Tuesday, 28 March 2017

R. J. Mitchell – no Flash in the Pan

The slightest reflection would suggest that the design of the Spitfire had been preceded by considerable experience of high speed flight and the winning of the Schneider Trophy four times. However, a listing of his most significant contributions to aviation reveals promise even as early as the 1920s: 

·      his Commercial Amphibian of 1920 won an enhanced award at the Air Ministry competition for commercial, amphibian, flying-boats. This aircraft was his first independent design and, although it came second to the Vickers Viking, the second prize of £4000 was doubled in recognition of the promise that the aircraft had shown;
·      his modification and up-rating of an earlier company machine, the Sea Lion II, won the Schneider Trophy competition for Britain in 1922;
·      his small fleet of Sea Eagle flying-boats constituted the first British scheduled flying-boat service, operating between Southampton and the Channel Isles between 1923 and 1928;
·      his Swan (1924), a larger scale development of the Commercial Amphibian and which joined the Sea Eagle fleet, was claimed by Supermarine to be the world’s first multi-engined amphibian passenger-carrying machine;
·      the above flying-boat service was incorporated into the newly formed Imperial Airways Ltd. in 1924;
·      his Scarab (also 1924) equipped the Royal Spanish Air Force with an aircraft which, for its time, represented a formidable amphibious bomber gun-ship. This order represented a significant step towards establishing Supermarine as a prosperous aircraft company;
·      in 1925, his Southampton flying-boat, a military development of the Swan, was ordered (unusually)  straight off the drawing-board and became the standard RAF coastal reconnaissance aircraft, replacing the less satisfactory machines of World War I.  Pilots reported that they were trouble free and ‘a joy to fly’ and Jane’s described the design as ‘one of the most notable successes in post-war design’. A total of twenty-four Mk.Is were built and marked real stability and prosperity for Supermarine. Its trend-setting upswept rear hull attracted the comment that it had ‘certainly the most beautiful hull ever built; 
·      in the same year, Mitchell also produced his S.4 Schneider Trophy racer which revolutionized the design of virtually all successive competition entries: he moved, in one bold step, from wire braced biplanes  to a cantilever monoplane. Compared with the top speed of 175 mph claimed for his Sea Lion in 1923, the S.4 gained the World Speed Record for Seaplanes and the outright British Speed Record for all types with 226.75 mph two years later;
·      in 1926 Mitchell appointed one of the first metallurgists to the aircraft industry and his metal-hulled Southampton II led the way towards all-metal aircraft construction. A total of 79 metal-hulled machines were produced as well as numerous hulls for retro-fitting to the wooden-hulled Mark I, even further enhancing the prosperity and status of Supermarine;
·      the increased efficiency of the Mk.II Southampton led the RAF to create a special Far East Flight of four machines which completed a 27,000 mile cruise between October 1927 and February 1928 to Singapore and around Australia (which had only been visited by aircraft on four previous occasions and only circumnavigated by one earlier machine). The 62 time-tabled stages were completed by all the aircraft – as Supermarine publicity said, ‘108,000 machine miles giving no trouble of any consequence’ and as The Daily Mail said: the flight will rank as one of the greatest feats in the history of aviation’;
·      In 1930, Supermarine were awarded a contract (later cancelled for economic reasons by the Government) to build the largest flying-boat in the world – with a greater wingspan than the famous Dornier Do.X and only to be surpassed by the Hughes H-4 Hercules of 1947;
·      by this time, Mitchell had designed his next two Schneider Trophy racers, the S.5 and S.6 which, respectively, won the 1927 and 1929 contests. In the following event of 1931, his uprated S.6B won the trophy outright and later went on the set a new Absolute Air Speed Record of 407.5 mph. This last machine was now of entirely metal, stressed skin, construction.
     Mitchell was now described in Supermarine publicity as ‘one of the leading flying-boat, amphibian and high-speed seaplane designers in the country, had been invited to give a talk on the B.B.C., had been elected a Fellow of the Royal Aeronautical Society and awarded the C.B.E. (aged 36);
·      in 1934, the last of his medium-sized amphibians, the Walrus, was ordered by the Royal Australian Air Force and, in the following year, by the Royal Air Force; eventually a total of 746 were built. It became the standard fleet-spotter  and provided the armed forces with their slowest aircraft  –as well as the fastest which, of course, was the Spitfire;

·    The prototype Spitfire of 1936 marked a dramatic increase of over 100 mph over the most recent RAF fighter in service and Supermarine received an even more dramatic initial order of 310, three months later. Mitchell died, aged 42, without seeing the fighter go into squadron service and without knowing that nearly 23,000 examples were built and in a multitude of main variants.

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For details of the aircraft mentioned, see my other blogposts.

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

Monday, 27 March 2017

R .J. Mitchell’s Early Modifications (1919 to 1921).


Whilst Mitchell was busy with his first medium-sized, slow-flying designs (the Commercial Amphibian and, later, the Seal/Seagull II development), his firm was still interested in the possibility of selling the concept of a small naval “scout” to the Navy and Mitchell was involved with the various modifications to this fast seaplane type.

    The company’s interest in the fast interceptor had begun with an Air Ministry requirement, N.1B, for a fast manœuvrable single-seat seaplane or flying-boat fighter with a speed of 95 kt at 10,000 ft and a ceiling of at least 20,000 feet. The resultant Baby had been designed by F. J. Hargreaves, who was in charge of the drawing and technical offices at Pemberton Billing and who continued for a little while after the company became “Supermarine”. Hargreaves’ close liaison with the Admiralty Air Department produced an aircraft with what appeared to be a dangerously small fin and rudder, typical of aircraft drawn up by this design team but the Baby was, in other respects, a more ‘in house’ response to the ambitious N.1B specification.

However, this machine did not go into production because of the ending of World War I but, as Mitchell had joined the firm in 1916 and had then been involved at least with the Nighthawk (see my Blogpost: 'What was R.J. Mitchell's First Design?'), it is entirely likely that he had had some design input in the three N.IB airframes that were built: by the time of the Armistice, N59 (see photo above) had been completed and was being evaluated by the Navy and N60 was largely complete. The third, N61, was under construction and was most probably (in view of its extensive departures from the N59 design) the one bought back from the Air Ministry for entry in the 1919 Schneider Trophy competition, in the hope thereby to gain some very useful publicity.  The modifications were such that it was re-named the Sea Lion I.

Sea Lion I.

Sea Lion I

The particular configuration of this aircraft suggests that the modifications to the Baby design were largely Hargreaves’. The fin and rudder were enlarged in a shaping not followed later by Mitchell (see fin sketches below); likewise, the base of the latter was used as a water rudder, the interplane struts were splayed outwards, and the wings had balanced ailerons on the top wing only and had an inverse taper. Also, the hull was decked to keep down spray and so the front of the fuselage was far less sleek than Mitchell’s later Sea Lion II and Sea King II:
Sea King I (see later)                   Sea Lion I                                   Sea Lion II

In appearance, the aircraft suggested that the man with overall responsibility for this aircraft seemed to have favoured rugged seaworthiness rather than speed through the air; as such, it was the Royal Aero Club’s choice over the slightly faster Avro 539A, for the third entry to the 1919 Schneider Cup competition – possibly hedging their bets because of the already proven sea-going qualities of Supermarine machines. But, by the time of the Schneider contest, Hargreaves had left the company and it was Mitchell who would have assumed last-minute responsibility for this aircraft.

However, the “non-event” of the 1919 Schneider Trophy contest was of no help to Supermarine’s hopes for this type but the company persisted with their fighter flying-boat concept with their next two fast flying-boats, the Sea Kings.

Sea King I.
As Mitchell’s design inputs began in 1916, it is more than likely that he had also been involved with the Sea King modifications to the original N.1B Baby design; however, little is known about his involvement in the N60 version, also bought back from the Air Ministry, and which, it seems likely, became the Sea King I.
This aircraft appeared, largely unmodified, at the 1920 Olympia Aero Show, after Mitchell’s  appointment as Chief Designer, but how long it had been in existence in this guise before this date is unknown; certainly the direct repetition of the earlier, apparently inadequate tail configuration looks backwards rather than to the future:
 N.1B Baby and Sea King I          Sea Lion I            Sea King II  (see below)

One speculates that, at this time, the profitable modifications to the A. D. Boats had so pre-occupied Supermarine that a relatively unmodified N60 Baby was sent to the Olympia Aero Show essentially as a marker for the company’s continuing interest in the naval fighter scout concept. There is no record of the aircraft having flown, thus adding to the speculation surrounding the Sea King I. The following publicity for this aircraft, apparently re-engined, would seem to imply that control might not be quite adequate; it also reveals that the company was hoping to sell to the many private flyers that World War I had produced, if military orders could not be achieved:
The ‘Sea King’ is a small fast single-seater which for general purposes follows the structural methods of the ‘Channel Type’ boat. With its 160 h.p. Beardmore engine it puts up a speed of 96 knots, so that it is either a thoroughly sporting little vehicle for the single or unhappily married man, or is a useful small fast patrol machine for Naval work along troublesome coasts. Its chief difference in design from the ‘Channel Type’ lies in the fact that it only has a monoplane tail of the depressing kind and so takes rather more flying on the part of the pilot than does the bigger machine.
Had there been any sales, perhaps Mitchell might have wished to modify the tail surfaces but, unfortunately, neither the military nor the ‘single or unhappily married man’ came along to buy one and it had to await the Mark II development by Mitchell two years later. 

 Sea King II.
In response to the continued Air Ministry interest in a fighter design for shipboard use, Mitchell now produced an amphibian modification of the Baby/Sea King I machine: ‘designed as a high performance fighting scout, specially adapted for getting off gun-turret platforms of capital ships, or getting off and landing on the decks of aircraft carriers. The strength and design of the hull are such that it can operate on and from the water under any weather conditions in which it would be possible to operate any other sea craft [boat] of equal size’ (Supermarine publicity). It was produced in 1921 and so its modifications can be attributed entirely to Mitchell and, indeed, it bore distinct evidence of his taking over the design department at Supermarine.
The most obvious revision of the earlier design was the more generous fin and rudder area (see sketches above) – and it would appear from the Supermarine publicity quoted below that this had a noticeably beneficial effect). As with his Seal (see my Blogpost: 'Precursors of R.J. Mitchell’s Walrus'), the tailplane was now placed almost midway on the fin and the retracting gear of the Seal was again utilized. At the same time, Mitchell also devised a very simple method for the removal of the undercarriage system and a Seal type combined tailskid and sea rudder was also employed.
   The wing-tip floats were the same full depth type as employed on the Baby, Sea Lion I and Sea King I and the tailplane outline was similar to that of the Sea Lion I or the Seal II but with the lower position of the latter – whose reversed camber (“of the depressing kind” continued the Baby tradition.  The aerodynamically balanced ailerons and rudder of the Sea King I were again abandoned in favour of the Baby configuration; the more streamlined Baby/Sea King I hull was retained.

The Supermarine description of this version of the single-seat flying boat fighter type also draws attention to its flying qualities as well as to the many practical features now incorporated by the designer (a theme that would become familiar in the Mitchell story):
The manœuvrability of the ‘Sea King’ Mark II is one of its most important features. It can be looped, rolled, spun, and stunted in every possible way. Longitudinally, the machine is neutral, and flying at any speed throughout its entire range either with engine on, gliding, or climbing, no load is felt on the control stick. This balance has been obtained entirely on the stabilising surfaces, and no mechanical adjustment by the pilot is required. . .The engine, a 300 h.p. Hispano Suiza, is mounted in a streamlined nacelle, which contains oil tank, radiator and shutters, piping, controls, etc. The whole unit is very accessible and the engine can be replaced very easily.Interchangeability and ease of upkeep and repair have been carefully studied. The complete wing structure, including power unit, can be removed from the hull by withdrawing eight bolts. The wing structure consists of top and bottom centre sections, and top and bottom planes of equal span. One set of struts are [is] carried on either side of the centre section. The top planes have a dihedral angle of 1° and the bottom planes one of 3°. The engine unit is carried on two sets of inwardly inclined N struts, and can be removed and replaced without interfering with any wing structure member . . .The amphibian undercarriage, which can be removed by the undoing of ten bolts in all, folds up under the wings, and when folded is well clear of the water. It is raised and lowered by a worm and bevel gear.

The Sea King II was designed and built in six months and made its first flight at the end of 1921 but, once more, no orders were received; however, there was some further development in 1922 and 1923 – see my Blogpost concerning Sea Lions II and III.

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

What Was R. J. Mitchell’s First Design?

Early evidence of Mitchell’s design work is his contribution to the P.B.31E Nighthawk of 1916.  He was, no doubt, also involved with Chief Designer Hargreaves’ Sea Lion I and, after the latter left in 1919, was involved in various conversions of the Admiralty designed aircraft, A. D.  Boats, which Supermarine bought back from the RAF to be converted for passenger and photographic survey work. However, the first overall design which might be attributed to R. J. was the so-called Commercial Amphibian of 1920.

The first aircraft involved in commercial flying after the end of World War I were conversions of military machines – like the Channels - the name given to Supermarine’s conversions of the A. D. Boat. As they were by no means well suited to their new roles, the newly formed Department of Civil Aviation at the Air Ministry announced, in March 1920, two competitions for commercial designs ‘of British Empire origin’ to promote ‘Safety, Comfort and Security’ in air travel. With a view to developing international travel, and bearing in mind that there were few airfields available, one of these competitions was specifically for amphibian seaplanes with a first prize of £10,000 and a second one of £4,000.
    It was not surprising that Mitchell was asked by Supermarine to design an entry for the seaplane competition, which was to commence on 1 September of that year. By later standards, entry requirements were extremely modest: in the amphibian category, these included seating accommodation for a minimum of two passengers; a range of 350 nautical miles at 1,000 feet at a speed of not less than 70 kt; and a load of 500 lb to include passengers and life belts but not including crew. There was also a requirement of a flight of three minutes at 5,000 ft. to check if the machine would fly itself at this height and with enough height to recover if necessary. Based at  the experimental station at Felixstowe, the amphibian competitors should take off from water and fly to the land-based experimental station at Martlesham Heath.

Commercial Amphibian at Martlesham
 As the Commercial Amphibian can be claimed to be the first comprehensive design by Mitchell,  it is surely very understandable that the end-product would be a conservative one. Also, there were only about twenty weeks separating the announcement date of the competition and that of the trials, leaving little time for innovative thinking. Not surprisingly therefore, Supermarine described the new design as ‘practically a "Channel" type boat, with a wheeled undercarriage hinged on each side’ although the comparable side views show considerable changes in the Mitchell design:
Channel II             Commercial Amphibian

As regards the Channel precedent, the Commercial Amphibian had a biplane layout in which similar dimensions of height, and length were adopted and the sea rudder was similarly placed to that of the Channel – vertically below the leading edge of the tailplane – but now converted to act also as a skid for taxiing over land. The wing-tip floats were also of the Channel sort and the oval hull and the general arrangement of its built-on planing surfaces continued the Linton Hope/Channel principle of hull construction [see my Blogpost: 'Mitchell's Wooden Hulls'].
   On the other hand, Mitchell increased the area of the lower wing; he also incorporated features of a much smaller aircraft, Hargreaves' Sea Lion I: the fin and rudder outlines were similar although a proportional increase in surface area above the tailplane allowed our designer to provide a more symmetrical appearance to the fin. And the Sea Lion's outwardly raked inter-plane struts were repeated in the new, and larger, machine.
    Between the Amphibian’s struts there were canvas stabilising screens, full length between the inner pairs and quarter length between the middle ones. These screens were relatively uncommon by the end of the 1914-18 War but survived on several later Supermarine designs as well as on the Channel and Sea Lion, perhaps (in the case of the inner ones, at least) mainly to protect the engine and propeller from spray on take-off or landing. It was the present machine which was most extensively fitted with them and, in this respect, it did not look particularly like an advanced design. As many of the features from the Channel and the Sea Lion I were thereafter abandoned by Mitchell, the present design can be regarded as something of a ‘time capsule’, a summing-up of earlier practices rather than a statement of the way forward.

But, nevertheless, Mitchell showed an early instance of boldness and originality by abandoning the biplane tailplane and twin rudders of the Channels (still evident in the Handley Page H.P.42 of the 1930s) in favour of a single fin and tailplane. It is worth noting that the competition rival Vickers Viking III went through three more variants before the Mark VII, the Vanellus, appeared five years later with a more modern-looking single tailplane and rudder. And Mitchell’s rudder was also a departure from the minimalist approach of previous Admiralty inspired rudders – perhaps his work alongside Hargreaves on the Sea Lion I had had some influence in this respect. Additionally, Mitchell remodelling of the nose with a prominent boat-like entry to counter spray was to prove successful in his future Sea Eagle, Scarab and Seagull designs.
   A further feature was Mitchell’s design for a retracting undercarriage, necessary because the Air Ministry competition was for an amphibian aircraft. At this time, an American landplane, the Dayton-Wright R. B. Racer, had a fully retracting landing gear designed specially for the Gordon Bennett race of 1920; on the other hand, the Air Ministry commercial competition was satisfied with devices which merely lifted the wheels out of the water, in order to facilitate take-off and alighting.  Supermarine’s concern for ‘boats which fly’ offered no previous experience of retractable undercarriages for Mitchell to call upon and so it is noteworthy that, for his specially designed mechanism, he chose a geometry which displaced the wheels outwards rather than forwards – thus avoiding any change of trim when the wheels were moved up or down.
    One other particular feature of the Commercial Amphibian must also be mentioned: the enclosed passenger cabin [see the opened cabin roof top in the photo above]. The competition’s intention of ascertaining ‘the best type of Float Seaplanes or Boat Seaplanes which will be safe, comfortable and economical’ might have seemed to make an enclosure for passengers inevitable but it should be noted that the other two amphibian entries had open cockpits for the passengers, one seated next to the pilot and the other two side-by-side behind. Open cockpits at this time were the norm and they saved weight, but they were far from ideal for operation over water and in northern climates – Cozens, a contemporary observer, described how previous Channel passengers ‘had an uncomfortable ride on many occasions’ and, although ‘wearing flying coats and helmets they looked wet and miserable as they got into a boat that was rowed out to meet them’.

No adjustments or replacements to the Mitchell aircraft were required, despite its one-off design and the short notice of the competition, and the Supermarine entry was the only one which completed all the tests that were stipulated and whose landing gear did not give trouble at any time. The judges also noticed with approval an effective tiller arrangement for steering whilst taxiing on water, the equipment for sea use, and the way in which the shape of the forward part of the hull kept spray off the passengers’ compartment. On the other hand,  the novel undercarriage gave rise to criticism for being none too clean, from the mechanical and the maintenance points of view. The lateral control of the Commercial Amphibian was also considered not immediately responsive enough.
   Unfortunately, the fitting of a Rolls-Royce Eagle engine in order to lift the considerable more loaded Channel design led to a  loss of  competition points, resulting in its coming second to the Vickers Viking.   However, the Air Ministry report on 11 October stated that ‘the results achieved for amphibians show that considerable advance has been attained … and the competing firms deserve congratulations on their enterprises.’ They also recommended a doubling of the second prize money to £8,000 as ‘the proportion of the monetary awards does not adequately represent the relative merits of the first two machines’.

A modest beginning to be sure but, as we shall see later, its general design and its overall performance gave rise to a call from the Air Ministry for a development of this machine which led to the Sea Eagle and the Seagulls between 1923 and 1926.

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

Sunday, 26 March 2017

Precursors of R.J. Mitchell's Walrus.

Seagull III, Papua (from painting by author).

The first success of Mitchell as Chief Designer was the Commercial Amphibian and this had brought an order from the Air Ministry for a  military development of the type as part of its policy to assist the struggling aviation companies to stay in business. This was obviously not a philanthropic gesture but a recognition that British air power needed the support of a healthy aviation industry especially as, by 1920, the RAF had been in action again with the new military tactic of ‘control without occupation’ – a very economical and swift-acting aerial alternative to the employment of large army land forces in the policing of colonial and League of Nations mandated territories – against tribesmen in Mesopotamia, Transjordania, the Sudan, and Somaliland, against the Bolsheviks in Russia, and against the Afghans on the Indian frontier.

In order to fulfill the Air Ministry requirement, Mitchell’s next design was to be a three-seat amphibian for use as a fleet spotter; it would be required to be extremely seaworthy and to have the lowest possible landing speed with good control – in order to land on to aircraft carriers. Mitchell’s response was known as the Seal II, presumably with the Commercial Amphibian being regarded as the Mark I predecessor.
     The Seal II had the outwardly-retracting landing wheel geometry first introduced on the Commercial Amphibian but the detail of the Seal’s retracting system shows that something had been learned from the criticisms of the earlier plane’s mechanism: the earlier machine had an undercarriage of two steel tubes, hinged below the lower centre-section join with the lower main planes and the wheels were raised or lowered by sideways pressure from a tube in the hull to the wheel axles; the new undercarriage now had a single strut, suspended from the lower wing and braced by two tubes hinged to points on the hull; it was moved inwards for retraction by means of a worm and bevel gear under the wing. This revised method was utilized on all future Supermarine amphibians up to and including the Sheldrake of 1927.
   Of the flying surfaces, only the tailplane followed the previous Hargreaves Sea Lion outlines and, although Mitchell placed the stabiliser lower on the fin, he retained the inverted aerofoil principle. This feature was also continued in aircraft up to the Sheldrake, being necessitated by the high thrust line of the engine which caused increasing nose-down forces as power increased. With the tailplane being ‘of the depressing kind’, as it was described in the publicity for Hargreaves’ earlier Sea King, the need for constant back pressures on the stick was therefore obviated at cruising speeds.
   On the other hand, the wing shape was new and this planform was retained by Mitchell for all his subsequent single-seat naval aircraft, up to and including the Sheldrake. But the rearward-folding wing requirement for a shipboard aircraft had not been tackled by the Supermarine company since the Baby of World War I and Mitchell adopted a similar approach – and one which he, again, continued with in military aircraft until the Sheldrake: the forward wing strut at the joint between the wing centre section and the main plane was doubled so that one of these members carried the weight of the leading section of the wing when folded back. The need for wing-folding also required large cut-outs to be made in the trailing edges of the wings, so that they could fold close to the plane’s centre-line to keep storage space to a minimum, and the wings were placed further forward than in the Commercial Amphibian so as not to project behind the trailing edges of the tail assembly when folded.
   The wing-tip floats, with their decreased side-area, were less clumsy than before and could be carried on struts to the waterline. The pilot was placed well forward and supplied with a machine gun which could be retracted and shielded during take-off and landing; the wireless operator was just aft of the wings and the rear gunner behind him but with the fuel tanks separating off the pilot from these other two crew members. 
    Because two of the crew members were placed behind the wings, a tractor layout had to be chosen for the engine to prevent the centre of gravity moving too far back. In Supermarine’s publicity for the Seal, attention is drawn to this placement, no doubt because of its novelty (at least in single-engined machines):
the engine is the Napier of 450 h.p. The engine mounting is unusual in that it is of the tractor type. This has been rendered possible by the fact that in this case the greater part of the useful load carried is aft of the wings in the tandem cockpits, and the success of the tractor mounting will allow this type of boat to be arranged either as a tractor in such a case as this or as a pusher in cases where the greatest useful load is concentrated forward. Very great attention has been paid in designing this engine installation to securing accessibility for inspection and adjustment of the engine and its accessories.
One notices the offer of the more conventional pusher layout – presumably in the hope of a civilian version which would not, one might reasonably assume, need a gunner behind the wings. The company publicity also draws attention to the new designer’s typical concern with the practicality of his machines – in this case, the ease of access to the engine.

As N146, the Seal II first flew in May, 1921 and, in the following year, one machine was sold to Japan who were keen to be kept abreast of Western technological developments. Despite this general lack of orders, the Seal is important in our story as it is the one early Mitchell design which most clearly looks forward to one of his three main aircraft types – the Seagull II to Seagull V/Walrus series of medium sized amphibians.

Meanwhile, the company had to come to terms with the post-war Anti-Waste League and the resultant Geddes Committee Report which led to a drastic reduction in all Government expenditure. The new Secretary of State for Air, Sir Samuel Hoare, reported that, in 1923, only 371 front line aircraft remained, either in the British Isles or abroad, and assessed the current situation thus: ‘Orders for military planes had almost come to an end and a demand for civil planes did not yet exist … Only two thousand five hundred men and women were left in the industry and the few firms engaged on machines and engines were on the verge of closing down.’
   On the other hand, the actions mentioned earlier of ‘control without occupation’ had to be backed up by support for the ailing aircraft industry. Thus it had been decided that, over the next five years, thirty-four new squadrons would be formed, bringing the air defence of Great Britain up to fifty-two squadrons by 1928. [In the event, the total home squadron numbers only rose to thirty-four by the date proposed.]

The first positive result of the new situation was seen when Supermarine received a letter from the Air Ministry which suggested that it ‘might be inexpedient’ to close down the works entirely as Supply and Research were considering an order, ‘the exact amount of which cannot yet be stated, but which might approach 18 machines, spread over the period ending March 31st, 1924’.
   In response to this Air Ministry lifeline, Mitchell modified the Seal II machine. A more powerful Napier Lion II engine was fitted – again in a tractor layout – and the fin consequently increased in area and the wingspan reduced. Thereafter, two new aircraft, N158 and N159, were completed by March, 1922, by which time, the wing-tip floats had been redesigned, the wings given a slight sweep back, the ailerons redesigned, and the fin area further enlarged. The number of modifications resulted in these first production Seagulls being designated Mark II.
   There was one particular modification of the Seal type which ought to be mentioned: the fuel tanks had now been moved from the fuselage to positions under the top wing centre-section, thus supplying petrol to the engine by gravity feed. [A Supermarine comment on the previous Sea King II design had been that ‘the petrol supply is by pressure, and every effort has been made to reduce the length of piping and eliminate as much as possible the carrying of piping into the hull’.] Perhaps because of the weight distribution of the basic Supermarine flying boat configuration, there appears to have been no undue problems created by the new fuel arrangements and there was also a particular bonus: Supermarine was now able to announce that ‘inter-communication between crew has been considered fully, and a through passage is arranged for this purpose’. [In passing, it should be noted that the constructional methods of the Linton Hope hull that Supermarine had adopted conferred another advantage as there were no internal bracings or structural bulkheads to be weakened by making a passageway between the pilot and the other crew members – see my Blogpost: ‘Mitchell’s Wooden Hulls, Structure and Finish’.]

A competitive test on HMS Argus between the Seagull and the Mark VII version of the Vickers Viking had found in favour of Mitchell’s machine and an  order for five Seagulls, N9562 to N9566, was then received in February 1923. This was followed by a requirement for another thirteen (N9642 to N9654), also in 1922. These aircraft equipped No. 440 (RAF) Fleet Reconnaissance Flight and some were placed aboard the aircraft carrier HMS Eagle. An additional machine was again sold to Japan.
    Further orders for the Seagull came in when the Australian government decided that their Air Force should assist in the hydrographic survey of the Great Barrier Reef. 101 (Fleet Cooperation) Flight was formed on 1 July 1925 and six Supermarine Seagull III amphibians were ordered (A9-1 to A9-6). These machines were essentially Mk IIs with larger radiators and the first of these was ready by February, 1926 – by which time six of the RAF aircraft had served a tour of duty with HMS Eagle but, thereafter, the type was pronounced as having ‘no potential naval use’.
  In sharp contrast, the Australian Seagulls were used more thoroughly, as their survey work extended into 1927 and continued on northwards to include some 10,000 square miles of Papua and one staged flight of 13,000 miles. Interestingly, three RAF Seagulls, engineless, had been acquired at the scrap price of one hundred pounds each and were intended to be used for spares. However, they were found to be in such excellent condition that they were re-erected and quickly put into service.
   This traditional Supermarine ruggedness was also evident after the survey work was completed, as the Seagulls were assigned to the newly constructed seaplane tender HMAS Albatross, commissioned in 1929, and continued in carrier use until 1933 when the vessel was placed in reserve.

The Seagulls had, by this time, lost their appeal for the RAF but, as a result, the Seagull design continued to occupy the minds of Mitchell’s design team even until 1928: fitting hydro-vanes was considered and, because of its porpoising tendencies, various permutations of the hull step position were tried out on N9565 and on N9606. And one aircraft, N9605, was fitted with Handley Page slots and a new tail unit with twin fins and rudders. This aircraft, designated Mark IV, was converted to take five passengers in 1929, when the Supermarine company was looking forward to the old Sea Eagle Southampton–Channel Islands routes being resumed [see my Blogpost: 'R.J. Mitchell's Sea Eagle Fleet'] – with a small fleet of Seagull IVs. A pilot service was begun in July by the prototype five-passenger conversion (G-AAIZ) but most of August was void owing to serious damage to the hull caused by its hitting a barely submerged rock. Then, on 2 September, the short-lived business ceased when the aircraft ran into engine trouble.
   Two other Seagulls, N9653 and N9654, were converted for civilian use: registered as G-EBXH and G-EBXI respectively they began a coastal service at Shoreham but this also failed, owing to inadequate public response.
   However, two other modifications of the Seagull were of great significance to Mitchell’s team. One was concerned with equipping a Seagull to initiate the testing of catapults for launching aircraft and the second was the changing of the usual water-cooled Napier engine to an air-cooled radial engine in a pusher configuration. As we shall see later, when the Seagull V/Walrus appeared, it was an aircraft engined in this particular way and stressed for catapult launching.

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