The Supermarine Spitfire was developed in the mid-1930s as a short-range, high-performance interceptor aircraft by chief designer R. J. Mitchell.
Only one prototype was made, receiving the military serial K5054. Following its first flight on 5 March 1936, pilot "Mutt" Summers made his famous but oft-misunderstood remark, "I don't want anything touched!" Its appearance and performance caused a significant stir wherever it appeared. The aircraft underwent progressive modifications throughout its life, eventually being converted to near-production standard. It crash-landed several times, finally crashing fatally and being written off just as World War II was breaking out.
Several replicas have been built, including a static one as a memorial to Mitchell. One three-quarter scale replica is flyable.
Development of the Spitfire
Supermarine began development of the Type 300 in 1934, as a private venture following the unsuccessful Type 224 prototype.McLelland 2013, p. 24 Chief designer R. J. Mitchell and his team took the Type 224 as their starting point and continued to draw on their experience with the Schneider Trophy seaplanes. The Type 300 was considerably cleaned-up, with progressive refinements including retractable undercarriage, an enclosed cockpit, oxygen-breathing apparatus, and smaller and thinner wings. The distinctive elliptical wing was developed during this phase, enabling it to accommodate the armament and undercarriage in the thinnest possible cross-section, and thus helping the aircraft achieve a high maximum speed. The newly-developed Rolls-Royce PV-XII V-12 engine, soon to become known as the 'Merlin', was adopted from the outset.
In November 1934, Mitchell started detailed design work.Price 1982, p. 17. On 1 December the Air Ministry issued contract AM 361140/34, providing £10,000 for the construction of a single prototype.Price 1977, p. 20, 32
In 1933 Frederick William Hill and his 13 year old daughter Hazel had analysed data from gun firing trials and concluded that eight .303 machine guns would be needed to give sufficient firepower at the predicted high speeds of the new generation of fighters. Following a recommendation by Squadron Leader Ralph Sorley of the Operational Requirements section at the Air Ministry, in April 1935 the Spitfire's armament requirement was changed from two Vickers machine guns in each wing to four Browning machine guns,.Glancey 2007. pp. 37-38, 43-44, 206."Prototype Spitfire", Tangmere Museum, www.tangmere-museum.org.uk. (Retrieved 12 March 2020) The outer wing section was too thin to fully enclose the additional guns, so small underside blister fairings would be added to production machines to make room for the mechanism. Meanwhile the PV-XII had changed its coolant from water to ethylene glycol, allowing the clumsy evaporative cooling system to be abandoned and replaced by a ducted radiator which had recently been developed by Frederick Meredith at the Royal Aircraft Establishment, Farnborough and actually provided a small amount of jet thrust.McKinstry 2007, p. 54. By August 1935 both changes had been incorporated into the design.McLelland 2013, p. 35
Prototype construction
Construction on K5054 started in December 1934, although the design continued to evolve during the early stages of build, with the prototype gaining an oval rear fuselage, slightly reduced wing span and rear vision cockpit glazing behind the sliding canopy.McLelland 2013, p.37. Like many prototypes of mass-production designs, the first Type 300 had to be largely hand-built and although its general structure followed that of the proposed production design, its details differed in many ways.
Although the basic wing plan was to stay the same for most production Spitfires, the prototype had integral tips and the alclad skinning was hand-cut to fit the double-curvature of the elliptical wing, the upper skinning being laid out in spanwise strips and the underside in chordwise strips. Similarly, the fuselage and tail was a single integrated assembly, with many small cowling panels to the engine.Robinson 1977.
Other initial design features which would later be changed included a fixed-pitch propeller, a stubby and partially-recessed engine air intake, a diagonal edge to the rudder tip balance (which matched the edges of the tail plane tip balances) and a tail skid. Underneath the port wing the radiator duct intake ran flush with the starboard undercarriage leg bay, its opening conforming to the angle of the bay. Farther out towards the wingtip a long pitot tube projected from the leading edge.Price 2002, pp. 36–38.
The Merlin engine was still under development when the airframe was finished. The engine fitted for initial trials was a prototype Merlin C 990 hp (738 kW), with six stub exhaust ports just protruding from each side, driving an Aero-Products "Watts" two-bladed, wooden fixed-pitch propeller.Price 1982, p.57.
The prototype was allocated RAF serial number K5054. When first rolled out for ground tests in February 1936, no armament was installed and the undercarriage doors were also missing. Its RAF markings were applied direct onto the unpainted airframe.McLelland 2013, pp. 17, 37.Cross 1971, p.16.
Mitchell wanted his Type 300, now named 'Spitfire', to be as fast and sleek as possible. After its first flights (see below), K5054 was given a high-grade paint finish closer to that on a Rolls-Royce car than a typical aeroplane. Workmen experienced on the car applied a coat of filler to cover all the rivets, panel joints and other surface blemishes, and rubbed it down to a smooth finish. They then applied several coats of paint to achieve a high gloss. The colour used has been the subject of debate. It has been variously described as "French Grey", "blue-grey", "pale blue" or "cerulean blue". The laborious finish proved fragile under flight conditions and also added excessively to the aircraft weight. It was later also applied to the Speed Spitfire.
Career Flight testing
For its maiden flight the prototype Type 300 was fitted with a fine-pitch propeller to aid in takeoff and the undercarriage locked down for safety. On 5 March 1936, Captain "Mutt" Summers, chief test pilot for Vickers, took it off from Eastleigh Aerodrome (now Southampton Airport).McLelland 2013, PP. 41-43.Morgan and Shacklady 2000, p. 27. The flight lasted eight minutes. On landing, Summers immediately told the ground crew that, "I don't want anything touched!" This is often misunderstood to mean that the Spitfire was flawless, but in fact Summers just wanted to talk the flight over with Mitchell and the design team before anything, especially the control settings, was altered.Quill 1983, p. 71.
For its next flight K5054 was fitted with a new, coarser-pitch high-speed propeller and its undercarriage unlocked. From now on, the undercarriage would be retracted during flight. Summers made three more flights from 10 March 1936. An updated engine was then fitted and from 24 March Summers left the test-flying to his assistants, Jeffrey Quill and George Pickering. They soon discovered that the Spitfire was a very good aircraft, but not perfect.McKinstry 2007, p. 55. The rudder was oversensitive, and the top speed was just , little faster than Sydney Camm's new Merlin-powered Hurricane.
Ground resonance testing of the aircraft at Farnborough took place in April. Excessive wing flutter was identified and a speed limit of imposed. Returning to Eastleigh, the rudder balance, air intake and engine cowlings were modified, the aircraft given the blue paint scheme described above and the undercarriage doors fitted. These included a second door, hinged off the main one, to close over the outer half of the wheel when in flight.McLelland 2013, p.49
On 11 May testing resumed. Handling had improved but the maximum speed was still only . A new propeller was designed and made, on 15 May taking the top speed to , at last visibly outclassing the Hurricane and earning it the reputation as the fastest military aircraft in the world.McLelland 2013 pp. 51-2."The RAF Display", Flight, 2 July 1936, p. 11.
RAF initial trials The prototype was delivered on 26 May to RAF Martlesham Heath for service evaluation by the Aeroplane & Armament Experimental Establishment (A&AEE). The RAF were so keen to get their hands on it that they broke with tradition and Flight Lieutenant Humphrey Edwardes-Jones took it up again on the same day. The staff were well used to new aircraft arriving, but the Spitfire created exceptional interest and even the cooks came out, still in their white hats, to watch. Edwardes-Jones gave a positive report of the aircraft, asking only that the Spitfire be equipped with an undercarriage position indicator because he had nearly forgotten to lower it for landing.McLelland 2013 p. 54.
As the trials continued, the Air Ministry did not wait for the full evaluation and report, but placed its first production order on 3 June.Price 1977, pp. 25, 27. Specification F.16/36, issued to accompany the order, incorporated so many improvements that what was effectively a full new set of design drawings was needed for the production version.Price 1982, p. 61.
Public displays On 16 June the prototype was ferried back to Eastleigh in readiness for a press day two days later, losing oil during the flight. Jeffrey Quill took it up anyway on the day, amid a crowd of press photographers, and the oil pressure dropped to zero while still on his takeoff run. By then committed to the takeoff, he completed a quick circuit and landed uneventfully. An oil pipe had come loose but despite this the engine had performed perfectly throughout.Price 1982, pp. 43-4.
Following further trials, Edwardes-Jones gave a flying display in K5054, in front of huge crowds at the Hendon RAF display on Saturday 27 June 1936. A couple of days later Summers took it to Hatfield for the SBAC show where it was the star exhibit, giving a display of aerobatics and attracting intense interest from media and industry alike.McLelland 2013, pp. 61-4."The S.B.A.C. Display", Flight, 2 July 1936, pp. 25-6.
Continuing development Back again at Martlesham Heath, speed tests proved the troublesome secondary undercarriage doors to be unnecessary and they were removed. A standard set of eight .303" Browning machine-gun armament was fitted with the wings, already designed to accommodate them, being modified accordingly.Price 2002, p. 49. The engine was also changed for an uprated Merlin F. Trials continued with split peas glued onto the airframe to simulate dome-headed rivets, which were less costly and time-consuming, but also caused greater drag, than flush countersunk ones. The results were used to determine the areas for each type of rivet on the production machines. A radio and aerial were fitted, and the tailskid replaced with a twin tailwheel assembly. This last was quickly replaced by a single tailwheel, due to a tendency to clog with mud.McLelland 2013, pp.64-7.
Following an engine failure due to low oil pressure and consequent wheels-up forced landing at the hands of Sam McKenna on 22 March 1937, a prototype triple ejector exhaust was fitted. Developed for the Merlin by Rolls-Royce, it would become characteristic of all the early production Merlins. Besides a number of other small improvements, the aircraft was repainted in standard RAF camouflage of Dark Earth/Dark Green on the upper surfaces with a silver dope finish underneath. On 19 September, it was found that the new exhausts developed 70 pounds of thrust, equivalent to about 70 hp at 300 mph and pushing the maximum speed up to . Price 2002, p. 51.
Development work continued, especially on the engine exhausts and gun heating system, with the occasional landing mishap, until in July 1938 K5054 was sent back to Farnborough. A planned attempt on the world speed record was shelved and the machine was instead used for continuing development work on the Merlin.