H.King Sopwith Aircraft 1912-1920 (Putnam)
Of all the names in the Sopwith 'menagerie' the one that heads this chapter was the most appropriate - not in the sense that the aeroplane which bore it was slow (for it was not any more than the Camel had been a clumsy beast) but because it had a shell-type, or monocoque, fuselage. That only one version of the type did, in actual fact, embody such a fuselage is of incidental, rather than salient, interest, for, as we shall see, the monocoque form of fuselage was perpetuated in the Snark.
Perhaps of greater importance is the fact that the Snail was built specifically to use a brand-new type of engine, the 170 hp seven-cylinder A.B.C Wasp, which was deemed conducive to compactness and light weight. These virtues the engine itself exhibited in notable degree. No less significant was the armament installation, which featured 'buried' Vickers guns.
So, all in all, the tiny Snail (for it was smaller even than the Camel or the Pup) was a fighter much out of the ordinary - the more so as, into the bargain, it had in one of its forms, a slight back-stagger. This last-named feature, allied with the fact that the wing span was almost exactly that of the D.H.5, gave a lingering impression that D.H.'s fifth wartime effort had outlived, or lived-down, its own unpopularity. One would not, however, overemphasise the backward stagger of the Snail, even though this was a feature which it shared with other Sopwith types (notably, of course, the Dolphin) for it was 5 in (127 mm) only, whereas on the D.H.5 it was no less than 27 in (686 mm). At the same time, it is fitting to give the wings priority of consideration over the two very different types of fuselage that were embodied, for the cellule - though differing in rigging and centre-section design - was essentially common to both Snail C4284 (conventional fuselage) and C4288 (monocoque). These two were the only Snails completed - though six had been ordered, to comply with Air Board Specification A.1(a), the '8F.1' suffix (or prefix, according to taste) being Sopwith's own type-designation.
The first order for Snails was placed on 31 October, 1917, the specified engine, as already noted, being the A.B.C. Wasp (which had first been submitted for official tests in that same month) and the form of fuselage construction conventional. Within a month - on 23 November, 1917 - Sopwith were asked to build two additional examples, these to have a monocoque fuselage of plywood a form of construction to which official attention had already been redirected by the British Aerial Transport Co, with their Koolhoven-designed, A.B.C. Mosquito-powered F.K.22. This last-named design, like the Sopwith Dolphin and Snail, provided for the pilot to sit with his head in a centre-section cut-out.
Whatever significance may be attached to the dating of orders, the 'conventional' Snail C4284 and the 'monocoque' C4288 were built concurrently. That some fairly basic changes in design-thinking then occurred is implicit in the intended reduction in back-stagger on 'conventional' (though never completed) Snails C4285-C4287 from 5 in (127 mm) to 3 3/4 in (95 mm) - and vastly more so on the monocoque C4288, the wings whereof had a positive stagger of no less than 22 in (599 mm). This being so, the pilot was seated further to the rear, his centre-section cut-out now being transferred to, and confined to, the trailing edge. (A point of some interest here is that the rival Westland Wagtail had both forms of cut-out in conjunction).
The facts behind these wide discrepancies in stagger may have some connection with the obvious fact that an aeroplane having so short a fuselage as the Snail's - measuring well under 20 ft (6.1 m) would be extremely sensitive to weight distribution. This same shortness in fuselage length may also have been a factor in the adoption of relatively large horizontal tail-surfaces - possibly, it appears, those of a Snipe.
One other Snipe-related feature was the top-wing mounting for the free-firing Lewis gun. This gun was mounted above the starboard edge of the centre-section cut-out, the rear end picking up a special fitting. In firing position, the gun was parallel with the aircraft centre line, but a pivoted arm attached to the rear face of the front spar allowed the gun to be swung inboard for reloading.
The forward centre-section struts on C4284 were uncommonly long (though the fact was partly concealed by the rounded fuselage sides) because they were attached to the lower longerons, and not to the upper ones as usual. The reason for this arrangement was that the upper longerons carried the two synchronised Vickers guns, the entire installation of which was exceptionally neat, for the rounded-section fuselage, of ample diameter, enabled the guns to be mounted in the sides of the cockpit. The sole external evidence that the guns were, in fact, present was a glimpse of the extreme muzzle-ends projecting into short troughs, and the chutes for the spent cartridge cases and belt links in the flanks of the cockpit. The Vickers guns appear to have been actually installed only on the first, or 'conventional', Snail (C4284); but whatever the extent of armament investigations may have been, an official inspection report recommended that flash tubes (or blast tubes, as they might otherwise have been called) should be fitted to the guns, the muzzles of which nested closely beneath the main petrol tank.
Photographs of the monocoque Snail C4288 suggest that not only were the Vickers guns themselves absent but that armament had been entirely abandoned, or that some wholly different scheme was intended or enforced; for apart from panels and holes associated with the Wasp engine, the beautifully finished fuselage appears immaculate, and more significant the centre-section strut arrangement is quite different.
The monocoque fuselage itself was elliptical in cross-section; the structure embodied many hoops and in the rear part four bulkheads. There were no longitudinal stringers or formers, the plywood skin being nailed to the hoops.
That the A.B.C. Wasp engine was installed with great care for a good aerodynamic entry is clear from the close-up photographs. Alas, like the larger Dragonfly, the Wasp was troublesome, and to this fact may be attributed delay in delivery of the engine for C4284 until 18 March, 1918. However, as a Sopwith-captioned photograph shows, C4284 was taxying (if not flying) at Brooklands during the following month; and meanwhile work was going forward on C4285 and C4286 - in addition to the monocoque C4288, which was among a number of Sopwith types shown off at Brooklands on 27 April, 1918.
Official interest in Wasp-engined fighters having lapsed, components of '85 and '86 were used as spares for the only completed specimens '84 and '88. Both these machines were sent to Martlesham Heath for trials in May 1918; but though speed and climb were good, compactness and four ailerons failed to confer manoeuvrability equal to the Camel's. There was little enthusiasm, in fact, on the score of handling generally, control at low speed being downright poor. The structural interest of C4288, however, led to the despatch of this machine to Farnborough, though performance figures quoted below apply to C4284.
Snail 8F.1 (A.B.C. Wasp)
Span 25 ft 9 in (7.9 m): length 19 ft (5.8 m); wing area (C4284) 228.6 sq ft (21.2 sq m). Empty weight (C4288) 1.390 lb (630 kg); maximum weight (C4288) 1,920 lb (870 kg). Maximum speed 124.5 mph (200 km/h) at 10.000 ft (3,050 m): climb to 10.000 ft (3,050 m) 9 min 55 sec; climb to 15,000 ft (4,570 m) 19 min 15 sec.
H.King Armament of British Aircraft (Putnam)
Snail. The Snail Mk.II single-seat fighter, which appeared in 1918 earlier than the Mk.I version (monocoque fuselage), carried its two Vickers guns in an extremely neat installation. The relatively large fuselage diameter enabled the guns to be mounted in the sides of the cockpit, the only external evidence of their presence being the extreme muzzle ends projecting into short troughs and the separate case and link chutes in the flanks of the cockpit. A Lew is gun was mounted above the starboard edge of the centre-section cut-out, the rear end picking up a fitting seen in the photograph. In firing position, the gun was parallel with the centre line, but a pivoted arm attached to the rear face of the front spar allowed the gun to be swung inboard for reloading. This was, in effect, a reversal of the system used on the Snipe. The windscreen was perforated for an Aldis sight. The Snail Mk.I does not appear to have carried its intended armament of two Vickers guns.
W.Green, G.Swanborough The Complete Book of Fighters
SOPWITH 8F.1 SNAIL UK
In October 1917, the A.B.C. Wasp seven-cylinder radial air-cooled engine was considered to offer much promise, and on the 31st of that month Sopwith was invited by the Air Board to tender designs for a single-seat fighter utilising that power plant. Four prototypes were ordered, these being of conventional construction, and, on 23 November, the company was asked to build two additional prototypes with plywood monocoque fuselages. In view of its intended function adoption of the name Snail for the new single-seater was bizarre, this being approved on 16 February 1918. Powered by a 170 hp Wasp I, the first prototype Snail was completed in April 1918, this having negative wing stagger and fabric skinning for its circular-section fuselage. Intended armament comprised two synchronised 0.303-in (7,7-mm) machine guns, a third weapon of similar calibre being mounted above the wing centre section, to starboard of the cut-out. The remaining three prototypes of conventional construction were not completed, the next Snail to fly being the first of the two with plywood monocoque fuselages and positive wing stagger. On 9 May, the monocoque Snail was sent to Martlesham Heath for official trials, the reports being less than complimentary about its manoeuvrability and low-speed control. When, in October 1918, it was decided to abandon the Wasp engine, further work on the Snail was terminated, the second monocoque prototype being discontinued before completion. The following data relate to the monocoque Snail.
Max speed, 115 mph (185 km/h) at sea level.
Time to 6,000 ft (1830 m), 6.25 min.
Empty weight, 1,390 lb (630 kg).
Loaded weight, 1,920 lb (871 kg).
Span, 25 ft 4 in (7,72 m).
Length, 19 ft 0 in (5,79 m).
Height, 7 ft 10 in (2,39 m).
Wing area, 228.6 sqft (21,24 m2).