O.Tapper Armstrong Whitworth Aircraft since 1913 (Putnam)
After Koolhoven left Armstrong Whitworth in 1917 to go to the British Aerial Transport Co, the design duties at Gosforth were undertaken by Frank Murphy, who had been the manager of the aeroplane department under Fairbairn-Crawford. The first aircraft to be built to Murphy's design was the F.M.4, the Armadillo, a single-seat fighter, powered by a Bentley B.R.2 rotary engine and fashioned to meet the requirements of the Air Board specification A1(a). The Armadillo was not ordered by the Government although in January 1918 the Air Board gave Armstrong Whitworth a licence '... to build two machines at their own risk and expense'. This was done because Armstrong Whitworth had expressed a wish to check the capabilities of the design staff with a view to taking up original design work once more. Thus, although the F.M.4 was nominally a contender for the fighter contract, it was, in fact, never seriously considered for this either by the company or by the Air Board. Indeed, officials of the Board were less than enthusiastic about the F.M.4, and an internal memorandum dated 26 February, 1918, stated that '... this machine is hardly likely to come into competition with other B.R.2 scouts'. In the event, the Sopwith Snipe had been ordered into production by the time the Armadillo appeared.
Although the licence specified two aircraft, only one, X19, was completed: the second aircraft, X20, being abandoned after it had reached a fairly advanced stage of construction. The first aircraft was designed to have three sets of interchangeable wings, two of which were designated 'AW No.1 Camber' and 'AW No.2 Camber', while the third set was of RAF 14 section and was of reduced span with a shorter overhang at the tips. The second F.M.4, besides other minor alterations, was to have had two sets of wings of RAF 14 and RAF 15 section. In appearance the Armadillo was a squat, two-bay biplane with a fuselage filling the rather narrow gap. The wings were of equal span, but the bottom wing, which alone had a slight dihedral angle, was narrower than the top. The 230 hp B.R.2 rotary engine was housed in a bulbous cowling set low on the fuselage with a top fairing housing two Vickers synchronized machine-guns. This also served to fair off the joint between the low-set cowling and the top line of the fuselage. Provision was also made for a hand-operated Lewis gun which could be elevated to fire forwards and upwards over the propeller. The pilot was seated just ahead of the trailing edge of the wing with his eyes slightly above the level of the wing; both upper and lower wings had a trailing-edge cut-out to improve the downward view. For the same reason the sides of the cockpit were also cut away quite deeply on either side, and this led to a discontinuity in the top longerons; to compensate for this the sides of the fuselage around the cockpit were covered with three-ply wood. For additional strength, the forward portion of the fuselage was reinforced with two channel-section duralumin girders which also supported the fuel tanks and the pilot's seat. The V-struts of the Armadillo's undercarriage were of rather light section and were later replaced by somewhat stronger members.
The design of the F.M.4 was completed in the autumn of 1917, and an officer from the Air Board inspected the mock-up in December 1917. At that time the bottom wing was carried on struts some ten inches below the bottom longerons. The inspector suggested that the fuselage should be made deeper to fill the gap between the wings; he also suggested a rearrangement of the guns, moving the Lewis gun from the centreline so as not to interfere with the fitting of a windscreen and a gun sight. The licence for the two aircraft was issued on 7 January, 1918, and construction of the first aircraft went ahead quickly; by the middle of the month Armstrong Whitworth were pressing the Board for an early delivery of the B.R.2 engine.
During January 1918 the airframe of X 19 was inspected by Commander Ogilvie of the Air Board and sometime in February he criticized the structural design, stating that in his opinion'... the machine is somewhat weak all over'. He added that the compression ribs were weak, the attachment of the tailplane front spar was unsatisfactory and the spindling of the wing spars had been continued too far towards the points of support. Correspondence on these matters went to and fro between the Air Board and the company during February and March 1918 (one letter from the Board referred to the aircraft as the 'armoured Dillo') until, at the beginning of March, the company wrote stating that the spars and internal bracing of the mainplanes had been strengthened, the bracing of the fuselage modified and the interplane struts and front outer lift wires increased in section. Other modifications included an alteration to the tailplane bracing and the fitting of a stronger main tube in the rudder.
Following these modifications and a further inspection by Ogilvie, Armstrong Whitworth were informed towards the end of March 1918, that the aircraft was now up to strength everywhere and that it was passed for experimental flying. Whether the previous criticisms were in fact justified will never be known, but the fact remains that from a structural point of view the Armadillo seems to have had some merit. This is evident from the fact that in April the Air Ministry's stress expert, Professor A. J. Sutton Pippard, noted that the structure weight of the aircraft, which worked out at 26 per cent of the total, was unusually low. Following this assessment, Armstrong Whitworth were asked to supply a detailed breakdown of the Armadillo's weight. This analysis, arrived at by weighing each component, gave a weight of 1,730 lb; after a further study of the design, Pippard stated that he could find no trace of weakness in the structure and suggested that the low weight could he due to the small gap, the light interplane struts and the absence of a centre section.
As was so often the case with new aircraft at this time, the first flight was delayed pending delivery of an engine; this was eventually received in March 1918 and on the 18th of the month Armstrong Whitworth wrote to the Air Ministry announcing the arrival of the engine and seeking permission to use Cramlington aerodrome for the Armadillo's first flight, stating that the Town Moor field was not suitable because of the surrounding obstructions and the rough surface. The company added that they had engaged a well-known test pilot to carry out the initial tests before the machine was handed over to the Air Ministry; this was probably Clifford Prodger, who did some further testing of the Armadillo at a later date. Permission to use Cramlington (then controlled by Headquarters, Training Division, RFC) was granted, and on 3 April Armstrong Whitworth telegraphed the Air Ministry reporting that the Armadillo would fly on the following Saturday, 6 April. Whether it did so or not is uncertain, but it undoubtedly flew before 1 May, on which day, a report states, '... it flew again'. On Wednesday, 8 May, the aircraft was tried out by an RAF pilot who reported back to the Air Ministry that he found it most unsatisfactory. According to this pilot the Armadillo was very tail heavy and flew left wing low at full power; the aileron control was very heavy and it was difficult to move the stick laterally at high speed. He also complained that the control column was placed too far forward and that it fouled the instrument panel if the hand was placed on top of the stick. Another criticism was that the tailskid was too short so that the rudder was damaged during taxiing. All these faults could no doubt have been put right relatively easily: more serious was the fact that the pilot's view when landing was very bad, a defect that would have been difficult to rectify without considerable redesign. As a result of this report, the Assistant Controller, Design, at the Air Ministry wrote to the company on 18 May, 1918, saying that in view of the bad outlook from the cockpit during landing, the aircraft would not he sent to Martlesham and it would not be flown again by Service pilots. The Ministry's concern for the well-being of the RAF test pilots did not, apparently, extend to their civilian counterparts, for the letter went on to suggest that Armstrong Whitworth should conduct their own trials so as to obtain as much data as possible.
After some further modification, which included the fitting of the more robust undercarriage, Clifford Prodger made some tests on 7 June, 1918, and the figures that he recorded, although almost certainly optimistic, seemed to indicate that the aircraft had quite a respectable performance. The climb to 10,000 ft was said to have been accomplished in about 6 1/2 min and the speed at that height was given as 112 mph; at an altitude of 4,000 ft the aircraft reached 120 mph with the engine turning over at 1,300 rpm. There is little on record regarding subsequent activities: the company stated its intention of trying out different propellers, one with four blades and another with a finer pitch but, in view of the discouraging attitude of the Air Ministry, no further serious development work was undertaken, Murphy having already turned his attention to the Armadillo's successor.
Dimensions: Span 27 ft 9 in (8.46 m); length 18 ft 10 in (5.74 m); height 8 ft 7 in (2.62 m); Wing area 232 sq ft (21.56 sq m).
130 hp Bentley B.R.1
Max weight: 1,860 lb (844 kg)
Empty weight: 1,250 lb (557kg)
Sea level: 125 mph (201 km/hr)
10,000 ft (3,048 m): 112 mph (182 km/hr)
to 10,000ft (3,048m) 6.5 min
Service ceiling: 24,000 ft (7,315 m)
Endurance: 2 3/4 hr
H.King Armament of British Aircraft (Putnam)
Armadillo. Competitor of the Sopwith Snipe, Austin Osprey, Boulton & Paul Bobolink and Nieuport B.N.I, the Armadillo (1918) had two widely spaced synchronised Vickers guns in a remarkable installation, completely enclosed in an angular cowling and firing through tunnels. Provision was made in the early design stages for a Lewis gun on the upper-starboard wing root, but the gun was not fitted.
P.Lewis The British Fighter since 1912 (Putnam)
The 230 h.p. Bentley B.R.2 rotary was also selected by F. Murphy as the engine for the F.M.4 single-seat biplane fighter which he evolved for Armstrong Whitworth when, in 1917, he succeeded F. Koolhoven as designer. Named Armadillo, the machine was far from elegant in appearance and embodied a boxlike fuselage which filled the relatively narrow gap between the two-bay wings. The two Vickers guns were housed in a peculiar fairing which curved from the front face of the engine cowling to the top of the upper wings. Being tested in September, 1918, the Armadillo prototype X19 was a late-comer among the War’s fighters and, with its comparatively poor view from the cockpit, stood little chance of a production order.
F.Mason The British Fighter since 1912 (Putnam)
Armstrong, Whitworth F.M.4 Armadillo
Variously described elsewhere as ‘pugnacious’ and ‘far from elegant’, the F.M.4 Armadillo was surely nothing short of ugly, and was possibly the brainchild of Frederick Koolhoven, who had left Armstrong, Whitworth to join the British Aerial Transport company following the failure of his F.K.10 and 12, his place being taken as chief designer by Fred Murphy.
Subject of Licence No 18, two prototypes (X19 and X20) of this small two-bay biplane were authorized, and X19
appeared in September 1918. Rigged with scarcely any stagger, the wings were of fairly broad chord, and the upper wing - without conventional centre section - was attached to the top shoulders of the square-section fuselage. This was in keeping with Koolhoven’s latest preoccupation, that of setting the upper wing level with the pilot’s eyes.
The fuselage was a plain wooden box girder with flat ply sheet covering the sides, but without any attempt to provide any rounded decking. The engine was a 230hp Bentley B.R.2 rotary with a cowling that completely enveloped the cylinders, and included a fairly small aperture for cooling air entry. A most incongruous feature was a humped fairing, curving up from the front of the cowling to the top line of the upper wing, inside which were mounted the aircraft’s twin Vickers guns.
The reasoning behind this wing layout was obviously to provide the pilot with an excellent field of view forward and above, but the bulk of the nose and the lower wings severely restricted the pilot’s view of the ground, especially when landing, despite cutouts in the wings, and the aircraft was severely criticised on this account - not to mention many others.
It is difficult to understand what lay behind the production of this machine so late in the War for, with over one hundred horsepower more that the Le Rhone Camel of the previous year available, the speed performance of the Armadillo showed scarcely any advance. It is not known whether the second example was completed.
Type: Single-engine, single-seat, two-bay biplane fighter.
Manufacturer: Sir W G Armstrong, Whitworth & Co Ltd, Newcastle-upon-Tyne.
Powerplant: One 230hp Bentley B.R.2 rotary engine.
Dimensions: Span, 27ft 9in; length, 18ft 10in; height, 7ft 10in; wing area, 232 sq ft.
Weights: Tare, 1,250lb; all-up, 1,860lb.
Performance: Max speed, 125 mph at sea level; climb to 10,000ft, 6 min 30 sec; ceiling, 24,000ft.
Armament: Two synchronized 0.303in Vickers machine guns under fairing over the nose.
Prototypes: Two; X19 and X20 authorised under Licence No 18. X19 flown in September 1918; X20 may not have been completed. No production.
W.Green, G.Swanborough The Complete Book of Fighters
ARMSTRONG WHITWORTH F.M.4 ARMADILLO UK
The Armadillo, designed by F Murphy, who had succeeded F Koolhoven as chief designer to Armstrong Whitworth, was initiated late in 1917, and the construction of two prototypes began early in 1918 as a private venture, the first of these being flown in April of that year. Powered by a 230 hp Bentley B.R.2 nine-cylinder rotary, the Armadillo had provision for an armament of two synchronised 0.303-in (7,7-mm) Vickers machine guns, but flying characteristics were declared to be most unsatisfactory and flight testing was terminated in June 1918, the second prototype never being flown.
Max speed, 125 mph (201 km/h) at sea level, 113 mph (182 km/h) at 10,000 ft (3 050 m).
Time to 10,000 ft (3 050 m), 6.5 min.
Endurance, 2.75 hrs.
Empty weight, 1,250 lb (567 kg).
Loaded weight, 1,860 lb (844 kg).
Span, 27 ft 9 in (8,46 m).
Length, 18 ft 10 in (5,74 m).
Height, 7 ft 10 in (2,38 m).
Wing area, 232 sq ft (21,55 m2).
Jane's All The World Aircraft 1919
The Armadillo, designed by F Murphy who succeeded F Koolhoven as chief designer to Armstrong Whitworth, was initiated late in 1917, and the construction of two prototypes began early in 1918 as a private venture, the first of these being flown in April of that year. Powered by a 230 hp Bentley B.R.2 nine-cylinder rotary, the Armadillo had provision for an armament of two synchronised 0-303-in (7,7-mm) Vickers machine guns, but flying characteristics were declared to be most unsatisfactory and flight testing was terminated in June 1918, the second prototype never being flown.
Max speed, 125 mph (201 km/h) at sea level,
113 mph (182 km/h) at 10,000 ft (3 280 m).
Time to 10,000 ft (3 280 m), 6 min 30 sec.
Endurance, 2 hr 45 min.
Empty weight, 1,250 lb (567 kg).
Loaded weight, 1,860 lb (844 kg).
Span, 27 ft 9 in (8,45 m).
Length, 18 ft 10 in (5,74 m).
Height, 7 ft 10 in (2,38 m).
Wing area, 232 sq ft (21,55 m2).
Flight, April 3, 1919.
THE ARMSTRONG-WHITWORTH MACHINES
The A.W. "Armadillo." 1918
As more powerful engines became available, the designs for a number of experimental machines were got out, among them being the 220 h.p. "Armadillo" and the 320 h.p. "Ara." The former was fitted with a B.R. 2 rotary engine, and the trial flights took place in September, 1918. The results were so promising that it is fairly safe to say that the machine would have been put into production in time for the 1919 spring offensive. From the illustrations it will be seen that the chief characteristic of the Armadillo is that the top plane is mounted on the top of the fuselage on a level with the eyes of the pilot. Owing to the small gap between the planes there are two pairs of inter-plane struts on each side, thus ensuring a better angle for the lift wires. The rotary engine is enclosed in a circular cowl, which is surmounted by a square, box-like excrescence, inside which the two machine guns are mounted, synchronised, of course, to fire through the propeller.