First design for a production helicopter

Igor Sikorsky (born in Kiev, now Ukraine, then emigrated to USA), designed the world's first true production helicopter. Sikorskys US Patent 1,994,488, filed on 27 June 1931, marked the crucial breakthrough in helicopter technology and led to the the world's first true production helicopter, the Sikorsky R-4, which proved itself in active sevice in the second world war and became the world's first mass produced helicopter. He also designed the world's first successful multi-motor aeroplane.