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Airco DH 11 Oxford
The DH.11 Oxford was designed by Geoffrey de Havilland for the Aircraft Manufacturing Company as a twin-engined day bomber to replace the Airco DH.10. It was designed (as required by the Specification) to use the ABC Dragonfly radial engine which promised to give excellent performance and had been ordered in large numbers to be the powerplant for most of the new types on order for the Royal Air Force.
Designs began early in 1918 when a contract was placed for three aircraft (Contract 35a/2150/C.2485) and by August the fuselage of the prototype, H5891, was well advanced in the Hendon factory. In September all work ceased because the Dragonfly engines were beset by problems and in November Siddeley Puma in-line, high compression engines were considered and the necessary engine bearer modifications were put in hand.
The D.H.11 had fabric covered, wooden airframes incorporating steel tubing for highly stressed or vulnerable members such as engine mountings, undercarriage and the empennage trailing edges. The type had horn balanced ailerons and the characteristic de Havilland rudder, and four degrees of dihedral on the upper mainplane compared with two degrees on the lower, gave the wings of the D.H.11 a diverging appearance and the fuselage filled the whole mainplane gap, making it possible to put the rear gunner on a raised floor in the mid upper position with a commanding field of fire in all upward directions.
A fuselage 6 ft. 0 in. deep and 4 ft. 0 in. wide enabled main fuel tanks of 170 gallons capacity to be slung from the top longerons of the centre fuselage with a walk way beneath. This gave the rear gunner access to the cockpit, in which the pilot sat on the starboard side, and thence to the front gunner. Entry to the aircraft was gained through a trap door between the spars of the lower wing which opened on to this catwalk. Armament consisted of a Scarff-ring-mounted Lewis gun fore and aft and approximately 1,000 lb. of bombs carried internally. Two 320 h.p. A.B.C. Dragonfly radial engines were housed in nacelles fixed directly to the lower mainplane but the eminently business-like and efficient divided undercarriage of the D.H.10 gave place to a narrow track.

By 1919 the machine, H5891,was ready and the mainplanes were being covered yet despite recurring magneto trouble it was decided to fit the Dragonflies after all. After the first few flights in January 1919 H5891 went back into the works for the engines to be repositioned but was short lived. Its last flight came when a connecting rod broke in one of the engines, which seized up just as the aircraft became airborne, but the pilot, F. T. Courtney, made a forced landing without damage.
Two further prototypes, Mk. IIs, H5892 and H5893, with Puma high compression engines, were cancelled in 1919, with no aircraft in the end being purchased to replace the DH.10. Serials later allotted to Sopwith Buffaloes.
Oxford Mk I
Engines: 2 × ABC Dragonfly, 320 hp (239 kW) each
Wingspan: 60 ft 2 in (18.34 m)
Wing area: 719 ft² (66.8 m²)
Length: 45 ft 2¾ in (13.79 m)
Height: 13 ft 6 in (4.12 m)
Empty weight: 4,105 lb (1,866 kg)
Max. takeoff weight: 7,020 lb (3,191 kg)
Maximum speed: 107 kn (123 mph, 198 km/h)
Service ceiling: 14,500 ft (4,400 m)
Power/mass: hp/lb (kW/kg)
Climb to 10,000 ft: 13 min 45 sec
Endurance: 3 hours
Crew: three
Armament: 2 × .303 in (7.7 mm) Lewis gun
Bombload: 4 × 230 lb (104 kg) bombs carried internally

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