Engine running pens at Dunsfold airfield, Dunsfold, Surrey

Summary

Two brick built jet-engine running pens, c1950, with the eastern example modified c1960 for V/STOL engine testing.

Description

Two brick built jet-engine running pens, c1950, with the eastern example modified c1960 for V/STOL (Vertical/Short Take Off and Landing) testing.

PLAN: the north-western pen is U-shaped in plan, with the curve being to the north and housing an aperture for the former diffuser (a device for dissipating jet engine thrust). The eastern example is also U-shaped but has sliding doors to the south. The pens are accessed from the south, which is where the aircraft would have been reversed in and secured to the ground with its engine facing into the diffuser.

MATERIALS: mixed-stock brick, concrete, steel and steel sheet.

DETAILS:

WESTERN PEN

This pen is a largely open structure, built of brick in an English bond, with regular brick piers supporting the walls which are topped with concrete copping. The walls are approximately 2m deep and 5m high. The main elevation faces north and is semi-circular, with the central section marginally higher than the flanking walls. It has a large ovoid aperture where the diffuser would have been positioned. Above this area is an internal dome like structure faced in aluminium. Either side there are oversized pedestrian door apertures which give internal access to the former diffuser area. The walls either side of the central curved section, extend to the south, and have a number of irregular access doors or apertures. The working space contained by the walls has been adapted to house a late-C20 truck-wash system. The internal face of the brick walls has a regular pattern of inserted black bricks. The flanking walls have single storey brick control rooms, one of which is internal (western side) and the other projects from the wall to the east. They have small rectangular timber casement windows, and flat roofs. The interiors were converted to toilets or rest rooms in the late-C20.

EASTERN PEN

This pen is similar to the north-western example but has been modified to allow testing of V/STOL aircraft. The central section of the north-eastern face is largely open underneath a steel beam which replaced the original diffuser. The walls either side have brick buttresses interspersed along their length, which continue onto the flanking walls. The working space is larger, having been extended to the north-east end. The floor of the pen is largely concrete, but to the north-east end there is a subterranean diffuser pit, which is now covered in metal plate. The inside face of the pen is covered with brushed metal panels, including built-in control rooms to the north-west and south-east. The example to the south-east has a line of small rectangular top-hinged metal windows facing into the working area. There is also a pedestrian door to the control room, which is fitted out with a bench and seating. To the south-west, there is a large double-depth sliding aluminium door, which served as the aircraft entrance.

History

The engine running pens were built to support the development and manufacture of jet aircraft from c1950 at Dunsfold airfield.

The airfield was constructed for the military in 1942 by Royal Canadian Engineers. Initially it was home to four squadrons of Tomahawks and Mustangs, tasked with training and reconnaissance. By August 1943 it had become a bomber base, supporting Mitchell bombers on European missions, and by 1944 the airfield had three runways and accommodation for over a 1,000 personnel.

In the early 1950s Hawker Siddeley were developing jet aircraft for which the short, grass landing strips then available to them were insufficient. Long hard-surfaced runways were required and Dunsfold was identified as a base which could work hand in hand with their existing factory in Kingston, Surrey. This was a period of consolidation for the many private British aircraft companies, and with the benefit of Britain’s lead in jet engine technology, these newly consolidated companies had the financial wherewithal and technical capability to lead the world in jet aviation. During the 1950s and 1960s, huge advances were made and for this brief period of time, Britain led the world in this area.

On taking over Dunsfold airfield, Hawker Siddeley developed a final assembly and experimental test facility including three engine running pens to test and develop the aircraft prior to delivery. The first aircraft to be developed and assembled at Dunsfold was the Hunter which at the time was at the cutting edge of military jet fighter development, and first took to the air in 1951. Flown by Squadron Leader Neville Duke, it later broke the world speed record achieving a speed of 727.6 mph on the 7 September 1953. Hunters were put into service by the Royal Air Force (RAF) in 1954, and after a number of teething problems, were in operational use until the 1990s.

By the start of the 1960s, the company was developing the concept of V/STOL (Vertical, Short Take Off and Landing) which involved the use of vectored thrust to lift a static or slow moving aircraft into the air. Once airborne, the engine thrust would be transitioned to the rear and the aircraft would achieve normal forward flight. Hawker Siddeley recognised a need for a fighter that could be operated away from large airfields, therefore reducing dependence on fixed airfields that were vulnerable to nuclear attack. In preparation, one of the engine running pens was redesigned to accommodate the need to test an engine that could create thrust in multiple directions. The existing diffuser (a device for dissipating jet engine thrust) and brick supporting structure were removed, to enable a larger floor area within the pen. This area was then excavated to form a void which was fitted with a blast grid to diffuse vertical thrust. At the same time, a second control room was added and the inside of the pen was fitted out with metal covered insulation. A double-depth metal sliding door was also installed at the entrance so that when closed, noise and debris were suppressed. On 15 July 1960, the first P1127 Prototype V/STOL Strike Aircraft serial XP831, was delivered to Dunsfold airfield to commence static engine testing in the engine running pen. On 31 August 1960, the Pegasus engine was run for the first time while inside the aircraft. The first free hover of the prototype occurred on 19 November. In parallel, conventional taxi-trials were performed at speeds of up to 70 knots, and on 13 February 1962, the first conventional flight was achieved.

The P.1127 evolved into the Kestrel and then the Harrier. By 1969, the RAF was using Harriers operationally, and by 1980 the Sea Harrier variant was in use by the Royal Navy. Harriers saw action as part of the Falklands Task Force in 1982, operating from the carrier HMS Hermes some 8,000 miles from England. They flew 1,435 operational sorties, accounting for the destruction of 28 enemy aircraft, with no losses in the air. The Harrier went on to become probably the most successful British military aircraft to date, with 112 sold to the US Marine Corps. In total 879 Harrier aircraft were built at Dunsfold with an estimated sales value of £2.6 billion (2017 values), all of which were tested in the engine running pen, prior to delivery.

One of the three original engine running pens has now been demolished, and the north-western example has been modified to accommodate a truck-washing system.

Reasons for Listing

The engine running pens at Dunsfold airfield, designed to develop and test Hawker Siddeley jet aircraft including the Hunter and Harrier jump jet, are listed at Grade II for the following principal reasons:

Historic interest:

* For their essential role in the testing of Hawker Siddeley combat aircraft, including modification for the development and testing of the Harrier jump jet. Collectively they help to tell the story of testing the Hawker Siddeley product line;

* The pair at Dunsfold are especially rare as both were designed for engine-in airframe research, development, and pre-delivery testing;

* Associative value with the Cold War; the Hunter being at the forefront of Britain's fighter defence against airborne nuclear attack, the Harrier jump jet designed to operate from remote sites, rather than major airfields which were likely to be lost during a nuclear attack.

Architectural interest:

* The architectural interest of these buildings and structures is in their technological fabric and in their display of the jet-age confidence inherent in the British aviation industry of the mid to late C20;

* The western engine pen is of particular interest due to its modification for V/STOL testing, including a subterranean diffuser pit, control room, and fully enclosed metal-sheeted walls developed to test and develop the vectored thrust of V/STOL aircraft.

Group value:

* The engine running pens, and the smaller western V/STOL blast grid form an important group of structures at Dunsfold, which are directly related to the creation, testing, and manufacture of the iconic Harrier jump jet;

* With the Grade II listed 1942 airfield memorial and the Royal Observer Corps observation post.

External Links

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