page_title: Saunders-Roe Princess
section_title: Design
hierarchical_section_title: Saunders-Roe Princess / Design
caption_attribution_description: English: Catalog #: 01_00087159 Manufacturer: Saunders-Roe Designation: SR.45 Official Nickname: Princess Notes: UK
context_page_description: 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 has the distinction of being 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 pre-war 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, it was decided early on to make use of newly developed turboprop technology, opting for the in-developed Bristol Proteus engine 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.
context_section_description: 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.
  The cockpit of the Princess was designed to be operated by a pair of pilots, two flight engineers, a navigator, and a radio operator. Early on, it had been intended for the aircraft to be outfitted with some form of powered flight controls, including an early fly-by-wire implementation, in order that pilots would be able to effectively actuate its large control surfaces, which would have to overcome equally larger forces. However, it was decided to opt for a traditional mechanical linkage approach that was augmented by a series of electrically-driven power assist units to effectively support actuation instead.
  The ailerons and rudder were split into multiple sections in order that, if a part of the servo-powered control system were to fail, a faulty section could be "trailed" so that it did not act against the remaining working sections. While the prototype aircraft had been fitted with advanced (but conventional) hydraulic controls, Saunders-Roe had intended production aircraft to use an analogue system based around electrical servos with hydraulic final control actuators. Such a system had been built and undergone ground-testing, but the Princess had been terminated prior to any aircraft having been fitted with the system.
caption: A Saunders-Roe SR.45 Princess during a taxiing run
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