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.

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?] 
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.

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