M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)
Deleted by request of (c)Schiffer Publishing
H.King Sopwith Aircraft 1912-1920 (Putnam)
Possible Twin-engined Gun Bus
In the chapter on 'Pushers and Gun Buses' mention is made of a seaplane known in the summer of 1913 as 'the 80-ft. span machine', and in this regard these points are stressed: (1) That Sopwith appear to have built the largest British aeroplane of its time, and (2) the company's early use of increasingly powerful engines ('in the 200 h.p.+ bracket’).
By reason of this second fact - the single engine concerned being a Salmson (Canton-Unne) no allusion is made to the apparent thought that was given to the fitting in this airframe of not one, but two engines, these being Austro-Daimlers ('Austrian-Daimlers' as they were termed) of 120 h.p.
But whatever the facts of this matter, it is worth remarking that at about the same time (1913) the Vickers company was busy with designs for a pusher aircraft (and actually made and tested floats for it) from which it was proposed to develop a twin-engined gun carrying machine. Had it materialised, this proposed machine would have probably been only about 10 ft less in span than the '80-ft.' Sopwith.
Whatever claim Sopwith may have had to large dimensions in early aircraft, however, a supplementary one (for twin engines) might now be cautiously advanced, though the description given of the Cobham triplane bomber in its own chapter 'the only multi-engined Sopwith to be built' - appears to stand inviolate.
The 'Possible Twin-engined Gun Bus' (as this present note has been prudently headed) was intended to carry wireless, in addition to one or more guns; and the prudence exercised with regard to its powerplant, and to the remote possibility of the aircraft itself having actually existed, is warranted by the fact that the gun-carrying seaplane No.93 appears to have had a single 120 hp Austro-Daimler, as noted under 'Pushers and Gun Buses'.
Further, the (nominally) 200 hp Salmson (Canton-Unne), which might conceivably have delivered 240 hp, was sometimes regarded before the 1914-18 War as being, in effect, 'two engines in one', as witness this comment of 1914: ‘The fourteen-cylindered [sic] 200 b.h.p. design consists of two groups of seven cylinders acting upon a one-throw crank, the junction of the crankshaft being made in the common crank-pin between two big-end pin cages. This fourteen-cylindered engine is noteworthy as it acts upon a six-stroke and not upon a four-stroke cycle, the valve cams being in consequence specially arranged, and the cam-shaft driven at one-third, and not one-half, of the crankshaft speed. This is done in order to obtain working impulses at equal angular intervals of crankshaft revolution with two seven-cylindered groups operating all on one extended crank-pin ...'
Small wonder that such a fascinating - as well as a powerful - piece of mechanism should appear to have captivated the Admiralty, and that official interest should have been transmitted to their new aircraft-builders, Sopwith. Therein may conceivably lie the background to this present note, though the Navy had long since had an introduction to twin-engined aeroplanes, for Cdr C. R. Samson had flown in the Short Triple Twin during 1911; thus an installation of two Austro-Daimlers in 1913 would have presented no drastic technical departure.