Short Empire
The Short Empire was a four-engined monoplane transport flying boat, designed and developed by Short Brothers during the 1930s to meet the requirements of the British Empire, specifically to provide air service from the UK to South Africa, Singapore and Australia in stages. It was developed in parallel with the Short Sunderland maritime patrol bomber, which served in the Second World War along with the piggy-back Short Mayo Composite.
Imperial Airways, as the primary customer, developed the requirements to which it was ordered and designed. Imperial Airways, and its successor, the British Overseas Airways Corporation, along with Qantas and TEAL, operated the type in commercial service. The Empire routinely flew between the British mainland and Australia and the various British colonies in Africa and Asia, typically carrying a combination of passengers and mail. The Empires were also used between Bermuda and New York City.
The Empire saw commercial and military service during the Second World War, for anti-submarine patrols and as a transport. The Royal Air Force, Royal Australian Air Force, and Royal New Zealand Air Force used the type.
Development
Origins
During the 1930s, demand for air travel was rapidly growing. The British national flag airline Imperial Airways sought to fully expand air service across the British Empire. Imperial Airways' technical adviser, planned a specification for a new type of aircraft to serve passenger and freight requirements throughout the world. This required an aircraft to carry 24 passengers in comfort, as well as airmail or freight while having a cruising speed of, a normal range of at least and the capability for an extended range of to cross the North Atlantic. At the time, and for various reasons, including technical and operational, it was determined that a flying boat would be required.Short Brothers had previously developed successful large flying boats for Imperial Airways and the Royal Air Force, and was the frontrunner to fulfil the requirement. Shorts was reluctant to build straight from the drawing board without a prototype, however this was rejected by Imperial Airways, which was desperate to replace obsolete types then in service that were unable to provide the full service needed. In 1935, Imperial Airways announced an order for 28 flying boats of an as-of-yet undesigned type, weighing 18 tonnes each. The order was claimed by the British press as being "one of the world's boldest experiments in aviation".
A design team led by Arthur Gouge created the Empire. To have adequate clearance between the propellers and the water, the wing needed to be as high as feasible and was initially to be attached to a hump above the fuselage as on the Martin M-130, but the fuselage height was instead increased, providing more internal volume than required but enabling a lighter and stronger integration of the cantilever wing to the fuselage.
Following water tank experiments, a simplified-vee planing bottom with a much higher length to beam ratio than was common at the time was chosen. The aerodynamic and hydrodynamic properties were tested on the smaller Short Scion Senior floatplane, which served as a half-scale prototype for the Empire and its sibling, the military's Short Sunderland.
Shorts developed its own machinery to produce the necessary T-shaped Hiduminium alloy lengths that comprised the main spar. A specialised and patented flap, known as Gouge flaps after its creator, caused only a small increase in drag, while the wing's lift coefficient was increased by 30 percent, the landing speed reduced by 12 per cent, and no trim changes were needed.
Initial production
On 4 July 1936, the first Empire built, registered G-ADHL, named Canopus, made its first flight with Shorts' chief test pilot, John Lankester Parker at the controls. Early flights were relatively trouble-free, and Parker was satisfied with its performance and handling. On 17 September 1936, G-ADHL first flew for Imperial Airways, with the final proving flight to Marseille, France took place on 22 October 1936. The first series of the Short Empires, the S.23, could carry five crew, 17 passengers, and of cargo at a maximum speed of and was powered by four Bristol Pegasus Xc radial engines.The second Empire and the first of the long-range models, registered G-ADHM, named Caledonia, made its first flight on 15 September 1936 and was delivered to Imperial Airways on 4 December 1936. From September 1936 onwards, one aircraft was produced per month and typically each aircraft's delivery occurring right after its first flight. The Empire was officially known as the C-class by Imperial Airways and each aircraft operated by them was given a name beginning with the letter C.
On 26 February 1938, the final three Empires of the initial order placed by Imperial Airways – Coorong, Coogee and Corio were diverted from Imperial Airways and delivered to the Anglo-Australian Qantas Empire Airways. In late 1937, Imperial Airways placed a follow-on order for another 11 Empires. When combined with the original order of 28, this had the distinction of being the largest order by a single customer placed for a British civil aircraft at that time. While the first three aircraft of the additional order were of the typical S.23 class, intended for Qantas Empire Airways, the rest had a number of detail changes and were designated the S.30. Short's Rochester factory produced all 43 Empires built.
Further development
The S.30 series was fitted with four Bristol Perseus XIIc sleeve valve engines in the place of the Pegasus engines. the Perseus engines were each lighter and 17.3% more fuel efficient, but developed less power. The airframe was strengthened, mainly by using heavier gauge sheeting on the fuselage and wings. The maximum takeoff weight increased to with a corresponding range of, the S.30 had a similar performance to the preceding S.23s.The first of the S.30 flying boats was registered G-AFCT and named Champion. In December 1938, the second S.30 aircraft registered G-AFCU, named Cabot became the first of the revised series to fly. The last three aircraft of this order, initially named Captain Cook, Clare and Aotearoa, were renamed and re-registered for use by TEAL. In 1939, a final S.30 flying boat, registered G-AFKZ and named Cathay, was delivered to Imperial Airways in late March 1940.
Four flying S.30 series flying boats, Cabot, Caribou, Clyde and Connemara, were equipped with in-flight refuelling equipment and extra fuel tanks to provide scheduled transatlantic airmail service. The aircraft was to take off light and, once airborne, take on extra fuel to reach an all up weight of, giving the aircraft a range of over. The extra fuel reduced payload to against the of the standard aeroplane. The refuelling was performed by three converted Handley Page Harrow bombers, one operating out of Ireland and two out of Newfoundland.
In 1939, Imperial Airways placed a further follow-on order for a modified S.30, designated the S.33. This series had the same construction as its predecessors, but the new Pegasus XI engine, a development of the powerplant used by the original S.23 series, was used. Out of these three final aircraft, only two, named Clifton and Cleopatra, would be completed and delivered to the newly renamed British Overseas Airways Corporation.
The S.26, designated as the G-class by BOAC, was a substantially larger development of the Empire flying boat, and an entirely new aircraft, albeit of similar configuration. It was roughly 15 percent larger, as well as using the much more powerful Bristol Hercules radial engine and a further improved hull design. It was intended to be used on the north Atlantic route. The three that were built were immediately impressed into military service during the Second World War.
Design
The Short Empire flying boat was a clean high-wing monoplane, initially powered by four wing-mounted Bristol Pegasus Xc radial engines which drove de Havilland-built variable-pitch propellers. The engines were each enclosed within NACA cowls and mounted ahead of the leading edge of the wings. This allowed portions of the leading edge adjacent to the engines to be hinged forward to be used as platforms to maintain the engines.The Pegasus Xc engines each produced on takeoff, decreasing to at an altitude of. Alternative engines were installed with both greater and reduced power outputs. Initial aircraft had a gross weight, however, by 1939, many aircraft had been strengthened, for an increased gross weight of. Its useful load included of fuel, of oil, assorted equipment, along with the payload and five crew. The S.23 series achieved a top speed of at an altitude of along with a cruising speed of and a minimum flying speed of.
The wings had a flush-riveted Alclad covering with Frise-type ailerons and the internally-developed Gouge flaps, the latter of which were actuated by an electric motor connected via a gearing system and screw jacks, allowing the flaps to be lowered in 60 seconds and raised in 90 seconds. Large cylindrical 325-gallon fuel tanks were in the wings, between the inner and outer engines. On long-range variants of the aircraft, additional fuel tanks were added in the wings, up to three containing 280 gallons, 325 gallons, and 175 gallons in each wing. Sections of the wing leading edge alongside the nacelles folded down to be engine servicing platforms. Tip floats were carried on struts attached to the main spar and featured shock absorbers to reduce impact forces being transmitted to the wings.
The hull used the same steps as earlier designs, but had a much finer beam to length ratio, and employed Shorts' traditional construction methods. The structure used a combination of Z-shaped stringers and I-shaped girders to form triangular sections that ran along the chines where the fuselage sides meet the planing bottom. To simplify manufacturing and to maximize usable internal volume, only a simple single curvature on the hull was employed that didn't require the use of a press for most of the airframe. On previous Shorts' flying boats, a more complex S-shaped curvature and a sudden reduction in beam just above the chines had been employed instead.
File:StateLibQld 1 190231 Seaplane S.23, Coriolanus, moored at Pinkenba on the Brisbane River, 1939.jpg|thumb|left|S.23 Empire G-AETV, named Coriolanus, moored at Pinkenba on the Brisbane River, 1939
The deep hull accommodated two decks, the upper deck forming a lengthy compartment divided into sections to accommodate of freight and mail along with a storage space and a ship's clerk's office. This office contained controls such as electrical fuseboxes and circuit switches, ventilation controls, and fuelcocks. The lower deck contained a large marine compartment containing an anchor, a pair of drogues, a mooring bollard and a boat hook, along with a ladder to the cockpit. The forward passenger saloon was aft of the mooring compartment and was followed by a central corridor flanked by the toilets and galley, a mid-ship cabin, a spacious promenade cabin, and finally an aft-cabin, each stepped to a different height. The cabins could be fitted with seating or sleeper bunks. Near the rear of the aircraft, an additional freight and mail compartment extended into the rear fuselage.
The flying crew was seated in a spacious bridge with the captain and co-pilot seated side-by-side while the radio operator sat behind the captain, facing the rear. The flight deck was well equipped and included an autopilot while flying instrumentation included a Hughes turn indicator, compass, and variometer, a Sperry artificial horizon and heading indicator, a Kollsman sensitive altimeter, a Marconi radio direction finder, a Smiths chronometer, and an attitude indicator. The radio operator had Marconi shock-proof radio sets for transmitting and receiving while the retractable direction-finding loop antenna could be rotated for visual or aural homing.
While designed as civil aircraft, examples of the type would not only see military service but were specifically refitted for this purpose. In 1941, two Empire flying boats – Clio and Cordelia were modified at Shorts' Belfast facility with gun turrets in dorsal and tail positions, bomb racks extending out of slots cut in the fuselage sides as on the Sunderland, and air to surface vessel radar equipment installed on the top and sides of the fuselage. They were used by Coastal Command. More extensive military use was made of the Empire's military counterpart, the Short Sunderland.