Thursday, 14 June 2012

Short Jet Sturgeon

The complicated development of the Short Sturgeon started with the S.6/43 requirement for a high-performance torpedo bomber and reconnaissance aircraft with a weight of no more than 24,000lb. Short Brothers were not invited to tender, but when the initial estimates from the firms that had been approached came in it became apparent that a twin-engined aircraft meeting all of the requirements was unlikely to weigh less than 26,000lbs, while a single-engined aircraft was unlikely to have better performance than those already in service. The S.6/43 requirement was allowed to continue, in case something useful might arise out of it, and there is some evidence to suggest Shorts submitted uninvited proposals for both single and twin-engined aircraft to meet S.6/43, which, like the proposals from other manufacturers, were not adopted.

Meanwhile the initial requirement was split in two with the torpedo bomber becoming O.5/43, and eventually the Fairey Spearfish, while the reconnaissance aircraft became S.11/43 for a reconnaissance aircraft with bomber capability to operate from the Ark Royal and Hermes class carriers that were building for service with the Royal Navy off Burma and Malaya and in the Pacific. Shorts submitted the twin Merlin S.38 Sturgeon as their tender, while Armstrong Whitworth proposed the twin Merlin powered AW.54 and, after the AW.54 was criticized for lack of power, the AW.54A with two MetroVick F.3 turbojets, submissions were also made by Blackburn and Fairey with twin Merlin designs and Westland with a mixed-power design with a Pratt and Whitney R.4360 radial in the nose and a Halford H.1 turbojet in the tail. On 19th October 1943 Shorts received an order for three Sturgeon S.1 prototypes, with the tailored requirements following in February 1944.

The Sturgeon S.1 flew for the first time on 7th June 1946, and proved to have excellent handling. As initially developed it was a neat and compact three-seater with navigator and radio-operator carried within the fuselage, powered by two 2080hp Merlin 140s driving contra-rotating propellers (in order to minimise the yaw from asymmetric power in the single engine out situation). Provision was made in the design for the later replacement of the Merlins with Griffons. Fuel tanks held 410 gallons of fuel. ASV radar was carried in the nose, while armament comprised 2 or 4 .50 Brownings in the lower nose, a single 1000lb bomb, or equivalent combinations of smaller bombs or depth charges, in the bomb bay, and up to 16 60lb/3 inch Rocket Projectiles under the wings. Two F.52 cameras and a single F.24 camera were carried for the reconnaisance role, which was intended to be flown with a crew of two and a 180 gallon long-range tank in the bomb bay.

A contemporary article on the Sturgeon S.1 can be found here.

Unfortunately by the time the Sturgeon flew the war was over and construction of the Ark Royal and Hermes class carriers had been suspended. It was theoretically possible to operate the Sturgeon from the Illustrious and Colossus class carriers, but at the cost of keeping the aircraft on deck at all times and of having to rework the arrester gear on the Illustrious class. The requirement for the Sturgeon S.1 was therefore abandoned. The Sturgeon did see successful service with the fleet, but as the largely shore-based Sturgeon TT.2 high speed target tug with a grossly elongated nose holding a camera position. Later in their career a handful were reworked as TT.3s with a nose much closer to the original design. Later still Shorts attempted to develop the Sturgeon into the SB.3 as a competitor for the Fairey Gannet, replacing the engines with Armstrong Siddeley Mamba turboprops and installing a grotesque nose housing both a large radar scanner and two sensor operator positions. Unfortunately the downward exhaust of the Mambas, which varied with thrust, destabilized the SB.3's handling throughout the envelope and it proceeded no further.

The Jet Sturgeon shown here is based on an illustration of a Shorts proposal reproduced in British Secret Projects 3, and probably originated with N.21/45, an urgent FAA requirement for a night fighter to replace the Fairey Firefly. It is likely the unidentified design is the Shorts S.41. N.21/45 was written around the modification of the De Havilland Sea Hornet for the night fighter role, however this was considered high risk as the Sea Hornet was designed as a single-seater with the most compact fuselage possible, meaning space would need to be found to shoe-horn a radar operator into the fuselage somewhere, while a radar scanner would need to be installed in the nose, which was almost completely masked by the Sea Hornet's engines. The Assistant Chief of the Naval Staff (Air) therefore directed that a night fighter variant of the Sturgeon should be investigated as an alternative design against failure of the Sea Hornet NF.21. It was recognised that the Sea Hornet would be the superior combat aircraft, with considerably better performance, but the Sturgeon conversion would be considerably lower risk. In the event the Sea Hornet NF.21 was successfully deployed with the fleet in 1949.

The Jet Sturgeon Nightfighter retained the wing of the Sturgeon S.1, but replaced the Merlins with two Rolls Royce AJ.40 turbojets (Axial Jet, 4000lb thrust - the well-known Avon started as the AJ.60). The fuselage was modified, raising the nose relative to the engine nacelles to maximise the arcs of the AI radar in the nose radome (the Sea Hornet NF.21 ultimately carried ASH radar in an elongated 'thimble' radome, but the considerably larger radome of the Sturgeon would potentially have been able to carry other AI sets with larger antennae), while the tailplane was moved half-way up the tail in order to clear it from the jet efflux. The crew was reduced to pilot and radar operator, the latter having a canopy of his own. The Brownings of the S.1 were replaced by 4 20mm Hispanos, while the space freed by the elimination of the radiators, bomb load, cameras and radio-operator was used to increase the fuel load to 910 gallons in 9 separate tanks.

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