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S.R. 45 Princess Flying-boat

To the United Kingdom, seeking by every means to increase her trade abroad, the swift onset of the air age presented a special challenge. Emerging from the war with tremendous military air strength - but little civilian - her airlines were striving to make up for lost time. B.O.A.C - British Overseas Airways Corporation was Britain's long-distance airline, organized to keep more than fifty planes moving above the globe every minute of the day and night.

The Brabazon committee’s recommendations provided the Industry with funding for a civil aircraft program to assist the adjustment from war to peace. Firms were also retained through the award of development contracts, some of which were duplicate projects to provide ‘insurance’ against project failures. However the program was costly and had few commercial successes. Project recommendations included a long-range piston-engined trans-Atlantic airliner (Bristol Brabazon); a short-range piston-engined airliner (Airspeed Ambassador); a short-range turbo-prop airliner (Vickers Viscount); a jet-powered mail carrier (to become the de Havilland Comet); and the Princess flying boat was added to the program in 1946.

Three prototypes of the giant Saunders-Roe (SARO) SR.45 Princess flying-boat were ordered in May 1946, intended for non-stop transatlantic service by BOAC. By 1949 it appeared that the Saunders Roe Princess flying-boat was unlikely to be in service before 1953. However, after successfully flight-testing the Princess aircraft, the customer decided to become a land plane only airline, with this magnificent aircraft subsequently scrapped. If they were used as civil aviation flying boats, they could take 120 passengers across the Atlantic and back in 24 hours and they could do for the sky above the Atlantic what the Queen Mary and the Queen Elizabeth have been doing for some years for the sea itself. It had been stated that if they were used for military purposes they could transport as many troops in one year as nine troopships and could save a great many manhours in doing so.

Larger than the Martin Mars and heavier than the Bristol Brabazon I, the Princess spanned 66.90m with its wingtip floats retracted, weighed 156,500 kg on take-off, and could attain a maximum speed of 580km/h. The normal operating crew would consist of two Pilots, two Flight Engineers, a Navigator, and a Radio Operator. During the trials an additional seat was provided for a supernumerary crew member, generally a Flight Engineer. The field of vision was excellent under all conditions of taxying or flight. Lateral view was sufficient to enable both floats to be seen by bending slightly forward. The clear vision panels were satisfactory to operate, but when they were opened the noise level increased unpleasantly and made intercommunication difficult. The draft with the panel open was also unpleasant.

The flaps on each side of the aircraft were divided into three separate units, inner, intermediate and outer. The floats retracted upwards and outwards to form the wing tips. Retraction and lowering was effected by separate hydraulic systems on each wing extremity. Each float could also be lowered by an emergency air system.

The first prototype flew for the first time on 22 August 1952. The Princess planes stood up very well indeed to every possible test in their operational trials. A total flying time of 96 hours 50 minutes was completed by the aircraft in 48 flights; a detailed engineering appraisal is not therefore possible. However, considerable experience on launching and beaching, as well as servicing and maintenance, was accumulated whilst, in addition, an appreciable amount of data on the functioning of the various installations was obtained. The only weakness shown in their operational trials was that the engine was not sufficiently strong for the plane, but that could easily be remedied if the planes were fitted with Proteus III engines, which were being monopolized by the Britannia planes.

The Princess was designed for the Proteus Mark III engines. The Bristol Company initially fitted Proteus Mark III engines to the Britannia. The Princess required coupled Proteus III engines, and since this is a special requirement not demanded by the Britannia, development work on the coupling was not undertaken.

Ten Proteus 2 (Series 600 and 610) free running propeller turbine engines were installed in six nacelles. A single engine was used in each out board nacelle driving a four bladed reversible pitch propeller. Each center and inboard nacelle housed a coupled unit of two engines driving eight-bladed contra-rotating propellers. The engines used were either prototype or sub-standard units, therefore the main endeavor during the trials was to maintain them in a serviceable condition, rather than to attempt any quantitative testing. Initially, compressor stalling in flight was a frequent source of trouble. This was found to be due to salt deposits on the compressor blades, and was overcome by regular after-flight compressor and turbine washing with a mixture of fresh water and kerosene. Fuel was carried in four integral tanks in the inner wing structure. The inner tanks supplied the inboard power plants, while the two outboard supplied the remainder.

Slotted type flaps in six sections were fitted, which extended over the inner sections of the wing. Although instrumentation was provided to measure structural loads and stresses during take-off, flight and landing conditions, it was not possible to make more than a very brief investigation into these problems. The measurements obtained from strain gauges on the main spar frames however showed reasonable agreement with theoretical estimates. On five occasions during take-off or landing at high all-up weight and in a moderately choppy sea there was slight hull pounding. Attempts were made to measure the pounding frequency and to relate this to acceleration records from various points in the hull and wings. Although recorders were operated during a number of take-offs the attempts all proved abortive, due either to there being no pounding or to the records being too confused for analysis.

Only three flights were made with the hull pressurizing system operating, and these were mainly devoted to performance measurements at 30,000 feet, the highest altitude attained. A maximum differential pressure of 4.25 psi was used as ground testing had not been completed for the full differential of 8 psi.

During flight in turbulent air conditions, such as occur in or below low cumulus clouds, the aircraft tended, from time to time, to develop lateral shudder for short periods. This appeared to be the result of airframe flexure and "was apparent as a low frequency, large amplitude, damped lateral oscillation, noticeable throughout the hull, but being less pronounced amidships, greater at the bow and largest at the stern. The phenomenon, which was normally encountered only during short periods of a flight, i.e. when entering the base of low cloud, was regarded mainly as a source of passenger discomfort and not as a probable structural stressing problem.

During final erection and assembly as well as during the period of flight trials, in all nearly three years, the aircraft was constantly exposed to a salt laden atmosphere. A complete inspection of the airframe and hull was made after flying had been concluded. This showed that the aircraft was in an extremely satisfactory condition with the exception of a few minor points.

In the Annual Report and Statement of Accounts of B.O.A.C. for the year ended 31 March 1950, it is said: ‘The Corporation continued to render all possible assistance in connection with the Government's SR45 project and to that end has recently installed a full-time resident representative at the manufacturer's works. The most suitable and most economic method of operating these aircraft in conjunction with the other aircraft of the Corporation's fleet is constantly under investigation in the light of engine development programme and traffic trends.’ That was as late as 27 July 1950.

On 23 July, 1950, when a delegation of Members of Parliament went down to the flying-boat base at Hythe, the Chairman of B.O.A.C. said: "B.O.A.C. is flying-boat-minded. I believe that Britain has a definite lead in flying-boat manufacture and operation. We want to see the passenger attraction of this type of aircraft upheld." On 13 October 1950, B.O.A.C. gave a handout to the Press. It was headed: "Formation of B.O.A.C. 'Princess' Unit. Preparing the way for Britain's great new flying-boat.’ ‘A B.O.A.C. 'Princess' unit is being formed to prepare for the introduction into the service by the Corporation of the 105-seater 'Princess' flying-boat, at present being built at the Saunders-Roe Works at Cowes, Isle of Wight."

The mayor of Southampton received a letter from the B.O.A.C. Chairman dated 20 December 1950, in which he said: "No one regrets the necessity to interrupt our flying-boat activities more than I do. I have always had a devotion to flying-boats, but as new types of land-planes came along, and the economics became more difficult, we have been forced, by the pressure of events, to abandon, at least temporarily, the operations we have so pleasantly conducted from Southampton for so long..."

The Labour Government, in very difficult circumstances, and against quite a lot of pressure from more than one direction, maintained the development of the Saunders Roe Princess flying boat. The attitude of the B.O.A.C. was that they were quite prepared to put the Princess into operation, but quite rightly successive chairmen of B.O.A.C. said to the Minister for the time being, in effect "Here we are, at your direction and under constant pressure from you, working for the day which has now arrived - when we shall show a profit, and we could not operate on routes with the Princess flying boat in a normal commercial manner." But they were prepared, and stated that they were prepared, to enter into negotiations for some abnormal arrangement which would enable them to put the Princess into service.

On 07 March 1951, the Parliamentary Secretary said, in reply to a Question by the Member for St. Albans (Mr. J. Grimston): "Owing to the rapid progress which has been made in the development of the Comet it is now thought likely that the Comet will be better adapted for the needs of civil aviation than the larger flying boats, and accordingly it has been decided that British Overseas Airways Corporation shall not introduce these boats into service." It was decided that the three Princess flying boats should be completed for the Royal Air Force.

As the work proceeded, it became evident that great economy would be achieved by waiting for the production of the more powerful Proteus III engines which are not yet available. It was, therefore, decided to postpone the work of completing the second and third Princesses. The second and third Princess prototypes did not fly, and were cocooned. The work of completing these, and fitting all three aircraft with suitable engines, would be likely to cost several million pounds more. About £9,127,000, including storage costs, had been spent on the aircraft.

The Minister of Supply said 17 March 1952: "In the meantime, the first Princess flying boat, which is now nearing completion, will be fitted with Proteus II engines, so that experimental test flights can proceed." The main point was that there was a limited amount of money available for spending on all forms of defense and to use the Princess in a transport role would need very expensive provision in the way of staging posts, terminal buildings, marine craft and so on. The provision of all these things was likely to make the Princess uneconomical for this purpose in peace.

In the late 1950s there was some discussion of equipping the Princess flying-boats with atomic power, thus starting a competely new venture in aviation, but nothing came of this talk. The purchaser took delivery and paid the agreed price in December, 1963. The flying boats were sold after open tender to the highest bidder, who was hoping to arrange for them to be used for an aeronautical purpose.