Saunders-Roe Princess

The Saunders-Roe SR.45 Princess was a British flying boat aircraft developed and built by Saunders-Roe at their Cowes facility on the Isle of Wight. It is the largest all-metal flying boat to have ever been constructed.

The Princess had been developed to serve as a larger and more luxurious successor to the prewar commercial flying boats, such as the Short Empire. It was intended to serve the transatlantic route, carrying up to 100 passengers between Southampton, United Kingdom and New York City, United States, in spacious and comfortable conditions. To achieve this, designers decided early on to make use of newly developed turboprop technology, opting for the Bristol Proteus engine still in development to power the aircraft. The project suffered delays due to difficulties encountered in the development of the Proteus engine.

On 22 August 1952, the first prototype Princess, G-ALUN, conducted its maiden flight. Between 1952 and 1954, the first prototype performed a total of 47 test flights, including two public appearances at the Farnborough Airshow. This work was carried out under a development contract for the Ministry of Supply, the intention being that this would lead to a contract for the aircraft from British flag carrier British Overseas Airways Corporation (BOAC). Although the initial development contract had been successfully met, BOAC eventually decided to focus on its land-based routes using the jet-powered De Havilland Comet, instead. The era of the large flying boat had effectively ended prior to the aircraft's completion.

Work on the Princess was ultimately cancelled after having produced three examples, only one of which flew. By the mid-1950s, large commercial flying boats were being increasingly overshadowed by land-based jet airliners. Factors such as runway and airport improvements had added to the viability of land-based aircraft, which did not have to compromise to accommodate the additional weight and drag of the boat hulls that were necessary on seaplanes, or the mitigating measures needed against the corrosion caused by seawater. Following the project's termination, the three airframes were stored with the intention of selling them on, but upon receipt of a promising offer for the aircraft, corrosion was found to have set in while in storage. As a result, all three aircraft prototypes were subsequently scrapped.

Development

Origins

Before the Second World War, British airline Imperial Airways had successfully used large, long-range passenger flying boats such as the Short Empire and Short S.26 to build up a network of long-distance routes. While restricted operations of commercial flying boats did continue, such as the use of Boeing 314s for the transatlantic route, many were requisitioned for service with the Royal Air Force (RAF), where they were typically used as maritime patrol aircraft.

During the prewar era, flying boats had been preferred for conducting long-distance flights, as unlike their land-based counterparts, they were not limited by available runway length – the majority of which were still grass-surfaced at this point – and as a long-range aeroplane would be required to carry a large load of fuel, a larger size of the aircraft could be permitted without needing to cater for factors such as limited runway and airfield sizes. In addition, for services to far-flung parts of the British Empire, the ability to land and takenoff from any available area of water was a distinct advantage for services to such places, many of which at the time had no airport facilities at all. With the end of the Second World War, flying boats services were resumed, with other types being operated, such as the Short Hythe, Short Sandringham, and Short Solent. However, the war had also produced a legacy of large runways and sizable airports formerly used for military purposes that could now meet the needs of a larger generation of land aircraft.

Even prior to the war's end, the British Air Ministry was enthusiastic on the prospects for reviving the shuttered flying-boat routes. The ministry approached two British flying boat manufacturers – Saunders-Roe (Saro) and Short – requesting that the two firms collaborate on the development and manufacture of a new aircraft, which would emerge as the Short Shetland. As such, Saunders-Roe designed the Shetland and manufactured the wing, while Short produced the remainder of the aircraft. While two examples of the Shetland were completed, the project was considered a failure and the two flying boats were scrapped in 1951. This design specification defined various criteria for the proposed aircraft, which would be the largest all-metal flying boat ever built; performance criteria included a weight of 140 tons, a pressurised "double-bubble" hull, a 214-foot wingspan, a height of 55 feet 9 inches, and a length of 148 feet. The proposed aircraft would be capable of a cruising speed of 340 mph at an altitude of 37,000 feet, a range (dependent on payload) of 5,190–3,640 miles, and be outfitted with luxurious accommodation for a total of 104 passengers. As announced in March 1952, though, while the first prototype would be completed, the second and third would be suspended to await more powerful engines. The initial flight lasted for 35 minutes, in which the flying boat performed a complete circumnavigation of the Isle of Wight. According to aviation author Phillip Kaplan, the Princess had not been intended to fly that day at all, and only taxiing tests had been scheduled to take place, but Tyson had decided to proceed due to the excellent conditions present on the day. In 1954, Aquila Airways had offered £1 million each for the stored Princesses, but this offer was rejected. In 1957, Saro itself had proposed the conversion of the aircraft to serve as landplane troop carriers/freighters.

In 1958, information on the Princess was shared with the United States Navy, which was at the time examining the possibility of converting the three stored aircraft to make use of nuclear power. This interest resulted in a delegation from Saro being dispatched to the US to discuss a sale of the preserved Princesses, but this interest ultimately amounted to nothing.

In the wake of the success of his Pregnant Guppy, constructor Jack Conroy discussed his concepts for other outsize transports with Air Progress in their publication, World's Greatest Aircraft (Petersen Publications, 1973). Conroy considered the creation of an outsize transport from the Princess to have been basically feasible, in that it shares a sectional double-bubble fuselage construction similar to that of the Boeing 377 Stratocruiser, on which the Guppies were based. The reason for considering producing such an aircraft was the desire of NASA to possess a means of transporting the first stage of the Saturn V rocket by air, if this were possible, to Cape Canaveral; the ability for the aircraft to conduct a water landing would also be advantageous for proximity landing at sea, or on nearby lakes in Florida. Ultimately, this plan was deemed to be impractical, though the existing Guppies continued to function throughout the Apollo program as efficient air transport of the outsize hardware used in these missions. Conroy quipped that the British were "offended when we named our aircraft 'The Pregnant Guppy'. Man, can you imagine what they would have said if we produced 'The Pregnant Princess' !"

They were the last fixed-wing commercial aircraft produced by Saunders-Roe. The company constructed one more fixed-wing design, the Saunders-Roe SR.53 mixed-power (rocket and turbojet) fighter design; aside from that venture, the company primarily concentrated its efforts on helicopters and hovercraft after this point.

Design

thumb|A Saunders-Roe SR.45 Princess during a taxiing run

The SR.45 Princess was a large flying boat, being the largest all-metal flying boat to have ever been constructed. The Princess featured a rounded, bulbous, "double-bubble" pressurized fuselage, which contained two full passenger decks; these decks had sufficient room to accommodate up to 105 passengers in great comfort. The planing bottom of the hull had only a slight step in the keel to minimize drag in the air. The Princess was powered by an arrangement of ten Bristol Proteus turboprop engines. These engines drove six sets of four-bladed propellers; of these, the inner four propellers were double, contra-rotating propellers, which were driven by a twin version of the Proteus, named the Bristol Coupled Proteus; each engine drove one of the propellers. The two outer propellers were single and each powered by a single engine. British Flying Boats and Flight 1952

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General characteristics

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Powerplant

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Performance

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Armament

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References

Citations

Bibliography

Kaplan, Philip. "Big Wings: The Largest Aeroplanes Ever Built." Pen and Sword, 2005. .
"Ten Turboprops Power Giant Flying Boat." Popular Science, August 1949.
"A winged ship takes form." Flight, 7 December 1951, p. 724.

External links

Sea Wings Gallery of Images
Video on Youtube
"Britain's Biggest Flying Boat," Popular Mechanics, September 1948

Development

Origins

Design

See also

References

Citations

Bibliography

External links