Thursday, 9 March 2017

R. J. Mitchell’s Stuka – Type 224.

Mitchell’s Stuka – the First ‘Spitfire’
Thanks to his Schneider Trophy racers, Mitchell’s qualifications for creating high-speed aircraft were outstanding but, as we shall see, much of the under-performance of his first attempt at a fighter was not of Mitchell’s making. Equally, its genesis contradicts any assumption that the Spitfire developed directly from these machines or via some single imaginative leap after the designer returned to work at the end of 1933, following his operation for cancer.
Two years earlier, when the Air Ministry specification F.7/30 appeared, Mitchell had had to turn his mind to a military aspect of aviation that he had only briefly been engaged upon with the Sea King II fighter of 1921 – and that aircraft was a flying boat, albeit a fast and manoevrable one at the time. Additionally, armament on his slower reconnaissance flying-boats was provided via gunners in cockpits not via guns which would now probably need to be buried in the wings. Alan Clifton recalled that Mitchell was uneasy about ‘his first venture into military aircraft’, recognising that he was ‘no expert in the field’.

Type 224.
Mitchell’s resultant design, Type 224, was an all-metal structure characterised by a thick cantilever, inverted, gull-wing and (surprisingly) a short fixed undercarriage with large fairings (hence the comparison with the Junkers Stuka (see below). Supermarine’s submission to the Air Ministry pointed out how this cranked wing configuration would produce a short, low drag undercarriage with a wide track for easy taxiing, and give ‘exceptional’ visibility for the pilot. Also, two of the four guns required by F.7/30 could be housed in the undercarriage fairings (the leading edges of the wings were to incorporate radiators for the chosen evaporative engine cooling system). In addition, tanks to collect the condensed water coolant could be fitted low down in these fairings.
A large air brake was provided but, nevertheless, the Air Ministry, concerned about night operation and small, grass field landing strips, felt that the estimated wing-loading of only 15 lbs. per sq. ft. was too high (The wing-loading of Mitchell’s S.6B Schneider Trophy winner had been 42 lbs. per sq. ft.). Therefore the wing was eventually drawn up with a generous 45ft.10in. span which, in combination with a fuselage about the same length as that of the 28ft.10in. span Schneider floatplane, looked somewhat out of proportion. 

 Type 224 first flew on 19 February 1933 and, unfortunately, it was found that the low pressure side of the pumps for the cooling system would often allow the coolant to turn into steam again, particularly during rapid climbs. Test pilot Jeffrey Quill has recorded an undiplomatic comment on the problem: ‘I said that with the red [warning] lights flashing on all over the place, one had to be a plumber to understand what was going on. [Mitchell] didn’t say anything, he just looked very sour. He was rather sensitive about the aeroplane and obviously I had trodden on his toes.’ He, understandably, was far from happy when the pilot had to level off until all was working normally again – thus defeating the Air Ministry requirement of the fastest possible climb to intercept enemy bombers.
      Apart from these cooling problems, the top speed of Type 224 also proved to be a disappointment and so modifications were proposed, including a retractable undercarriage, and elimination of the cranked wing. These proposals were submitted in July 1934 and were expected to improve the maximum speed of Type 224 by 30 mph but the Air Ministry officials were lukewarm and none were implemented. Test flying continued and Vickers publicity even named the aircraft ‘Spitfire’ but the way forward was unlikely to be with an imperfect cooling system and with the conflicting ministry requirements of slow speed landing performance and fighter agility.
      Meanwhile, Junkers were producing the similarly configured Stuka. with an inverted cranked wing and fixed undercarriage; in the case of the early models, the wheels were similarly encased:
It first flew on 17 September 1935 and, a year later, Blohm und Voss produced their Ha 137, a fighter type which also had a cranked wing and a ‘trousered’ undercarriage. As these aircraft first flew after Type 224, Mitchell’s chosen configuration of a cranked wing and a short fixed undercarriage was not an eccentric choice, nor derived from other aircraft; no doubt the wing loading restriction must have been one of the main reasons why the Vickers chairman subsequently claimed that he then instructed Mitchell to design a private venture aircraft, the future Spitfire, without any  ‘interference’ from the Air Ministry.

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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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