S. Coast Guard service, the helicopter was known as the Sikorsky HNS-1. In British service it was known as the Hoverfly.
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සංඛ්යා ප්රසිද්ධ මූලාශ්රවලින් එකතු කළ ඒවා බැවින් ආසන්න අගයන් විය හැක; ප්රභේදය සහ සැකසුම අනුව වෙනස් විය හැක.
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ඡායාරූපය 1: RuthAS / Wikimedia Commons · CC BY 3.0
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