Sikorsky S-59 / XH-39
In 1953, the U.S. Army awarded Sikorsky a contract for the experimental conversion of the H-18 (S-52) helicopter from piston to turbine power. This would be the Army's and Sikorsky's first use of a gas turbine engine in a helicopter. Along with the addition of the turbine, the H-18/S-52 was extensively modified and included retractable landing gear (another first for Sikorsky), strengthened fuselage and updated electronics. The new craft, designated XH-39 by the Army and S-59 by Sikorsky, first flew on June 1, 1954.
On August 26, 1954, an XH-39 piloted by U.S. Army Warrant Officer Bill Wester set a world speed record for a helicopter of just over 156 mph over a closed course at Bradley Field in Windsor Locks, CT. On October 17, 1954, Bill Wester set a world helicopter altitude record of 24,500 ft. at Bridgeport, CT.
The XH-39 lost out in a competition with the Bell XH-40 which became the UH-1 "Iroquois", more famously known as the "Huey." The Army continued to fly the XH-39 for another three years to gain data on turbine powered helicopters.
Only three were aircraft were produced: two XH-39s for the Army and one S-59 for use for company demonstrations which is the craft now on display in the Museum after completing its restoration and a visit back to Sikorsky.
Source: Sikorsky Historical Archives