The first Heron,
Series 1A suffered deficiencies, as NAC soon discovered. First, the aircraft was generally underpowered. Its quite heavy engines (weighing about each), had an output of only 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. Secondly, the lightweight aluminium alloy wingspars were prone to constant cracking due to the heavy loading on the wing caused by the overweight engines and rough landings on unpaved runways. NAC resolved this by replacing the aluminium spars with heavier steel spars, reducing the performance of the Heron Series 1A (re-classified 1B) to uneconomic levels for the services required of them in New Zealand. NAC disposed of them in 1957. 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 could provide reliable and comfortable service with seating for 17 passengers, in individual seats on either side of the aisle. With its larger fuselage, passengers could stand up whilst moving down the aisle and large windows were also provided. Baggage was stored in an aft compartment with an additional smaller area in the nose. A few peculiarities appeared; 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 relatively "leisurely", and after production at de Havilland's Chester factory 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. Ohio in 1982. It is operated by Fischer Brothers for
Allegheny Commuter. One U.S. airline that carried out Riley-type conversions at their
Opa Locka Airport, Florida, engineering facility was
Prinair, of Puerto Rico, which replaced the Gipsy Queens with
Continental IO-520 engines. Prinair also considerably stretched Heron 2
N574PR to allow extra passengers to be carried.
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 of life as a number of examples were converted in the 1970s and 1980s including
N415SA, a Riley Heron still flying in Sweden as of 20 May 2012 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 changed the configuration as well as the "look" of the whole aircraft with two powerful
turboprop engines replacing the lethargic four-engine arrangement, a stretched fuselage, the shape of the windows changed and the wingtips squared instead of rounded. ==Variants==