The Saunders-Roe SR.45 Princess was the largest all-metal flying-boat
ever built. Only three were made, and none was ever sold.
The project was started by the Ministry of Supply immediately
after the Second World War, when it invited Saunders-Roe to bid for a
new long-range flying-boat for BOAC. Work began in 1946.
By 1951, BOAC decided it had no need for the aircraft, but
Saunders-Roe continued construction as a transport plane for the RAF.
By the next year, clearly, the RAF had expressed its lack of interest;
only one of the three prototypes was to be completed (indeed, it flew
that year) and work on the others was to be paused.
The huge aircraft had ten Bristol Proteus engines in six mounts,
driving ten propellers (the inner four being contra-rotating pairs).
The pressurised fuselage contained two passenger decks, with room for
105 passengers in extreme comfort. Predicted range was about 5,000
nautical miles at 313 knots, enough to cross the Atlantic in perhaps
ten hours and reach
most of the inhabited world in a single hop.
Princess Air Transport was formed as a subsidiary of Saunders-Roe to
look for a use for the things, but nothing came to light, and all
three aircraft were coccooned. Various plans were hatched, including
re-engining with jets, conversion to landplane troop carriers, driving
the propellers with an on-board nuclear reactor (that was the US Navy,
of course, in response to the USAF's NB-36H experiments), and even (in
1964) to use them as heavy freighters to transport Saturn V rocket
components. However, it seems that preservation had not been as
effective as hoped, and all three airframes were badly corroded and
unusable; they were all broken up by 1967.
In effect, the long-range flying-boat was dead, killed by improvements
to airfields. Flying-boats could never fly as efficiently as
land-based aircraft because of the aerodynamic compromises needed for
a boat hull, and were subject to seawater corrosion and the need for
calm water (though at this size it was probably more tolerant than
most of rough conditions).
The follow-up aircraft, the Duchess, which would have been slightly
smaller and powered by six de Havilland Ghost turbojets, never got off
the drawing-board.
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