IMORTANT MESSAGE

IMPORTANT MESSAGE: My book, Schneider Trophy to Spitfire; the Design Career of R. J. Mitchell is no longer in print and the copyright has reverted from the publisher to myself. I am now putting finishing touches to a much expanded, completely up-to-date, second edition with 50% more photos, and 25% more text – 300 pp. instead of 250. There are general arrangement drawings of Mitchell’s 22 main types which flew, as well as 40 other drawings. I intend the book to be a deluxe production, doing justice to R. J. Mitchell and worthy of what I consider will be the definitive account of the man and his work at Supermarine.

As I wish to have complete control of the appearance and quality of this edition, but at an affordable price, I will self-publish it at cost (in hardback) at an estimated £20.

Final details will be available nearer publication date (October, 2016) but it would be helpful if you notify me as soon as possible of a likely intention to purchase – please contact me using the form in the sidebar.

Sunday, 29 April 2012

Mitchell's S5 and S6 – mods and mishaps





Mitchell’s S5 and S6s Mods and Mishaps
 


Supermarine S.5 (painting by author)
 
Some recent posts on Seawings related to my last Blog about R. J. Mitchell’s S.6B trim tabs and one was reminded of other modifications: the amount of engine oil was reduced and lead weights were added to the front of the floats as the new position of the oil reservoir in the fin had moved the machine’s centre of gravity too far back, resulting in instability on turns and on take-off; also, near fatal flutter had necessitated balance weights being placed on forward leaning brackets on rudder and ailerons and stiffening of the rear fuselage plating. The net result was an aircraft as viceless as its S.6 predecessor, where the engine power had gone up from 900 to 1900 hp. and the wing loading had risen from 28 to 40 lb./sq. ft. – as Fl. Lt. R. D. H. Waghorn reported:
While flying, she gave me the feeling of great stability, and when not flying low, the slow revs. of the engine gave me the impression that I remember I got when I flew a Horsley [bomber] after having just left the seat of a Gamecock [fighter]. On turns she was delightful. Perhaps she was a little heavier laterally than the S.5 and the Glosters, but then she was a much bigger and heavier machine. There was no noticeable torque effect against a left-hand turn which had been so tiring in the S.5, and, generally speaking, gave me a feeling of great trust and confidence, and I never had cause to change my opinion. . . The S.6 appeared to stall about 3 mph slower than the S.5, but air speed indicators are not infallible at such a speed. However, it can be taken that she stalled in the region of 95 and was certainly no faster than the S.5 She was extraordinarily stable at the stall. The S.5 would quiver at the stall and flick over either side at the slightest provocation. The S.6 showed no tendency to drop either wing, but would sink on an even keel. On one such occasion, while testing the stalling speed, I found the machine on an even keel sinking at about 87 mph. When one considers the behaviour of her elder brother at a similar speed it is all the more interesting, especially when you realise the extra top speed of the S.6.
Two years later, the S.6 airframe was strengthened to take account of greater fuel loads and a power increase from 1900 to 2350 hp. The two new S.6Bs built with these various features were given the serials S1595 and S1596 and the two 1929 machines, N247 and N248, were modified accordingly as they were also to have the new, more powerful, engine. As such, they were redesignated S.6As. In 1931, both the S.6As went to the bottom of the Solent but with little reflection upon Supermarine’s build or modifications. A piece of the cowling from N248 worked loose in flight and, as the pilot was managing a successful emergency landing, the wash from a passing ship caused the machine to cartwheel and sink. The pilot survived but was withdrawn from the team because of a punctured eardrum. [Incidentally, he was the son of the influential hull designer associated with the early days of Supermarine. As Group Captain Hope, AFC, he was killed in action in August, 1941.] He was replaced by Lieutenant G. L. Brinton who, on his first take-off in N247, seemed not to get the recommended take-off technique right – at a height of about ten feet, it would appear that he had pushed the stick forward too soon and the machine hit the water, bounced back at a sharper angle of attack, hit the water again, and then, from about thirty feet, dived in, with fatal consequences.
Linton Hope’s machine was recovered and was readied for the Trophy contest. As neither France nor Italy could provide a challenge in time, it was decided that S1595 was to complete the course without putting undue strain on the engine or airframe – and, in any event, Mitchell’s valiant efforts to prevent engine overheating could not quite cope with prolonged full throttle flying. If this aircraft were to fail for any reason, then the repaired S.6A would aim to finish the course and win the Trophy outright. S1596, would be available to make trebly sure of a win but it was hoped that it would be retained – to give the crowds the additional thrill of seeing the setting of a new World Speed Record. The Commanding Officer gave the senior pilot, Fl. Lt. G. H. Stainforth, first choice and he opted for the proposed attempt on the speed record; the next most senior man, Fl. Lt. J. N. Boothman, then opted to fly first in the competition itself and, hopefully, to have the honour of winning the trophy.
Events turned out as hoped and  Stainforth later became the first man to exceed 400 mph – this time in S1595, as during a test flight in the other S.6B, his foot jammed under the rudder bar on landing and another machine went under the waves. N248 can be seen at the Solent-Sky Museum, Southampton, and S1595 at the Science Museum, London. [n.b. Was S1596 broken up??]
 This brief account of the perils and pitfalls of flying at the limits of current technology reflect well on the basic soundness of Mitchell’s S.6 design, despite the accidents.

There remains the question of the other S racer which went into the Solent. Did Kinkead’s S.5 crash in 1928 because of a structural fault or pilot error? Julian Lewis’ admirable book on the pilot leads one to seriously question the inquest finding of stall while landing; misjudging the machine’s height above the water in the hazy conditions prevailing is much more likely although I lean towards the possibility of a structural failure at the tail, similar to that which nearly terminated one of the S6s – the subject of a later Blog, I hope.


For reference sources see my "Blog Subjects, Sources and References".

Fuller account of the above in my forthcoming 2nd Edition of Schneider Trophy to Spitfire.

Wednesday, 18 April 2012

Supermarine S.6B; trim tabs and servo tabs

S.6B  (painting by author)
In his book, The Schneider Trophy, Wing Commander Orlebar described how Mitchell overcame nose-heaviness during level flight in the S.6B by adding ‘a splendid gadget’ – metal strips nine inches long and one inch wide attached to the elevator trailing edges and bent downwards slightly. He reported that "I was able to take my hand and feet off the controls at about 330 mph and the machine carried on straight ahead perfectly happily. It was an extraordinary good shot to get her so exactly right the first time".

The principle of an ancillary device to assist the moving of a rudder had been established by Anton Flettner during World War I and was evident in the servo rudders on the D. H. 10 and on the Short Singapore I of 1926. Readers of Seawings are no doubt familiar with these devices, as seen on subsequent British flying-boats: the Saunders A.3 Valkyrie and A.7 Severn of 1927 and 1930 respectively; the Short Singapore I had this device fitted in 1927, and the Calcutta began life with one in 1928. 
It is interesting to note that Mitchell never needed to employ this device in his three-finned Southampton and that the Blackburn Iris and Short Singapore II followed suit. When the Iris III appeared in 1929, the three rudders were now reduced to two and were now fitted with narrow-chord servo tabs.
However, as far as I can see, none had any form of elevator trim tab. Perhaps the earliest British adoption of an in-flight elevator trimming device was with the Boulton and Paul Overstrand of 1934. And trim tabs were mentioned as an advanced feature in the Boeing 247 which first flew in 1933.
Of course, the stratagem of fitting strips to the S.6B  was an improvisation in the heat of Schneider Trophy preparations and they were not adjustable in flight but
1/. one wonders if it was a first (1931) for this adoption of the Flettner principle to tailplanes   [n.b. drawings of the Vickers Type 151 Jockey (of 1930) usually show trim tabs fitted to rudder and elevator but were these fitted when the aircraft was modified in 1932?] 
and
2/.  was Mitchell first among  British aircraft designers with the servo trimming of his Stranraer of 1934?

Any views, anyone?


For reference sources see my "Blog Subjects, Sources and References".

Fuller account of the above in my forthcoming 2nd Edition of Schneider Trophy to Spitfire.

Saturday, 7 April 2012

Supermarine Southampton II

If you are unaware of the Flying Boat Forum at www.seawings.co.uk  I recommend it to you. The section  "Between the Wars - The 'Golden' Era - 1918 to 1939 " is of particular interest to R.J. Mitchell fans (me!) and is a good place to raise the sort of questions that I’ve posted here.

So, casting my net widely here as well, I repeat a few puzzles:

1/. Did the Baltic tour by four British flying-boats in August 1927 include the new metal-hulled Southampton II prototype (N218)?  The Blackburn Iris II prototype was chosen as the flagship for this tour and carried the Air Minister, Sir Samuel Hoare, to an aero exhibition in Copenhagen. It had just been completed with a metal hull and was paired with the new, all-metal, Short Singapore. It would therefore seem likely that the prototype Supermarine Southampton with its new hull was also chosen to showcase advanced British technology.

2/. Did the fourth flying-boat, the Saunders Valkyrie, and the Southampton both crash on take-off in heavy seas at the end of the Baltic tour?  This conflicts with an account that, in fact, the Air Minister returned from Copenhagen in the Southampton.

3/. Most predecessors of the metal hulled flying-boats had relatively slab-sided, internally braced hulls, whereas the original wooden Southampton fuselage was planked over closely spaced hoops, giving crew easy access to all parts of the aircraft. The earlier hull, being uncluttered by bracing etc. was replicated in the Mark II but must have involved a complete re-think of the structure by Mitchell  The resultant Southampton II hull, basically still spherical in cross-section, would thus seem to put Supermarine in the forefront of a metal fuselage technology that was not based upon more slab-sided precedents.
Are there any engineers out there who can support a claim for the Southampton II structure setting the precedent for much later (non-flying-boat) designs, in the U.K. and abroad?


So many questions!  But at least I give something in return:



Supermarine Southampton Mark II (from painting by author)


For reference sources see my "Blog Subjects, Sources and References".

Fuller account of the above in my forthcoming 2nd Edition of Schneider Trophy to Spitfire.