H.King Sopwith Aircraft 1912-1920 (Putnam)
Such was the general nature of the Antelope - with two passengers in a cabin behind the pilot, and an engine of about 200 hp - that the question might well be asked: if Sopwith had the Gnu, why should they build this too?’
The simple answer is that the Antelope was a near-relation of the Wallaby, designed to use a war-surplus water-cooled engine (instead of the air-cooled rotary round which the Gnu design took shape) partly, at least, with a view to obtaining lower petrol consumption, allied with lower maintenance costs. Like the Wallaby (which it ultimately joined in Australia) the Antelope was strictly a 'one-off’, and though lighter and less powerful than the Wallaby, it latterly had a heavier look about it because of its four-wheeled landing gear - an impression that was little mitigated by slight stagger on the wings, for these were very much greater in area than those of the comparable Gnu.
These seemingly prosaic facts notwithstanding, it may be judged from what follows that the Antelope was quite a notable aeroplane in the development of civil flying as, indeed, it had to be to gain the second prize in the Air Ministry Small Commercial Aeroplane Competition in 1920.
The one-and-only Antelope was built by Sopwith in 1919, with a normal V-strut landing gear, and a maker's description of it in the summer of 1920 was in these terms: 'The "Antelope" is intended to serve the purpose of a utility machine, characterised by the highest possible performance compatible with great structural strength and having a wide speed range - 38 to 100 mph [61-161 km/h]. Accommodation is provided for pilot and two passengers, the former being located high up between the main planes, whilst the latter are enclosed in a comfortable cabin of 50 cubic ft [1.4 cu m] capacity, aft of the planes. A door in the side of the cabin enables the passengers to enter straight from the ground. Triplex windows in the cabin provide a good field of view, whilst one of the passenger's seats is adjustable so that, on sliding open a door in the roof, the passenger may sit in the open if desired. The engine, a 180 h.p. Hispano-Suiza "Viper", is enclosed by a quickly detachable cowling, giving extreme accessibility, and is fitted with a Black and Manson self-starter, operated from the pilot's cockpit. A fireproof bulkhead is interposed between the fuel tanks and engine. There are no welded joints in the machine.’ It was otherwise explained that, although in one form the Antelope had the simple V-type landing gear already mentioned, lugs were provided for attaching, if desired, 'a pair of front wheels which will protect the propeller and prevent the machine from nosing over on landing.’ And finally: 'A steel tube steerable tail skid is provided, and the opening in the floor of the body through which the skid passes has a flexible cover of oilcloth which prevents dirt thrown up by the skid from getting inside the fuselage.’
Trivial or obvious as some of these points may seem today, some, nevertheless, should have a particular significance for students of airliner design, especially respecting passenger-convenience; for to be able to enter a (reasonably) comfortable cabin, having vis-a-vis seating as the car enthusiasts acclaimed it, 'straight from the ground' was assuredly a boon to ladies in hobble skirts. The adjustable seat mentioned was the rear (forward-facing) one, and the occupant was raised by sitting on the hinged back-rest which could be folded forwards on to the arm-rests of the wicker seat. The passenger's head then protruded through an apparently conventional cockpit opening, with vee-shaped windscreen, the so-called 'door' in the roof being, more descriptively, a panel, shaped to the turtle-decking of the fuselage (i.e., the cabin roof) and sliding in side-channels running forward of the opening.
Especially interesting is this preoccupation with enabling one of the passengers at least to 'sit in the open if desired’, the primitive joys whereof were a legacy from war. What passenger today could expect such individual attention? In any case, there existed, at about the time of the Antelope's design, a lack of unanimity about enclosing passengers, just as there was in later years about enclosing fighter pilots - and even the big Vickers Vimy was offered with row after row of open passenger-cockpits, in a bomber-style fuselage, as an alternative to the bulbous, enclosed, and finally accepted, ‘Commercial'.
As for the Antelope's engine installation, the 'quickly detachable cowling', mentioned as another special feature of the design, was, in reality, even more interesting than it sounded, accessibility being exceptional by virtue of hingeing the two heavily louvred aluminium side-panels along the bottom longerons, allowing them to be folded down after a few bonnet-fasteners had been undone (thus following automobile practice, as designers of those times were much inclined to do).
Certainly the Antelope made a good impression when shown at Olympia in July 1920, and a little later in that year its technical merits were more openly manifest when, with a new landing gear, and ailerons reduced in chord by being tapered inwards (though still horn-balanced as formerly) it participated in the Air Ministry Small Commercial Aeroplane Competition conducted at Martlesham Heath. The engine was then declared as a 200 hp Wolseley Hispano Viper, giving an 'actual output' of 210 hp at 2.100 rpm; and the aircraft and the occasion were thus discussed by Flight:
'The machine entered by the Sopwith Aviation and Engineering Co. [note the correct company-name then used - though the familiar 'Sopwith Aviation Co." was still in common currency] is the "Antelope" exhibited at Olympia. A few minor alterations have, we understand, been made to various parts, but the machine is essentially as shown at Olympia. One difference will be noted, however, in the undercarriage. This is of the four-wheeled type, an extra pair of wheels having been fitted since the show. It may be remembered that one of the tests to be made at Martlesham consists in landing over obstacles 50 ft. above the ground and coming to rest inside a circle marked out on the ground. As side-slip landings are not permitted, and the machine must be brought to rest after the shortest possible run, special arrangements have been made on several of the machines entered for pulling-up quickly, and the extra pair of wheels on the "Antelope" may be expected to form part of such a scheme. What the nature of the arrangement is on this particular machine cannot be stated at the moment.'
The 'nature of the arrangement' concerning which such reticence was observed was the fitting of brakes not quite so remarkable as might be supposed, for four-wheeled Voisins had brakes in earlier years, and the sensational Sopwith-built A.B.C. 400 cc motor-cycle (engined by Granville Bradshaw) had internal-expanding drum brakes on both wheels. During the course of the Martlesham competitions Hawker came gliding in with brakes already applied, thus bursting both main tyres and one of the smaller forward ones. (An alternative explanation was that the brakes were applied too quickly after a heavy landing). In any case, this occurrence stopped the Antelope within the stipulated distance, though this unmatched achievement failed to secure official recognition as the aeroplane was not intact. Nevertheless, the Antelope was awarded the second prize of ?3,000. The winner was the Westland Limousine.
Yet this was not the Antelope's finish, for with F. P. Raynham as pilot it won the Surrey Open Handicap Race at Croydon in June 1922, and re-engined (apparently temporarily) with a Siddeley Puma and re-registered as G-AUSS (The British registration was G-EASS) was transferred by the makers to the Larkin-Sopwith Aviation Company in Australia during April 1923. This company later became the Larkin Aircraft Supply Co. Ltd, and went into liquidation in 1934. Two entries in the 1923 diary of the Australian pioneer F. S. Briggs have a particular interest respecting the Antelope and its more powerful near-relation, thus: 'September 1st. Arrived Hay today, ferried a Sopwith Antelope 160 h.p. Wolseley Viper [sic], Adelaide September 7th, Arrived here today, ferried Sopwith Wallaby from Hay so that it will be in position to fly first air-mail out of Adelaide.'
For good measure, Briggs' entry for 19 May read: 'Ferried a Sopwith Gnu ...' and also in his log book was Dove G-AUJJ!
The powerplant change mentioned - from a Viper to a Puma may have been less drastic than might be supposed, having a parallel, for instance, in the Bristol Fighter.
Antelope (200 hp Wolseley Viper)
Span 46 ft 6 in (14.1 m): length 31 ft (9.4 m); wing area 531 sq ft (49.3 sq m). Empty weight 2,387 lb (1,083 kg); maximum weight 3.450 lb (1.565 kg). Maximum speed 110.5 mph (177 km/h); cruising speed 84 mph (135 km h); climb to 5,000 ft (1.525 m) 7.5 min; approximate range 450 miles (724 km).