F.Manson British Bomber Since 1914 (Putnam)

Blackburn T.B.

   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.

P.Lewis British Bomber since 1914 (Putnam)

Another of the seaplane designs of 1915 was the comparatively unusual Blackburn T.B. biplane which was completed in August of that year. The T.B.’s main contribution to unconventionality lay in its duplicated side-by-side fuselages, each of which housed a 100 h.p. Monosoupape Gnome in the nose in 1510, the first prototype. 1517, the second example, received a pair of 110 h.p. Clerget rotaries. The main purpose behind the design was to meet an Admiralty need for a machine capable of climbing above marauding Zeppelins and attacking the quarry with steel darts, the total load of which was to be 70 lb. The two members of the crew were carried one in each fuselage, the wings were of unequal span, and the pairs of main and rear pontoon floats were mounted independently. An essential requirement of the task which the T.B. was proposed to accomplish was a high rate of climb to achieve interception of its high-flying objective, a performance feature which could not be subject to compromise. The T.B., however, was a relatively large and unwieldy machine, the climb performance of which was not assisted by the comparatively low power of the engines selected. Although tested by the R.N.A.S. at the Isle of Grain, no production ensued.

J.Bruce British Aeroplanes 1914-1918 (Putnam)

Blackburn T.B.

  THIS remarkable aeroplane was the Blackburn company’s first attempt to produce an aircraft designed for warlike purposes; it made its appearance in August, 1915. The T.B. was designed to fulfil Admiralty requirements for an anti-Zeppelin aircraft, and the specified armament was to consist of a load of steel darts. No doubt these missiles were Ranken Darts, an ingenious weapon which was designed to catch in the envelope of an airship and explode inside. The darts were usually carried in canisters of 24.
  Any justification for the adoption of the complicated twin-fuselage layout for the aircraft is hard to find: it may have been hoped to produce an aeroplane capable of lifting a heavy load of fuel to obtain a long flight endurance, in which case it might have been thought necessary to provide two pilots to minimise crew fatigue. However, the relatively low power of the engines which were fitted did not permit the lifting of heavy loads.
  Two prototypes were built. The first had two 100 h.p. Gnome Monosoupape rotary engines, and the second had two 110 h.p. Clergets. Blackburns were Admiralty contractors for the B.E.2C at the time of the construction of the T.B., and the two fins of the big twin were standard B.E.2C components, whilst the rudders were also of B.E. design but were slightly modified in outline.
  The structure was conventional throughout. The fuselages were wooden box-girders, cross-braced with wire and covered with fabric. Each fuselage had a main float at its forward end and a small tailfloat under its tail; the main floats were of the pontoon type and were not connected to one another. The long extensions of the upper wings were braced from above and below by cables. Ailerons were fitted to both upper and lower mainplanes: those on the upper wing were long and inversely tapered; the lower ailerons were very short.
  The performance of the Blackburn T.B. was quite creditable in view of its layout, but it could hardly have fared well in service. Difficulty of communication between the occupants of the two fuselages would have been a formidable handicap in action.
  The T.B. was tested at the R.N.A.S. Station, Isle of Grain, and the second machine, No. 1517, was there in 1916.


SPECIFICATION
  Manufacturers: The Blackburn Aeroplane & Motor Co., Ltd., Olympia, Leeds.
  Power: First machine: two 100 h.p. Gnome Monosoupape. Second machine: two 110 h.p. Clerget.
  Dimensions: Span: upper 60 ft 6 in., lower 45 ft. Length: 36 ft 6 in. Chord: 5 ft 6 in. Gap: 6 ft 6 in. Stagger: nil. Dihedral: 40. Incidence: 40.
  Areas: Wings: upper 341 sq ft, lower 244 sq ft, total 585 sq ft. Ailerons: total 35-25 sq ft. Tailplane: 37 sq tt. Elevators: 27-25 sq ft. Fins: 15-25 sq ft. Rudders: 36 sq ft.
  Weights: Empty: 2,310 lb. Military load: 70 lb. Crew: 360 lb. Fuel and oil: 760 lb. Weight loaded: 3,500 lb.
  Performance (with Gnome engines): Maximum speed at sea level: 86 m.p.h. Climb to 5,000 ft: 12 min. Endurance: 4 hours.
  Armament: 70 lb of steel darts.
  Serial Numbers: 1510 and 1517.

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.

Журнал Flight

Flight, December 11, 1919.

"MILESTONES"
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.