Sikorsky S-55 & Westland Whirlwind

United States of America

Mid size utility helicopter

Like many Sikorsky helicopters, the S-55 started out as a military helicopter for the US armed forces that was later adapted for commercial service. Sikorsky developed the S-55 in response to a US military requirement for a large general purpose helicopter. The US Defense Department awarded Sikorsky a contract to develop such a helicopter in 1948, and the first prototype flew for the first time on November 10 1949. The S-55 saw widespread US military service as H-19 in the Air Force, as H-19 Chickasaw in the Army, as HO4S in the Navy and Coast Guard, and as HRS in the Marine Corps. Civil certification for the commercial S-55 series was first awarded on March 25 1952. The initial civil variant was the S-55, powered by a 450kW (600hp) Pratt & Whitney Wasp radial piston engine. Later civil variants include the S-55A which introduced a 520kW (700hp) Wright R-1300 radial piston engine, while the S-55C had a P&W R-1340 engine and the repositioned tail boom of the S-55A. Westland in the UK licence built 400 S-55s as the WS-55 Whirlwind for mainly military but also commercial use. Early Whirlwinds were similar to the S-55 save for their Alvis Leonides radial engine, later developments were powered by a 785kW (1050shp) Rolls-Royce Bristol Gnome H.1000 turboshaft. S-55 licence manufacture was also undertaken in Japan by Mitsubishi and in France by Sud-Est. In January 1971 Aviation Specialties was awarded a type certificate for its turbine powered conversion of the S-55, dubbed the S-55T. Aviation Specialties formed the Helitec Corp to market and convert aircraft, and approximately 40 were fitted with a Garrett AiResearch TSE331 turboshaft. The conversion reduced the S-55's empty weight by approximately 410kg (900lb). In 1993 VAT (Vertical Aviation Technologies Inc) started the development of a super quiet conversion of the S-55, the S-55QT Whisper Jet. Full certification was awarded in December 1999. The 3-bladed main rotor of the standard S-55 was replaced by a 5-bladed one, and the powerplant is an Allied Signal TSE 331-10 turbine engine. It is certified at a MTOW of 3492kg (7700lb). As the S-55QT was specially developed for sightseeing, an additional left side cabin door, center floor window, and larger cabin windows were fitted, and sightseeing-optimized systems and equipment were added. The first customer for the Whisper Jet was Papillon Grand Canyon Helicopters.

S-55C - One 520kW (700hp) Pratt & Whitney R-1340-3 nine cylinder radial piston engine driving a three blade main rotor and two blade tail rotor. S-55T - One 625kW (840shp) Garrett AiResearch TSE331-3U-303 turboshaft derated to 485kW (650shp).

S-55C - Max speed 163km/h (88kt), cruising speed 137km/h (74kt). Initial rate of climb 700ft/min. Hovering ceiling in ground effect 2000ft. Service ceiling 10,500ft. Range 645km (350nm). S-55T - Max speed 183km/h (99kt), cruising speed 157km/h (85kt). Initial rate of climb 1200ft/min. Hovering ceiling out of ground effect 6700ft. Range with reserves 595km (320nm).

S-55C - Empty 2245kg (4950lb), max takeoff 3265kg (7200lb). S-55T - Empty equipped 2132kg (4700lb), max takeoff 3265kg (7200lb).

Main rotor diameter 16.16m (53ft 0in), fuselage length 12.87m (42ft 3in), height 4.06m (13ft 4in).

Flightcrew of two. Typical seating in main cabin for eight to 12 passengers. Many aircraft configured in executive configurations or to carry freight. Can also carry an external sling load.

Total Sikorsky S-55 production of 1281 aircraft, most for military service with US forces, 44 built under licence in Japan and 400 as Westland Whirlwinds. Approximately 40 S-55T conversions.

Sikorsky S-55 & Westland Whirlwind