Igor Sikorsky left Russia when the last Tzar was overthrown in the Bolshevik revolution. He designed aircraft for the Tsar, he had built a huge passenger airplane, the Le Grande. In the West, he turned his hand as an aircraft designer to build a three engine transport, and a seaplane.
Ssikorsky had always been interested in designing helicopters. The first working helicopter that Sikorsky built was the VS-300, first flown in 1940. It had a body made of welded steel tubes, a 90 hp engine, three 14' main rotors, and three auxiliary or tail rotors. The pitch of all the rotors could be changed. The design patented in 1931 must have been an early model, having two main rotors and two tail rotors.