Sunday, 5 March 2017

R. J. Mitchell’s Bomber and his death.

Painting by the author, is based upon
 Supermarine  Drawing 31600 Sheet 2  and works models.
By the early part of 1937, Mitchell was to be seen less and less at Supermarine as it had become clear to his family that the cancer operation of 1933 had not been a successful procedure. Yet, in the last full year of his life and even when he was putting the finishing touches to the Spitfire design, another major innovative project for a bomber had been occupying his mind.
    This was in response to Air Ministry  specification B.12/36 which called for a high-speed, four-engined, long-range bomber with a range of 3,000 miles, capable of carrying a 14,000 lb bomb load or 24 soldiers. It also had to be able to be broken down into component parts for transport by the existing railway system and to lift off from a 500 ft runway, clearing a height of 50 ft at the end; for this last purpose there was added a requirement to provide a catapult take-off capability (because of the small airfields currently in use and, particularly, in order to extend the bomber's potential range and load capacity). At the same time, the wingspan was to be limited to no more than 100 ft (to discourage over-large projects which would take too much precious time and materials to produce rather than because of the size of existing hangars, as is often claimed). It also had to have a retractable ventral turret as well as nose and tail guns and had to be capable of staying afloat for several hours in the event of being forced down in the North Sea or Channel, as might be expected if the international situation did not improve.
    It is interesting that Shorts and Supermarine were each awarded contracts for two prototypes rather than, for example, the Handley-Page or Vickers firms which had extensive experience of the larger sort of land-based machines. But, in view of some of the Ministry requirements, it might be noted that Supermarine and Shorts had a great deal of experience of water-resistant hulls and Supermarine had just provided the RAF and Navy with the very efficient Stranraer and the catapult-stressed Walrus.
   In the same month that the Martlesham Heath report on the Spitfire prototype was received, Mitchell's tender for the bomber had been sent to the Air Ministry and must have confirmed the officials' regard for Mitchell's importance to the aviation industry: despite having a proposed wingspan of 97 feet, it nevertheless was to make use of a single spar wing supported by torsion-resistant leading edge boxes on a similar principle to that developed for the Spitfire. Unusually for its time, fuel was to be carried in these leading edges, thereby saving weight, and with the tanks adding to the rigidity of the wing. Behind this spar component, the structure allowed sufficient room for the main stowage of bombs, thus avoiding the need for conventional tiered bomb stowage which would have substantially increased the fuselage cross-section and its drag component – another example of Mitchell ingenuity. Prior to this design, the  Polish PZL  P.37 medium bomber had made extensive use of bomb bays in the wing between the engines and the fuselage, as did an Armstrong Whitworth A.W. 42 proposal but Mitchell’s bomb stowage arrangements in the wings was more extensive and not adopted in any of the other front-line bombers of World War II.
 

Drawing 31600 Sheets 5/6 showing leading edge tanks and stowage of 29x250 lb/27x500 lb bombs

Had this extensive wing bomb stowage not been the proposed, the fuselage would have had to be considerably more bulky – further evidence of Supermarine’s Schneider Trophy concerns to increase airframe efficiency by paying, instinctively as it were, particular attention to the reduction of frontal area. A further refinement was the proposal to place the required armament well below the eye-line of the gunners, not only giving them an improved view but also enabling a reduction in the cross-section of the turret and a more rapid traverse of the guns.
Three versions of the Bomber were proposed: Type 316 with Bristol Hercules engines, deltoid shaped wing (see  drawing above) and single fin:
from Drawing 31600 Sheet 1

Type 318 with Rolls-Royce Merlin engines but otherwise similar to 316; and Type 317 with Bristol Hercules engines, twin fins, and wing leading and trailing edges tapering almost equally:
Supermarine model of Type 317 heavy bomber.

In November, 1938, Mitchell’s team was able to submit a lighter and smaller design than their rival for the same specification and produced a set of estimated performance figures which make an intriguing comparison with published figures for the earliest Marks of the most well-known British four-engined bombers of comparable size:

Aircraft
Power Rating
Range
Bomb Load
Max. Speed
Supermarine (estimate)
1330 hp
43,680 miles
8,000 lb.
330 mph
Stirling I
1590 hp
41,930 miles
5,000 lb.
260 mph
Halifax BI
1145 hp
41,860 miles
5,800 lb.
265 mph
Lancaster I
1390 hp
42,530 miles
7,000 lb.
287 mph






More often than not, Supermarine estimates were actually achieved when their designs flew, but it will always be a matter of conjecture as to whether the extraordinarily competitive figures for Supermarine’s proposed bomber would have been attained – with an estimated speed close to that of the new fighters. It might, however, be maintained that, with the need for volume production – using standard gun turrets and probably being forced to add a dorsal one too – the performance figures that the Supermarine bomber might have achieved would have been much closer to those of Britain's actual four engined bombers.
  Unfortunately the matter remains a matter of speculation as previous lack of urgency in aircraft development resulted in the project only reaching the stage of two prototype fuselages when they were destroyed by enemy bombing:

 
One of the bomber fuselages before their destruction by enemy action.
Also, the Chief Designer never lived to learn of the fate of his last projects, just as he never actually saw his Spitfire go into squadron service before World War II started. Towards the end of February, 1937, he went into a London hospital. The prognosis was not good and a stay at the Cancer Clinic in Vienna was arranged in the April. Letters testify to his dismay at not being able to continue his input into the design of the bomber but it became clear that this was not possible. Mitchell returned to Southampton on the 25 May, 1937, and he died on 11 June, aged 42.
As he invariably gave full credit to his design staff in his speeches, it was fitting that he requested they be given first place at his funeral and it is perhaps significant that Harry Griffiths’ recollection of Mitchell’s death prompts a memory of his relationship with this team:
On the day he died Arthur [Black, chief metallurgist] and I were standing at the bench discussing a problem when Vera Cross, R J’s faithful secretary over many years, came in and just said , ‘It’s all over.’ Arthur looked at me and shook his head then he turned away and was silent for a long time.
At the annual dinner that year we stood in silence in his memory and then drank a toast: ‘To a very gallant gentleman.’
The Christmas before his untimely death he arrived late for the annual design staff dinner, and in spite of a place having been kept for him at the head of the table he insisted on sitting at the other end with us lads and sharing a joke and some wine.


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I am indebted to John Dell for some of the information contained above.
For other 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 (details below) which also provides material for wider reading, grouped according to specific areas of interest. 

More information on the above, as well as a full account of all Mitchell's completed designs and of the man behind them, will be available in a few weeks' time:
Advance Notice – 
R.J.Mitchell at Supermarine; Schneider Trophy to Spitfire.
This is a much expanded, completely up-to-date, second edition of my earlier work with 50% more photos, and 25% more text – 380 pp. instead of 250. There are general arrangement drawings of Mitchell’s 21 main aircraft types which flew, as well as 40 other drawings. There are 24 photographs, featuring or including Mitchell, as befits the first fully detailed and, I hope,  definitive account of the man and his work at Supermarine.
To obtain a copy at pre-publication prices, please enquire via the contact form in the sidebar.


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