The Short Stirling was the RAF's first four engined bomber of the second World War. It took a major part in the strategic offensive until 1943, then it was switched to transport duties, Stirling crews gallantly played a major role in the Arnhem landing after towing gliders to Normandy, and again during the Rhine crossing.
Until 1936, the Royal Air Force had operated either single or twin engine bombers; however, the activities of the Americans and Russians in building four engine bomber prototypes led the Air Staff to begin discussions aimed at producing a similar aircraft for the RAF. These discussions led to issuing a specification for the RAF's first four engine bomber under the title Specification B12/36. Short was one of the companies asked to submit proposals based on Specification B12/36. The Short's proposal emerged as a four engine, mid-wing bomber originally to be powered by four liquid cooled Rolls Royce Goshawk engines.
This cockpit is a full size replica with original Stirling instruments and custom made panels and fuselage.
The aircraft would have a crew of six; two pilots, an observer/navigator, wireless operator, and two gunners manning the nose and tail turret. Provision was also made for a remote control turret in the lower portion of the rear fuselage. Armor would be fitted along with sound proofing and even a toilet. By late 1936, the Air Staff ordered a fuselage mock-up of the design. In order to keep the takeoff and landing run within limits, Short's Chief Designer, Mr.Lipcombe, felt that the wing length should be enlarged from under 100 feet to around 112 feet. This request was rejected, with the Air Ministry stating that existing RAF hangars would not accomodate wing spans of more than 100 feet. This decision created a severe altitude and range limitation because of a decreased wing aspect ratio.
Below: Navigator operated receiver R1155 for D/F bearing and for homing, used in early Stirlings.
Short constructed a half-scale flying prototype during 1938, which was intended to reveal any aerodynamic problems. Powered by four 90 hp Pobjoy engines and constructed of plywood, the aircraft was officially designated the S31, but was better known as M4. The S31/M4 first flew on 19 September 1938 with Short's Chief Test Pilot John Lankester Parker at the controls. Within a few weeks the flight tests had been completed, while generally satisfied, RAF officials expressed concern over the prototype's takeoff and landing runs, which were felt to be excessive. The proposed solution was to almost double the wing angle. Short decided to drastically lenghten the undercarriage legs to achieve the required additional 3 degrees of wing incidence.
Two similar, self-contained systems were carried in the wings, one on each side of the fuselage. The systems could be interconnected if necessary by operating an inter-system balance cock in the centre section. Auxiliary tanks could be fitted in the wings bomb cells for long range duties. In each system the fuel was carried in seven tanks, all tanks except those in the leading edge had self sealing covering.
A total of 2692 gallons of fuel could be carried. Later aircraft had a nitrogen fire protection system fitted.
The single stage landing gear leg was discarded due to the increased length of the undercarriage rods which proved too long to be retracted into the engine nacelle wheel wells. A two stage undercarriage was built which retracted vertically and then back- wards into the nacelle. The undercarriage retraction motors were originally located inside the nacelle, but were later relocated inside the fuselage to allow for manual retraction in the event of motor failure...
The underarriage was a complicated structure, retracted or lowered in two operations by electric motors which were prone to breakdown. The undercarriage was a weak point of the Stirling, it sometimes collapsed under strong side loadings. The considerable height above ground, and the rake of the pilot's seat made it very difficult for the pilot to accurately judge touchdown attitude and precise ground position.
The picture on the right shows the weak point of the landing gear, it could cause the whole stalky structure to collapse under strong side-loadings.
The powerplants were also changed from the 90 hp Pobjoy engines to 115 hp Niagara IV engines. While testing resumed with the S31/M4, construction began on two full size prototypes now officially known as the Stirling MkI/P1. Shortly after construction of the prototypes began, the Air Ministry decided to order the Stirling into production with a contract of 100 Stirling MkI's. The prototype S29 was rolled out of the company's Rochester factory on 13 May 1939.
Glider Towing, Supply drops and Paratroops
The first Stirlings used for Glider towage were MkIV's, also a paratroopers hatch was made in the floor of the rear fuselage, a glider towing hook and a strop-guard to prevent static lines of parachutes to get entangled on the tail section were added. The Stirling transported gliders to Normandy, Arnhem and the Rhine. Paratroops, Containers and SOE agents were also dropped by the MkIV
The Stirling had 4 Bristol Hercules VI or XVI air cooled radial engines, each 1635 hp, they used a fully-feathering constant-speed propeller. The engines were started electrically but provision was made for hand turning. A seperate oil system was provided for each engine. Power supply for electrical system was provided by two 24 volt, 1000 or 1500 Watt generators, driven by the inner engines. These charged four 12 Volt, 40 Amp accumulators connected in series-parallel to give 24 Volts, 80 Amp to feed the electrical systems.
Given the RAF serial number L7600, the prototype made its maiden flight on 14 May. After a graceful takeoff and short test flight it suffered an undercarriage failure on landing and was damaged beyond repair. The failure was traced to the light alloy undercarriage back arch braces which were replaced on succeeding aircraft by stronger tubular steel units.
The second prototype (L7605) was fitted with the strengthened undercarriage and made its maiden flight on 3 December 1939 For this flight the gear was left down, but happily for both Short and the RAF, the revised undercarriage held up when put to the tests of retraction, lowering and landing During the spring of 1940, the prototype spent four months undergoing service tests at Boscombe Down.
Stirling Technical Details
Short Stirling Mk I
The early MkI had Hercules II engines but they were replaced later by the Hercules XI The first production Stirling rolled off the assembly line in August 1940
Short Stirling MkII
During 1940-41 plans were put into motion to have a number of Stirlings made by Canadian industry, initially the plan called for production of 140 aircraft which would be almost identical to the MkI. The aircraft would be powered by American 1600 hp Wright Cyclone R-2600-A5B radial engines, housed in redesigned cowlings. A total of four aircraft were converted in England to use the American engines and two aircraft (N3657 and N3711) were test flown at Rochester in the Autumn of 1941. These tests revealed the the American engines gave no increase in performance and during early 1942 the entire MKII production project was cancelled
Short Stirling Mk III
The underfuselage turret was not adopted as standard because of center or gravity problems, although a number of No 7 Sqdn aircraft were fitted with the belly turret.
Interior of the Stirling
In early Stirlings the crew consisted of 8, First and Second Pilot, Navigator, Radio Operator, Flight-Engineer and 3 Airgunners, later the 2nd Pilot was removed and the crew reduced to 7