O.Tapper Armstrong Whitworth Aircraft since 1913 (Putnam)
In spite of the disappointing performance of the first aircraft, a second, much modified, version was built. This was, indisputably, designated the F.K.10 and it had a more powerful Clerget engine rated at 130 hp. It had a similar wing arrangement but with the span increased by six inches, and, in order to give more room for the crew, the fuselage was both deeper and wider. The tail surfaces were also modified; instead of the fixed tailplane and no upper vertical fin, the second aeroplane had balanced elevators without fixed surfaces and vertical fins above and below the fuselage supporting a conventional, if rather small, rudder. In an attempt to overcome the undercarriage weakness of the previous aircraft, the longerons, from the undercarriage struts forward, were strengthened with plywood, but the structure was still not strong enough and it was reported that the diagonal struts within the fuselage, designed to take the compression loads from the undercarriage, were bent when the aircraft was delivered for official trials.
These trials were undertaken in March 1917, and the performance seems to have been slightly inferior to that of the lower-powered version. This may have been due to the fatter fuselage, but it is equally possible that the difference between the two aircraft arose because of variations in piloting skill and because of the somewhat imprecise methods of performance measurement then in use. The test pilot reported that the machine handled well, with good controllability and with very little tendency to spin. The take-off and landing distance was measured as 80 yards. As might be expected with an all-moving tailplane, the aircraft was somewhat unstable longitudinally, and the pilot noted that the controls could not, therefore, be left alone. In other respects the aircraft was considered easy to fly. Minor criticisms were that the windscreen was inefficient and that it was necessary to remove the engine cowling in order to replenish the oil tank. Like its predecessor, the second aircraft was reported as having a performance below that specified.
In view of the poor performance, an order for fifty F.K.10s which had been placed with Angus Sanderson and Co was cancelled in March 1917, and the serial numbers A8950 to A8999 set aside for this batch were reallocated. However, small batches of the F.K.10 were produced by Armstrong Whitworth, Angus Sanderson and the Phoenix Dynamo Manufacturing Co. Most of the production aircraft had the 130 hp Clerget engine, but at least one of those built by Armstrong Whitworth was powered by a Le Rhone engine of 110 hp. There is some uncertainty about the numbers of quadruplanes actually built: two, with the serial numbers A5212 and A5213, were ordered from Armstrong Whitworth, one of which may have been the original F.K.9, and a further five, numbered 83996 to 84000, were ordered from Angus Sanderson, but it is not known whether all were delivered. Three more, N511, N512 and N514, were built for the Royal Naval Air Service, the first two by Phoenix Dynamo and the third by Armstrong Whitworth. The missing number, N513, was originally allotted to an Angus Sanderson F.K.10 which was cancelled, and there is some evidence that this number was subsequently re-allocated to an Armstrong Whitworth biplane, presumably an F.K.8, with a Sunbeam engine: this aircraft is said to have force-landed near Beverley on 7 April, 1917, while en route from Newcastle to Martlesham Heath.
In spite of the official test reports, which indicated that the aircraft at least handled reasonably well, pilots seem to have been suspicious of the F.K.10 from the start. It certainly had a rather daunting appearance, and no doubt this, coupled with the maintenance problems, seems to have resulted in the few available aircraft being little used. The two RNAS machines, N511 and N514, were reported to be at Manston aerodrome in April and May 1917, but they were apparently considered to be unsafe and by the late summer had been grounded. The RFC aircraft may have lasted rather longer, but they, too, were never taken seriously and eventually, in July 1917, were handed over to the technical department for use as ground targets. Thus, the F.K.10 faded from the scene with, apparently, few regrets.
That Koolhoven's interest in the multiplane arrangement was not altogether damped by the failure of his three- and four-winged prodigies is evident from drawings that exist showing a design, known perhaps as the F.K.11, which had no less than fifteen narrow wings, each about 18-inches wide, attached to an F.K.10 fuselage. This project was never built, but the 'Venetian blind' arrangement of aerofoils had been tried before. One of the first to toy with the idea was Horatio Phillips, who tried out an apparatus with forty slats (if contemporary drawings are to be believed) on a circular track at Harrow in 1893. After the 1914--18 war the idea was revived by H. G. Leigh who, in collaboration with Bert Hinkler of the Avro company, fitted a modified form of the slatted-wing arrangement to the fuselage of an Avro Baby.
Dimensions: Span 28 ft 3 in (8.61 m); length 25 ft 6 in (7.77 m); height 11 ft 6 in (3.50 m); wing area 361 sq ft(33.54 sq m).
130 hp Clerget
Max weight: 2,019lb (916kg)
Empty weight: 1,236lb (561kg)
Sea level: -
3,000ft (914 m): 95 mph (153km/hr)
6,500ft (1,981 m): 84 mph (135km/hr)
10,000 ft (3,048 m): 74 mph (119km/hr)
6,000ft (1,829 m): -
6,500ft (1,981 m): 15.8min
10,000ft (3,048 m): 37.2min
Service ceiling: 10,000ft (3.048 m)
Endurance: 2 1/2 hr
P.Lewis The British Fighter since 1912 (Putnam)
In the unending quest for fighter supremacy designers in Britain explored most layouts and, in 1916, the Armstrong Whitworth designer F. Koolhoven was responsible for a two-seat fighter reconnaissance quadruplane which, despite the complexity of its four wings, struts and pair of cockpits was, none the less, a clean and pleasing machine, especially in its final form. The prototype used the 110 h.p. Clerget engine while the modified later version, of which a few were built, had the 130 h.p. Clerget. Tests showed that the F.K.10 was not a particularly successful machine and it remained simply one of the more unusual designs of the 1914-18 War.
Following the F.K.10 quadruplane design Armstrong Whitworth investigated an extraordinary development by Koolhoven to be known as the F.K.11 which was intended to be borne on a set of wings reminiscent of those tested by Horatio Phillips a decade before. The F.K.11’s small-chord mainplanes would have numbered fifteen, set with pronounced stagger on the same style of fuselage as that used on the F.K.10.
The F.K.11 was not proceeded.
O.Thetford British Naval Aircraft since 1912 (Putnam)
ARMSTRONG WHITWORTH F.K.10
Four of these unconventional two-seat quadruplanes were built for the RNAS in 1917, serialled N511-514. They were built under licence by the Phoenix Dynamo Manufacturing Company of Bradford. The first naval F.K.10 was equipped as a two-seat fighter and the second as a bomber. One 130 hp Clerget engine. Loaded weight, 2,019 lb. Maximum speed, 84 mph at 6,500 ft. Service ceiling, 10,000 ft. Span, 27 ft 10 in. Length, 22 ft 3 in.
H.King Armament of British Aircraft (Putnam)
F.K. 10. Several examples of this two-seat 'fighter-reconnaissance# quadruplane were built during 1916-17. The pilot's fixed Vickers gun was on the centre line, with faired breech casing, and the observer's Lewis gun was generally on a rocking-pillar mounting, though at least one specimen of the F.K. 10 had a Scarff ring-mounting.
Jane's All The World Aircraft 1919
Derived from the F.K.9 but embodying considerable redesign, the F.K.10 two-seat fighter-reconnaissance quadruplane retained virtually no more than the basic wing structure of its immediate predecessor. A production contract for 50 F.K.10s was given to Angus Sanderson & Company of Newcastle-on-Tyne on 30 December 1916 on behalf of the RFC but only five of these were destined to be completed before the contract was cancelled, and three were ordered for the RNAS, two of these from the Phoenix Dynamo Manufacturing Company and one from Armstrong Whitworth, these eventually being completed and tested. The F.K.10 was normally powered by a 130 hp Clerget 9B rotary, but at least one was flown with a 110 hp Le Rhone, and armament comprised one fixed 0-303-in (7,7-mm) Vickers gun and one free 0-303-in (7,7-mm) Lewis.
Max speed, 84 mph (135 km/h) at 6,500 ft (1 980 m),
74 mph (119 km/h) at 10,000 ft (3 050 m).
Time to 6,500 ft (1 980 m), 15 min 50 sec.
Endurance, 2 hr 30 min.
Empty weight, 1,236 lb (560 kg).
Loaded weight, 2,019 lb (916 kg).
Span, 27 ft 10 in (8,48 m).
Length, 22 ft 3 in (6,78 m).
Height, 11 ft 6 in (3,50 m).
Wing area, 390-4 sq ft (36,27 m2).
W.Green, G.Swanborough The Complete Book of Fighters
ARMSTRONG WHITWORTH F.K.10 UK
Derived from the F.K.9, but embodying considerable redesign, the F.K.10 two-seat fighter-reconnaissance quadruplane retained virtually no more than the basic wing structure of its immediate predecessor. A production contract for 50 F.K.10s was given to Angus Sanderson & Company of Newcastle-on-Tyne on 30 December 1916 on behalf of the RFC, but only five aircraft were destined to be completed before the contract was cancelled. Three were ordered for the RNAS, two of these from the Phoenix Dynamo Manufacturing Company and one from Armstrong Whitworth, these eventually being completed and tested. The F.K.10 was normally powered by a 130 hp Clerget 9B rotary, but at least one was flown with a 110 hp Le Rhone, and armament comprised one fixed 0.303-in (7,7-mm) Vickers gun and one free 0.303-in (7,7-mm) Lewis.
Max speed, 84 mph (135 km/h) at 6,500 ft (1980 m), 74 mph (119 km/h) at 10,000 ft (3 050m).
Time to 6,500 ft (1980 m), 15.85 min.
Endurance, 2.5 hrs. Empty weight, 1,236 lb (560 kg).
Loaded weight, 2,019 lb (916 kg).
Span, 27 ft 10 in (8,48 m).
Length, 22 ft 3 in (6,78 m).
Height, 11 ft 6 in (3,50 m).
Wing area, 390.4 sq ft (36,27 m2).
Flight, April 3, 1919.
THE ARMSTRONG-WHITWORTH MACHINES
The A.W. Quadruplane, Type F.K. 10, 1917
Next in the series comes the A.W. "Quad," which was first tested some time in 1917. By that time the single-seater fighting scouts were being employed in great quantities, and the question of good visibility was one of paramount importance, a pilot whose machine obscured the view to a great extent in any direction being at a considerable disadvantage. This question of visibility was attempted to be solved in the A.W. "Quad," in which, as will be seen from the accompanying illustrations, the stagger was very pronounced, while the second plane passed across some little distance above the top of the fuselage, the third and fourth planes passing through and under the body respectively, and obstructing, owing to their narrow chord, the view to a small extent only. When this machine first appeared the triplane had been tried with fair success, but the multiplane was somewhat of a dark horse, as regards its aerodynamic properties. From the table of performance it will be seen that the speed and climb of the A.W. Quad, were, if anything, inferior to those of contemporaneous triplanes with the same engines, while being a good way behind small biplanes with engines of 130 h.p. It, therefore, appears that quadruplanes do not give so good results as biplanes or triplanes as regards performance, and we understand that they are not particularly nice to fly. It will be noticed that on the A.W. Quad, there is no fixed tail plane. This is probably in order to render the elevators as effective as possible, a necessary precaution on a quadruplane with its comparatively great height over the aerofoils.