Friday, 13 July 2012

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

My painting above is based upon
 Supermarine Drawing 31600 Sheet 2  and Supermarine works models.
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 up to 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.
In the same month that the very positive Martlesham Heath report on K5054 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; and, 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 and, indeed, it anticipated post-war designs – 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.

From Drawing 31600 Sheets 5/6 showing leading edge tanks and stowage of 27x500 lb/29x250 lb bombs
 A further refinement was the proposal to place the required guns well below the eye-line , not only giving the gunners an improved view but also enabling a reduction in the cros 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:

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.
Photographs of the almost completed fuselage do not show what tail and wing type was to be fitted although  the Type 317 wing would have been less complex to design and build – an important consideration at the time.It might also be noted that Mitchell's aerodynamicist, Beverley Shenstone, who was familiar with advanced wing theory and who was, no doubt, a strong influence on the Type 316/8 deltoid wing shape, had left the company by 1938 and so the more conventional and less complex wing shape most likely prevailed.
      By November, 1938, Mitchell’s team was able to submit 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:

Power Rating
Bomb Load
Max. Speed
Supermarine (estimate)
1330 hp
3,680 miles
8,000 lb.
330 mph
Stirling I
1590 hp
1,930 miles
5,000 lb.
260 mph
Halifax BI
1145 hp
1,985 miles
5,800 lb.
265 mph
Lancaster I
1390 hp
2,530 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 these figures for Supermarine’s proposed bomber would have been attained  – after all, it was conceived at the same time as the Stirling and Halifax but with an estimated speed close to that of the new fighters; and its projected range and bomb load were also impressive. 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 Supermarine estimates might have been proven to be rather optimistic.
 Unfortunately the project only reaching the stage of two prototype fuselages when they were destroyed by enemy bombing and the Chief Designer never lived to learn of the fate of his last main project, just as he never actually saw his Spitfire go into squadron service before World War II started.

One of the bomber fuselages before their destruction by enemy action.

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, the very day that his first Spitfire, Type 224, was finally retired, to eventually become a ground target at the gunnery range at Orfordness. 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.

I am indebted to John Dell (Dinger's Aviation Pages) for some of the information contained above.

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 (details below) which also provides material for wider reading, grouped according to specific areas of interest. 

More information and photographs, 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.

No comments:

Post a Comment