It was designed by Raoul Hafner for a variety of transport roles including troop transport, supply dropping and casualty evacuation. It was operated by the Royal Air Force (RAF) from 1961 to 1969. The Belvedere was Britain's only tandem rotor helicopter to enter production, and one of the few not built by Boeing or Piasecki. The Belvedere was based on the Bristol Type 173 10-seat (later 16-seat) civilian helicopter which first flew on 3 January 1952. The 173 project was cancelled in 1956 and Bristol spent time on the Type 191 and Type 193 to Royal Navy and Royal Canadian Navy specifications. These two naval variants were cancelled, but the RAF expressed an interest in the aircraft and the Type 192 "Belvedere" was created. Three Type 191 airframes were almost complete when the order was cancelled, but they were used to aid the development of the Type 192. The first two were used as test rigs for the new Napier Gazelle engines and the third was used for fatigue tests. The Type 192 shared some of its design features with the cancelled naval variants, which made it less than ideal for transporting troops. The front undercarriage was unusually tall, originally designed to give adequate clearance for loading torpedoes underneath the fuselage in the anti-submarine warfare role. This left the main passenger and cargo door 4 feet (1.2 m) above the ground. The engines were placed at either end of the cabin. (By comparison the purpose-designed troop transport contemporary Boeing Vertol CH-46 Sea Knight had its engines above the aft cabin to permit a rear loading ramp). To provide access to the cabin from the cockpit there was a small entry past the engine that resulted in a bulge on the left side of the fuselage. The first Type 192 prototype XG447 flew on 5 July 1958 with tandem wooden rotor blades, a completely manual control system and a castored, fixed quadricycle undercarriage. From the fifth prototype, the rotors fitted were all-metal, four-bladed units. Production model controls and instruments allowed night operations. The prototype machines had an upwards-hinged main passenger and cockpit door, which was prone to being slammed shut by the downwash from the rotors. This was replaced by a sliding door on the later aircraft. Twenty-six Belvederes were built, entering service as the Belvedere HC Mark 1. The Belvederes were originally designed for use with the Royal Navy but were later adapted to carry 18 fully equipped troops with a total load capacity of 6,000 lb (2,700 kg). The two rotors were synchronised through a shaft to prevent blade collision, allowing the aircraft to operate through only one engine in the event of an emergency. In that case, the remaining engine would automatically run up to double power to compensate. For more information on operational history and variants, click here.
