Profile – Bristol Britannia

Early in 1948 BOAC was in a dilemma regarding the course that they should take. They wanted the aircraft to enter airline service in 1954 but were reluctant to place an order prior to the prototype’s first flight. If they waited until the maiden flight which was some years away there was no way that the Type 175 would be entering BOAC service during 1954. Rather than delay matters any longer while BOAC balanced their options, the British Ministry of Supply on 5 July 1948 ordered three prototypes. It was intended that all three aircraft would have Centaurus engines but that aircraft two and three would be suitable for modification to the Proteus powerplant and that aircraft number three was to be in airline configuration for the BOAC fleet. Later that year BOAC decided that they wanted a larger aircraft powered by either the Centaurus or Proteus with a 140 ft span and an up weight of 118,000 lb with the former and 119,000 lb with the latter engine, up to 64 passengers to be carried. On 28 July 1949 BOAC signed a contract for 25 aircraft designed to utilise the Proteus but which would be powered by the Centaurus initially.

Development continued and by 1950 bench running of the Proteus was coming along so well, that BOAC dispensed with their requirement for the aircraft to be powered by the Centaurus and requested that their 25 aircraft use the Proteus. Bristol had also suggested the suitability of the aircraft for the Atlantic route. To accomplish this, the Type 175 was further increased in size to a gross weight of 130,000 lb and with a fuel capacity of 5790 imperial gallons. The resultant increase in the payload to 23,500 lb lifted the accommodation to 83 passengers. Technically, the only significant alteration was the substitution of a four-wheel bogie undercarriage for the existing two-wheel arrangement. Experience with the Brabazon aircraft project some years earlier, had provided Bristol with a vast reservoir of knowledge from which to draw on to construct such a large aircraft and much of this was incorporated in the Type 175.

Static testing of a full-scale wing with part of the fuselage attached during 1951 proved most satisfactory and led to an increase in gross weight to 140,000 lb, fuel capacity to 6750 gallons and passenger load to 90. A generous fuselage diameter of 12 feet extended for 50 feet of the fuselage length. Consultation with BOAC led to their agreement to this increase in weight for their aircraft and the second prototype was modified accordingly. An interesting type of flying control was used which comprised surfaces actuated by servo-tabs which under aerodynamic forces moved the control surface properly. Similarly, the throttle connection was different in that they were linked electrically to the engine control valves instead of the usual lever or cable set-up. On the less technical side, agreement was reached between the Ministry of Supply and BOAC which led to the selection of the name Britannia for the Type 175 project.

At 5. 12 p. m. on 16 August 1952, the first prototype, G-ALBO, flown by Chief Test Pilot Bill Pegg took to the air for the first time. As the Proteus 705 was not yet ready, the 2800 ehp Proteus 625 was installed. Soon after becoming airborne, it became evident that the elevator control was very much on the light side. The aircraft was alternately climbing or diving but eventually control was regained and a climb was made to a safe altitude. Because of the elevator problems, Pegg was anxious about the landing. After selecting the undercarriage, two greens came on for both the nose wheel and port main wheel but nothing for the starboard assembly. To add to the colour of the occasion, a smell of burning commenced and blue smoke began to issue from under the cockpit floor. As the Britannia came over the airfield boundary at an altitude of 50 feet, the third green light came on and a safe landing was made. It was later established that the smoke came from an overheating electric motor under the cockpit floor. Soon after landing the aircraft was jacked up and the undercarriage performed flawlessly. This led the crew to suspect that perhaps the trouble was a faulty indicator light and that no malfunction of the landing gear had occurred.

The aircraft was taken through some fast taxi runs the following day to duplicate those performed just before the flight of the previous day. After these runs the aircraft was immediately jacked up and put through a continuous series of operations of the undercarriage mechanism. After twenty minutes of this procedure, the starboard undercarriage again jammed in the retracted position. This elapsed time coincided exactly with the duration of the flight that had passed prior to the undercarriage problems encountered on the first flight. With this knowledge, the trouble was quickly traced to overheating wheel brakes which had transmitted their heat to the central bearing on which the bogie revolved. The time for the heat transfer to take place was 20 minutes. To solve this, the undercarriage bogie bearings were opened up to allow for expansion. The elevator control sensitivity was reduced by removing some of the aerodynamic balance and so the first teething troubles were corrected before the next flight. The Britannia made its public debut soon after at the 1952 Farnborough Air Show.

Thus commenced four years of development work on the Britannia which were intended to cover a minimum of 2000 hours of trials. The second prototype, G-ALRX, made its first flight on 23 December 1953 and joined G-ALBO in the test programme. However, this period of testing was to be somewhat disrupted by the loss of G-ALRX not long after. On 4 February 1954, G-ALRX took off on a routine flight with 12 on board including a crew of three. Amongst the passengers were the Chief Designer, the Sales Manager and an airline pilot. After reaching cruise at 10,000 feet the oil temperature of the No. 3 engine began to rise and the engine was shut down. After an analysis of the situation, the decision was made to restart the engine and after a few minutes the oil temperature began to rise again. Just as the order to shut it down again was about to be given by Test Pilot Bill Pegg, a loud bang was heard and a severe shock was felt throughout the Britannia. As the engine was shut down and the propeller feathered, the Chief Designer made a speedy entry onto the flight deck to announce that flames extended from the No. 3 engine to the tailplane. All fuel was shut off from the two starboard engines and G-ALRX continued flying on the two port engines.

Despite the activation of the fire extinguisher system, the 3 engine fire continued unabated and the aircraft was approximately 50 miles from the airfield at Filton. Even a dive to a lower altitude failed to reduce the flames. After the fire had been burning for 15 minutes and large pieces of molten metal had been coming away, the aircraft was still several miles from Filton.

The decision was then made to attempt an emergency landing on the mud flats of the River Severn. However, as the Britannia was flying above the flats at a speed of about 200 knots the fire prevention system did what it was designed to do, but what was not wanted, it shut down the two port engines. The engineer hurriedly isolated the circuit and restarted the engines in time for the aircraft to line up on its designated piece of mud flat. The engines were then cut and the Britannia hit the mud flat and came to a halt after travelling about 400 yards. No one was injured in this wonderful piece of airmanship. The ooze effectively quenched the flames from the No. 3 engine although smoke continued to billow forth. A subsequent examination revealed that a pinion in the high-speed train of gears in the main reduction gear to the propeller had failed, causing the propeller to release from the turbine allowing it to overspeed and break through the engine casing. The flames burst through the hole, setting the oil tank on fire. Although the fire extinguisher put out the main engine fire it was unable to cope with the oil tank fire.

Although this incident caused the loss of the second prototype, it spoke volumes for the structural integrity of the airframe and the men of the test team who successfully accomplished a most difficult emergency landing. Following the loss of G-ALRX the first prototype, G-ALBO, was modified to a gross weight limit of 140,000 lb although the original fuel capacity was retained. During March 1954 it flew in its new configuration, but not long after a flap torque tube failed causing the aircraft to half roll and although the pilot, Walter Gibb, promptly retrieved the situation, the aircraft suffered an overload of 3 g. Because of this, G-ALBO was immediately withdrawn for wing repairs. To sustain the flight test schedule, the first production Britannia G-ANBA was diverted to development flying following its maiden flight on 5 September 1954. Additionally, it had been decided to use the next three aircraft, G-ANBB/D to carry out a 2000-hour C of A and route proving schedule in which BOAC crews would assist Bristol’s people. G-ANBB first flew on 18 January 1955 and G-ANBC on 29 June. Extensive tropical trials were carried out by G-ANBA at Khartoum and Johannesburg in which landing and takeoff weights of 123,000 lb and 155,000 lb were reached. These three aircraft later joined the BOAC fleet and G-ANBD which had also been earmarked for the test programme did not participate and went straight to BOAC.

Another problem to beset the Britannia was first encountered in March 1956 when icing conditions caused an engine flame-out while an aircraft was on a flight over Uganda. To assist the investigation, G-ALBO flew with a rig mounted in front of the inner starboard nacelle. This rig was used to spray water into the nacelle during the test programme. The cause was identified and modifications were implemented which solved the problem. Hot air jets were used to remove ice from the air intake area and platinum glow plugs were placed in four of the eight combustion chambers to allow an automatic relight to take place.

Because of all the delays, the inaugural passenger flight of the Britannia did not take place until 1 February 1957 when BOAC introduced it onto the Johannesburg service. By the end of the year it had replaced Constellations and Argonauts on routes to the Far East and Australia. The inaugural Sydney-London service took place on 5 March 1957 and reduced the time of the Lockheed 749As they replaced from 75 hours to 50 hours elapsed time (43 hours flying time). The route flown was Sydney – Darwin – Djakarta – Singapore – Calcutta – Karachi – Istanbul – Zurich – London. The aircraft was widely referred to as the ‘Whispering Giant’ and indeed it was, as it only recorded a figure of 81 decibels on takeoff.

Several distinct versions of the Britannia were produced or proposed. The initial one was the Series 100 and the others were the all cargo Series 200 which was not produced, Series 250 long fuselage version for passenger/cargo use, Series 300 which was a passenger-only version of the Series 200 with medium-range fuel capacity, and the Series 310 with long-range fuel capacity, strengthened landing gear and thicker fuselage skin with an all up weight of 175,000 lb. Production of the Britannia was carried out at Bristol’s Filton factory and at a second production line at Short Brothers and Harland, Belfast. Each of the above series numbers refers to a basic design designation and as orders were received a specific number was allocated to a particular operator. For example, the Series 312 was in response to the BOAC order and the Series 313 was for El Al.

Some further details of the different series follow.

Series 100. This was the original version with 114 ft fuselage. Two type 101 prototypes were constructed and a BOAC production order for type 102 aircraft was reduced to 10.

Series 200. An all-cargo version with 124′ 3″ fuselage but did not proceed.

Series 250. This was a basic series designation for a longer-range passenger version of the Series 200. The Series 252 featured a strengthened floor and cargo doors and were delivered to RAF Transport Command. Was later designated as the Britannia C Mk 2. The Series 253 also for the RAF could carry up to 115 troops or other combinations and was known as the Britannia C Mk 1.

Series 300. Passenger version of the Series 200 with medium-range fuel tanks. The Series 301 was the prototype built by Bristol and two Series 302 and five Series 305 were built by Shorts at Belfast and others within this series were destined for both civil and military operators.

Series 310. Basic designation for the civil version with long-range fuel tanks of 8580 gallons capacity, the extra fuel was carried in the outer wing. Powered by 4120 ehp Proteus 755 and had strengthened undercarriage. Several were sold to various operators. Initially called the 310LR (Long Range).

The Series 310 Britannia was an extremely fine aircraft and was at the time of its introduction into service, the largest propeller airliner in the world. Several operators were to make valuable use of them before the introduction of the big jets. In addition to the 18 aircraft of this version to go to BOAC, El Al and Canadian Pacific were also notable operators. El Al received three Series 313 aircraft in late 1957 and one the following year. The long range capabilities were inscribed into the record books on some notable flights. On 19 December 1957, a proving flight was flown non-stop from New York to Tel Aviv and the 6100 miles were covered at an average speed of 401 mph. This was a distance record for a civil aircraft. The following month their second aircraft, 4X-AGB, covered the 3444 miles between New York and London at a brisk block speed of 445 mph. Canadian Pacific purchased eight aircraft, the first four were a batch of Series 314 aircraft built in Belfast, taken into their fleet during April-June 1958. In their hands the stalwart long-distance qualities of the Britannia were demonstrated on the trans polar routes between Amsterdam and Vancouver. Services began on 1 June 1958 and ten return flights a month were flown, the average time for a return journey was 30 hours. When Canadian Pacific introduced the Britannia on the Vancouver-Tokyo route on 24 August 1958 another record was captured not long after when the 4700 miles were covered on 20 September in 11 hours 44 minutes.

Britannias were also purchased by several other airlines, but BOAC was the largest operator of the type. Because of its delay into service, it never achieved the success it was worthy of. The long development period meant that its BOAC career was going to be unfortunately short. For example, their 18 Series 312 aircraft delivered to them in 1957 were to be used by them for a maximum of seven years. Retirement of the BOAC Britannias commenced in 1962 when the 14 Series 102 aircraft were withdrawn from services, to be followed by five Series 312 sold to British Eagle International Airways in 1963. When the Vickers VC10 joined the fleet the remaining Series 312 were retired during 1964. It seems a shame that so much hard work was rewarded with so short a career. However, the arrival of the bet age spared no propeller airliner on the long distance routes, not even the fine Britannia.

Apart from the numerous civilian operators, the Royal Air Force had a large fleet for its transport requirements. The Ministry of Supply placed an order in February 1955 for three Series 252 aircraft which were built by Short Brothers and Harland at Belfast. Initial plans to lease these aircraft to civil operators for military charter work did not come to fruition. The aircraft were subsequently transferred to RAF Transport Command with the designation Britannia C Mk 2. They featured a strengthened floor and large cargo door designed by Shorts. Although they first carried British civil registrations they later wore RAF serials. This version, originally known as the Series 253 by Bristol had more powerful Proteus 255 engines and fittings required by the RAF for military use. Construction was divided between Shorts With five aircraft being built at Belfast and Bristol who produced 15 at Filton. The first flight took place on 29 December 1958 and deliveries were completed on 2 December 1960 when Britannia serial XM509, which was in fact the last Britannia to be delivered to any operator, was handed over. So ended the British production of the Bristol Type 175.

However, the story of the Britannia does not stop there, as the Canadian aircraft industry took up the design and produced two interesting versions. The Royal Canadian Air Force was investigating during 1952 a replacement for its Avro Lancaster 1OMA aircraft used for maritime patrol work. The decision was made to modify the Britannia for this role and a contract was signed in March 1954 granting the right to Canadair Ltd to produce this version and also a transport aircraft for the RCAF. The maritime variant was the CL-28 Argus (designated the CP-107 by the RCAF) and although based on the Britannia had some major changes. It had wings, tail surfaces, landing gear and part of the flying control system almost identical to that of the Britannia. The big difference was in the fuselage and the engines. As most of its work was at comparatively low altitudes, the fuselage was unpressurised and an 18 ft weapons bay was situated fore and aft of the wing. To improve fuel economy and enhance its patrol duration, four Wright R-3370 TC981 EAl-1 engines of 3700 hp were installed. This gave the CL-28 a maximum endurance of 26½ hours and a maximum range of approximately 4420 nautical miles. Electronics appropriate to its mission were fitted and a weapons load of 8000 lb could be carried comprising a mix of torpedoes, mines, depth charges, bombs, photoflash bombs and practice bombs. Two versions of the Argus were produced, differing only in their electronics. The initial flight was on 28 March 1957 and a total of 33 aircraft of both types was produced. Maximum speed was 288 cruising speed 207 mph, initial rate of climb 900 ft/min, service ceiling 24,200 feet.

The other Canadian adaptation of the Britannia arose from an RCAF requirement for a transport aircraft. Canadair was approached in 1957 to produce a larger version of the CL-28 modified for transport duties. This emerged as the CL-44 and as was to be expected, differed in several respects from the Argus. The fuselage was pressurised and was 12′ 4″ longer and the aircraft reverted to turbine power. The design was based on the RAF Series 253 version and initial plans were to power it with the Bristol. Orion turboprop. Bristol installed an Orion on the Britannia prototype G-ALBO in the port outer position in August 1956. However, the British Treasury would only permit the development of one new turboprop engine and work on the Orion ceased in 1958 as· the new Rolls Royce Tyne was the more favoured project. Accordingly, the new Canadair CL-4 was also to have the Rolls Royce engine. Known in RCAF service as the CC-106 Yukon, important changes were made to improve cargo movement and two large doors were located on the P(?rt side front and rear. Canadair developed a swing tail version, the CL’:. 44O-4 for civil operators and this aircraft was similar to the CL-44-6 of the RCAF. This was somewhat a milestone as the swing tail CL-44 was the first aircraft of its type to be constructed. Two hydraulic actuators in the dorsal fin enabled the tail to be swung in 90 seconds. The tail was secured in the closed position by eight locks and an inflatable seal which encircled the point of joining ensured that the cabin pressure was not affected.

The prototype CL-44, an RCAF aircraft serial 15501 had its first flight on 15 November 1959 and the first swing tail version made its debut on 16 November 1960. The ultimate development of the CL-44, and for that matter of the entire Britannia line was the CL-44J. This example had a further 15′ 2″ fuselage tension (1O’ 1″ in front and 5′ 1″ behind the wing) which increased passenger accommodation to 189. Although the maximum weight remained at 210,000 lb, the landing weight increased to 175,000 lb which required some strengthening in the wing and undercarriage. As a result of the fuselage lengthening the swing tail did not operate on this version. Four aircraft were converted to this configuration. Another noteworthy con, the version was made to CL-44 No. 16 which had the fuselage greatly enlarged to transport bulky cargo. This aircraft, N447T, a CL-44-0 was converted in 1969 and named ‘Conroy Guppy Airlifter’ ‘. It was leased to Trans Meridian/TMAC the following year and named ‘Skymonster’. A total of 39 CL-44 aircraft was built with production terminating in 1965.

The sad aspect about the Britannia is that it was a fine aircraft denied the acceptance it was capable of attaining. During a tour of the USA by a Britannia in 1957 a taste of orders which could have come their way was observed by Bristol. Howard l Hughes indicated that he was interested in purchasing 30 Britannias for TWA, but only if 17 aircraft could be delivered within six months to enable the Britannia to enter US service in 1958. As the production rate was 28 aircraft per year and all of the 1958 production was committed, it was impossible to meet the conditions of the TWA proposal. American Airlines had also shown interest for 35 aircraft but only if a rapid rate of delivery was possible. Both US airlines were mindful of the soon-to-emerge jet era and unless a qui9k acquisition of Britannia was feasible, deliveries would be too late to be of use. So unfortunately Bristol missed out on some valuable orders.

The Britannia rewarded its owners with some high annual utilisation figures. BOAC achieved a level of 3800 hours per aircraft, while El Al in 1960 reached a figure of 4200 hours for each aircraft. It should also be pointed out that the Britannia had a connection with another transport aircraft. Bristol had proposed a high-wing aircraft, the Type 195 using a Britannia wing. Much information was exchanged between Bristol, Canadair and Shorts and the end result was the Short Belfast, the wing for which was designed and built by Bristol at Filton.

Bristol delivered 82 Britannia between 1952 and 1960 but by 1983 only 10 remained in service. The impressive aircraft which was once so predominant on many of the blue riband routes has been relegated to less glamorous roles. However, there is no doubt that the Britannia will always be fondly remembered by those associated with her and will occupy a noteworthy place in the developmental history of transport aircraft.

Specifications of some of the main versions follow