Wednesday, 5 March 2014

Blog Subjects, Sources and References

Source Material and References.
The excellent Putnam book on Supermarine is still the main reference source but its scope was not concerned directly with Mitchell’s development during his two decades as Chief Designer – which must be inferred from its survey of the company’s aircraft. The Spitfire Story by Alfred Price is very informative about the genesis and development of Mitchell’s fighter but, of course, it is not concerned with his whole career. One thus turns to the work of his son, Gordon Mitchell, which does give considerable biographical information and a chronological survey of his father’s whole design output. Whilst Dr. Mitchell performed an important service by raising the profile of his father, some of the material approaches that of hagiography and quite a few aircraft are only briefly dealt with. There are no three-view drawings of the machines and no comprehensive set of photographs.
The reminiscences of such test pilots as Biard, Orlebar, Schofield, D’Arcy Grieg, Waghorn, Quill and Henshaw, and of the two navy pilots, Livock and Nichol, supply much information about that essential factor in any designer’s output – what it was like to fly the machines. They also give revealing insights into the character of the designer, as do several Supermarine employees whose accounts also make it possible to discover much about the complex nature of the man behind the machines.
   My own book (see below) was written to collect together such biographical material and to give an overall survey of all Mitchell's main designs, in chronological order and related to their historical period, supported by photographs and drawings, whilst drawing attention to the Schneider Trophy contests as these were crucial to Mitchell's ability to produce the Spitfire when he did.

Supermarine Aircraft since 1914 – C.F. Andrews and E.B. Morgan. Putnam,          1981. 
Schneider Trophy to Spitfire: the Design Career of R.J. Mitchell – J.K. Shelton. Haynes, 2008.
Forty Years of the Spitfire – Proceedings of the R.J. Mitchell Memorial Symposium, 6th March,  1976. Royal Aeronautical Society, Southampton Branch.
Jane’s All the World’s Aircraft 1921 to 1937. Sampson Low.
“Schneider Trophy Machine Design, 1927 ” – R.J. Mitchell.   Proceedings of       the Third Meeting, 63rd Session of the Royal Aeronautical Society.
“Racing Seaplanes and their Influence on Design” – R.J. Mitchell. Aeronautical Engineering Supplement to The Aeroplane, 25th December, 1929.
“The Schneider Trophy Seaplane – Some Notes on the Special Features of the S.6B” – prepared by the design staff of Supermarine under R.J. Mitchell. Aircraft Engineering, October, 1932.
“Seaplane Development” – R.E. Penny. Journal of the Royal Aeronautical Society, September 1927. (Contribution by R.J. Mitchell.)
“R.J. Mitchell, Aircraft Designer” – Joe Smith. The Aeroplane, 29th January, 1954.
“The First Mitchell Memorial Lecture” – Joe Smith. Journal of the Royal Aeronautical Society, 58, 1954.
“R.J. Mitchell – Designer of Aircraft” – A. Black in The Reginald Mitchell County Primary School Commemorative Brochure, 1959.
R.J. Mitchell - Schooldays to Spitfire – edited and in part written by Dr. Gordon Mitchell. Nelson and Saunders, 1986; reprinted by Tempus Publishing, 2006.
Schneider Trophy to Spitfire: the Design Career of R.J. Mitchell – J.K. Shelton. Haynes, 2008. 
Never a Dull Moment at Supermarine: a personal history – Denis Le P. Webb. J and KH Publishing. n.d.
Testing Times; Memoirs of a Spitfire Boffin – Griff (Harry Griffiths) United Writers, Cornwall, 1992.
Spitfire Odyssey – C.R. Russell. Kingfisher Railway Productions, 1985.
“Concerning the Aircraft Industry in South Hampshire” – G.A. Cozens. Unpublished MS., Solent Sky Museum.
“The Schneider Cup Race, 1925” – Maj. J.S. Buchanan. Proceedings of the Tenth Meeting , 61st Session of the Royal Aeronautical Society.
 “The Schneider Trophy, 1929” – Flt. Lieut. R.D.H. Waghorn. Royal Aeronautical Society, May, 1930, Yeovil Branch.
The Schneider Trophy – Wing Commander A.H. Orlebar, A.F.C. Seeley Service and Co. , 1933.
 “Memories of the Last Schneider Trophy Contests” – F.R. Banks. Journal of the Royal Aeronautical Society, January, 1966.
The Schneider Trophy Races – R. Barker. Chatto and Windus, 1971.
“Technical Aspects of the Schneider Trophy and the World Speed Record for Seaplanes” – Dr. E. Bazzocchi. Journal of the Royal Aeronautical Society, February, 1972.
The Schneider Trophy – D. Mondey. R. Hale, 1975.
Schneider Trophy Aircraft, 1913 - 1931 – D.N. James. Putnam, 1981.
Schneider Trophy Racers – R. Hirsch. Motorbooks International, 1993.
The Schneider Trophy Story – E. Eves. Airlife Publishing, 2001.
Schneider Trophy to Spitfire: the Design Career of R.J. Mitchell – J.K. Shelton. Haynes, 2008. 
The Schneider Trophy Seaplanes and Flying Boats; Victors, Vanquished and Visions – Ralph Pegram.  Fonthill Media, 2012.
The Spitfire Story – A. Price. Jane's, 1982.
Spitfire: the History – E.B. Morgan and E. Shacklady. Kay Publishing, 1987.
Spitfire: Portrait of a Legend – L. McKinstry. Murray, 2007.
How the Spitfire Won the Battle of Britain – D. Sarkar. Amberley, 2010.
“Spitfire 70 “ – A FlyPast Special. Key Publishing, 2006.
Schneider Trophy to Spitfire: the Design Career of R.J. Mitchell – J.K. Shelton. Haynes, 2008. 
The Supermarine Walrus; the Story of a Unique Aircraft – G.W.R. Nicholl. G.T. Foulis and Co., 1966.
From Sea-Eagle to Flamingo – N. Doyle. The Self Publishing Association Ltd., Upton-upon-Severn, 1991.
"Twentyfirst Profile", Vol.1 No.6 (the B.12/36 Bomber); Vol.1 No.9 (the Air Yacht) – 21st Profile Ltd. ISSN 0961-8120
Wings – H.C. Biard. Hurst and Blackett, 1935.
Racing Ace; the Fights and Flights of“Kink” Kinkead – Julian Lewis. Pen and Sword, 2011
The High Speed and Other Flights – Flt. Lt. H.M Schofield. John Hamilton Ltd., 1932.
A Pride of Unicorns: Richard and David Atcherley of the RAF – J. Pudney. Oldbourne Book Co. Ltd., 1960.
“Schneider Trophy Flying” – Grp. Capt. L.C. Snaith – 1968 Lecture to the Royal Aeronautical Society Historical Group.
To the Ends of the Air – G.E. Livock. H.M.S.O. 1973.
Sigh for a Merlin – A. Henshaw. Blackett, 1977; reprinted by Crecy Publishing, Ltd., 2007.
Early Aeronautics in Staffordshire – J. Godwin. Staffordshire Libraries, Arts and Archives, 1986.
British Aviation: the Great War and Armistice: 1915-1919 – H. Penrose. Putnam, 1969.
British Aviation: the Adventuring Years: 1920-1929 – H. Penrose. Putnam. 1973.
British Aviation: Widening Horizons: 1930-1934 – H. Penrose. Putnam,1979.
Empire of the Air: the Advent of the Air Age, 1922-1929 – Viscount Templewood [Sir Samuel Hoare]. Collins, 1957.
Annals of British and Commonwealth Air Transport 1919-1960 – J. Stroud. Putnam, 1962.
The Centenary Journal of the Royal Aeronautical Society, 1866 -1966.
Aviation: Its Technical Development – J.L. Nayler and E. Ower. Owen, 1965.
Biplane to Monoplane Aircraft Development, 1919 - 1933 – ed. P. Jarrett. Putnam, 1997.
A History of Aerodynamics and its Impact on Flying Machines – J.D. Anderson. Cambridge University Press, 1997.
The Royal Air Force and Aircraft Design, 1923 - 1939 – C. Sinnot. Frank Cass, 2001.
The British Aircraft Specifications File, 1920-1949 – K.J. Meekoms, and E.B. Morgan, Air Britain, 1994.
The Cinderella Service: RAF Coastal Command, 1939-1945 – Andrew Hendrie. Pen and Sword, 2006.
“Transport Flying-Boats: Life and Death” – B.S. Shenstone. Journal of the Royal Aeronautical Society, December, 1969.
Sea Flyers – C.G. Grey. Faber and Faber, 1942.
Saunders Aircraft since 1920 – F.K. Mason. Putnam, 1961.
Bristol Aircraft since 1910 – C.H. Barnes. Putnam, 1964.
Shorts Aircraft since 1900 – C.H. Barnes. Putnam, 1967.
Blackburn Aircraft since 1909 – A.J. Jackson. Putnam, 1968.
Vickers Aircraft since 1908 – C.F. Andrews and E.B. Morgan. Putnam, 1974.
Gloster Aircraft since 1917 – D.N. James. Putnam, 1971.
Fairey Aircraft since 1915 – H.A. Taylor. Putnam, 1974.
Hawker and Saro Aircraft since 1917 – P. London. Putnam, 1974.

The Flying Radiators – Part II, R. J. Mitchell's S.6B

With the possibility of a third win in 1931 and, therefore, the outright capture of the Schneider Trophy, Supermarine and Rolls-Royce began discussions with the Air Ministry predicting an increase of 25 mph over the Schneider course, assuming that the S.6 machines would be loaned back for modifications and that they would be piloted by High Speed Flight pilots. The estimate of the cost of a successful defence of the Trophy in 1931 was considered to be in the region of £100,000, and involved the production of two new and improved machines and engines to support them but, in view of the worsening economic climate, the government declined any help whatsoever.
      The response, especially in aviation circles was outrage but to no avail. Fortunately, the formidable and extremely wealthy Lady Houston was approached and she promised the required sum to sponsor Britain's entry and, incidentally, to embarrass the Labour Prime Minister and his government. By the time that political points had been scored and the necessary money allocated, there was less than a year left for all the work required in time for the competition in the coming September. Because of this time constraint and the finite funds available, the British hopes would have to be concentrated upon uprating the current Rolls-Royce engine and upon modifying the S.6 design to handle an expected increased in power.
   Derby had once more to put up with the noise of the engine testing (see my Blogpost:" The Flying Radiators: Pt.1") and the Mayor of Derby had to appeal to the patriotism of its citizens as the tests ran from April 1 to August 12 before the uprated engine could run for an hour at full power– by which time the 1900 hp of the 1929 engine had been increased to 2350 hp.

The S.6B
In view of this increase, Supermarine estimated that ‘something like 40,000 B.T. units’ had to be dissipated every minute – the equivalent of over 300 modern fan heaters running at full power. Mitchell had to provide additional radiator surfaces on the floats right down to their chines so that almost half of the 948 sq. feet of the aircraft's available surface area was now to be used for cooling: it is understandable why Mitchell, in a radio broadcast after the competition, described his new aircraft as a ‘flying radiator’.
   Enlarging the cooling area was assisted by an increase in the size of the floats as the anticipated increase in the fuel consumption of the new engine required their capacity to be enlarged, as did a modification to the competition rules: the aircraft were now required to take-off and land immediately prior to the start of the race proper instead of the navigability and seaworthiness tests being carried out with minimal fuel the day before. Wind tunnel and tank testing led to a narrower float design, although of increased length and the side plating was extended by ¾ in. below the chines and as far as the step to improve running and to inhibit spray. And the elevators no longer had a vee cut-out close to the fuselage but were now made to operate with minimum clearance in order to reduce turbulence at this point.
The revised design was accordingly designated "S.6B" and it was possible to afford two, with the serials S1595 and S1596; additionally, the two 1929 machines, N247 and N248, were uprated and, as such, they were redesignated "S.6A". The only noticeable difference between the two pairs of machines was that the latter had its original floats, which were two feet shorter than those of 1931.
The first of the S.6Bs at Calshot.

As there were to be four Supermarine racers, Flying Officer L. S. Snaith was added to the High Speed Flight which had now consisted of Flight Lieutenants J. N. Boothman, E. J. L. Hope, F. W. Long, and G. H. Stainforth. Flying with the contest machines began when N247 arrived on May the 20th but an alarming oscillation of the rudder developed during an early high speed run, causing the buckling of rear fuselage plates, stress cracks around some of the rivet holes, and stretched control wires. In the short time available, Mitchell had streamlined weights on forward projecting brackets fitted to both sides of the rudder and the ailerons – in order to bring the centre of gravity of these surfaces to coincide with their hinge lines and so to dampen any future oscillations which might occur. The last bay of the fuselage was also strengthened.
     Weights were also needed in response to some instability on take-off and during turns. Mitchell decided that the problem was due to the centre of gravity being too far back and so he had about 25 lb. of lead placed in the nose of each float and reduced the amount of oil (which was, again, carried all the way back to a tank in the fin). However, Orlebar had also reported nose-heaviness during level flight and Mitchell (before the widespread use of trim tabs) ‘produced a splendid gadget to cure the trouble’ – metal strips were fitted to the trailing edge of the elevators and bent downwards by about one degree, thus using the slipstream at high speed to deflect the elevator upwards slightly and to counteract any load on the stick.
    Additionally, the engines were prone to cutting out because of choked fuel filters. This was found to be the result of the fuel mixture causing the excess compound used to seal the joints in the fuel system to come adrift. Mitchell’s response was both practical and blunt: ‘You’ll just have to bloody-well fly them until all this stuff comes out’.
    There was another problem, also experienced in 1927 – the first new S.6B, which had arrived on July 21st, could not be made to fly as it gyrated in ‘a very good imitation of a kitten chasing its tail’. In the course of these rotations, S1595 hit a barge and had to be returned from Calshot for repair.  This year, a different caise was suspected and the smaller diameter propeller of the S.6B was fitted to N247, which then behaved like its younger sister. This suggested that the slipstream from this diameter propeller was producing a side pressure that the rudder was unable to counteract. When S1595 was returned on July 29th a larger diameter unit was fitted and the new machine then took off with no more difficulty than was usual with these machines.
    In view of the peculiar take-off requirements, combined with the increased speed and weight of the new aircraft, it is not surprising that the British team now began to have accidents. Linton Hope virtually wrote off one of the S.6A machines: a piece of the cowling from N248 worked loose in flight and, whilst managing an emergency landing, he encountered the wash from a passing ship which caused the sensitive machine to cartwheel and sink. The pilot survived but was withdrawn from the team because of a punctured eardrum.
  Hope was replaced by Lieutenant G. L. Brinton who, on 18 August, on his first take-off in N247, was killed. Greig told how, if porpoising developed during take-off, it was imperative to close the throttle and start again; otherwise, the pitching of the aircraft invariably increased until the machine was eventually thrown into the air without flying speed and an accident was inevitable.  It appeared that  Brinton did not heed the advice in time and the aircraft cleared the water for a second and then dropped back. The S-6A bounced 40 feet in the air and then plunged down into the water. It was first assumed that Brinton's body had been lost at sea, but later was found jammed into the rear of the fuselage. It is not recorded how the actual discovery of the body was received by Mitchell but, in view of his well-known concern for the pilots of his machines, an explanation of the need to cut into the damaged machine for its recovery must have required considerable tact.

At about the same time, a French machine was considerably damaged in a landing accident and another was completely destroyed, killing its pilot. Meanwhile, Macchi were developing their M.67 layout into a new machine, which was also to kill one of its pilots.
As a result of such accidents and other setbacks, the French and Italian teams requested a postponement of at least six months but, by the time it was received on 3 September by the Royal Aero Club, it seemed that all the significant problems with the S.6Bs had been solved and Hope’s N248 had been salvaged and was well on the way to being restored to flying condition. Holding the competition on the due date was insisted on and, as a result, the Air Ministry was informed on the 5th of September that neither France nor Italy would be able to compete. 

In the end, the only postponement of the twelfth contest, again at Calshot, was for one day owing to bad weather and the following day was almost perfect with visibility of over ten miles. In view of the fly-over situation, it was decided that S1595 was to complete the course without putting undue strain on the engine – the increase in propeller diameter had produced a higher engine temperature and, again, Mitchell had had to accept a slightly lower airspeed than his design was capable of. If this attempt were to fail, then the repaired S.6A would aim to finish the course and, therefore, to win the Trophy outright. The second S.6B would be available to make trebly sure of a win but it was hoped to retain it to give the crowds the additional thrill of seeing the setting of a new World Speed Record.
   The Commanding Officer, Orlebar, gave the senior pilot, Stainforth, first choice and he opted for the proposed attempt on the speed record; the next most senior man, Boothman, then chose to fly first in the competition itself and, hopefully, to have the honour of winning the trophy. And so, just before 1 p.m. on September 13, Boothman taxied out in S1595, which had never having flown in practice for longer than 27 minutes. Nor had it been considered wise to practice the landing which the 1931 rules required, with the full load of fuel for the 350 kms of the competition course and as well as for the required preliminary maneouvres. Nevertheless, he took off without any apparent difficulty, landed at about 160 mph without mishap, and then flew the required seven laps, all within about four mph of each other, slightly throttled back, taking the turns wide and with a gentle bank and finished with an average speed of 340.08 mph – just over 11 mph faster than Waghorn in 1929. Then, as if to emphasise the superiority of the Rolls-Royce/Supermarine partnership and also to post a more impressive speed, Stainforth took out the other S.6B a little later and proceeded to capture the World Absolute Air Speed Record at 379.05 mph.
  Lady Houston had attended on her steam yacht, Liberty, to watch her machines and, two days later, gave a celebratory lunch on board, attended by Mitchell and his wife and by the High Speed Flight. She had been afforded the rare privilege of mooring on the RAF buoys at Calshot and in the evenings Liberty had a string of electric lights from her bowsprit to the mastheads and down to the stern.

The Air Ministry then set about disbanding the High Speed Flight and restoring the Calshot base to its normal flying-boat duties but Rolls-Royce particularly wanted to have produced the first aero engine to exceed the new magic mark of 400 mph and Mitchell had indicated the same in an interview with the Southampton Daily Echo:‘with a specially tuned up engine, I am very hopeful we may get very near to an average speed of 400 mph, which is our ambition’.  For this special sprint machine, Mitchell had the wing-tip air scoops removed and a specially prepared engine was to be supplied, using a new more potent fuel mixture. After delays caused by bad weather, Stainforth squeezed into the cockpit of S1595 and the required runs were photographically measured. There was some concern that bad light and a low evening sun might prevent confirmation but eventually, at 4 a.m., the results were telephoned through and Mitchell was informed; it was reported that he was ‘too sleepy to be more than mildly enthusiastic’ that the World Absolute Speed Record had just been raised by nearly 30 mph to 407.5 mph.

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 on the 1931 Schneider competition, photographs and three-view drawing of the S.6B, 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. 

Tuesday, 18 February 2014

R. J. Mitchell's Giant

Whilst the early Dornier Wal series had had a very obvious effect on the design of Mitchell's Air Yacht [see my Blogpost:"R.J. Mitchell's Air Yachts"], the huge Mark X version made a far wider impression when it arrived at Calshot in November, 1930, for a two week stay. With a wingspan of over 157 feet and something approaching steamship luxury, including a smoking room with its own bar, and a dining salon, it had a crew of ten and was capable of carrying 66 passengers on long distance flights and 100 travellers on shorter ones. It was powered by twelve 610 hp engines which could be accessed via a passageway within the wings.
Not to be entirely outdone, in 1929, the Air Ministry sent Supermarine a specification for a forty-seat civil flying-boat which Mitchell first projected as a high-winged monoplane, with three fins, a relatively flat-sided fuselage and with bulbous floats attached to the underside at each wing root, bulky enough to act as sponsons. Six engines were to be mounted in tandem on pylons above the wing, Dornier X fashion, and the very thick wing allowed the innovation of passenger seating in its leading edge. And this wing also distinguised by the first appearance in a Supermarine design of an elliptical planform, the distinctive feature of Mitchell’s famous fighter; its proposed torsion-resisting nose section also looked forward to the wing structure of the Spitfire, as did the use of a single spar – although in this case it was to be six feet in depth.
  Had Mitchell’s design been completed, its size would certainly have put his company well ahead of other large flying-boat contenders: it was to have a wingspan sixty-five feet more than the contemporary six-engined Short Sarafand and nearly three feet more than that of the 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. It should, however, be pointed out that, whilst 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 ten feet greater. With a wingspan of 185 feet, its name ‘Giant’ was therefore appropriate and it would have represented a significant departure from the almost universal formula of braced, fabric-covered biplanes.
Nearly a year later, the rather untidy general arrangement with 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 used as a steam condenser for the cooling system, a variation on the wing surface radiator system of the S.5 and 6 types. The three rudders were to be replaced by a single one and an auxiliary tailplane was to be mounted above the main unit; additionally, the passenger seating in the wings was to be eliminated in order to accommodate the evaporative cooling system. 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:
Supermarine publicity photograph
Whilst the first proposals for the Giant showed a tentative move forward from the angular Air Yacht,  the upswept tail section, the nicely streamlined engine nacelles  and the fore part of the hull, reveal Mitchell’s thinking to be in advance of forthcoming larger American flying-boats. For example, the Sikorsky S-40, of the same year as the keel of the Giant was laid down, represents a traditional approach of struts and wires and 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

By 1934, the Sikorsky S-42 had a tail unit integral with the main fuselage and had lost most of its predecessor’s struts and wires; and, coming a few years later than the proposed Giant, it had its engines neatly faired into the wing but it did, however, still retain wing and tailplane struts – compared with the Giant’s projected cantilever structures – and this in a machine that was to have a wingspan of 185 feet, compared with the 118 foot span of the American flying-boat.


Unfortunately, early in 1932, the Supermarine project was cancelled in view of the continued economic problems that faced the country and consternation was not limited to Supermarine, for questions were asked in the Parliament – where the Under Secretary for Air justified the government’s decision by claiming that over 70% of the estimated cost would be saved by cancellation. [In its defence, it might be noted that the Germans did not put their Do.X into quantity production either.] 

Had the Giant been built, perhaps Mitchell’s bomber [see my Blogpost: 'R.J.Mitchell's Bomber and his Death'] might have been designed earlier and might even have been in the air when the need for a large British bomber became critical. It was also thus fated that Mitchell would not be remembered (as might otherwise have been predicted) for his contribution to the  proliferation of the Imperial Airways routes or for the creation of later equivalents of the well-known wartime monoplane flying-boats, the Sunderland and the Catalina.

More information on the Giant, and photographs, 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.

Monday, 10 February 2014

The Flying Radiators: Pt.1 – R. J. Mitchell's S.6

In the 1927 Schneider Trophy contest, Britain and Mitchell had been more fortunate than the Italians in that the winning Napier Lion engine had not been a new and unreliable design. It had been continuously developed since its use in the Supermarine 1922 Schneider Trophy winner and, although it had never failed in any of the racing aircraft it powered, it was nevertheless reasonable to ask whether this fine engine had now reached the end of its development potential, especially as a supercharger had not yet been produced.
     By now, Rolls-Royce had produced the successful 490 hp Kestrel, in response to the American Curtiss D -12 engine which powered the Schneider Trophy winning aircraft of 1923 and 1925 and were now offering supercharging and reduction gearing. Mitchell and Major G.P. Bulman, the Air Ministry official responsible for the development of aero engines, decided to take the gamble of ordering a racing engine from Rolls-Royce – identified as the 'R' engine.

The S.6.
Mitchell decided to rely on the basic suitability of his previous design (see my Blog: The High Speed Designer Confirmed – R.J. Mitchell’s S.5) for the new engine and so his main design effort was in respect of an all-metal version, but larger than the S.5, in order to accommodate the projected heavier engine: the 930 lbs. of the Napier Lion in 1927 was to be superceeded by an engine weighing 1530 lbs. 
     An immediately obvious alteration to be made was to the cowling required by the change from the ‘arrow’ shape of the Lion engine to the ‘V’ of the new Rolls-Royce unit and, as the empty weight of the S.6 was 1791 lb. heavier than that of the S.5, the wingspan was increased by more than three feet and the front float struts had to be moved further forward on the fuselage to support the heavier and longer engine. Also, the increase in fuel consumption from the Lion engine with a 22 litre capacity to the proposed Rolls-Royce R engine of 36.7 litres would require both floats to be used for the fuel tanks.  The extra weight of the new engine also required moving the pilot's position further back.

 The S.6 airframe receiving the new Rolls-Royce R engine.caption

     Solving the above mentioned constructional and loading problems in itself had justified the new design's ‘S.6’ designation, but these matters were relatively straightforward compared with contending with the heat produced by the new engine which represented a power increase of 211% over the previous Lion engine (for what turned out to be a loaded aircraft weight increase of only 78%). Mitchell was reported to have said: ‘Go steady with your horsepower’ – no doubt anticipating the cooling problems that would be encountered. 
    The areas of oil-cooling channels which had run along the sides of the S.5 were now increased and new ones were added to the underside of the fuselage. Particular attention was given to the efficiency of these radiators. Mitchell’s Chief Metallurgist, Arthur Black, came up with a method whereby the oil, which ran from and to the engine, passed around copper tongues soldered in the channels at right angles to the oil flow – in such a way that they did not impede this flow, whilst ensuring maximum contact of the oil with the surfaces being cooled by the slipstream of the aircraft. Additionally, the hot oil was sprayed from piping at the top of the fin to trickle down guttering to the return channels, thereby causing the fin to act as both oil tank and radiator. Nevertheless, the High Speed Flight pilot, Greig reported that the position of the oil pipes, attached to a very narrow fuselage, ‘turned the inside of the cockpit into something approaching an extremely hot Turkish bath’ with the oil temperature gauge reading ‘around 136 degrees centigrade.’]
    Meanwhile, Supermarine were anxious to point out that their move to metal construction was not just with respect to the framework of their machine but that it placed them in the forefront of the use of load-bearing external skinning – particularly in respect of the wings where, instead of being plywood-covered with the radiator panels externally attached, as with the S.5, they were now covered by the radiator panels alone. Additionally, made now of aluminium, they took torsional loads and, as Supermarine announced, ‘saved a considerable amount of weight over previous practice’.

Despite there now being a gap of two years between competitions, the scheduled start of the eleventh event was less than six weeks away before Mitchell’s new airframes could be tested in the air. In May, the new R engine had reached 1545 hp but failures began to occur and it was only at the end of July that the new engine passed the one hour mark at full throttle and supercharger boost. A few days later, with the blending of a special fuel, an engine run of 100 minutes and 1850 hp was achieved – much to the relief of the citizens of Derby, as the tests had also required the simultaneous running of three Kestrel engines. They drove fans to cool the new R engine, to dispel fumes from the test shed, and to enable the carburettors to be set up in simulated flight conditions. People living up to fifteen miles away reported still being able to hear the engine runs and and the ears of the Rolls-Royce workers were plugged with cotton wool. They were also well supplied with milk to counteract the laxative effect of breathing in the engine oil fumes, particularly in the early stages of testing: the engine would consume 60 gals of castor oil in 25 minutes, the majority of which was ejected out of the exhaust ports and deposited on the walls of the test cell.
Meanwhile, the High Speed Flight now consisted of Greig's fellow members of the aerobatic team for the last RAF Display at Hendon : Fl. Lts. G. H. Stainforth and R. D. H. Waghorn and Fl. Off. R. L. R. Atcherley. The command was then handed over to Sq. Ldr A. H. Orlebar with the new title: ‘Officer Commanding the High Speed Flight’. Waghorn has described how they used  practice machines to devise the best method for cornering, with the help of scientists from the Royal Aircraft Establishment, who installed instruments to measure speed, acceleration, and climb. A compromise between high G very tight turns, with loss of speed, and wider arcs, which incurred less drag, was thus worked out. But, with the increased speed in the turns, pilots had now to get used to blacking out.
     These preparations received a considerable setback when the actual contest aircraft finally arrived and it was discovered that the possible effects of the much greater torque of the new engine had not been fully realized.  Against the turn of the fixed pitch propeller, the S.6 would dig in the left float, describing circles in the water which Orlebar reported ‘had rather shaken’ Mitchell. One can easily imagine the Chief Designer’s feelings, seeing his aircraft quite unwilling to fly and when Orlebar pointed out to him that 247, the number of the first of the new machines, added up to 13, ‘the poor chap replied with feeling that he had not designed that’.
     Before the invention of variable pitch propellers, it was discovered that a breeze, kept on the left quarter, allowed the aircraft to get onto the step and lift off. To assist the pilots, Mitchell lengthened the starboard float by a foot so that it could contain 90 gallons of fuel and allow the capacity of the submerging float to be reduced to 25 gallons. But having achieved take-off, engine over-heating became a problem and so radiator piping had to be fitted along the sides of the floats. Small wing-tip scoops were also fitted under the wing tips, facing forwards and with exhaust ports at the wing roots, thus creating a flow of air over the inner surfaces of the radiators – an unexpected bonus for using the radiators as load-bearing wing surfaces.

Waghorn's winning S.6

The Italians also received their new aircraft late and it was soon found that the hydrofoil equipped Piaggio Pc.7 was unable to take off at all. Also, one of the two Fiat C.29s caught fire and later stalled on take-off and sank. On the other hand, the first of the Macchi M.67s was looking much more promising, reaching a speed of over 360 mph, but then it too crashed, killing its pilot. Accordingly, Italy requested a one month postponement on August 22 but the Royal Aero Club stuck to the rules and refused the next day; the FAI concurred and the eleventh Schneider Trophy contest was still set to begin  at Calshot on 7 September.

To prevent Britain winning by a fly-over, Italy had decided not to withdraw despite their problems and sent over their remaining, as yet, untested aircraft – the second Fiat C29, a Savoia-Marchetti S.65, and the two Macchi M.67s – as well as two older Macchi M.52s. By this time, both the Supermarine aircraft were ready but, as the Glosters’ fuel problems could not be solved in time, it was decided to call up one of the 1927 S.5s to complete the country's permitted three contest aircraft.
    British tactics were to take account of a compromise that had had to be worked because cooling was so critical that a temperature of 95 degrees had not to be exceeded by the new Rolls-Royce engines It was decided that Waghorn would therefore fly as fast as possible, consistent with keeping to a safe engine temperature; Atcherley, in the second S.6 would risk a higher temperature if the performances of the two preceding Italians made it necessary to go faster than Waghorn; it was expected that Greig, in the slower S.5, would provide additional back-up, as would Molin in the M.52.
     In the event, these tactics were unnecessary: Cadringher retired on lap two as he had been nearly blinded and suffocated by fumes from his exhaust and Monti, in the second M.67, also had fume problems and was forced to made a hasty landing when steam and nearly boiling water blew back from the engine.  
    Atcherley also had a visibility problem – caused by spray from a long take-off run; he tried to replace his goggles with a substitute pair but these were swept away in his slipstream. Thus he saw the pylon at the first turn rather late and unfortunately turned inside it; he was therefore disqualified.   
     And so Waghorn, in the new S.6, was first with an average speed of 328.63 mph; Molin was second in the 1927 M.52, at an average speed of 284.2 mph; and Greig, also in an aircraft from the previous contest, averaged 282.11 mph. Atcherley, in the second new S.6  completed the course, although disqualified, and thus Mitchell was denied the satisfaction of having both of his new aircraft design coming first and second as well as being the only 1929 machines to complete the course. However, he and Atcherley were compensated for the disqualification of N248 by its setting up World Closed Circuit Speed Records for 50 km and 100 km at 332.49 and 331.75 mph respectively, on the sixth and seventh laps. 
    Three days later there followed a competition between the Gloster VI, whose fuel supply problems were now being overcome, and the S.6 to establish a new World Absolute Air Speed Record. The Gloster machine achieved 336.3 mph but Orlebar took the record with 355.8 mph. The previous Italian record of 318.62 mph was further improved on two days later, on September 12, when the S.6 achieved 357.7 mph. 

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

More information about the 1929 competition and the aircraft involved, including photographs, 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.