Monday, 20 March 2017

R.J. Mitchell’s Annus Mirabilis, 1925 : Part I – the Southampton Flyingboat

It is surely no exaggeration to identify 1925 as the year when two of Mitchell’s aircraft stood out dramatically from what had preceded them. This year marked his full emergence as a designer who had transcended the design conventions that he had inherited and who was now striking out boldly into the future. The young man who had joined his aero firm in 1916 at the age of 21, assisting with the designs of others, now produced – nine years later – the first standard naval reconnaissance aircraft since the end of World War One and the racing floatplane which set the basic design configuration for all subsequent Schneider Trophy machines. 
     By this time, the question of a suitable replacement for the Felixstowe F. series of military flying-boats was becoming critical and the aim of developing air links with the outposts of Empire seemed a long way off – as Hoare recalled: ‘In 1922, there were no aeroplanes capable of maintaining a long distance service. The existing heavier-than-air machines were low-powered, very noisy and uncomfortable. Flying boats had almost ceased to exist and there was no plan for an Empire air line of any kind.’
    Thus the successful trials, at Felixstowe, of the Swan (see my Blog: “R. J. Mitchell’s Ugly Ducklings: the Scylla and the Swan”) had not gone unnoticed at the Air Ministry, whose officials had been very impressed by the standards set by the Sea Eagle, the year before. As a result of this appreciation of the new standards in flying-boat performance which Mitchell had now established, the Air Ministry took the unusual step of ordering, straight off the drawing board, a number of reconnaissance flying-boats on the basis of the Swan amphibian passenger carrier.
The Southampton I – the new standard reconnaissance machine

Supermarine Southampton (from painting by author)

By the time that Supermarine received Specification R.18/24, in the August of 1924, for a modified and slightly enlarged Swan-type flying-boat, Mitchell was already having this aircraft’s hull lines redrawn to improve the streamlining. The eventual modifications were such that a ‘Swan Mark II’ designation was less appropriate than a completely new name – “Southampton”, signifying Supermarine’s increasing status where its factory was sited and whose dignitaries had welcomed home the successful Sea Lion II in 1922. Indeed, a silver shield with the Southampton coat of arms was fixed to the bow of N9896, the first production machine–visible in the photograph below:
The first Southampton
The company could, with some confidence, thus mark their increasing importance in the manufacturing community of the area as the Air Ministry order was substantial by the criteria of the day: it had called for six standard military aircraft (N9896-N9901) and for an experimental one, N218, to be fitted with a metal hull. And these aircraft were also the largest aircraft yet to come from the Supermarine production line.
    The new machine continued the planing configuration that Mitchell had been developing since 1923 with the Sea Eagle but it was now a part of one of the most elegant hulls that Mitchell had ever been responsible for; indeed, the transformation of the lines of its prototype, the Swan, was dramatic. Taking advantage of the new, more utilitarian military requirements, he removed the ad hoc looking high-drag crew compartment above the Swan’s lower wing and utilized the passenger baggage compartment area for the pilot and navigator, sitting in tandem in open cockpits. He also streamlined the Swan nose and dramatically swept the rear of the hull upwards to keep the empennage well clear of the water.
    Whilst this last feature had been seen earlier on both the small Latham L-1 and the FBA Schneider aircraft, as well as on the World War I Grigoravich machines, its incorporation in the large Southampton hull was a novel and bold move. Elsewhere, in larger hull designs, Curtiss and Sikorsky moved from the previous Felixstowe unswept approach to the employment of ‘canoe’ type hulls.
Sikorsky S-40
In contrast, the elegance of Mitchell’s sweeping lines was emphasised and complemented by the redesign of the Swan fins which were now swept back in a single curve, resulting in the new Southampton being regarded as ‘probably the most beautiful biplane flying-boat that had ever been built’ and ‘certainly the most beautiful hull ever built’.
     We can be sure, however, that the aeroplane’s ability to maintain height on one engine as well as its maximum range of 500 miles weighed the stronger in Air Ministry minds than any aesthetic considerations. No doubt they appreciated the extreme practicality of the design: as with the Swan, Warren girders separated the centre section of the wings without the need for wire bracing and so enabled a change of engine or servicing to take place unimpeded and without interference to the airframe. This centre-section was plywood covered, again for ease of operation by mechanics; the leading edges of the outer panels were also plywood covered to ensure a smoother aerodynamic entry.]
     The lower wing roots were not incorporated into the boat hull; instead the wing superstructure had attachment points on the top of the hull and external struts from the lower-wing centre-section spars to reinforced frames in the hull. In this way, Mitchell retained as much flexibility as possible in the Linton-Hope type hull and in the Swan this arrangement had also created an unencumbered and roomy passenger space with adequate headroom. In the Southampton, it also had the advantage of enabling good crew communications as well as mobility.
     Ahead of the pilot was a bow cockpit for a forward gunner and, a little further back from where the Swan crew had been located, were two staggered cockpits for rear gunners, one on each side of the centre-line. Hammocks, basic cooking, and lavatory facilities were also provided – thus beginning the tradition of providing the RAF with maritime aircraft which could be reasonably self-sufficient for prolonged periods of time.
Officials must have also been impressed by the efficiency with which the first Southampton was delivered to them. As Supermarine’s publicity recorded: ‘Something of a record in design and construction was achieved with the first machine of this class, for it was designed and built in seven months, was flown for the first time one day and delivered by air from Southampton to the RAF at Felixstowe the next day’ (11 March, 1925). Its cause could not have been harmed when, after being damaged there in a collision with a breakwater, it was taxied all the way back to Woolston for repairs. Pilots subsequently reported that it ‘never gave the slightest trouble … and was a joy to fly’, ‘a great step forward, a delight to fly and operate’ – summed up by Penrose when he reported for the year 1925 that ‘it was the beautiful new Supermarine Southampton flying-boat which was receiving unstinting approbation from RAF pilots.’
     As soon as deliveries to 480 Coastal Reconnaissance Flight began – in the summer of 1925 – four Southamptons flew a twenty-day cruise of 10,000 miles around the British Isles, including exercises with the Royal Navy in the Irish Sea, and the first Southampton to be completed made a three-day round trip from Felixstowe to Rosyth in Scotland, followed by a fourteen-day exercise with the Scilly Isles as its base, and then by a week’s cruise around coastal waters.
     Significantly, the Supermarine entry in Jane's All the World's Aircraft for 1925 records, for the first time, the identity of the company's Chief Designer: ‘The firm has a very large Design Department continually employed on new designs, under the Chief Designer and Engineer, R. J. Mitchell, who has established himself as one of the leading flying-boat and amphibian designers in the country’. Another view of Mitchell’s achievement in the field of seaplane design came from the caption to a picture of a Southampton I flying-boat at the beginning of Jane’s for the same year: ‘one of the most notable successes in post-war aircraft design’. The Designer had just passed his 30th birthday.

It can be no exaggerationto say that the advent of the Southampton marked the real point at which Supermarine finally achieved economic stability and prosperity. The original order of six machines was eventually increased to a total of twenty-five – including the experimental metal-hulled machine which gave rise to the Southampton II appearing in 1926. And this total was later increased to 83 when the metal-hulled Marks II to IV were ordered and when sales were extended to Japan, Argentina and Turkey.

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For reference sources, see my Blog: “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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