As soon as deliveries to No. 480 Coastal Reconnaissance Flight began, the RAF undertook a series of long-range proving flights. N9896 made a three-day round trip from Felixstowe to Rosyth in Scotland, followed by a fourteen-day exercise with the Scilly Isles as a base, and then a week’s cruise around coastal waters; also, four Southamptons covered 10,000 miles in a twenty-day cruise around the British Isles, including exercises with the Royal Navy in the Irish Sea.
These flights established a new standard in naval reconnaissance aircraft. They also marked the point at which Supermarine achieved real economic stability and prosperity. Supermarine publicity pointed out features likely to appeal to potential customers – its ruggedness and the many practicalities of its design – and went on to describe features which the RAF had proved:
The machine has been flown continually on one engine, and can be manoeuvred and turned against the pull of the one engine without difficulty. The well-known qualities of the Napier ‘Lion’ engine have been used to the fullest extent by an efficient installation, with the result that not the slightest troubles have been experienced from the power units throughout the many thousands of hours of flying these machines have carried out.
A Southampton II, the sixth of the 1929 Argentinian batch of eight. (Courtesy of Solent Sky Museum)
Mention was also made of the metal hull version of the Southampton that had been ordered by the Air Ministry – which gave rise to the Southampton II appearing in 1926. As a result, the total order for the type eventually rose to eighty-three, when the metal-hulled Marks II to IV were ordered and when sales were extended to Japan, Argentina and Turkey.
The Royal Air Force Far East Flight
The new Mark II machine also encouraged the Air Ministry, in 1926, to order four new Southamptons, with increased petrol and oil capacities and with larger radiators, specifically to initiate a proving cruise to the far reaches of the Empire. As the Secretary of State for Air put it, ‘it was our settled policy to show the Air Force, as the Navy showed the Fleet, in the distant parts of the Empire’.
The confidence in the Supermarine machine is evident from the fact that the cruise, by essentially standard RAF machines, was to incorporate overflights of many countries only previously visited by the pioneering Cobham, and to go as far as Australia, which had only been visited, singly, by four previous aeroplanes. Additionally, it was to circumnavigate that continent – a feat which had been achieved only once to that date, by a Fairey IIID on 6–18 May 1924.
Readers of the 1927 issue of Jane’s would, therefore, have been well aware of the ambition and confidence of Supermarine when the company announced:
A number of the metal-hulled ‘Southamptons’ are now being completed to equip the RAF Far East Flight. These Southamptons will be flown out to India, via the Mediterranean, and then on to Singapore and along the Dutch East Indies to Australia, where an extended flight round the Australian seaboard, in conjunction with the Royal Australian Air Force, is contemplated.
The leader of an earlier Mediterranean flight of the Southampton I, Squadron Leader Livock, was again chosen, as well as Flight Lieutenant H.G. Sawyer, who, as a junior officer, had taken part in one of the early British Isles proving flights. But, on the occasion of this much more extensive and important Far East Flight, a Group Captain was put in command – H.M. Cave-Brown-Cave (who, on arrival in Australia, became known as ‘Home-Sweet-Home’). His orders were ‘to open the air route to Australia and the East, to select landing sites, to see how far flying boats and their crews were capable of operating away from fixed bases and under widely varying climatic conditions, and to show the flag’.
Thus, while there was a clear imperialist motive behind the proposed flight, the other main concern was to prove the feasibility of reliable air transport, with scheduled stops for servicing and for inspections to see how the aircraft were standing up to the testing itinerary.
The main cruise began from Plymouth on 17 October 1927, and finished at Seletar, Singapore, on 28 February 1928. The engines were replaced on arrival at Singapore and one of the aircraft, as prearranged, was dismantled and sent back to England for detailed inspection. The flight then proceeded to circumnavigate Australia, and fly around the China Sea to Hong Kong and back. In all, they flew 27,000 miles, in formation, at an average speed of 80mph and in sixty-two timetabled stages of about 400 miles at a time. During the whole cruise, the Southamptons only fell behind schedule three times, twice because of bad weather and once with engine trouble; one machine was delayed by a cracked airscrew boss.
Another extended formation flight carried out by Mitchell’s aircraft, the Baltic flight, included the cities of Esbjerg, Copenhagen, Stockholm, Helsinki, Tallin, Riga, Memel, Gothenburg and Oslo. A total distance of over 3,000 miles was covered, again without mishap. Squadron Leader Livock, who was second in command of the Far East Flight and leader of the formation, gives a full account of these flights in his autobiography, To the Ends of the Air, which is well worth reading for its accounts of the difficulties and frustrations encountered when pioneering air routes in areas where, understandably, there was little comprehension of aviators’ special needs.
Southamptons of 201 Squadron during the 1930 Baltic flight. (Courtesy of E.B. Morgan)
Two out of a flight of four Douglas DCWs had flown round the world during 1924, and other nations made more publicised formation flights in following years. Yet the Southamptons’ Far East Cruise in particular, which was completed in scheduled stages by the entire formation, must be regarded as directly instrumental in the establishment of the Imperial Airways Empire routes of the 1930s, and as one of the milestones in aviation history. The Daily Mail was in no doubt: ‘As a demonstration of reliability, the flight will rank as one of the greatest feats in the history of aviation.’
Another assessment of Mitchell’s achievement in the field of seaplane design appeared in the caption to a picture of a Southampton I flying boat featured at the beginning of Jane’s for 1925: ‘One of the most notable successes in post-war aircraft design.’ It was surely no coincidence that the Supermarine entry in Jane’s for the same year records, for the first time, the identity of its 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.’
He had just passed his 30th birthday.
THE REVOLUTIONARY
SCHNEIDER FLOATPLANE
After Supermarine’s resounding defeat in the 1923 Schneider Trophy competition, funding and support for future competitions was now made available by the Air Ministry. This allowed Mitchell the luxury of designing an aircraft that was not dependent on straitened company resources and recycled airframes, and it turned out to be a significant departure from all the Supermarine aircraft which had preceded it.
Sea Urchin.
Savoia S.51.
As with the Spitfire, however, his immediate response was not especially original. Indeed, his initial proposal, the ‘Sea Urchin’, still looked towards the flying boat approach, and might be regarded as essentially an improvement on the Italian Savoia S.51 racer, whose 1922 speed record for seaplanes (174.08mph) had been only marginally less than the top speed of the later Supermarine Sea Lion III. Nevertheless, Mitchell proposed a sesquiplane configuration similar to that of the Italian design and with a similar high thrust line. On the other hand, it might be noted that his hull revealed somewhat similar styling to that of his Southampton, particularly in respect of the upswept rear hull. Additionally, the drag penalty of the high-mounted engine was to be reduced by situating the engine in the hull and driving the propeller through bevel-geared shafting – some response, at least, to the successful American in-line engined CR-3.
The Sea Urchin proposal was not pursued because of serious doubts about the practicality of the propeller shaft gearing and, fortunately, the American hosts for the 1924 event s
portingly postponed the competition as none of the other nations who were expected to compete were sufficiently prepared. As the American winner of the last Schneider Trophy contest achieved an average speed 20mph more than Mitchell’s modified Sea Lion III, a comprehensively different design had really been called for and Mitchell now had time to produce such an airframe.
The allocated Air Ministry serial number for the new machine was N197, although this was never carried, and despite what turned out to be a revolutionary design Supermarine referred to the new machine only as the S4 – ‘S’ presumably referring to Schneider and ‘4’ indicating that it was the successor of the Mark III Sea Lion.
The S.4
When the secrecy surrounding its build was lifted, its sensational appearance was well summed up by Flight:
One may describe the Supermarine Napier S.4 as having been designed in an inspired moment. That the design is bold no one will deny, and the greatest credit is due to R.J. Mitchell for his courage in striking out on entirely new lines. It is little short of astonishing that he should have been able to break away from the types with which he had been connected, and not only abandon the flying boat type in favour of a twin float arrangement, but actually change from braced biplane to the pure cantilever wing of the S.4.
The dramatic leap from the type of aircraft he had modified for the previous two trophy competitions can be readily appreciated from the opposite side views.
It ought to be noted that nearly a year earlier the French speed record holder, the Bernard V-2 land plane, had displayed some features which might have prompted Mitchell’s design. Its Hispano-Suiza engine was a broad arrow design similar to that of the S4’s Napier Lion engine and it was faired almost identically into the fuselage and wings; it also had cantilever flying surfaces, underwing radiators and a similar pilot’s cockpit position.
Nevertheless, when Penrose later wrote of ‘the startlingly novel and beautiful Supermarine S4’, he was at least reflecting the dramatic appearance of a revolutionary floatplane design and was surely right in responding to its fine lines. In comparison, it might not be unduly partisan to consider that the Bernard land plane had a much more clumsy appearance.
Supermarine’s Alan Clifton gave a more clinical ‘in-house’ response and singled out the unique attachment of the floats: ‘It was an exceptionally clean design, with a central skeleton of steel tubing which included daring cantilevered float struts.’ This ‘central skeleton’ consisted of two sturdy ‘A’ frames, with the engine mounting bolted to the front frame and the rear fuselage section fixed to the rear one; between these two frames, the wing centre-section was positioned. The floats were attached to the feet of the frames, carefully faired into the tops of the floats, with similar fairings at the fuselage join. This characteristically and deceptively simple arrangement of the frames was known in the works, less reverently, as ‘the clothes horse’.
Perhaps because approval to begin building had only been received on 18 March 1925, and also because of this move from flying boat building, Supermarine subcontracted provision of the floats to Shorts, whose own testing tank had been specifically built for simulating aircraft conditions. As the cantilever wing proposal represented a bold departure from the earlier wire-braced company types – and, indeed, from almost all other aircraft of the time – stringers were rebated into the ribs and an early form of stressed skinning was achieved by sheeting the wing, top and bottom, with load-bearing plywood which decreased in thickness towards the tips.
The Sea Lion II (1922).
The S4 (1925).
Thus it was that Mitchell felt able to take the radical step of dispensing with struts and wire bracings for the wings and tail surfaces. He also did away with bracing wires for the floats, although they were fitted with two thin-section cross members. An appreciation of the conceptual leap represented by the S4 can be gained by a comparison of its forward-looking cantilevered structure with that of the previous Sea Lion, which had thirty-three struts and forty-two bracing or external control wires.
With the new machine, the control surfaces were activated from within the structure via rods and torque tubes, and streamlining was also achieved by mounting the newer Lamblin radiators horizontally on the underside of the wings – their fins and the oil-cooling pipes on the underside of the fuselage were the only significant protuberances on the whole machine, with the coolant being carried to and from the engine via piping buried in the underside of the wings.
The following reminiscence of Cozens reminds one that the S4, despite its futuristic shape and polished metal cowlings, was built with traditional woodworking techniques. Its sound, however, was something else – no doubt the result of its ungeared racing engine, producing propeller tip speeds around the speed of sound (2,600rpm turning an 8ft 6in airscrew – go figure):
After being beaten in 1923 by trying to make the best of an outdated machine, Mitchell went to the other extreme and produced something that was far ahead of its time. It was, of course, of wooden construction, not surprising as neither the designers nor the workforce were capable of building a sophisticated metal machine, and [the fuselage] exploited the Linton Hope technique to the limit … It was built in great secrecy which gave rise to even more curiosity and expectancy than was usual for a Schneider Trophy, always a sensitive subject and it was guarded like a racehorse in a training stables.
By raising the compression ratio the Napier’s power was increased and the metal Fairey Reed propeller was quite new in design and construction, so that when it finally emerged and the engine was run up a new sound came, something that the local people had never heard before, and indeed, very few people ever heard in all their life, a sort of high pitched scream of immense power.
Radiator drag was reduced to a minimum by building it flush into the wings, and because it was made of thin copper plates soldered together it had to be very carefully formed and fitted …
Plainly, this aeroplane needed very skilful handling, more so because the mid-wing shape made visibility poor, and Captain Biard was the only man who could fly it, and an eyewitness said that even he made an airborne hop of a mile before he finally got off between Lee-on-Solent and Calshot …
Apart from the mid-wing configuration, the pilot also had limited vision on account of being situated low down; Biard claimed to have nearly collided with the liner Majestic on take-off – having not seen it at all until the last minute – and, when he came to land, he nearly hit a dredger. However, having survived the traumas of the first flight, the new machine went on to gain the world speed record for seaplanes and the outright British Speed Record: 226.75mph – nearly 40mph more than the Curtiss CR-3 record established the previous October.
When the S4 team arrived at Chesapeake Bay, near Baltimore, for the forthcoming Schneider Trophy competition, the tented accommodation for the aircraft and for the workshops was found not to be ready. Having arrived on 5 October, it was only possible to begin erecting the aircraft on 12 October, and days then elapsed before weather conditions allowed test flying to begin. Then Biard went down with influenza and a gale caused tents to collapse. A heavy pole fell across the tail unit of the S4, which was only repaired in time for the navigation tests on the 23rd of the month. By this time, Biard was up and about and insisted on flying the S4 as only he had had experience of handling this revolutionary machine.
Unfortunately, the S4 story was not to have a Boys’ Own ending, as it crashed into the bay following a steep turn which appeared, perhaps, to have been caused by ‘flutter’; a high-speed stall or wing distortion was also suggested by contemporary observers. Whatever the cause, it luckily occurred at low level and Biard survived. Mitchell, always concerned for the safety of his pilots, had set out to rescue him but his boat had engine failure. Biard was picked up after some time in very cold water. His own account of the accident was that, as he came out of a turn at speed and dived down for a straight run, the control stick set up such violent side-to-side oscillations that he lost cont
rol.
The phenomenon of flutter was being experienced at about this time with military aircraft. Penrose quotes Flight Lieutenant Linton Ragg of the Royal Aircraft Establishment at Farnborough as experiencing similar stick behaviour: ‘wing flutter had caused trying experiences, such as coming down with hand and knees badly bruised by the control column as it played hide-and-seek round the cockpit’. Biard’s description of similar side-to-side movement of the control column points to aileron flutter, and later remarks at Supermarine confirm this conclusion: Mitchell, later concerned about the need to avoid overbalancing of the Spitfire ailerons in a dive, wrote somewhat enigmatically, ‘I believe this is the cause of several accidents involving ailerons’, and Ernest Mansbridge, explaining the thickness of the preceding Type 224 wing being due to caution, was more direct, ‘We were still very concerned about possible flutter, having encountered that with the S4 seaplane’.
Major John Buchanan, who had represented the technical department of the Air Ministry at the competition, merely reported that the S4 had stalled, although he may have suspected ‘pilot error’ (such as unfamiliarity with high speed stalling). His recommendations for future responses to Schneider Trophy competitions included the employment of pilots specially trained for high speed flight – as per the American Navy and Army teams of the last two contest wins.
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