Sikorsky YH-19

The YH-19 was the first practical single-rotor utility helicopter. The first in Sikorsky's successful S-55 series, it solved the center-of-gravity problems of earlier models by shifting the engine to the front and the passenger compartment to beneath the rotor hub. Other innovations included offset-flapping hinges and hydraulically boosted irreversible controls. Designed for the Air Force for arctic rescue, the S-55 served all U.S. military branches throughout the 1950s, especially during the Korean War and in most major military conflicts of the early Cold War. Civilian versions pioneered helicopter airline service in the United States and abroad.