This installation had been tested with the modified S-52-2 YH-18A, s/n 49-2890 c/n 52007, known as the S-52-5 YH-18B in which the original power plant, a 245 hp Lycoming O-425-1, was replaced by an Artouste II mounted on top of the fuselage by being bolted direct to the transmission gear-box. Because of airframe limitations, the Artouste II used in the S-52-5 was de-rated from a maximum take off output of 400 hp to 320 hp.
The ultimate design, the H-39, incorporated several design changes, notably in the fuselage, to adapt it to the new power plant. The 400 hp Artouste II engine, main transmission and rotor head formed a complete package which was mounted above the fuselage and could be removed and re-installed in two hours.
The forward section of the fuselage contained the cabin which, in addition to the pilot, had 81 cu.ft (2.29 cu.m) of payload space, and offered adequate accommodation for three passengers and 100 lb (45 kg) of baggage, or two stretcher patients and a medical attendant, or 800 lb (363 kg) of cargo. The three-wheel retractable landing gear formed part of this section.
The rear fuselage and the tail pylon, including the tail and intermediate gear-boxes were quickly removable to facilitate rotational maintenance. The four main rotor blades were completely interchangeable, as were the tail rotor blades. All blades were of all-metal construction.
The S-52-5 YH-18B, s/n 49-2890, was converted to the sole YH-39A (new c/n 59001) and first flew on June 1, 1954. Flown by Sikorsky pilot Billy I. Wester, the aircraft set up a speed record over the 3-km. course over Bridgeport, Connecticut, at 156 mph (249.6 kmh) on August 29, 1954. October 17, 1954, Wester flew the aircraft to a helicopter altitude record of 24,500 ft (7,472.5 m). The aircraft is preserved at the Museum of Army Aviation, Fort Rucker, Alabama.
The S-52-2 YH-18A, s/n 49-2891 c/n 52008, was also converted to an S-59, military designation YH-39. It was registered as N7741 with the new c/n 59002, but reportedly never flew in turbine configuration and eventually was converted back to an YH-18A. Pictured is the civil S-59, previously flown as the civil S-52-2 and S-52-3 versions."
Rotor diameter: 35 ft 0 in (10.67 m)
Rotor disk: 961.6 sq.ft (89.37 sq.m)
Length (rotors operating): 41 ft 7 in (12.68 m)
Length, fuselage: 30 ft 3 in (9.22 m)
Height (over rotor head): 9 ft 8 in (2.95 m)
Weight empty: 2,200 lb (1,000 kg)
Loaded weight: 3,560 lb (1,616 kg)
Max speed: 146 mph (234 kmh)
Cruise speed: 138 mph (221 kmh)
Climb: 800 ft (223 m)/min
Service ceiling: 16,000 ft (4,880 m)
Range: 250 mls (400 km)