De Havilland Highclere

de Havilland

Industry	Aerospace
Founded	1920
Founder	Geoffrey de Havilland
Headquarters	London , United Kingdom
Products	Aircraft, including the DH.54 Highclere

Template:Infobox aircraft The de Havilland DH.54 Highclere was a single-engine biplane airliner capable of carrying fifteen passengers, created as a successor to the de Havilland DH.34. Its development was discontinued after Imperial Airways opted exclusively for aircraft with multiple engines.

Development

The DH.54 Highclere was developed in response to Air Ministry specification 40/22, calling for a larger variant of the highly successful de Havilland DH.34. The two models shared numerous similarities in both their structural design and overall configuration. Compared to the DH.34, the Highclere increased passenger capacity from nine to twelve, saw a 56% rise in maximum takeoff weight, and expanded wing surface area by 70%. Both aircraft were single-engine, two-bay biplanes featuring fabric-covered wooden wings and fuselages framed with wood and covered in thin plywood.

Aside from size differences, the Highclere’s wings exhibited distinct characteristics: they lacked stagger and upper wing dihedral, and the gap between the wings was larger. The upper wing was supported by Cabane strut#Cabane struts rather than being directly affixed to the upper fuselage. To address concerns over the DH.34’s relatively high landing speed, full-span flaps were incorporated into the design. For enhanced safety during water landings, the undercarriage was designed to be jettisonable, and the fuselage was sealed to be watertight. Passenger seating was arranged in four rows, with single seats on the left side and doubles on the right. Adjustments to luggage compartments created space for onboard toilets. The Highclere also featured balanced elevators. Due to the increased weight, a more powerful engine was necessary; thus, it was equipped with a 650 hp (485 kW) Rolls-Royce Condor IIIA water-cooled inline engine, which extended the length of the nose and powered a four-bladed propeller measuring 14 ft (4.27 m) in diameter.

Operational history

The Highclere took to the skies for the first time under the control of H.S. Broad on 18 June 1925 and quickly began carrying non-paying passengers while achieving success in competitive races. Retained by the Air Ministry throughout its operational existence, it underwent rigorous airworthiness evaluations at RAF Martlesham Heath in early 1926, culminating in the award of its Certificate of Airworthiness on 23 April 1926. However, by that point, Imperial Airways had resolved to cease transporting passengers using single-engine aircraft due to safety concerns. Consequently, the only Highclere was reassigned to RAE Farnborough on 7 March 1926 for use in experimental projects. Later, on 7 November 1926, it was lent to Imperial Airways at Croydon Airport to serve as a cargo aircraft, with some consideration given to adapting the Highclere for enhanced freight operations. Unfortunately, the aircraft was lost when a hangar collapsed under heavy snowfall at Croydon on 1 February 1927.

Unbuilt variants

DH.55

This was a proposed design featuring a 12-seat configuration powered by three 120 hp (90 kW) Airdisco engines but was never constructed.

DH.57

An unbuilt evolution of the DH.55 concept, intended to be equipped with three 230 hp (172 kW) Siddeley Puma engines.