H.King Sopwith Aircraft 1912-1920 (Putnam)
Appearances notwithstanding, this aeroplane was a fighter, or 'long- reconnaissance' aircraft, having not only three wings but three seats also; and although the question once arose whether the triplane layout was signified by the 'T.' or the 'Tr.' in the designation. 'Tr.' was evidently the operative symbol, the 'T.' connoting 'tractor', as in SL.T.BP.
That the Sopwith triplane now studied was the ungainliest single-engined fighter ever built with the possible exception of the rival Armstrong Whitworth triplane sometimes called F.K.12 - is a point hardly to be questioned, though this dubious distinction can be attributed not only to the triplane wings, with the gunner's nacelle on the topmost one (the rival type mentioned had two such nacelles, both on the middle wing) but even more so to the four-wheeled chassis, which, though embodying the characteristic Sopwith 'divided axle' was more strongly suggestive of agricultural than aeronautical practice. Upon this conception the forward wheels whereof minimised the risk of nosing over, and hence the peril of the nacelle gunner the aeroplane normally towered tail-in-air, though there was a tailskid also to allow it to sit tail-down. For lateral protection there was a rearwardly-raked skid beneath each bottom wing, in line with the outermost set of plank-type interplane struts.
Yet another suggestion of the farmyard rather than the flying field was the triplane's sobriquet 'Egg-box' - an appellation that was especially apposite by reason of the neat cockpit recess in the streamlined top-wing nacelle, which smooth receptacle seems never to have been compromised by a gun-mounting. More important, this nacelle may give an essential clue to design philosophy, for its location afforded in theory a well-nigh untrammeled field of fire, and one that certainly precluded any need for deflector or synchronising gear - the latter still being a comparative novelty when the design of the aircraft was under way early in 1916.
Yet the very mention of synchronising gear is suggestive of machine-gun armament; and though it may well be that the nacelle (which was originally designed to be smaller and, in any case, underwent at least one change in shape - the later version being shorter in the nose, blunter, and housing a gravity-feed petrol tank) was intended to have a Lewis gun, one inclines to the view that heavier ordnance may have been in mind. The likelihood is that this would have been a gun of the Davis recoilless type, the installation whereof - whether fixed or free - would have been of relatively small account by reason of the aircraft's low-set vertical tail-surfaces. The pictures clearly show that not only was there an under-fin, but that a substantial part of the rudder was below the fuselage - though it must be recognised that large vertical tail-area must in any case have been demanded by the very deep nose and the jutting-out nacelle and landing gear. As for weight, a 2 pdr Davis gun might have accounted for only about 70 lb, and no great number of shells would have been carried.
Conversely, the fitting of a gravity tank in the nacelle, if this tank was meant to supplement the very large one under the pilot's cockpit (for he was seated bodily above the top longerons) may have signified an alternative emphasis on endurance, at the expense of armament. Even in this case, however, the aircraft would not have been unarmed, for immediately behind the pilot was a cockpit for a second gunner, who had a Lewis gun on a swivelling pillar mounting, characterised by a perforated gun-arm. Additionally, he had a second set of flying controls.
The foregoing facts and surmises are clearly in accord with the prescribed duties of long-range escort work and anti-Zeppelin patrol; and one feature that is obviously compatible with long range, or long endurance, is the very high aspect ratio of the staggered triplane wings, the chord whereof was a mere 4 ft or so, giving an aspect ratio of about 13 to 1. This was a very high figure for 1916 though rivalled it would seem by the Caproni Ca.41 and possibly also by the earlier 80-ft-span Sopwith pusher but even though the spars were very closely spaced, each of the six wing-panels carried an aileron. Contrarily, these lateral-control surfaces were of low aspect ratio.
One other notable feature of the three-bay wing cellule the struts whereof were Sigrist-patented in form, comprising a wooden nose and tail, held either side of a central H-section metal strut with bolts from nose to trailing edge was the fitting of upward-hingeing airbrakes at the root-ends of the bottom mainplanes. These braking surfaces were cable-actuated by a handwheel in the pilot's cockpit.
Even so, the interest of the L.R.T.Tr. was not confined to armament and aerodynamics, for the engine was the first Rolls-Royce to be installed in any Sopwith aeroplane. Known contemporaneously as the 250 h.p. Rolls-Royce, or 250 h.p. Rolls-Royce Mk.I, this was an early member of the historic Eagle family (see later under 'Atlantic'), and though there had been a scheme for installing the radiator aft of the engine, this item was, in the event, fitted frontally, with the reduction-gear housing largely exposed.
So, its ungainliness notwithstanding, the L.R.T.Tr. displayed features of uncommon interest, though it was one of those aeroplanes that Sopwith never recalled with pride - which would account for its reported rapid relegation to a Brooklands hangar.
(250 hp Rolls-Royce Mk.I) Span 53 ft (16.1 m); length 38 ft (11.6 m).
H.King Armament of British Aircraft (Putnam)
L.R.T.Tr. This long-range, or anti-Zeppelin, fighter (1916) may be compared with the Armstrong Whitworth F.K.12. Contrasting with the ungainly masses of the airframe and undercarriage, was a carefully streamlined nacelle built into the top centre-section. Forward of the leading edge was a cockpit for a gunner, and just ahead of this was a socket for a pillar-mounted Lewis gun. The nacelle underwent at least one modification in shape. The pilot had no gun, but immediately behind him was a third cockpit for a second gunner who had a Lewis gun on a swivelling pillar mounting which carried the gun on a perforated arm.
W.Green, G.Swanborough The Complete Book of Fighters
SOPWITH L.R.T.TR. UK
The L.R.T.Tr., presumably signifying Long-Range Tractor Triplane, was designed to meet an RFC requirement for a combined escort fighter and airship interceptor. Other contenders were the Armstrong Whitworth F.K.6, also of triplane arrangement, and the Vickers F.B.11, which was of more conventional biplane layout. Of bizarre appearance, the L.R.T.Tr. was a three-bay triplane with narrow-chord wings, all of which were fitted with ailerons. Power was provided by a 250 hp Rolls-Royce Mk I (Eagle I) 12-cylinder water-cooled engine, and the crew comprised a pilot and two gunners. One gunner occupied the rear cockpit and the other a streamlined nacelle built around the upper wing centre section, both having a single 0.303-in (7,7- mm) machine gun. By the time flight test commenced in 1916, it was appreciated that the concept of the L.R.T.Tr. had been rendered outdated by the advent of practical gun synchronisation equipment and the success against airships enjoyed by more conventional aircraft. This clumsy aeroplane, meanwhile assigned the epithet of Egg Box, was duly abandoned.
Span, 52 ft 9 in (16,08 m).
Length, 35 ft 3 in (10,74 m).