The Spitfire was the inspired design by Reginald J Mitchell, a young engineer who completed his apprenticeship in a Stoke-on-Trent locomotive works, in search of the stimulation offered by the fledgling aeronautical industry. In 1917 he secured employment at the Supermarine Aviation Works at Eastleigh, near Southampton. He rose rapidly in the company to become the Chief Designer in charge of new programmes. In 1928 the company became a subsidiary of Vickers (Aviation) Ltd. Mitchell led the company’s design entries in the Schneider Trophy floatplane races, securing the trophy in perpetuity for Great Britain in September 1931 with its model S6B. Later that month the aircraft attained a world air speed record of 407.5 mph.

The Spitfire lineage can be traced back to development work on designs to satisfy a 1931 Air Ministry Specification F7/30, for a new and fast interceptor aircraft to be armed with 4 machine guns. Mitchell’s career was centred within a period of rapid advancement in the field of aeronautics. As a war in Europe threatened, he focused his brilliant mind upon designing a fighter aircraft to supersede the biplanes of the day and provide the RAF with a true deterrent. After producing a disappointing initial design (Supermarine Type 224), Mitchell made a fresh start and incorporated everything that was essential and could be realistically achieved, within the design of a new machine, the Supermarine Type 300. A fast, streamlined aircraft was the key feature of Mitchell’s new design. It evolved through a number of revisions until it suitably impressed the Air Ministry, who in January 1935 awarded a contract against a revised specification F10/35, drawn up against the Spitfire. This was then amended to include eight 0.303 inch (7.7 mm) Browning machine guns. Prototype K5054 first flew on 5^th March 1936. It possessed a twin blade fixed pitch wooden propeller powered by the Rolls Royce Merlin V-12 in-line engine, itself undergoing intensive development as a production standard high thrust/weight ratio liquid cooled engine. On 3rd June 1936, the Air Ministry placed an order for 310 Spitfires prior to the completion of a formal report being received from its Aeroplane & Armament Experimental Establishment (A&AEE). In June 1937, Mitchell died of cancer at only 42 years of age. His position was taken over by Joseph Smith, who stayed true to Mitchell’s ideal; that the Spitfire should be worthy of every military demand placed upon it.

Mitchell’s aim was to build an aircraft that satisfied the engineering and functional requirements of the Air Ministry’s specification within a low drag airframe; one that could achieve the best speed and manoeuvrability possible, over the required altitude range. Overall, the paramount attention to drag reduction presents a superbly elegant form but the resulting aircraft was a complex product by the standards of the day. The low thickness/chord ratio wing used an elliptical planform, to reduce the lift dependent drag but allow sufficient depth for the undercarriage, machine guns and ammunition. The introduction of 20 mm wing canons was, however, initially a problem both in terms of installation volume and wing strength. The tailplane and fin adopted curved planforms and low drag aerofoil sections. Compound curved surfaces were prevalent, and wing (incidence) washout was employed over the span between the root and tip chords. The main wing spar used a novel set of telescopic sub-assemblies and the aft fuselage cross section was formed by a series of oval frames. This was not an aircraft offering simple parts’ manufacture and ease of assembly. However, the all-metal streamlined airframe allowed the aircraft to perform at increasingly higher speeds, as engine powers grew during the course of WW2. The design evolved through many versions and adaptations, increasing weights and engine powers. Multi blade variable pitch propeller units were refined to efficiently convert increasing shaft power into thrust, as the Merlin engines ended their development lives with double the original power and Rolls Royce brought the higher capability Griffon engines into production. The aircraft’s handling qualities were mostly excellent and could be reclaimed where modifications were made for operational reasons. The value of the Spitfire to the Allied cause is evident from the challenges of change that were overcome to keep the aircraft in front line service.

The three Czech fighter squadrons, No. 310 and 312, operated with Hawker Hurricanes before converting to the Spitfire. The Spitfire Marks used for the majority of the operational sorties flown by the three squadrons are summarised in the Table below:

Spitfire Vb specifications:

A history of Spitfire AR501 is here.

© 2010 Victor K L Marshall M Sc, C Eng, M I Mech E