: In 1939, he designed and flew the VS-300 , the first viable American helicopter. This pioneered the single main rotor and tail rotor configuration that remains the industry standard today.
: In technical manuals for helicopters like the Sikorsky R-4, a "free-wheeling unit" is a critical component that allows the rotor to continue spinning (autorotate) if the engine fails. Simulators & Content captain sikorsky free