Wednesday, 8 March 2017

R. J. Mitchell's Spitfire – a Close Run Thing

When Mitchell’s first fighter design, Type 224, was failing to satisfy the Air Ministry specification F.7/30, there was another monoplane which might very well have attracted favourable Ministry support instead: the Bristol Type 133, the first British fighter design with both retractable wheels and stressed-skin construction. But, when the aircraft was almost ready to go for competitive tests at Martlesham Heath, it entered into a flat spin; the test pilot had to abandon the one-and-only prototype and so time was available for Supermarine to try to improve upon their proposal – although it should be noted that, in view of the British manufacturers’ disappointing responses to F.7/30 that there was even talk in the Ministry of purchasing Poland’s all-metal monoplane, the PZL P.24.
     Meanwhile personnel were changing in the Air Ministry: the Chief of the Air Staff, Sir Hugh Trenchard, who had favoured the bomber as a deterrent, had retired and his successor, Sir John Salmond and his Deputy, Sir Charles Burnett, were more sceptical of this approach. They were very actively supported by Hugh Dowding who joined the Air Staff in 1930 as Air Member for Research and Supply; as he later became the Commanding Officer of RAF Fighter Command, it is not surprising that he held the view that ‘the best defence of the country is fear of the fighter’.
    It was thus fortunate for Mitchell that the Air Ministry and its departments were headed by RAF officers who had by now come to the conclusion that fighter development had to be significantly stepped up. Whilst F.7/30 can be seen as the milestone specification which brought our seaplane designer into the reckoning, the future support of certain Air Ministry officials in some difficult days ahead for the Spitfire-to-be had much to do with the close and mutually respectful relations between Supermarine and the RAF since the Southampton and S.5/6 Schneider Trophy days. It might also be noted that two particular Ministry men were active at this time: Group Captain Cave-Brown-Cave, the Director of Technical Development from 1931 to 1935, who had led the Far East Flight in one of Mitchell’s Southamptons which had never let his team down, and Major Buchanan, who had been the Air Ministry representative at the 1925 Schneider Competition and vocal afterwards in his support for British participation in these events.
   It should thus come as no surprise that, even before trials of the F.7/30 prototypes had been concluded, Specification F.5/34 was issued, which  stated that a retracting undercarriage was required and eight machine guns to provide ‘the maximum hitting power’. It also specified that ‘the maximum speed at an altitude of 15,000 feet shall not be less than 275 mph and at 5,000 feet not less than 250 mph’; and ‘the time taken to reach 20,000 feet is not to exceed 7½ minutes’. As Mitchell’s Type 224 modification had only promised a top speed of 265 mph and a climb to 15,000 feet in over eight minutes, it is not surprising that it had only received a lukewarm response from the Air Ministry.
    Fortunately, the Air Ministry, in October, 1934, agreed to Supermarine submitting a quotation for a different machine and Rolls-Royce had, by then, decided that their current engines were not capable of being developed into the sort of power plant needed for the next generation of fighters. Something between their 22 litre Kestrel and Goshawk engines and their 37 litre Schneider Trophy ‘R’ engine, was thought to be appropriate and so the company had begun design work on a further 12-cylinder Vee engine, initially expected to deliver a healthy 1,000 hp. As this new engine had passed its 100 hour test in the July of 1934, the board of Vickers (Aviation) Ltd decided on 6 November to finance the design of a fighter, powered by this new engine. Sir Robert McLean, the chairman of the board, some time later described how he had decided that Mitchell and his design team, in view of the adverse effect of Air Ministry requirements on the Type 224 [see my Blogpost: 'R.J. Mitchell's Stuka'],  should design a ‘real killer fighter’ in advance of any Air Ministry specification and that ‘in no circumstances would any technical member of the Air Ministry be consulted or allowed to interfere with the designer’.
   This intervention by Sir Robert was a result of his appreciation of Mitchell’s work which went right back to the take-over of Supermarine in 1928 – although McKinstry has recently pointed out that the chairman was, in fact, not unwavering before his support for the Supermarine designer finally won out. The alternative proposal which had attracted the attention of the chairman was the Venom, a development of the promising but ill-fated F.7/30 entry, the Vickers 151 Jockey, which had also succumbed to a flat spin. Like the Spitfire, the Venom had a stressed skin cantilever wing, retractable undercarriage and a metal monocoque fuselage (in fact, when it did fly, three months after the Spitfire prototype, it attained a top speed only 37 mph lower than the Supermarine prototype – with a less powerful radial engine). Clearly, this machine could have developed into a very serious challenge to the Supermarine project and, indeed, Beverley Shenstone, Mitchell’s aerodynamicist, later reported that ‘in my opinion the Spitfire would not have been born if Mitchell had not been willing to stand up to McLean, particularly in the era when McLean clearly preferred the Venom concept to the Spitfire concept because it was cheaper and lighter’.
   But once Mitchell’s proposal had been agreed upon, the combination of a Vickers/Supermarine/Rolls-Royce/Mitchell design must have stirred things up within the Air Ministry, for events moved very quickly thereafter. On December the 1st, £10,000 was allocated for the building of a prototype and a full design conference was called at the Air Ministry on the 5th of the same month. The whole contract situation was quickly regularized when a very brief Specification F.37/34 was formally signed on the third of January, 1935. It should be noted that this new specification was headed ‘Experimental High Speed Single Seat Fighter (Supermarine Aviation Works)’ and it stated that, basically, ‘the aircraft shall conform to all the requirements stated in Specification F.7/30 – that is, Mitchell was permitted to design a four-gun ‘experimental’ aircraft but without other firms being invited to tender in the usual way. It would seem that the three successive Schneider Trophy wins by the Rolls-Royce/Supermarine combination had not been forgotten by the new Air Ministry officials.
   Notwithstanding this initiative, three months later, the Air Ministry issued requirement F.10/35 in April 1935, which called for at least six, and preferably eight, guns to ‘produce the maximum hitting power possible in the short time available for one attack’. Thus the Supermarine fighter being designed had to offer something special, for F.10/35 called for a  maximum speed of ‘not less than 310 mph.’ – and so one suspects that Supermarine and Vickers were looking well beyond their four gun model and towards new armament requirements when their elliptical wing shape was decided upon – the thin wing approach that Mitchell had come to believe in could only accommodate increased weaponry with a broad chord wing well outboard of the fuselage and beyond the required retracting undercarriage housing.
   In this connection, the later comments of Mitchell’s stress man, Clifton concerning Mitchell’s doubts about information derived from model testing deserve recording:
I think that Mitchell decided to make the wing as thin as he did, and I wouldn’t like to be positive about this, but my recollection was that it was against some advice from the National Physical Laboratory in that case where wind tunnel tests, I believe, showed that there was no advantage in going below a thickness chord ratio of 15%, whereas, the [Spitfire] wing was 13% at the root and 6% at the tip. . . subsequently it was found that when you made proper allowance for that, there was an advantage, as the testing could be shown to prove, in going thinner.
At that time, Hawkers had been advised by the National Physical Laboratory that their recent wind tunnel results had shown no drag penalty with the thicker Hurricane wing; however, the Laboratory scientists later found this advice to be incorrect. Fortunately Mitchell’s instincts were proved correct.
   It was also fortunate that, about this time, F. W.  Meredith of the Royal Aircraft Establishment, Farnborough, came up with a ducted under-wing radiator that not only made little difference to the lines of the machine but actually used the heat exchange of the radiator to produce some thrust at high speed rather than to create drag, as in previous practice, thus encouraging confidence in Supermarine’s predicted 350 mph for their new fighter.
K 5054  the Spitfire Prototype (from a painting by the author)
    Nevertheless, when the new prototype first flew early in 1936, Mitchell confessed to being very disappointed that the top speed was ‘a lot slower than I had hoped for’ –– and, as its test pilot, Jeffrey Quill, said: ‘unless the Spitfire offered some very substantial speed advantage over the Hurricane, it was unlikely to be put into production. Thus the disappointing speed performance of our prototype at that early stage was something of a crisis and Mitchell was reported to be 'a very worried man’.
   And so the prototype was given a special new paint job and, by 9th May, 1936, re-emerged with a very smooth light blue-grey finish, thanks to fillers and to automobile paint supplied by Rolls-Royce. Yet the speed of K5054 was still less than hoped for, as the aircraft’s top speed of 335 mph was still too close to that of the Hurricane, rumoured to be achieving 330 mph. Just after the prototype Hurricane had flown, Mitchell saw it for the first time. ‘He did not see it close up but only at a distance. He came back to Itchen very worried, and walked into the erection shed and looked at the first incomplete Spitfire. He said, "Camm’s got a tiny little machine. Ours looks far too big"’.
    In fact, the Hurricane had three feet more span than the Spitfire but the supposed narrow margin between the top speeds of the two new aircraft might very well have resulted in a contract going exclusively to the Hawker. Luckily, the fitting of a new propeller (Quill recalled the previous flight testing of ‘some 15 to 20 different designs’) on 15th May produced a dramatic increase to 349 mph – a very impressive leap of more than 100 mph over that of the Gladiator which, as a stop-gap, had eventually been awarded the F.7/30 contract.
   When one remembers how two promising F.7/30 contenders were eliminated when the one-and-only models crashed, it is worth recalling that the equally unique Spitfire prototype nearly came to grief when handed over to Fl. Lieut. (later Air Marshall Sir) Humphrey Edwardes-Jones at the test centre, Martlesham Heath:

There was no air traffic control in those days and I had no radio. As I made my approach I could make out a Super Fury some way in front of me doing S turns to lose height before it landed. I thought it was going to get in my way but then I saw it swing out to one side and land, so I knew I was all right. But it had distracted my attention at a very important time. As I was coming in to land I had a funny feeling that something was wrong. Then it suddenly occurred to me: I had forgotten to lower the undercarriage! The klaxon horn, which had come on when I throttled back with the wheels still up, was barely audible with the hood open and the engine running. I lowered the undercarriage and it came down and locked with a reassuring ‘clunk’. Then I continued down and landed. Afterwards people said to me, ‘You've got a nerve, leaving it so late before you put the wheels down’. But I just grinned and shrugged my shoulders. In the months that followed I would go quite cold just thinking about it: supposing I had landed the first Spitfire wheels-up! I kept the story to myself for many years afterwards.
With hindsight, one wonders how a crash-landing of the one-and-only untried prototype would have affected its future, given the usual Air Ministry practice of only ordering one prototype from a firm [for the German contract exercise, equivalent to the British F.7/30 requirement, four firms had each been authorized to build three prototypes].

Events in Europe were certainly now creating an even greater urgency to find an adequate replacement for the standard RAF fighters of the day and so Edwardes-Jones had been instructed to telephone the Air Ministry as soon as he got down from this first flight:
Normally, a firm’s test pilot would bring in a prototype aircraft for service testing, and it would be first handed over to the boffins who would weigh it very carefully and check that the structure was as it should be. It was usually about 10 days before it came out for its first flight with us. With the Spitfire prototype, it was quite different. Mutt Summers brought her over, and orders came from the Air Ministry that I was to fly the aircraft that same day and report my impressions…
Once down I rang the number at the Air Ministry I had been given, as ordered. The officer at the other end [Wilfred Freeman, Air Member for Research and Development] said … ‘All I want to know is whether you think the young pilot officers and others we are getting in the Air Force will be able to cope with the aircraft’. I took a deep breath – I was supposed to be the expert, having jolly nearly landed with the undercarriage up! Then I realised that it was just a silly mistake on my part and I told him that if there were proper indications of the undercarriage position in the cockpit, there should be no difficulty. On the strength of that brief conversation the Air Ministry signed a contract for the first 310 Spitfires on 3 June [1936], eight days later.

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For reference sources, see my Blogpost: “Source Material and References" – an extended bibliography is included in my R.J.Mitchell at Supermarine; Schneider Trophy to Spitfire which also provides material for wider reading, grouped according to specific areas of interest. 

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