Sikorsky S-52

The Sikorsky S-52 is a utility helicopter that Sikorsky Aircraft developed in the late 1940s and the first US helicopter with all-metal rotor blades. Design began in late 1945 and the two-seat prototype, first flown in 1947, used a 178-horsepower Franklin air-cooled flat-six piston engine; it was developed into the four-seat S-52-2 and S-52-3. The Navy and Marine Corps designated it HO5S-1, the Coast Guard HO5S-1G and the Army YH-18A, and after military retirement it was used extensively by civil operators. It received a Civil Aeronautics Authority type certificate on 25 February 1948.