De Havilland DH.27 Derby

de Havilland

Industry	Aerospace, Defence
Founded	1920s
Products	Aircraft

Template:EngvarB Template:Infobox aircraft The de Havilland DH.27 Derby was a substantial, single-engine biplane designed as a heavy day bomber in response to an Air Ministry specification. It ultimately did not enter mass production.

Development

The de Havilland DH.27 Derby was created to satisfy Air Ministry specification 2/20 calling for a long-range heavy bomber. This aircraft was a large, single-engine biplane featuring two bays and wings without sweep or stagger. Both the upper and lower wings were wooden frames covered with fabric, equipped with ailerons, and designed to fold outward beyond the inner interplane struts. Except for the upper centre section—which was thicker, had a greater chord, and was attached to the fuselage via a streamlined pylon housing fuel tanks rather than the conventional centre section (Cabane strut) struts—the wings maintained a constant chord. The undercarriage utilized a split-axle configuration, permitting bombs to be dropped from beneath the fuselage. Main landing gear legs were fixed to the front spar beneath the inner interplane struts, with extended axles angled slightly upward; their inner ends were braced both back to the top of the leg and independently to the fuselage.

The fuselage adhered to evolving de Havilland design principles, constructed from spruce longerons reinforced by cross-bracing and covered with thin plywood panels. The control surfaces included balanced rudder and elevators, while the fin and rudder bore the distinctive de Havilland profile. The pilot’s cockpit was positioned directly under the wing’s leading edge, complemented by a dorsal observer/gunner station. Between these positions lay a cabin for the navigator/bomb aimer, featuring three portholes on each side of the fuselage. Power came from a water-cooled 650 hp (485 kW) Rolls-Royce Condor III engine fitted with a rectangular radiator at the nose and driving a four-bladed propeller.

Two prototypes were constructed, with the first taking flight on 13 October 1922. The Air Ministry ultimately favored the Avro Aldershot over the Derby; this preference was influenced by the Derby’s all-wood construction which resulted in greater weight compared to the Aldershot’s mixed materials. Additionally, unlike the Aldershot, the Derby lacked an internal bomb bay, leading to no production orders. Both prototypes were stationed at RAF Martlesham Heath and at the Naval base on the Isle of Grain until around 1924, serving in general testing and operational duties.