In the mid-1930s, aviation design teams around the world began developing a new generation of all-metal low-wing fighter aircraft. The French Dewoitine D.520 and the German Messerschmitt Bf 109, for example, were designed to take advantage of new monocoque construction techniques and the availability of new high-powered liquid-cooled in-line air engines. They also included refinements like retractable landing trains, fully enclosed cockpits with low drag, all metal wings (all introduced in civil planes years before, but slow to be adopted by the military, which favored the simplicity and maneuverability of the biplane).
After the disappointment of the Type 224 in 1934 to meet the specification of the British Ministry of Aeronautics, RJ Mitchell presented the Type 300 which was also rejected by the British Government, but together with the support of Supermarine, began the improvement project of the Type 300. The project then went through a series of changes, including the incorporation of a new fairing, closed cockpit, individual oxygen system, smaller and thinner wings, and the newly developed and more powerful Rolls-Royce PV-XII V-12 engine, later called "Merlin".
On 1 December 1934, the Ministry of Aeronautics issued contract AM 361140/34, providing £10,000 for the construction of the improved Mitchell project. On 3 January 1935, they formalized the contract with a new specification, written around the aircraft. In April 1935, the armament was changed from two 7.3 mm Vickers machine guns on each wing to four 7.7 mm Brownings, following a recommendation by Squadron Leader Ralph Sorley of the Operational Requirements section at the Ministry of Aeronautics.
On 5 March 1936, the prototype (K5054) took off in its first flight from Eastleigh airfield (later called Southampton airport). In command Captain Joseph "Mutt" Summers, chief test pilot of Vickers. This eight-minute flight came four months after the first flight of fellow countryman Hawker Hurricane.
The K5054 was equipped with a new propeller, and Summers flew the aircraft on March 10, 1936, during this flight the landing gear was first picked up. After the fourth flight, a new engine was fitted, and Summers left the test flight to his assistants, Jeffrey Quill and George Pickering. They soon found out that the Spitfire was a very good plane, but not perfect. The rudder was excessively sensitive and the maximum speed was only 528 km/h, little faster than the new Hurricane. A new and better shaped wooden propeller allowed the Spitfire to reach 557 km/h in level flight. The aircraft was delivered to Lieutenant Humphrey Edwardes-Jones who flew the prototype for the RAF. He had received orders to fly the aircraft and then make his report to the Ministry of Aeronautics. The report of Edwardes-Jones was positive that only request was that the Spitfire be equipped with a landing gear position indicator. A week later, on June 3, 1936, the Ministry of Aeronautics placed an order for 310 Spitfires.
Large-scale production of the Spitfire began at the Supermarine plant in Woolston, Southampton, but it quickly became clear that the order could not be completed within 15 months as promised. Supermarine was a small company, already busy building the flying boats Walrus and Stranraer, and Vickers was busy building the Wellingtons. The initial solution was to outsource the work. The first production Spitfire rolled off the assembly line in mid-1938, and was flown by Jeffrey Quill on 15 May of that year, almost 24 months after the initial order.
The fuselage of the Spitfire was complex: the semi-monocoque aerodynamic duralumin fuselage presented a large number of compound curves built from a 19-shape skeleton, also known as frames, starting from the frame number one, immediately behind the propeller unit, up to the unit fixing tail frame. The first four frames supported the glycol head tank and engine fairings. The structure 5, to which were the engine fasteners, supported the weight of the engine and accessories, and the loads imposed by the engine: this was a reinforced double frame that also incorporated the fireproof bulkhead and, in later versions of the Spitfire, the oil tank. This frame also tied the four main fuselage longerons to the rest of the fuselage. Behind the bulkhead were five 'U' shaped profiles that accommodated the fuel tanks and cockpit. The rear fuselage began at the eleventh frame, to which the pilot’s seat and (later) the armor were attached, and ended at the nineteenth, which was mounted at a slightly forward angle of the fin. Each of these nine frames were oval, reducing in size to the tail, and incorporated several lighting holes to reduce their weight as much as possible without weakening them. The U 20-shaped structure was the last fuselage frame and the structure to which the tail unit was attached. The frames 21, 22 and 23 formed the fin; frame 22 incorporated the opening of the tail wheel and frame 23 was the rudder column.
Mitchell and the design team decided to use a semi-elliptical wing shape to solve two conflicting requirements: The wing needed to be thin, to avoid creating too much drag, while still being able to house a retractable landing gear, as well as armament and ammunition. An elliptical plane is the most efficient aerodynamic form for a non-twisted wing, generating smaller induced. Mitchell was sometimes accused of copying the wing shape of the Heinkel He 70, which first flew in 1932, but as Beverley Shenstone, the aerodynamics expert on Mitchell’s team, explained: "Our wing was much thinner and had a very different section than the Heinkel. In any case, it would have been simply asking problems to have copied the wing shape of an airplane designed for an entirely different purpose.
All the main flight controls were originally metal structures covered with fabric. The designers and pilots felt that having ailerons that were too heavy to move (in terms of effort, not mass) at high speed would prevent the possible aileron reversal. However, during the Battle of Britain, pilots found that Spitfire ailerons were too heavy at high speeds, severely restricting side maneuvers such as "rolls" and high-speed turns, which were still a feature of air-to-air combat. Flight tests showed that the fabric covering of ailerons at high speeds adversely affected aerodynamics. They replaced the fabric lining with light alloy and dramatically improved the ailerons at high speed.
The airflow through the main radiator was controlled by pneumatic outlet flaps. In the early models (Mk I to Mk VI) the flap was simply operated manually using a lever on the left of the pilot’s seat. When the two-stage Merlin was introduced in the Spitfire Mk IX the radiators were cracked to make way for an intercooler radiator.
As the Spitfire gained more power and was able to maneuver at higher speeds, the possibility that pilots would encounter aileron inversion increased, and the Supermarine design team began redesigning the wings to counter this. The original design of the wing had a theoretical aileron inversion speed of 980 km / h, which was somewhat lower than that of some fighters of the time. The Royal Aircraft Establishment noted that at 400 mph (640 km/h) IAS, about 65% of aileron effectiveness was lost due to wing twist.
The new wing of the Spitfire F Mk 21 and its successors was designed to help alleviate this problem. The stiffness of the wing was increased by 47%, and a new aileron design using new hinges and compensation flaps made the theoretical aileron reversal speed be increased to 1,328 km / h. Beside the redesigned wing, Supermarine also tried out the original wing, raising the lead by 2.54 cm, with the hope of improving the rider’s vision and reducing drag. This wing was tested on a modified F Mk21, also called the F Mk 23, (sometimes referred to as "Valiant" instead of "Spitfire"). The increase in performance was minimal and this experiment was abandoned.
Supermarine has developed a new laminar flow wing based on new aerodynamic profiles developed by NACA in the United States, with the aim of reducing drag and improving performance. Supermarine estimated that the new wing could give an increase in speed of 55 mph (89 km/h) over the Spitfire Mk 21. The new wing was initially fitted on a Spitfire Mk XIV and later a new fuselage was designed, and the new fighter became the Supermarine Spiteful. Somewhat surprisingly, the new trapezoidal wing had less critical Mach than the old elliptical wing, and one of the test pilots who flew the "Spiteful" (the Supermarine Attacker) commented that the original wing should have been used in the jet.
At the beginning of its development, the lack of fuel injection in the Merlin engine meant that Spitfires and Hurricanes, unlike the Bf 109E, were unable to simply make a steep dive. This meant that a Luftwaffe fighter could simply dive with high power to escape an attack, leaving the Spitfire behind as its fuel was forced out of the carburettor by negative "g". RAF fighter pilots soon learned to "half-roll" their planes before diving in to chase their opponents. Carburettors were adopted because, as Sir Stanley Hooker explained, the carburettor "increased the performance of the supercharger and thus increased the power of the engine."
Due to the scarcity of Brownings, which had been selected as the new standard calibre rifle machine gun for the RAF in 1934, the Spitfires were equipped with only four guns, with the other four being fitted later. Early tests showed that while the guns worked perfectly on the ground and at low altitudes, they tended to freeze at altitude, especially wing guns. This was because the RAF Brownings had been modified to fire from an open bolt and while that prevented overheating of the cordite used in British ammunition and allowed cold air to flow through the barrel unimpeded. Even if the eight Brownings worked perfectly, pilots soon found that they were not enough to destroy larger aircraft. By November 1938, tests against armed and unarmoured targets had already indicated that the introduction of a weapon of at least 20 mm calibre was urgently needed. A variant of the Spitfire design with four 20 mm Oerlikon guns had been offered, but the order for prototypes had gone to the Westland Whirlwind in January 1939.
In June 1939, a Spitfire was fitted with a Hispano powered drum on each wing, an installation that required large bubbles on the wing to cover the 60-rpm drum. The gun suffered frequent stoppages, mainly because the guns were mounted on its sides to fit as much magazine as possible inside the wing. However, 30 more Spitfires armed with cannons were ordered for operational tests, and soon became known as the Mk IB, to distinguish them from the Browning-armed Mk IA and were delivered to Squadron 19 from June 1940. The Hispanics were so unreliable that the squadron asked for an exchange of their aircraft with Browning’s older plane armed with an operational training unit. By August, Supermarine had perfected a more reliable installation with an improved feed mechanism and four . 303s on the outer wing panels. The modified fighters were then delivered to Squad 19.
The operational history of the Spitfire with the RAF began with the MkI, which entered service with the 19th Squadron at RAF Duxford on 4 August 1938. The Spitfire achieved legendary status during the battle of Britain, a reputation helped by the "famous fund of the Spitfire" organized and directed by Lord Beaverbrook, minister of aircraft production. In fact, the Hurrikan outnumbered the Spitfire throughout the battle, and pushed the burden of defense against the Luftwaffe. However, because of their higher performance the overall friction rate of the Spitfire squadrons was lower than that of the Hurricane units, and the Spitfire units had a higher win-lose ratio. The main objective of the Fighter Command was to stop the bombers of the Luftwaffe. In practice, the tactic, whenever possible, was to use Spitfires to counter German escort fighters, then based in northern France, particularly the Bf 109s, while Hurricanes squadrons attacked bombers.
The Spitfire continued to play increasingly diverse roles throughout World War II and beyond, often in air forces other than the RAF. The Spitfire, for example, became the first high-speed photo-reconnaissance aircraft to be operated by the RAF. Sometimes unarmed, they flew at high, medium and low altitudes, often reaching enemy territory to observe closely the Axis powers and provide an almost continuous flow of valuable intelligence information during war. In 1941 and 1942, PRU Spitfires provided the first photographs of the radar systems of Freya and Würzburg and, in 1943, helped to confirm that the Germans were building Vergeltungswaffe V1 and V2 photographing Peenemünde on the German Baltic coast.
In the Mediterranean, the Spitfire mitigated the heavy attacks on Malta by the Regia Aeronautica and Luftwaffe and, from 1943 onwards, helped pave the way for the Allied invasions of Sicily and Italy. On 7 March 1942, 15 Mk V’s carrying 90-litre fuel tanks under their bellies took off from the HMS Eagle off the coast of Algeria on a 600-mile flight to Malta. Those Spitfires V were the first to carry out service outside of Great Britain.
The Spitfire also served on the Eastern Front: approximately one thousand were supplied to the Soviet Air Force. Although some were used on the front line in 1943, most of them saw service with the Protivo-Vozdushnaya Oborona (English: "Anti-air Division of Defense").
The Spitfire also served in the Pacific Theatre. During the Malaya campaign in defense of Singapore, the Spitfire found its match in the Japanese Mitsubishi A6M Zero. "RAF pilots were trained in methods that were excellent against German and Italian equipment but suicide against acrobatic Japanese". As Lt.Gen. Claire Lee Chennault had to note. Although not as fast as the Spitfire, the Zero could flip the Spitfire easily, could sustain a climb at a very steep angle, and could stay in the air for three times longer. To fight the Zero, the Spitfire pilots had to adopt a "cut and run" policy and use their superior speed and dive superiority to fight, avoiding classic combat. Also what did not help is that Southeast Asia was an area of lower priority and that few Spitfires and other modern fighters were allocated compared to Europe, which allowed the Japanese to easily achieve air superiority in 1942. Over the Northern Territory of Australia, RAF and RAAF spitfires helped defend the port city of Darwin against the air attack by the Japanese Naval Air Force. The Spitfire MKVIII participated in the last battle of World War II involving the western allies, in Burma as a ground attack, helping to defeat a Japanese escape attempt.
Supermarine developed a two-seat variant known as the T Mk VIII to be used for training, but none was ordered, and only one specimen was built (identified as N32/G-AIDN by Supermarine). In the absence of an official two-place variant, a number of cells were roughly converted into the field. These included a 4 SAAF Mk from the VB squadron in North Africa, where a second seat was installed instead of the upper fuel tank at the front of the cockpit. The only unofficial conversions of two places that were equipped with double controls was a small number of Russian loan/ lease Mk IX aircraft. These were referred to as Mk IX UTI and differed from the proposals of Supermarine, using a "greenhouse" type in-line hinge instead of the "bubble" type raised from the T Mk VIII.
In the post-war era, the idea was revived by Supermarine and a number of two-seat aircraft were converted from old Mk IX cells. Ten of these TR9 variants were then sold to the Indian Air Force, along with six to the Irish Air Corps, three to the Royal Dutch Air Force and one to the Royal Egyptian Air Force. Currently, there are several trainers including the US-based T Mk VIII, the US-based T Mk IX and the "Grace Spitfire" ML407, a veteran operated operationally by the 485 (NZ) Squadron in 1944.
The Seafire, a name derived from the sea, was a naval version of the Spitfire specially adapted for aircraft carrier operation. Although the Spitfire was not designed for the rough-and-hard operations of deck, it was considered to be the best fighter available at that time. The basic design of the Spitfire imposed some limitations on the aircraft’s use as an air base fighter. Poor visibility over the nose, for example, meant that pilots would have to be trained to land with their heads outside the cockpit and look next to the Seafire’s port hood, and also, like the Spitfire, the Seafire had very fragile landing gear, which meant that it was not ideal for deck operations. The early Seafire models had relatively few modifications to the standard Spitfire structure, however cumulative frontline experience meant that most later versions of the Seafire had reinforced fuselages, Folding wings, brake hooks and other modifications culminating in the Seafire F/FR Mk 47, built specifically for operations from deck.
The Seafire II was able to outperform the A6M5 Zero at low altitude when the two were tested against each other during simulated combat exercises during the war. However, the Allied fighters at that time, such as the Hellcat F6F and Corsair F4U were considerably more robust and more practical for operations from aircraft carriers. Performance was much higher when later versions of the Seafire were fitted with Griffon engines, but these came too late for World War II.
The Spitfire was produced in larger numbers than any other British aircraft. It was also the only British fighter to be in continuous production throughout the war. The Spitfire continues to be popular with enthusiasts. About 54 remain airworthy, while many more are on static displays in aviation museums around the world.
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