F.Manson British Bomber Since 1914 (Putnam)

Airco D.H.15 Gazelle

   Although intended from the outset as an experimental test bed for the big Galloway Atlantic engine, the Airco D.H.15 (named the Gazelle, in line with the current practice of naming all military aeroplanes) was ordered by the Air Ministry on 7 September 1918. The single prototype, J1937, was a standard D.H.9A airframe with local structural modifications to accommodate the new engine, and retained all the standard D.H.9A’s armament, including provision to carry its bomb load - presumably so that a realistic performance comparison could be made with the standard aeroplane, as well as other variants.
   The Galloway Atlantic was evolved in much the same manner as the Siddeley Tiger, except that two standard cast-iron BHP cylinder blocks were brought together on a common crankcase. Drive to the two-blade propeller was without reduction gear, and a large rectangular frontal radiator, similar to that of the Liberty 12, was provided. Two other features readily distinguished the Gazelle. The long, almost horizontal exhaust pipe on each side of the fuselage extended as far aft as the gunner's cockpit, while the pair of front centre-section wing struts were rigged almost vertically, whereas previously they had been raked forward.
   J1937 was completed in July 1919, and was eventually delivered to Martlesham Heath for performance trials the following May. Compared with the standard Liberty-powered D.H.9A’s maximum speed of about 114 mph at 10,000 feet (without bomb load), the Gazelle achieved 133 mph under the same load conditions; it also displayed a 10 per cent all-round performance superiority over the 450hp Napier Lion-powered version of the D.H.9A.

   Type: Single-engine, two-seat, two-bay biplane experimental light bomber.
   Manufacturer: The Aircraft Manufacturing Co Ltd, Hendon, London NW9.
   Powerplant: One 500 hp (BHP) Galloway Atlantic twelve-cylinder water-cooled in-line engine driving two-blade propeller.
   Dimensions: Span, 45ft 11 3/8 in; length, 29ft 11ft; wing area, 486.73 sq ft.
   Weights: Tare, 2,312 lb; all-up, 4,773 lb.
   Performance: Max speed, 139 mph at sea level, 133 mph at 10,000ft; climb to 10,000ft, 8 min 12 sec; service ceiling, 20,000ft.
   Armament: One forward-firing synchronized 0.303in Vickers machine gun on nose, and one Lewis gun with Scarff ring on observer’s cockpit; provision to carry 460 lb bomb load.
   Prototype: One, J7936, flown in July 1919. No production.

P.Lewis British Bomber since 1914 (Putnam)

Of the pair of D.H.15 Gazelles - J1936 and J1937 - which were ordered, only J1937 was constructed. The airframe was that of a conventional D.H.9A, but was given extra power by installing the water-cooled, twelve-cylinder vee 500 h.p. B.H.P. Atlantic developed by the Galloway Engineering Company through combining two 230 h.p. B.H.P. engines on a single crankcase. The Liberty-style frontal radiator was still used, and the Gazelle was equipped with the standard D.H.9A armament of a Vickers gun for the pilot and a Lewis on a Scarff ring for his observer. The main purpose behind the conversion to D.H.15 form was the testing in flight during 1919-20 of the new engine.

J.Bruce British Aeroplanes 1914-1918 (Putnam)

de Havilland 15, the Gazelle

  THE D.H.15 was essentially a D.H.9A airframe which had been modified to accommodate the 500 h.p. B.H.P. Atlantic twelve-cylinder vee engine. As a modification of a tried and tested type, it may have been designed as an insurance against the failure of the D.H.14.
  The Atlantic engine was first made in 1918 by the Galloway Engineering Co., and was produced by combining two ordinary B.H.P. cylinder blocks on a common crankcase. These were of cast iron and, as on the original B.H.P. engine, there was no reduction gear.
  The new engine was selected for mass production, and twenty-five had been delivered by October 31st, 1918. However, just as the original B.H.P. or Galloway Adriatic had given way to the Siddeley Puma, so was the Galloway Atlantic re-designed to become, in effect, a double Puma, with aluminium cylinder blocks. The re-designed engine was named Siddeley Pacific, and was ordered on a large scale.
  The D.H.15 served as a flying test-bed for the Galloway Atlantic engine, and made its first flight in 1918. In appearance it differed little from the D.H.9A, for the shape of radiator used with the Atlantic differed only slightly from that of the Liberty. The chief distinguishing feature of the D.H.15 lay in its long horizontal exhaust pipes; and the forward centre-section struts were more nearly vertical in side elevation than were those of the D.H.9A.
  Despite its experimental nature, the D.H.15 was given an official name: under the scheme of nomenclature defined in Technical Department Instruction No. 538 it was designated Airco Gazelle.


SPECIFICATION
  Manufacturers: The Aircraft Manufacturing Co., Ltd., Hendon, London, N.W.
  Power: 500 h.p. B.H.P. (Galloway) Atlantic.
  Dimensions: Span: 45 ft 11 f in. Length: 29 ft 11 in. Chord: 5 ft 9 in. Span of tail: 13 ft 10 in.
  Areas: Wings: upper 249-03 sq ft, lower 237-7 sq ft. total 486-73 sq ft. Ailerons: each 18-59 sq ft. total 74-36 sq ft. Tailplane: 38 sq ft. Elevators: 24 sq ft. Fin: 5-4 sq ft. Rudder: 13-7 sq ft.
  Weights: Empty: 2,312 lb. Loaded: 4,773 lb.
  Performance: Maximum speed at ground level: 139 m.p.h.; at 6,500 ft: 136-5 m.p.h.; at 10,000 ft: 133 m.p.h. Climb (at 4,230 lb loaded weight) to 6,500 ft: 4 min 55 sec; to 10,000 ft: 8 min 12 sec. Ceiling: 20,000 ft.
  Tankage: Petrol: 108 gallons. Oil: 14 gallons.
  Armament: One fixed forward-firing Vickers machine-gun on port upper longeron just in front of pilot’s cockpit, synchronised by Constantinesco C.C. Gear; one Lewis machine-gun on Scarff ring-mounting on rear cockpit.
  Serial Numbers: J.1936-J.1937.

H.King Armament of British Aircraft (Putnam)

D.H.15 Gazelle

   More or less contemporary with the Okapi, the Gazelle was a direct 9A development (Galloway Atlantic engine) and armament remained unchanged.