Bristol Types 173, 191 and 192 Belvedere

Two crew, 13 passenger tandem rotor civil transport helicopter to Specification E.4/47 to meet the requirements of OR.251. The fuselage was a metal monocoque structure in four parts: a front section containing the flight deck for the two crew was mainly Perspex panelled, and had access doors either side. Aft of this was the front engine bay, followed by the main cabin with one row of five seats either side of the cabin plus a tree seat bench aft opposite the main port-side access door. The main cabin featured six large windowsper side, and provision was made for baggage or a small toilet to the rear. Finally, behind the main cabin was the aft engine bay. The aircraft had two three bladed main rotors, identical to that of the Sycamore, the forward mounted above the forward fuelage roof, the aft on a pylon above the rear fuelage, the two rotors being 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.The undercarriage was a fixed quadracycle type. Initially a highly upswept tailplane was fitted, but by 1957 this was replaced by a low set flat type with end plates, and the rotor system replaced by a four bladed units. Two 550 h.p. Alvis Leonides 73 powerplants.

Initially as the Mk.1 with four bladed rotors, but featuring a revised landing gear, with castoring front wheels and fixed rear wheels, and small stub wings at the front and rear, with fins on the aft wing tips. For naval trials, the stub wings were replaced with the earlier upswept tailplane, later replaced by a low set flat type with end plates.

As Mk.2 with upswept tailplane, but featuring four-bladed rotors, a taller aft pylon and stronger airframe. The third machine, XE288, was intended for carrier trials at sea and featured a shortened fuselage and long-stroke landing gear. Two 850 h.p. Alvis Leonides Major powerplants.

Type 173 Mk.1 Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
47 ft 5 in	55 ft 2 in	89 ft 1 in	15 ft	7820 lb	10600 lb		115 mph/ 100 kn	185 mi
14.45 m	16.81 m	27.15 m	4.57 m	3547 kg	4808 kg		185 km/h	298 km

Three crew, tandem rotor anti-submarine helicopter to Specification HR.146 to meet the requirements of NSR/NA.43. A derivative of the Type 173 Mk.3, the front undercarriage was unusually tall, originally designed to give adequate clearance for loading torpedoes underneath the fuselage in the anti-submarine warfare role. Two 850 h.p. Alvis Leonides Major powerplants (prototypes) or 1,465 h.p. Napier Gazelles (production).

Three crew, tandem rotor general purpose helicopter to Specification HR.150 to meet the requirements of OR.325. A derivative of the Type 191, it was adapted to carry a payload of 6,000 lbs which translated into 30 seated passengers, 19 fully equipped troops or 12 stretchered casualties plus 3 seated personnel. An external freight hook permitted an under-slung load of 5,250 lbs.. Initially the aircraft featured wooden rotor blades, a completely manual control system and a castored, fixed quadricycle undercarriage, all derived from the Type 173. 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. Two 1,465 h.p. Napier Gazelles powerplants.

Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
48 ft 11 in	54 ft 4 in	89 ft 9 in	17 ft	11085 lb	19000 lb		138 mph/ 120 kn	460 mi	17300 ft
14.91 m	16.56 m	27.36 m	5.18 m	5028 kg	8618 kg		222 km/h	740 km	5273 m