From Nighthawk to Spitfire

by John K Shelton

  The three-engined layout that had been requested by Denmark was also found to produce trim problems, because the additional power at the high thrust line caused the machine to become distinctly nose heavy as power increased. Mitchell’s response was to fit a somewhat ad hoc auxiliary stabiliser higher up between the three fins, but this lowered the flying speed below that contracted for. And so, in the end, the Royal Danish Navy took delivery of a standard Southampton instead.

  Fortunately, in 1928, the Honourable A.E. Guinness was persuaded of the potential of a private flying boat, in addition to Fantome, the largest and most spectacular barque-rigged yacht in the British registry. Thus the unwanted Nanok was converted into an ‘Air Yacht’ with comfortable cabins for up to twelve passengers. Now named ‘Solent’ and registered G-AAAB, it soon became a familiar sight, flying from the Hythe seaplane base on Southampton Water to Lough Corrib, County Galway, close to Ashford Castle, its owner’s home.

  The Supermarine Solent. (Courtesy of E.B. Morgan)

  The Air Yacht

  The second Air Yacht was to follow in 1930 and began as an Air Ministry specification, calling for an armed reconnaissance flying boat. At this time, one might have expected a traditional metal-hulled biplane but, instead, what eventually appeared was an uncompromising all-metal monoplane with a wingspan of 92ft and powered by three engines which were now faired into the wings – as with all Mitchell’s later multi-engined flying boats.

  It had a plank-shaped parasol wing with sloping V struts supporting the wing about two-thirds out from the centre line. The hull, instead of the curvaceous design made famous with the Southampton, was a slab-sided type, strengthened with horizontal corrugations; it also had extremely angular fins in keeping with the rest of the general arrangement. The new design still had fabric-covered flying surfaces but it had one feature which made it stand out from all other Supermarine aircraft and its contemporaries, and this was the employment of sponsons attached to the lower sides of the hull instead of the customary wing-tip floats.

  However, despite its unique appearance among British aircraft, its similarity to the (smaller) German Dornier Wal series of flying boats was, to say the least, very close (see drawing overleaf). In fact, one of the Wal machines had been tested at Calshot, and Denis le P. Webb, who had joined Supermarine in 1926, later wrote: ‘my impression was that R.J., who had always been more of a practical engineer than technician, had allowed himself to be lured by some of his bright boys into following other people’s ideas instead of his own.’

  The Supermarine Air Yacht.

  Dornier Wal.

  Air Yacht.

  Perhaps because it was such a departure from the well-tried Supermarine biplane types, the new approach was not an immediate success. Its maximum speed was well below the 120mph that the joint Vickers/Supermarine Southampton X achieved the following month, with only slightly more powerful engines. It was accordingly re-engined with 525hp Armstrong-Siddeley Panthers and was then found to be capable of 117mph. However, it was still not possible to maintain height with any significant payload when one of the three engines was throttled back.

  Despite the fact that the Short Singapore II biplane, built in the same year, could achieve 140mph, the Air Ministry continued to support the novel Supermarine monoplane by, at least, paying for repairs and for the replacement of the sponsons when they failed in fairly rough seas – giving the lie to the usually held view that officialdom at that time was entirely hostile to the monoplane concept.

  Harald Penrose, reporting on the interwar aviation scene, did compare its design favourably with two more traditionally-built flying boats, but recorded that ‘unfortunately the sponsons suffered battering by waves and even on calm water gave inferior take-off compared with the usual chined British hull’. Nevertheless, he went on to say that ‘assessed as an engineering structure of considerable aerodynamic cleanness, the Air Yacht was a big step forward compared with the established three-engined Iris biplane, of which four were in the course of delivering to the RAF, or the Calcutta-derived Short Rangoon prototype due to fly in the summer’. (Or, in fact, compared with Mitchell’s own subsequent biplanes, the Scapa and the Stranraer flying boats!)

  Indeed, Penrose’s suggestion that the Air Yacht might represent the future is supported by a comparison with the American Consolidated Commodore, which also had a parasol fabric-covered wing of about the same span. It appeared in the same year as Mitchell’s machine but was far less clean, aerodynamically, with well over thirty supporting struts. But despite its potential promise, Harry Griffiths, another Supermarine employee, gave the Air Yacht a negative report:

  It had a very long take-off run and there was always doubt as to whether it would leave the water at all with a full load of passengers, stores and fuel. Refuelling in those days was done with hand pumps from barrels taken out on a barge. There is a story (unconfirmed but, knowing the man, possibly true) that Biard, the test pilot, refused to attempt a full load take-off and ‘went through the motions’ of filling with fuel by pumping from a number of barrels, some of which were empty.

  And so, by 1931, Supermarine began to try to salvage matters by seeking civil registration (G-AASE), in the expectation of fulfilling an order from the Honourable A.E. Guinness for a replacement of his Solent Air Yacht.

  The new machine’s boxy hull certainly provided very advantageous dimensions for the passenger cabin, which Supermarine quoted as a generous 35ft length, 6ft 6in height and 8ft width. It was luxuriously appointed, with owner’s cabin complete with bed, bath and toilet, a galley with full cooking facilities, and additional wash basins, toilet and comfortable lounge with settees and sideboards in a separate cabin for five other passengers. Electric lighting was fitted throughout the interior, which Biard described as ‘one of the most luxurious that anyone had then seen’ and ‘fitted out in glass and silver, with deep-pile rugs underfoot … the chairs were deeply sprung, the cabins softly lighted … no offending smell of petrol or oil ever filtered into the passenger accommodation’, and the temperature could even be regulated by a blown air system.

  Unfortunately, Guinness turned to a Saunders-Roe product and the Air Yacht was put in storage until rescue came in the form of the formidable American, Mrs June Jewell James, a keen motorboat and flying enthusiast. Mrs James had been shown over the aircraft stored at the company’s Hythe base and, as a result, she negotiated its purchase from Supermarine in 1932. She named her new acquisition ‘Windward III’ and became so impatient to have the use of her new purchase for a cruise to the Mediterranean and North Africa that she insisted on starting some days before the prearranged departure date.

  Biard, who had been seconded to her by Supermarine, supplied a description of the frantic preparations and of the one, and only, cruise attempted in the aircraft. Despite some exaggerations, his (ghosted?) account is of interest to social historians as well as to those interested in the ability of another Mitchell design to withstand what were, clearly, extremely unfriendly conditions when it anchored in Cherbourg Harbour. After Mrs James and her companions were nearly drowned there in a fierce storm, Biard flew the Air Yacht down to Naples where Mrs James proceeded to obtain audiences with both the Pope and Mussolini.

  Having flown to France to collect Mrs James, who had by now gone on to Paris, Biard had to hand over the Air Yacht at Naples to a relief pilot as his stomach muscles, which had been torn in the S4 crash of 1925, needed surgery. This pilot, Flight Lieutenant Thomas Rose, although very experienced, suffered an engine failure and stalled into the sea in the vicinity of Capri on 25 January. The owner suffered a broken leg, but otherwise there were no very serious injuries sustained; however, the aircraft was too badly damaged to be worth recovering.

  Thus ended the Air Yacht. By this time, any hopes of a military role for it were well past, yet this unique Supermarine aircraft did look forward eight years to the Saunders-Roe A33. This aircraft, another 90ft parasol monoplane with similar supporting struts from its sponsons, was built
in 1938, but the old porpoising problem caused structural failure of the mainplane on the first high speed taxiing test and it was not proceeded with.

  Had Mitchell lived long enough, and had the Air Ministry generally shown a more single-minded faith in the future of monoplane flying boats, one wonders if Mitchell’s last flying boat, the Stranraer biplane, would have been a Supermarine Air Yacht type equivalent to the American Catalina which equipped twenty-one RAF and Royal Canadian Air Force (RCAF) squadrons during the Second World War. Incidentally, the actual predecessor of the Catalina was the Consolidated Commodore, mentioned earlier as being aerodynamically far less clean than the Supermarine Air Yacht.

  The Seamew

  For the sake of completeness, the Seamew ought to be mentioned. Its first flight was in the year following that of the Nanok, and it also proved to be a disappointment. It had been designed as a three-man deck-landing reconnaissance seaplane and Mitchell decided on a twin-engined approach, even though it had about the same wingspan as his Seagull, Scarab and Sea Eagle machines. These single-engined designs, especially the ones with rear facing airscrews, were less affected by spray than the Seamew, where smaller propellers had to be substituted in order to counteract rapid deterioration due to water ingestion. However, this expedient resulted in a reduced rate of climb, and the aircraft was also found to be very nose heavy and suffering from extensive corrosion to the type of metal being used in the airframe, as well as in the mainplane fittings. Two prototypes were built but they did not lead to any orders.

  GIANTS

  While the early Dornier Wal series had had a very obvious effect on the design of the Air Yacht, the huge Mark X version made a great impression in wider aviation circles when it arrived at Calshot in November 1930, for a two week stay. This version had a crew of ten and was capable of carrying seventy passengers, in something approaching steamship luxury. This included a smoking room with its own bar, a dining salon, and seating for the sixty-six passengers which could also be converted to sleeping berths for night flights. It was powered by twelve 610hp engines, accessible via a passageway in the wings.

  The Type 179 Giant

  Not entirely to be outdone, in 1929 the Air Ministry sent Supermarine a specification for a forty seat civil flying boat, which was first projected as a high-winged monoplane, with three fins, a relatively flat-sided fuselage and with bulbous floats attached to the underside of each wing root, bulky enough to be almost classified as sponsons. Six engines were to be mounted in tandem on pylons above the wing, Dornier X fashion and, notably, it had provision for passenger seating in the leading edge of the very thick wing.

  While the new design was essentially a development from the Air Yacht, the former plank-shaped wing was now replaced by the first appearance of Supermarine elliptical flying surfaces. Its proposed torsion-resisting nose section also looked towards the wing structure of the Spitfire, as did the use of a single spar – although in this case it was to be 6ft in depth.

  Had Mitchell’s design been completed, its size would certainly have put his company ahead of other large flying boat contenders. It was to have a wingspan 65ft more than the contemporary six-engined Short Sarafand and nearly 3ft more than that of the imposing Dornier X. About this time, there was another very large, seven-engined aircraft – the K-7 designed by Constantin Kalinin – which, interestingly, also featured an early example of the elliptical wing (see the drawing on p.150). It should, however, be pointed out that, while the Russian plane has always attracted the attention of air historians because of its size (and because it flew), Mitchell’s projected machine would have had a wingspan that was larger by 10ft. With a span of 185ft, its name ‘Giant’ was therefore appropriate, and it would have represented a significant departure from the previous, almost universal, formula of braced, fabric-covered biplanes.

  Almost a year later, the rather untidy arrangement of three rows of forward facing engines was revised, whereby two inner nacelles now housed two engines apiece, facing fore and aft, and two outer nacelles had a single engine each, driving a tractor propeller. Rolls-Royce steam-cooled engines were now proposed, with the leading edge of the wing to be used as a steam condenser for the cooling system, a variation on the wing-surface radiator system of the S5 and S6 types. The passenger accommodation in the wings was to be eliminated in order to accommodate the evaporative cooling system, and this allowed the wing to have a thinner, more efficient, cross section. Mitchell had also decided upon a return to conventional wing-tip floats instead of the high-drag sponson type arrangement.

  Thus by early 1931, when the keel of the Giant was laid down, most of the Dornier X influence had disappeared, as a company publicity photograph revealed (below).

  While the early proposals for the Giant showed a tentative move forward, the upswept tail section, the nicely streamlined engine nacelles and the fore part of the hull now reveal Mitchell’s thinking to be in advance of forthcoming larger American flying boats. For example, the Sikorsky S-40, of the same year that the keel of the Giant was laid down, represents a traditional approach of struts and wires; also, the ‘canoe’ hull and the necessary twin booms for the tail section, which no doubt achieved a good weight/strength ratio, did not represent the way forward for later flying boat designs (see drawing on p.81).

  A graphic illustration of Supermarine’s forward thinking (compare the Southampton, bottom left, on the Supermarine slipway). (Courtesy of Solent Sky Museum)

  The Sikorsky S-42.

  The later Sikorsky S-42 had a tail unit integral with the main fuselage, and had lost most of its predecessor’s struts and wires. Coming a few years later than the proposed Giant, it had its engines neatly faired into the wing. It did, however, still retain wing and tailplane struts – compared with the Mitchell’s projected cantilever structures – and this in a machine that was to have a wingspan of 185ft, compared with the 118ft span of the American aircraft.

  Alas, early in 1932, the project was cancelled in view of the continued economic problems that faced the country, leaving Joe Smith, the chief draughtsman, the unpleasant task of laying off twenty of his drawing office staff. Consternation was not limited to Supermarine, for questions were asked in Parliament, where the Under Secretary for Air justified the government’s decision, claiming that over 70 per cent of the estimated cost would be saved by cancellation. (Incidentally, nor had the Germans felt justified in putting their huge Do X into quantity production.)

  Had the Giant been built, perhaps Mitchell’s bomber (see pp.162 foll.) might have been designed earlier and might even have been in the air when the critical need arose for such weapons.

  Meanwhile, one British aircraft of a somewhat similar type did actually fly. This was the Blackburn Sydney, a monoplane with a metal-skinned wing, albeit braced and of only 100ft span. This machine could also have spearheaded the movement away from the traditional British fabric-covered biplane, but the Air Ministry did not place a production order. It was thus fated that, owing to circumstances outside the control of Supermarine, Mitchell would not be remembered (as might otherwise have been predicted) for his contribution to the main flowering of the Imperial Airways routes, nor for the creation of later equivalents of the well-known wartime monoplane flying boats, the Sunderland and the Catalina.

  MITCHELL’S SEAPLANES AT WAR

  Most of Mitchell’s seaplanes were designed for military purposes, although naval reconnaissance rather than bombing had been the main requirements from the Air Ministry. Foreign orders were more specifically aggressive: the Scarab amphibian bomber for Spain and the Nanok torpedo carrier for Denmark. All the aircraft were, basically, traditional biplanes and Mitchell was also to design two other military biplane flying boats, closer to the outbreak of the Second World War, despite the obsolescence of their configuration.

  The Scapa

  The first of the new designs, which was to become known as the Scapa, was ordered as a successor to the long-serving Southampton, to be supplied with a metal hull and superstru
cture and with the new Rolls-Royce Kestrel engines. In the relatively depressed economic situation in Britain and with other companies offering multi-engined flying boats, a more aerodynamically efficient version of the Southampton with the cheapness of using only two of the new, efficient engines seemed a good proposition, and so Supermarine offered the last Southampton, S1648, as the proposed prototype, without extra cost to the Air Ministry.

  The new aircraft was designated the Southampton IV and so it might have been regarded as, essentially, an ‘improved Southampton’, particularly as its water-planing lines resembled that of the previous aircraft. Indeed, tank testing now available via the new parent firm, Vickers, did not suggest any real need to depart from the earlier basic shape – a compliment to the intuitive design of the hull of 1925. In fact, a widening behind the step, to counteract spray hitting the tail surfaces, was abandoned when it was found to produce an unpleasant pitching on take-off.

  In other respects, the new machine was, effectively, a new design. ‘Stretching’ the Southampton with a lengthened bow and a deeper forefoot, allied to a flatter top-decking, allowed for more useable space within, as well as significantly altering the appearance of the new machine. Also, the slab-sided approach of the Air Yacht and of the slightly later Walrus (another reflection of the economic situation?) was evident, although the upward sweep of the tail and other curvatures restored something of the elegance of the Southampton hull.