Short Stirling

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Stirling

Short Stirling N6101 from No. 7 Squadron Pathfinder Force being "bombed up."
Type	heavy bomber
Manufacturer	Short Brothers, Rochester Short Bros and Harland, Belfast, Austin Motors Ltd
Designed by	C.T.P. Lipscomb
Maiden flight	14 May 1939
Retired	1945
Status	Retired
Primary users	RAF RCAF Egypt (postwar)
Produced	1939-1943
Number built	2,383

The Stirling was the first four-engined British heavy bomber of the Second World War. Built by Short Brothers, it was to have a relatively short operational career and was surpassed by other four-engine RAF bombers, specifically, the Handley-Page Halifax and Avro Lancaster, eventually taking over its role and relegating it to second-line duties.

1 Design and development
2 Operational history
3 Victoria Cross recipients
4 Operators and units
5 Specifications (Short Stirling I)
6 References
7 External links
8 Related content

[edit] Design and development

Throughout the 1930s, the Royal Air Force was interested primarily in twin-engine bombers. These designs put limited demands on engine production and maintenance, both of which were already stretched with the introduction of so many new types into service. However, the limitations in terms of power were so serious that they invested heavily in development of huge engines in the 2,000 horsepower (1,500 kW) class in order to improve performance. Meanwhile the US and USSR were developing bombers with four smaller engines, which proved to have excellent range and fair lifting capacity. So in 1936 the RAF decided to try their hand at the four engine bomber as well.

The Air Ministry wasn't entirely clear what it wanted in the new design with the resulting Specification B.12/36 an odd mix of requirements. In addition to a 14,000 lb (6,350 kg) bombload carried to a range of 3,000 miles (4,800 km) (incredibly demanding for the era), the aircraft should also be able to be used as a troop transport for 24 soldiers. The idea was that it would fly troops to far corners of the British Empire and then support them with bombing. To help with this task as well as ease production, it needed to be able to be broken down into parts for transport by train. Since it could be operating from limited "back country" airfields, it needed to lift off from a 500 ft (150 m) runway and able to clear 50 ft (15 m) trees at the end, a specification most small aircraft would have a problem with today. The wingspan was limited to 100 ft (30 m) so the aircraft would fit into existing hangars.^[1]^[2] The wingspan limit was also imposed in an unsuccessful attempt to ensure the Stirling's weight was kept down.^{[citation needed]}

The Shorts' submission was one of 11 designs returned in response to the requirements, but were likely to be the only company that could have realistically started production in a short time. They were already producing several four-engine flying boat designs of the needed size and created their S.29 design by removing the lower deck and boat hull of their S.25 Sunderland. Their new S.29 design was largely identical otherwise; the wings and controls were the same, construction was identical and it even retained the slight upward bend at the rear of the fuselage, originally intended to keep the Sunderland's tail clear of sea spray.

Shorts managed to persuade the RAF to dismiss most of its unrealistic design goals when they saw the S.29 would be an excellent bomber. On one point the RAF stood firm: the S.29 used the Sunderland's 114 ft (35 m) wing, and they demanded it be reduced to less than 100 ft (30 m), the same limit as imposed on the Handley Page Halifax and Avro Manchester. In order to get the needed lift from a shorter span and excess weight, the redesigned wing was thickened and reshaped.

The Short S.31 half-scale replica used for aerodynamic tests of the Stirling design

Shorts built a half scale version as the S.31 (also known internally as the M4, which was the designation on the tailfin), powered by four Pobjoy Niagara engines (left), which first flew on 19 September 1938, piloted by Shorts' Chief Test Pilot J. Lankester Parker. Everyone was happy with the design, except that the takeoff run was thought to be too long. Fixing this required the angle of the wing to be increased for takeoff, normally meaning the aircraft would be flying nose down while cruising (as in the Whitley). Instead, Shorts lengthened the undercarriage struts to tilt the nose up on take-off, leading to its spindly gear which in turn contributed to many takeoff and landing accidents. ^[3] The Short S.31 was scrapped after a takeoff accident at Stradishall in February 1944.

The first S.29, now the Stirling, flew on 14 May 1939 with four Bristol Hercules II radial engines. Upon landing one of the brakes locked, causing it to slew off the runway and collapse the landing gear. A redesign added much stronger and heavier struts on the second prototype. On its first mission, two months later, one of the engines failed on takeoff, but the plane landed easily. From then on, the record improved and service production started in August 1940 at Shorts' Rochester factory. The area, which included a number of major aviation firms, was heavily bombed in the opening days of the Battle of Britain, including one famous low-level raid by a group of Dornier Do 17s. A number of completed Stirlings were destroyed on the ground and the factories were heavily damaged, setting back production by almost a year.

Although it wasn't as large as the US and Soviet experimental designs, the Stirling had considerably more power and far better payload/range than anything then flying. The massive 14,000 lb (6,340 kg) bombload put it in a class of its own, double that of any other bomber. It was larger than the Handley-Page Halifax and comparable to the Avro Lancaster, which would replace it, but both of these were originally designed to have twin engines. The Stirling was the only British bomber to see service designed from the start with four engines. (The Avro Lancaster was a re-engined Avro Manchester while the Halifax was originally planned to be powered by twin Vulture engines but was re-designed to use four Merlins in 1937.^[4])

The design mounted nose and tail turrets (the latter was notable for the wide angles of fire), and included a retractable ventral ("dustbin") turret just behind the bomb-bay, fired by remote control. This proved almost useless due to the limited visibility through the sighting system, with the added distraction that the turret tended to drop and hit the ground when taxiing over bumps. It was removed almost from the start and replaced by a dorsal turret. However, this installation also had problems; it had a metal back fitted with an escape hatch which turned out to be almost impossible to use. The later Stirling Mk III instead used a fully glazed turret (the same FN.50 as in Lancaster) that had more room and an improved view.

Ground crew performing maintenance tasks

The first few Mk Is received the Hercules II engines, but the majority received the 1,500 hp (1,100 kW) Hercules XIs. The Mk III, introduced in 1943, was similar with the exception of the new dorsal turret and the improved 1,635 hp (1,200 kW) Hercules VI or XVI engines, which improved maximum speed from 255 to 270 mph (410 to 435 km/h).

Even before the Stirling went into production, Short had improved on the initial design with the S.34 in an effort to meet requirement B.1/39. It would have been powered by four Bristol Hercules 17 SM engines, optimised for high-altitude flight. The new design featured longer span wings and a revised fuselage able to carry dorsal and ventral power-operated turrets each fitted with four 20 mm Hispano cannon. However, despite the obvious gains in performance and capability, the Air Ministry was not interested.

In 1941, Short proposed an improved version of the Stirling, this time for the B.8/41 requirement, optimistically called "The Super Stirling" in the company's annals. This Stirling would feature a wing span of 135 ft 9 in (41.38 m), and a powerplant of four Bristol Centaurus radials and a maximum takeoff weight of 104,000 lb (47,174 kg). The performance estimates included 300 mph (483 km/h) speed and a 4,000 mile (6,437 km) range with a weapons load of 10,000 lb (4,536 kg). This design was also rejected by the Air Ministry.

[edit] Operational history

Operational status wasn't reached until January 1941 by No 7 Squadron RAF. The first three Stirlings flew a mission on February 10 1941 over fuel storage tanks in Rotterdam, and from spring of 1942 it started to be used in greater numbers. From May 1943, air raids on Germany started with over a hundred Stirlings at once.

Despite the "disappointing performance" at maximum altitude ^[5], Stirling pilots were delighted to discover that, due to the thick wing, they could out-turn the Ju 88 and Me 110 nightfighters they faced. Its handling was much better than that of the Halifax and some preferred it to the Lancaster. Based on its flight characteristics, Pilot Murray Peden of No. 214 RAF Squadron flatly described the Stirling as "one of the finest aircraft ever built." ^[6]

Another consequence of the thick wing however was a low ceiling and many missions were flown as low as 12,000 ft (4,000 m). This was a disadvantage on many raids, notably if they were attacking Italy and had to fly through (rather than "over") the Alps. When operated with other RAF bombers flying at higher altitudes, the Luftwaffe concentrated on the low-flying Stirlings. Within five months of being introduced, 67 out of the 84 aircraft delivered had been lost to enemy action or written off after crashes.

The Stirling's huge maximum bomb load was only able to be carried relatively short distances of around 590 miles. On typical missions deep into Germany or Italy a smaller 3,500 lb (1,590 kg) load was carried, consisting of seven 500 lb (227 kg) bombs. This was the sort of load being carried by the RAF's medium bombers such as the Vickers Wellington and, by 1944, by the de Havilland Mosquito. Perhaps the biggest problem with the design was that the bomb bay had two structural dividers running down the middle, limiting it to carrying nothing larger than the 2000 lb (907 kg) bomb. As the RAF started using the 4000 lb (1,815 kg) "cookies" and even larger "specials," the Stirling became less useful. The Handley-Page Halifax and especially the Avro Lancaster offered better performance (the Lancaster could carry twice the Stirlings bombload over long distances, and was at least 40 mph faster while having an operating altitude of about 4000 ft higher ,^[7]), so when they became available in greater numbers from 1943, it was decided to withdraw Stirlings to secondary tasks.

By December 1943, Stirlings were being withdrawn from frontline service as a bomber, increasingly being used for deploying mines outside German ports, electronic countermeasures and dropping spies deep behind enemy lines at night (through the now unused ventral turret ring). Also at that time, there became a need for powerful aircraft to tow the heavy transport gliders such as the GAL Hamilcar and Airspeed Horsa and the Stirling fitted this role admirably. In late 1943, 143 MK III bombers were rebuilt to the new Mk IV series specification (without nose and dorsal turrets), for towing gliders and dropping paratroops, as well as 461 new Mk IVs being produced. They were used in the Battle of Normandy and Operation Market Garden. From late 1944, 160 of the special transport variant Mk V were built, which had the tail turret removed and a new opening nose added, most of these being completed after the war.

In service with Bomber Command Stirlings flew 14,500 operations, dropping 27,000 tons of bombs, losing 582 in action with 119 written off.

[edit] Victoria Cross recipients

Two awards of the Victoria Cross, both posthumous, were made to Stirling pilots.

Flight Sergeant Rawdon Hume Middleton of the Royal Australian Air Force the pilot-in-command of a No. 149 Squadron RAF Stirling I was awarded his VC for valour during a raid on Turin in November 1942. Acting Flight Sergeant Arthur Louis Aaron, the captain of a No. 218 Squadron RAF Stirling was also awarded his VC for valour during a raid on Turin, in August 1943.

[edit] Operators and units

United Kingdom, Royal Air Force

[edit] Specifications (Short Stirling I)

Short Stirling of 26 Conversion Flight (CF) Squadron c.1941 operating out of RAF Waterbeach

General characteristics

Crew: 7
Length: 87 ft 3 in (26.6 m)
Wingspan: 99 ft 1 in (30.2 m)
Height: 28 ft 10 in (8.8 m)
Wing area: 1,322 ft² (122.8 m²)
Empty weight: 44,000 lb (19,950 kg)
Loaded weight: 59,400 lb (26,940 kg)
Max takeoff weight: 70,000 lb (31,750 kg)
Powerplant: 4× Bristol Hercules II radial engines, 1,375 hp (1,030 kW) each

Performance

Maximum speed: 255 mph (410 km/h) at 21,000 ft (6,400 m)
Range: 2,330 mi (3,750 km)
Service ceiling: 16,500 ft (5,030 m)
Rate of climb: 800 ft/min (4 m/s)
Wing loading: 44.9 lb/ft² (219.4 kg/m²)
Power/mass: 0.093 hp/lb (0.153 kW/kg)

Armament

8 x 0.303 in (7.7 mm) Browning machine guns: 2 in the nose, 4 in the tail, 2 dorsal
Up to 18,000 lb (8,164 kg) of bombs

[edit] References

^ Mondey 1994, p.189.
^ Winchester 2005, p.48.
^ Winchester 2005, p.49.
^ Mason 1994, p.329.
^ Bashow 2005, p.39.
^ Peden 1979, p.229.
^ Mason 1994, p.315-316.

Bashow, David L. No Prouder Place: Canadians and the Bomber Command Experience 1939-1945. St. Catharine's, Ontario: Vanwell Publishing Limited, 2005. ISBN 1-55125-098-5.
Mason, Francis K. The British Bomber since 1914. London: Putnam Aeronautical Books, 1994. ISBN 0-85177-861-5.
Mondey, David. British Aircraft of World War II. London: Chartwell Books Inc., 1994. ISBN 0-7858-0146-4.
Peden, Murray. A Thousand Shall Fall. Stittsville, Ontario: Canada's Wings Inc., 1979. ISBN 0-920002-07-2.
Winchester, Jim. The World's Worst Aircraft: From Pioneering Failures to Multimillion Dollar Disasters. London: Amber Books Ltd., 2005. ISBN 1-904687-34-2.