A.Jackson Blackburn Aircraft since 1909 (Putnam)
In May 1914 the Blackburn company received an Admiralty order for a batch of the Farnborough-designed B.E.2c biplane trainers which, together with larger and later batches, were built in new and bigger premises, the Olympia Works. They also built the Sopwith Cuckoo torpedo-bomber in quantity but still found time to work on a number of their own original prototypes. The first of these, first Blackburn design to bear the now legendary 'BA' monogram of the new company, and its first true military aircraft, was built in 1915 to an Admiralty specification which called for a long-range Zeppelin interceptor capable of operating over the sea at night. Its warload of Ranken incendiary steel darts, carried in canisters of 24, was intended to penetrate the airship's envelope and ignite the gas inside.
Known as the T.B. or Twin Blackburn, the machine was a large biplane of unusual design having two wire-braced, fabric-covered, box girder fuselages, each with its own rotary engine, joined by a 10 ft centre section forward and a common tailplane at the rear. The fuselages were supported on the water by separate and unconnected bungee-sprung, stepped pontoons, and small tail floats were attached at the rear by short steel struts.
Fabric-covered wooden mainplanes, built up from I-section spruce spars and ribs of three-ply spruce braced internally with drift struts and tie rods, were rigged in three bays. The considerable overhang at each end of the upper mainplane was wire-braced to triangular steel pylons above the outboard interplane struts. Fins and rudders were B.E.2c components taken from the Blackburn company's own production and slightly modified in shape.
Long-range capability was to have been achieved by fitting the T.B. seaplane with a new type of 150 hp engine said to have an exceptionally low fuel consumption and a dry weight of only 380 lb. This was the ten-cylinder Smith radial, designed by John W. Smith, an American who brought his designs to England in January 1915 and somehow gained immediate Admiralty interest. A prototype engine was bench-tested successfully and a production contract was awarded to Heenan and Froude Ltd of Worcester, but only a few were delivered. When flown experimentally later in 1915 in the A.D. Navyplane and Vickers F.B.5 pusher biplane, the Smith engine proved unsatisfactory, and so eight of the nine T.B. seaplanes ordered by the Admiralty were completed with 100 hp Gnome Monosoupape rotary engines and the ninth and last with 110 hp Clergets.
The first Gnome-powered machine, 1509, was rolled out at the Olympia works in August 1915 and, together with 1510 and the final Blackburn T.B., 1517 with Clergets, underwent type trials at RNAS Isle of Grain in 1916. In his memoirs, the flight test observer E. W. Stedman recalls how the pilot J. W. Seddon sat in one fuselage with all the flying and engine controls, while he sat several feet away in the other with no controls except the starting handle for the engine on his side. Starting on the water needed discipline, courage and agility, for a pool of excess petrol, which formed on the float when the Gnome was primed, promptly ignited when the engine fired. The observer's job was to lie on the lower centre section and put out the fire on the pilot's side with an extinguisher, scramble into his own cockpit to start the second engine and then leap out again to extinguish the fire on his own float.
Once in the air, mainplane deflection was such that the aileron control cables became slack and all lateral control was lost. This defect was soon put right by the manufacturers but there remained a disconcerting amount of relative movement between the fuselages caused by flexibility in the wire-braced centre section. Furthermore, on only two-thirds of the designed power, performance was mediocre, and to achieve a worthwhile four-hour endurance the military load had to be limited to 70 lb of steel darts. Hand signalling, the only means of communication between the crew members, was hardly an ideal arrangement when in action against an enemy airship, thus, despite the fact that the three trials aircraft and four others were sent to RNAS Killingholme, they were little used and were eventually broken up. This fate also overtook the two remaining aircraft, 1511 and 1512, which were held in store at the RNAS Depot, Crystal Palace, London, until struck off charge.
SPECIFICATION AND DATA
Manufacturers: The Blackburn Aeroplane and Motor Co Ltd, Olympia Works, Roundhay Road, Leeds, Yorks.
Two 150 hp Smith
Two 100 hp Gnome Monosoupape
Two 110 hp Clerget 9b
Span (upper) 60 ft 6 in (lower) 45 ft 0 in
Length 36 ft 6 in Height 13 ft 6 in
Wing area 585 sq ft
Weights: (Gnomes) Tare weight 2,310 lb All-up weight 3,500 ib
Maximum speed at sea level 86 mph
Climb to 5,000 ft 12 min Endurance 4 hr
Production: Nine aircraft 1509-1517, all Gnome-powered except 1517 with Clergets. 1509, 1510 and 1517 Isle of Grain trials aircraft 1916, broken up at RNAS Killingholme August 1917; 1511 and 1512 stored at RNAS Crystal Palace, s.o.c. June 1917, broken up July 1917; 1513-1516 to RNAS Killingholme, broken up August 1917.
F.Manson British Bomber Since 1914 (Putnam)
Although only tenuously qualifying for inclusion in this work as a bomber, the Blackburn T.B. was the third seaplane with twin fuselages to be built to an Admiralty requirement, in this instance as an anti-Zeppelin interceptor 'bomber', to be armed with canisters of Ranken incendiary darts which, it was proposed, would be dropped on enemy airships from above to ignite their gas envelopes.
The Blackburn Aeroplane and Motor Company at Leeds, under its founder Robert Blackburn, had been engaged in building aeroplanes since 1909, and had attracted the Admiralty's attention with several of its prewar aircraft, leading to a close association with the Royal Navy that was to survive for over half a century. Expressing a favourable opinion of the high degree of workmanship that enamated from Blackburn's shops, the Admiralty placed an order for R.A.F. B.E.2Cs in May 1914, and in due course 111 examples were completed for both the RNAS and the RFC.
The first appearance by German bombing airships over England during the winter of 1914-15 prompted the Admiralty to issue a requirement for a dart-armed, two-seat aeroplane capable of long endurance and an ability to reach an altitude of at least 12,000 feet while carrying a minimum of three Ranken dart canisters (each loaded with 24 onepound darts).
Coinciding with these events was the arrival in Britain of the American John W Smith, bringing with him his design drawings of a ten-cylinder air-cooled radial engine. According to Smith this engine developed 150hp with an installed weight of only 380 lb, and possessed an exceptionally low specific fuel consumption. Such characteristics recommended this engine for use in Blackburn's proposed anti-airship aircraft and, an order for nine T.B.s (Twin Blackburns) was placed in about March 1915, Smith Static engines being specified.
The T.B. featured twin wire-braced, fabric-covered wooden box-girder fuselages, each with a tractor engine at the front, joined together with a 10ft parallel-chord wing centresection; the outer wings were of three bays rigged without stagger and with ailerons on the upper wings only; construction was of spruce spars and ribs, the considerable upper wing overhang being braced using kingposts. The twin fins and rudders were adapted from Blackburn's production B.E.2C components, and beneath each fuselage was mounted a short main float and a tail float. Each fuselage accommodated a crew member, the pilot on one side (with all flying and engine controls) and the observer on the other.
Although early bench testing of the Smith engine seemed to confirm its designer's performance figures, resulting in a production order being placed with Heenan and Froude Ltd at Worcester, flight trials proved less than satisfactory, and it was found necessary to turn to an alternative powerplant of equivalent interrelated weight and specific fuel consumption, the choice falling on the 100hp Gnome monosoupape, an excellent engine but clearly unequal to the performance demands.
The inability of the Gnome-powered T.B.s to come close to the required performance, in particular their inability to climb above 8,000 feet with the three dart canisters, was only one of several reasons that the aircraft did not gain acceptance for operational use; more serious were the shortcomings evident in handling in the air, aileron control being badly affected by wing flexing, to some extent due to inadequate bracing of the centresection. With no more than two-thirds of the intended power available, and then at a markedly higher specific fuel consumption, it was necessary to limit the weapon load to two canisters in order to carry sufficient fuel for four hours' flying, but even this was regarded as academic if the aircraft had little chance of even reaching the altitude of attacking airships, let alone climbing above them to deliver the darts. Nor does it appear to have occurred to the aircraft designer that the necessary hand-signalling between the two crew members, situated ten feet apart, was likely to be unreliable to say the least during the hours of darkness - when the German airships most frequently operated.
Although the ninth and final T.B. to be completed was powered by 110hp Clerget engines, the performance was only just discernably improved. Several aircraft, including the Clerget-T.B., underwent trials at RNAS Isle of Grain during 1916, but it was clear that the whole idea of attempting to attack approaching airships with bomber-type aeroplanes, with little speed margin and poor manoeuvrability, was badly flawed, especially when it was shown that the German airships could achieve far greater rates of climb at high altitude when danger presented itself, simply by jettisoning ballast. Indeed, the T.B.s proved a blind alley, and little was heard of them after 1916, and only four aircraft served for a short time at RNAS Killingholme before being broken up.
Type: Twin-engine, two-seat, two-bay biplane anti-airship bomber with twin fuselages and central wing-bay.
Manufacturer: The Blackburn Aeroplane and Motor Co Ltd, Leeds, Yorkshire.
Powerplant: Two 100hp Gnome monosoupape; two 110hp Clerget 9b.
Dimensions: Span, 60ft 6in; length, 36ft 6in; height, 13ft 6in; wing area, 585 sq ft.
Weights: Tare, 2,310 lb; all-up, 3,500 lb.
Performance (Gnome): Max speed, 86 mph; climb to 5,000ft, 12 min; endurance, 4 hr.
Armament: Intended to be three canisters each with 24 one-pound Ranken darts.
Production: Nine aircraft, Nos 1509-1517. No 1509 first flown in August 1915 by J W Seddon. No 1517 powered by Clerget engines.
Service: Four aircraft saw limited service at RNAS Killingholme in 1917.
H.King Armament of British Aircraft (Putnam)
T.B. Ranken Darts formed the sole recorded armament of this anti-airship seaplane of 1915. The figure of 70 lb quoted by the makers for 'military load' doubtless included the weight of the canisters and associated gear.
Flight, December 11, 1919.
THE BLACKBURN MACHINES.
The next machine to be designed and tested was of very unusual design, and was produced as a result of instructions from the Admiralty to design a twin-engined machine for dropping darts. In those days the dart was considered quite a weapon, and certainly the number that could have been carried on a large twin-engine machine should have been sufficient to cause unpleasant punctures in the Hun.
The "Type T.B." Seaplane. (August, 1915)
as this machine was called, represented a very drastic departure from usual practice. Instead of having a central fuselage, and the engines placed in nacelles on the wings, the T.B. had two fuselages, each with its engine and pilot. The fuselages were connected at their forward end by the main biplane structure and at the rear by the tail. As the machine was of the seaplane type, each fuselage had under its forward end a plain non-stepped float and a smaller tail float under its stern. In spite of the twin fuselage arrangement, which is not usually conducive to beauty of outline, the T.B. was, as will be seen from the accompanying illustrations, by no means an ugly machine, and her performance was very good, both as regards speed and climb. In fact, we understand that as regards the latter she established a record for altitude.
The first experimental machine was fitted with two 100 h.p. Gnome monosoupape engines, but these were replaced, in the production machines, by two 110 h.p. Clergets.