Short Sturgeon - Design and Development

Design and Development

The development process leading to the S.38 Sturgeon began with the 1943 S.6/43 requirement for a high-performance torpedo bomber with a bomb bay that could accommodate six 500 lb bombs or any of the current standard aerial torpedoes, operating from Audacious and Centaur-class aircraft carriers. A maximum all-up-weight of 24,000 lbs was specified. Short Brothers were not invited to respond to S.6/43, but the preliminary responses from the other participating manufacturers indicated that a twin-engined design meeting all requirements was likely to weigh in excess of 24,000 lbs, while a single-engined design was unlikely to exceed the performance of in-service aircraft.

S.6/43 was allowed to proceed, and there are indications that Shorts submitted two uninvited tenders, a single-engined Bristol Centaurus design and a twin Merlin design. However, none of the original S.6/43 submissions was adopted and no reference to the Shorts submissions has been located in the official documentation. Focus instead shifted to splitting the requirements, with the torpedo bomber requirement becoming O.5/43, eventually leading to the Fairey Spearfish, while S.11/43 was written for a reconnaissance aircraft able to operate as a bomber.

Specification S.11/43 called for the design and construction of a twin-engine naval reconnaissance aircraft for visual and photographic reconnaissance and shadowing, by day or night, and also able to operate as a bomber. The specification included a maximum all-up weight of 24,000 lb, height (stowed) of 17 ft, length of 45 ft and a wingspan of 60 ft (spread) / 20 ft (folded). Powered wing-folding was also required.

Shorts submitted the twin Merlin S.38 Sturgeon as their tender to S.11/43, while Armstrong Whitworth proposed the twin Merlin powered AW.54. After the AW.54 was criticized for lack of power, the AW.54A with two MetroVick F.3 turbojets was submitted. Submissions were also made by Blackburn and Fairey (also with twin Merlin designs) and by Westland with a mixed-power design comprising a Pratt and Whitney R.4360 radial in the nose and a Halford H.1 turbojet in the tail. On 19 October 1943, Shorts received the "Instruction to Proceed" and an order for three prototypes designated Sturgeon S.1, with military serials RK787, RK791 and RK794 assigned. The final tailored S.11/43 requirements followed in February 1944.

The pilot's cockpit was a sub-assembly bolted to the front of the spar, placing him level with the leading edge if the wing, the navigator was behind the centre section of the wing and the radio operator — separated from the navigator by his equipment — behind him. The navigator and radio operator entered through a door, which acted as a ladder when opened, in the starboard side with their seats being offset to port. The cameras were installed in the fuselage behind the radio operator. One of the Sturgeon's unfortunate failings was in placement of controls. The fire extinguisher switch was located next to the cockpit switches required for firing the engine starter cartridges, resulting in some inadvertent mishaps and some unintended hilarity for ground crews.

Armament would be two .5 inch Browning machine guns in the nose with a 1,000 lb bomb or two 500 lb bombs or 4 250 lb depth charges carried in the bomb bay and 16 underwing 60lb Rocket Projectiles carried under the wings. ASV radar was fitted and two F.52 cameras and a single F.24 camera were carried for the reconnaissance role. Normal fuel load was 410 Gallons, but for reconnaissance missions a 180 Gallon long-range fuel tank could be carried in the bomb bay.

The first Short Sturgeon I RK787 flew at Rochester Airport on 7 June 1946, proving to have excellent handling and appearing at Farnborough in July. By this time, Shorts had adopted the S.B.A.C universal designation system and the S.38 was re-designated the S.A.1. Deck landing trials were successfully completed in 1947. The contract was re-assigned fom Short Brothers to Short Brothers & Harland and the incomplete aircraft were moved to Belfast where the second prototype, RK791, flew from Sydenham, Belfast on 18 May 1948. RK791 competed in the Air League Challenge Cup Race of 1949 with an average speed of 295 mph.

With the end of the Second World War and the suspension of the Audacious and Centaur class carriers the Royal Navy no longer had the platforms from which the Sturgeon was intended to operate and the requirement for the Sturgeon S.1 was cancelled. The production order for 30 aircraft was reduced to 23 and changed to a variant reworked under Q.1/46 to accommodate a largely shore-based target tug role as the S.39 (later re-indexed as the S.A.2) Sturgeon TT.2. The third prototype, RK794, was completed to TT.2 standard with a new serial, VR363.

The TT.2 was a large, but clean-looking twin-engined, mid-wing cantilever monoplane design with a distinctively elongated glazed nose in its target tug configuration. The all-metal monocoque fuselage was built in four sections ending at a cantilever tailplane with single fin and rudder. Rudder and tailplanes were fabric covered. The wing design featured a swept leading edge and taper on outboard sections, and wing folds outboard of the twin Rolls-Royce Merlin 140 engines driving contra-rotating propellers (which allowed shorter blades and the Merlins to be mounted closer to the centreline). The main wheels retracted rearwards into the engine nacelles while the tail wheel retracted forwards into the fuselage. Radiators were mounted in the leading edge between the nacelles and the fuselage.

The Sturgeon's post-war role began as a naval liaison and target tug aircraft with modifications to the nose, lengthened to provide a manned camera position forward of the propeller arcs, and a winch system. The crew of two included the pilot and the all-purpose "observer" who had to perform the functions of navigator, wireless operator, target operator and camera operator, for which the fuselage was deepened to allow the observer to crawl beneath the pilot's position, moving between stations in the nose and rear fuselage. In 1953, with the abandonment of throw-off target practice, the requirement for the camera nose disappeared and five TT.2s were converted into the S.B.9 Sturgeon TT.3 variant with a nose profile similar to that of the S.1.

The penultimate and last Sturgeons were rebuilt in 1949 as prototypes for the S.B.3, a proposed anti-submarine aircraft to M.6/49, powered by two Armstrong Siddeley Mamba AS Ma3 turboprops of 1,147 hp (1,100 kW) driving two four-bladed propellers. The engine exhausts were directed downwards instead of to the rear. Another major modification was the grafting on of a gigantic bulbous nose that housed two radar operators in stations forward of the engines and the radar itself, below. Acute problems arising from the modifications led to the demise of the project, namely, "the efflux from the Mamba turboprops seriously destabilized the aircraft at some power settings and destroyed the good handling characteristics. It proved impossible to trim for safe flight on one engine which was a necessity for long endurance on anti-submarine patrols."

Two S.B.3 prototypes were ordered with the first, WF632 flying on 8 December 1950 at Belfast. The design proved extremely difficult to trim when flying on one engine and so unstable that no effort was made to resolve these problems; consequently, the project was cancelled before the second prototype, WF636 flew. Both aircraft had very short lives, being scrapped in 1951.