Back Bristol Type 173

Bristol 173 Mk.1

The Belvedere general purpose transport helicopter, which entered service with the RAF in the autumn of 1961, had behind it a 14-year development period during which, at different times, it had been considered as a commercial passenger carrier, and a naval antisubmarine helicopter. It originated as the Bristol Type 173, two Mk.1 prototypes of which were begun in 1948 to Ministry of Supply Specification E.4/47. The first of these machines, G-ALBN, made its maiden flight on 3 January 1952, after some eight months of ground trials and tethered flights. It was Britain's first tandem-rotor helicopter design, and in this early form was powered by two 575hp Alvis Leonides 73 piston engines and utilised two 3-blade main rotors, with their control systems, of the type fitted to the single-engined Bristol Type 171 Sycamore. In 1953 this machine was handed over to the Admiralty for Naval trials. On 31 August 1953 a prototype 173 Mk.2 (G-AMJI) was flown, differing from the first machine in having two pairs of stub wings to off-load the rotors, the rear pair carrying upright fins at their extremities. These features were later removed, G-AMJI reverting to the Vee-tailed configuration of the Mk.1 and joining its stablemate for Naval trials as XH379. It subsequently returned to the civil register for a spell in BEA colours before being written off in a landing accident in 1956.

Meanwhile three more prototypes had been ordered, with 850hp Leonides Majors and metal instead of wooden rotor blades. In the event, only one of these (XE286) was flown, the other two being utilised for ground testing. In 1956 the Royal Navy decided to adopt the Bristol machine for the antisubmarine role, placing an order for sixty-eight aircraft. The production version, to be known as the Bristol 191, was to have folding rotor blades and a shorter fuselage, to enable it to use existing carrier deck-lifts, and the rear legs of the quadricycle undercarriage shortened to facilitate loading of an external torpedo. At about the same time the RAF ordered twenty-six of the standard model as the Bristol 192.

K.Munson "Helicopters And Other Rotorcraft Since 1907", 1968



Ten-passenger tandem rotor transport helicopter with oval-section straight fuselage with tail pylon and Type 171 nose and cockpit section. Fitted with fixed four-leg u/c and large V-tailplane. Powered by two 550hp Alvis Leonides - one at each end of fuselage driving three-blade rotors. Prot. G-ALBN FF 3 Jan. 1952.

173 Mk.2


Developed Type 173 with modified u/c, front and rear stub wings with large endplate fins on rear. Prot. G-AMJI.

173 Mk.3


Type 173 with 850hp Alvis Leonides Major engines and four-blade rotors. Prot. XE286.

Bristol 173 Mk.2

The 173 was the first British two-engined helicopter to be developed. Its development and life span are spread over 19 years and though like many heavy helicopters it was a largely military machine, it was also intended as the first helicopter airliner for BEA service.

The 173 appeared on the drawing board in 1948 and ground tests started three years later. It was interesting not only because of its two three-blade counter-rotating rotors, but also because it could fly on one Alvis Leonides 73 engine and the centre of gravity could be displaced. The two rotors were synchronized by a shaft in conjunction with a gearbox. In the event of a breakdown the shaft could transmit power from the working engine. The rear rotor was carried on a pylon which was part of the vertical fin structure. Two tailplanes were set at a sharp angle to improve longitudinal and lateral stability.

Ground resonance was cured by linking the right and left oleo struts of the undercarriage with small-bore hydraulic piping. As G-ALBN the first 173 flew on August 24, 1952.

A Mk.2 followed with stub wings and an improved undercarriage. The Mk.3 however, with more powerful engines, (two Alvis Leonides Majors rated at 850shp each) as well as four-bladed rotors, marked an even greater advance. Seating too, was up from 14 in the Mk.1 and 2 to 16 in the Mk.3. Unfortunately however, the Mk.3 suffered from cooling problems and its service trials in 1956 were not entirely successful.

In July 1958 the Bristol 192 made its maiden flight and this marked the successful climax to the development of the 173.

Bill Gunston "The Illustrated Encyclopedia of Commercial Aircraft", 1980

Bristol 173 Mk.3

This, the first British two-engined twin-rotor helicopter, first went on to the drawing-board in 1948 and started its ground tests in May 1951. Besides the two three-bladed contra-rotating rotors set in tandem, this rotorcraft had two interesting features: firstly, its centre of gravity could be appreciably displaced; secondly, it could continue to fly on one engine only. The 173 had virtually the 171's transmission system, rotor assemblies and engine installation, except that one engine rotates in the opposite direction to the other.

The two rotors could be synchronized by a shaft in conjunction with a gearbox. This shaft was also used in the event of breakdown in one engine to transmit power to the affected rotor from the engine still working. The rear rotor was carried on a pylon forming part of the fixed vertical fin structure. On each side there was also a tail-plane structure set at a marked dihedral angle to increase both longitudinal and lateral stability.

Ground resonance originally caused some trouble. The problem was overcome by linking the right- and left-hand oleo-struts of the undercarriage by small-bore hydraulic piping. The latter formed the two arcs of a circle seen above the upper part of the legs.

P.Lambermont "Helicopters and Autogyros of the World", 1958

Bristol 173 Mk.1

Technical data for Type 173 Mk.1

Number of seats: 14, engines: 2 x Alvis Leonides 73 rated each 550hp, rotor diameter: 14.81m, overall length: 23.83m, weight fully loaded: 4808kg, empty weight: 3537kg, cruising speed: 137km/h, inclined climb: 360m/min, absolute ceiling: 5975m, range: 450km

The drive for the twin rotors of the Bristol 173

Nigel Mathewson, e-mail, 27.07.2016reply

That is strange, I to have a photograph of this same incident my father took, I must must have been about six.

Robin Harman, e-mail, 18.01.2013reply

I seem to recall this helicopter was used by the RAF from RAF Chivenor to drop hay and other feed to animals trapped on Exmoor during the 1963 Winter blizzards

Wendy Hill, e-mail, 02.02.2011reply

I was at an Air Show at Filton in the late 50's. I can't remember the exact details but do remember a single rotor helecopter colliding in mid air with a twin rotor helecopter. There was a lot of black smoke and debris around. I beleive it was the last air show at Filton for many years. Can anyone help me with any information.

Neville Gio-Batta, e-mail, 19.03.2011reply

I saw the crash of the Bristol helicopter at an air display at Filton. The crash happened directly in front of where I was standing, maybe 150 yards away, or less. As I recall it crashed with the nose down after hovering / manouvering at low level.

Jennifer Finlayson, e-mail, 09.07.2011reply

Did the 173 or any of its variants ever fly on BEA routes?

John H Stevens, e-mail, 25.11.2011reply

At the moment I am working on the Bristol 173 at the Bristol Aero Collection at Kemble, Gloucestershire. I am stripping all the old paint off as it is so dirty and coroded. It will eventuall be repainted to look like new, hopefu;lly. 25 /11 /2011

John Daniell, e-mail, 04.03.2010reply

jon.jayne(@), 17.01.2010

I was an engineer at Bristol employed on this development at the time and I can assure you it was 100% British. It was in effect a 'twin engined twin rotor Sycamore', the Sycamore being the Type 171 helicopter. Chief designer was Raoul Hafner.

jon, e-mail, 17.01.2010reply

can any one tell me if this was a british invention or was it an american idea first, it would settle a long standing argument.

Nigel Lines, e-mail, 06.10.2009reply

Whilst working in a drawing office many years ago. An older ex RAF winchman (a perfect gentleman) called Ken Teece worked in the same office. Every so often we used to ask him to get the old photo out. It was an twin rotor helicopter that appeared to explode after "a hard landing at an airshow" he said he was nearest to the door and 15 paratroopers got out before him. Only one injury was a broken leg and the appharent explosion was just dust and debris. I would love to see that photo again and your description seems about right for the time.

Clive Moore, e-mail, 29.03.2009reply

I have a photograph of a crash at filton involving a twin rotor helicopter and have been trying to identify it.

http: / / /photos /mao_zhou /3394105019 /?addedcomment=1#comment72157615979275577

This is it.

Geoff Roberts, e-mail, 14.01.2009reply

Did one of these crash at the Filton Air Show in 1958, piloted by 'Socks' Hosegood? I have a photograph of the impact and want to identify it. Thanks

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