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).
P.Lewis The British Fighter since 1912 (Putnam)
The Sopwith tender to the specification was a three-seat triplane also, designated L.R.T.Tr. but less frighteningly unusual than the F.K.6. The most significant feature of the Sopwith design was the gunner’s nacelle - of excellent aerodynamic form - mounted on the centre-section of the top wings. From this commanding position the field of fire was first-class and a second Lewis-gunner occupied the rear cockpit to guard the machine from attack in that quarter. The 250 h.p. Rolls-Royce Mk.l was installed in the L.R.T.Tr. and the wings, besides incorporating ailerons on each tip, embodied airbrakes in the lowest set of planes.
F.Mason The British Fighter since 1912 (Putnam)
Designed at a time when the RFC was still seeking a long-range escort fighter capable of firing a gun directly forward without perpetuating the old Gunbus formula, the Sopwith L.R.T.Tr. was certainly the weirdest-looking aircraft to emerge from that company’s shops during the War. Accorded the nickname ‘The Egg Box’ by those at Sopwith, the aircraft (whose initials are thought to have stood for Long-Range Tractor Triplane) featured heavily-staggered, three-bay wings of equal span and chord with I-type interplane and cabane struts similar to those on the Sopwith Triplane scout.
The top wing carried a large streamlined nacelle in the nose of which was situated a gunner’s cockpit intended to have been provided with a pillar mounting for a Lewis gun. The pilot’s cockpit was located beneath the trailing edge of the upper wing, and immediately aft of this was a second gunner’s cockpit, also with a Lewis gun for rearward defence.
The fuselage was a very robust structure built up around a deep, wooden box-girder with rounded top decking. Power was provided by a single 250hp Rolls-Royce Mark I (Eagle I) water-cooled vee-twelve in-line engine with its radiator in the extreme front. The undercarriage with twin V-struts and mainwheels was located almost directly below the aircraft’s c.g. and was supplemented by a chassis extending forward with two balancing wheels. The aircraft could therefore rest tail-up on the balancing wheels or tail-down on the tailskid, depending on the number of crew and quantity of fuel carried.
It is likely that the big Rolls-Royce engine bestowed a useful maximum speed, but by the time the triplane was flown, towards the end of 1916, the RFC’s requirement had lapsed owing to the imminent arrival in service of the Bristol Fighters.
Type: Single-engine, three-seat, three-bay triplane fighter.
Manufacturer: The Sopwith Aviation Company Ltd, Kingston-upon-Thames, Surrey.
Powerplant: One 250hp Rolls-Royce Mark I (Eagle I) in-line engine driving two-blade propeller.
Span, 53ft; length, 38ft.
Performance: Max speed, approx 107 mph Armament: One 0.303in Lewis machine gun on gunner’s position in nose of wing-mounted nacelle, and another on the rear gunner’s cockpit in the fuselage amidships.
Prototype: One. No production.
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).
J.Bruce British Aeroplanes 1914-1918 (Putnam)
THE big Sopwith three-seat triplane was the most remarkable aeroplane produced by the company during the war. It was designed for the R.F.C. as a long-range escort fighter to the same specification as the Armstrong Whitworth F.K.12 and Vickers F.B.11, and had the same engine, the 250 h.p. Rolls-Royce Mk. I.
The design had been begun before the advent of a practical interrupter gear for machine-guns and, as on the Sopwith’s two contemporaries, radical measures had to be taken to ensure a good all-round field of fire. The entire upper hemisphere and a wide field in front of the aircraft were covered by the gun of the upper gunner, who occupied a finely streamlined nacelle built into the centre-section of the top wings. The pilot sat in line with the trailing edge of the middle wing, and behind him was a second gunner to protect the triplane’s tail.
The fuselage was a deep and massive structure, mounted on a four-wheel chassis on which the machine could sit tail high. The main wheels were so placed that the aircraft could also rest upon its tail-skid. The fin was of generous proportions, and a balanced rudder was fitted.
The three-bay wings were of high aspect-ratio, and had plank-type interplane struts similar to those of the Sopwith single-seat triplanes. Ailerons were fitted to all wings. Air-brakes were fitted to the bottom wings: these consisted of flaps in the trailing portion of the wings between the fuselage and the first interplane strut on each side. It seems probable that these flaps, like the 1 1/2-Strutter’s air-brakes, moved upwards until they were at right angles to the line of flight. They were actuated by means of a wheel control in the pilot’s cockpit; an external cable moved the flaps.
By the time the Sopwith L.R.T.Tr was completed, gun synchronising gears had become available, and it was obvious that fighting duties should be left to the fast single-seaters. The big Sopwith triplane rejoiced in the nickname of “The Egg-box”, a soubriquet which requires no explanation.
Manufacturers: The Sopwith Aviation Company, Ltd., Canbury Park Road, Kingston-on-Thames.
Power: 250 h.p. Rolls-Royce Mk. I.
Dimensions: Span: 53 ft. Length: 38 ft. Gap: 3 ft 6 in. Stagger: 2 ft.
Armament: One Lewis machine-gun on pillar-type mounting behind rear cockpit; a second Lewis gun was mounted in front of the third cockpit on the top wing.
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.