The de Havilland DH.114 Heron was a small, propeller-driven British airliner that first flew on 10 May 1950. It was a development of the twin-engine de Havilland Dove, with a stretched fuselage and two more engines. It was designed as a rugged, conventional low-wing monoplane with tricycle undercarriage that could be utilised on regional and commuter routes. One hundred and fifty were built, exported to around 30 countries. Herons later formed the basis for various conversions, such as the Riley Turbo Skyliner and the Saunders ST-27 and ST-28.
Design and development
Immediately after the Second World War, the aircraft manufacturer de Havilland developed the DH.104 Dove, a small, two-engined passenger aircraft intended as a replacement for the earlier Dragon Rapide, and which soon proved to be successful. As a further development, the company basically enlarged the Dove; the fuselage was lengthened in order to provide room for more passengers or freight, and the wingspan was increased to make room for two additional engines. The Heron was of all-metal construction, and was laid out as a conventional design; the resulting aircraft was able to use many of the parts originally designed for the Dove, thus simplifying logistics for airlines employing both types.
The emphasis was on rugged simplicity in order to produce an economical aircraft for short to medium stage routes in isolated and remote areas which did not possess modern airports. The Heron was designed with a fixed undercarriage and reliable ungeared, unsupercharged Gipsy Queen 30 engines.
The Heron prototype registered to the de Havilland Aircraft Company, Hatfield, UK as G-ALZL undertook its first flight with Geoffrey Pike at the controls on 10 May 1950 . The aircraft was unpainted at the time, and after 100 hours of testing, was introduced to the public on 8 September 1950 at the Farnborough Airshow, still glistening in its polished metal state. By November, the prototype had received its formal British Certificate of Airworthiness and had embarked to Khartoum and Nairobi for tropical trials.
The prototype was then painted and "prepped" as a company demonstrator, undergoing a trial in 1951 with British European Airways on their Scottish routes. Following the successful completion of the prototype trials as a regional airliner, the Heron began series production. The first deliveries were to National Airways Corporation (NAC, later part of Air New Zealand).
The first Heron, Series 1A suffered from a number of deficiencies, as NAC soon discovered. First of all, the aircraft was generally underpowered. Its quite heavy engines (weighing approximately 882 lb/400 kg each), had an output of only 250 hp (190 kW) each. By comparison, later modifications or rebuilt aircraft had as much as 50% more power (in the case of the Saunders ST-27). Unlike the Dove, the Heron came with a fixed undercarriage and no nosewheel steering, which simplified maintenance, but reduced top speed.
After 51 Series 1 aircraft had been built, production switched to the Series 2, featuring retractable landing gear, which reduced drag and fuel consumption, and increased the top speed marginally. The 2A was the equivalent of the 1A, the basic passenger aircraft while the 1B and its successor the 2B had higher maximum takeoff weight, the 2C featured fully-feathering propellers, the Heron 2D had an even higher maximum takeoff weight, while the Heron 2E was a VIP version.
In service, the Heron was generally well-received by flight crews and passengers who appreciated the additional safety factor of the four engines. At a time when smaller airliners were still rare in isolated and remote regions, the DH.114 was able to provide reliable and comfortable service with seating for 17 passengers, in individual seats on either side of the aisle. With its larger fuselage, customers could stand up and large windows were also provided. Baggage was stored in an aft compartment with an additional smaller area in the nose. A few peculiarities cropped up; passengers who filled the aft rows first would find that the Heron gently "sat down" on its rear skid. Pilots and ground crews soon added a tail brace to prevent the aircraft from sitting awkwardly on its tail.
Performance throughout the Heron range was "leisurely", and after production ceased in 1963, several companies, most notably Riley Aircraft Corporation, offered various Heron modification "kits," mainly related to replacing the engines, which greatly enhanced takeoff and top speed capabilities. Riley Aircraft replaced the Gipsy Queens with horizontally-opposed Lycoming IO-540 engines. One airline that carried out conversions was Prinair, which replaced the Gipsy Queens with Continental IO-520 engines. Connellan Airways also converted its Herons, using Riley kits. When available aircraft reached the end of their service lives, the engine conversions gave the elderly airliner a new lease on life as a number of examples were converted in the 1970s and 1980s including N415SA, a Riley Heron still flying as of 2005 and a Riley Turbo Skyliner, tail number N600PR currently registered in the United States (this example appeared in the 1986 movie Club Paradise).
The most radical modification of the basic Heron airframe was the Saunders ST-27/-28, that basically changed the configuration as well as the "look" of the whole aircraft with two powerful turboprop engines replacing the lethargic four-engine arrangement, the easily recognisable "hump" over the cockpit disappearing, the shape of the windows changed and the wingtips being squared instead of rounded.
Specifications (Heron 2D)
Published in July 2009.
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