|S.6B (painting by author)|
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.