Friday, 8 February 2013

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. 

The 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.

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, photographs, and a three-view drawing of the Sea King II 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.

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