World records set by Sikorsky S-52-1 (modified)
Saturday, December 31, 1949
The exact month and day are unknown and will be updated.
Fitted with a Franklin O-425-1, 245 hp (183 kW) powerplant, the S-52-1 (1949 variant) established the World's speed record of 129.1 mph (207.8 km/h) and the World's altitude record of 21200 ft (6462 m).
Source: "Helicopters from 'A to Z,' Part III", Alex, Ralph P., American Helicopter Society Newsletter , Vol. 7 No-12, December, 1961, Page 16.