The main runway has the unique Vertical Take Off Grids (VTO Grids or Hover Grids) – used for the tethering of jump jets such as the Harrier whilst hovering. These are located on aprons that adjacent the main runway and are within the Operational Readiness Platform [ORP]. Beneath these gratings is a large void chamber to take the hot air, condensation and gases from the downdraft of the jet engines of the aircraft. Within the eastern Engine Testing Pen there is a similar arrangement that is a unique feature to Dunsfold.
The VTO Pads were given Grade II Listed Building status in December 2017. Historic England’s notification of Listing report Excerpts from HE’s report are below:
The VTO (Vertical Take Off and Landing) blast grids were built to support the development of a V/STOL fighter aircraft during the early 1960s at Dunsfold airfield…
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 engine running pens to test the jet engines in 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 which involved the use of vectored thrust to lift a static or slow moving aircraft in to 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.
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 pens. On 31 August 1960, the Pegasus engine was run for the first time while inside the aircraft. Early testing of the concept was performed from the purpose-built VTO blast grid, which was located at the western end of the main runway.
This was a new technology and the physics of vectored thrust were not fully understood. The grid was designed to deflect the hot exhaust gases away from the hovering aircraft, and protect the runway tarmac. It was also thought to be essential in eliminating the adverse effects of thrust losses due to re-ingestion of these hot gases, which was important as the thrust of the prototype engine was only adequate to lift the aircraft with a small fuel load, and all non-essential equipment removed. The designers were also concerned that the aircraft might depart controlled flight in the hover, so tethering points and lines were added to the grid, so that it could be held back in an emergency. Initially the tethers were set at a length of 1ft, and the first hover in this configuration was achieved by Bill Bedford on the 4 November 1961, with one of his legs still in plaster from an earlier car accident. Later, when the tethers were lengthened to 4ft the reaction controls of the aircraft were found to be inadequate. When the aircraft departed from the ground, it had a tendency to lift one wing ahead of the other, and there was too little roll-power within the controls to correct this. This lack of control caused the aircraft to ‘cavort around like a drunken cow’, until the controls were modified. The first free hover occurred on 19 November.
In parallel, conventional taxi-trials were performed at speeds of up to 70 knots. Finally, 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 aircraft were built at Dunsfold with an estimated sales value of £2.6 billion (2017 values). The VTO blast grid has been covered over with steel-plate but is believed to be otherwise intact.
Two other larger steel-sheeted blast platforms (one to each end of the runway) were constructed in the 1970s, and were probably used for tests that would have otherwise harmed the runway tarmac.
Historic England Advice Report 04 December 2017 : Details Steel V/STOL blast grid of 1960, located at the western end of the main runway at Dunsfold airfield.
MATERIALS: boxed-steel, brick, concrete and steel-plate.
PLAN: the grid is rectangular and measures approximately 10m by 20m. The longer edge faces broadly east-west along the main runway.
DESCRIPTION: for safety reasons, the grid is now completely covered with sections of steel-plate, but it is likely that the below ground structure survives. The following description is based on photographs taken during construction; the blast grid is sunk around 2m into the tarmac runway surface and is formed of multiple steel box-sections of approximately 0.5m by 1m, which are supported by steel uprights of circa 1.5m in height. Within each box-section there is a curved metal vane designed to disperse exhaust gases into the void below. The void is formed by brick walls and a concrete floor. To the centre of the grid there is an inset lifting door of finer box-section measuring approximately 2m by 3m, which probably provides access for maintenance to the underside of the grid. Historic England, November 2017
Editor’s Note: Since application for a Conservation Area and Waverley Borough Council’s rejection there have been a number of assets considered for Listed Building Status. Historic England have since designated 5 Listed Structures on the Airfield site:
Primemeads Farm – Grade II
VTO Blast Pads – Grade II
Engine Running Pens – Grade II
Royal Observer Corps Monitoring Post – Grade II
Canadian War Memorial – Grade II
Please note: The aerodrome is private land and an active airfield. Access is not permitted to some of the buildings and features and we strongly discourage access without permission.