Engine running pens at Dunsfold airfield

The engine running pens at Dunsfold airfield consist of two brick-built structures dating to circa 1950, with modifications made to the eastern pen around 1960 for Vertical/Short Take Off and Landing (V/STOL) testing.

The north-western pen is U-shaped, with the curve facing north. It contains an aperture which formerly housed a diffuser, a device for dissipating jet engine thrust. The eastern pen is also U-shaped, featuring sliding doors to the south. Both pens were accessed from the south, with aircraft reversed in and secured to the ground, engine facing into the diffuser.

The pens are constructed of mixed-stock brick, concrete, steel, and steel sheet. The western pen is largely open, built of brick in an English bond, with brick piers supporting walls topped with concrete copping. The walls are approximately 2 metres deep and 5 metres high. The north-facing elevation is semi-circular, with the central section slightly higher than the flanking walls. A large ovoid aperture marks the position of the former diffuser. Above this area is an internal dome-like structure faced in aluminium. Oversized pedestrian door apertures are positioned on either side of the curved section, providing access to what was the diffuser area. The walls extending south from the curved section include a series of irregular access doors and apertures. The internal space has been adapted to house a late 20th-century truck-wash system. The internal face of the brick walls incorporates a regular pattern of inserted black bricks. Single-storey brick control rooms are positioned on either side; one is internal (on the western side), and the other projects from the eastern wall. These control rooms have small rectangular timber casement windows and flat roofs. The interiors were converted to toilets or rest rooms in the late 20th century.

The eastern pen is similar in design but was modified for V/STOL aircraft testing. The central section of the north-eastern face is open, with a steel beam replacing the original diffuser. Brick buttresses are interspersed along the walls, continuing onto the flanking walls. The working space within the pen has been extended to the north-east end. The floor is largely concrete, but a subterranean diffuser pit exists at the north-east end, now covered with metal plate. The interior walls are clad with brushed metal panels, incorporating built-in control rooms to the north-west and south-east. The south-east control room has a line of small, top-hinged metal windows facing into the working area, and includes a pedestrian door fitted with a bench and seating. A large double-depth sliding aluminium door, used as the aircraft entrance, is located to the south-west.