Vertical spinning tunnel built between 1948 and 1955.
Reasons for Designation
The vertical spinning tunnel, built between 1948 and 1955, and located on Thurleigh Road, Milton Ernest, is listed at Grade II for the following principal reasons:
* it is a well preserved example of a very rare building type which retains its structural integrity and survives in a form that directly illustrates its original use;
* it was the only steel pressurised VST ever made, and its construction pioneered the technique of welding on site of pre-formed plates for the assembly of large pressure vessels;
* it was part of the largest post-war development by the RAE and was one of the most advanced aviation research facilities in Europe;
* it is illustrative of the new specialised facilities to investigate aerodynamics and flight systems which became centres of post-war scientific and technological excellence;
* it was a significant element in a post-war research establishment which reflected Britain’s aspiration to remain as a global superpower, with the independent capability to develop and manufacture complex weapons systems.
During the Second World War the government decided that aviation was the primary sector to be exploited in the country’s post-war industrial recovery. To achieve this, it was recognised that large and expensive research facilities would be required in order to be internationally competitive, particularly with the USA. Post-war aviation technology was transformed by the introduction of the jet engine which permitted aircraft to achieve far higher speeds but also placed far greater strains on their airframes. These created a demand for new specialised facilities to investigate aerodynamics, aeroengines, aviation medicine and flight systems. The large aviation research establishments were directly operated by the government and illustrate the importance of the state as the prime funder of scientific and technological research.
In 1944 a site north of Bedford encompassing the three wartime airfields at Twinwood, Thurleigh and Little Staughton was chosen for a new Royal Aircraft Establishment (RAE) site, the main one having been built at Farnborough. The Government’s decision to proceed with its construction was announced by Sir Stafford Cripps, Minister of Aircraft Production, in February 1945, and by mid-1946 plans for the airfield (at Thurleigh) and the wind tunnel site (adjacent to Twinwood) were well advanced. The wind tunnel site included the High Speed Laboratory (HSL) which was designed to provide office, workshop and laboratory accommodation for four conventional wind tunnels and the vertical spinning tunnel (VST). Construction of the VST began in 1948 and it was run for the first time in June 1955. Its construction pioneered the technique of welding on site of pre-formed plates for the assembly of large pressure vessels. The heavy engineering work was carried out by Dorman Long and Co Ltd of Middlesborough, and Whessoe were the contractors.
The main purpose of the VST was to enable the behaviour of free-fall aircraft models in spinning flight to be observed and to investigate methods of recovery from a spin. The phenomenon of an aircraft going into a spin, from which recovery is difficult, claimed many lives, particularly during the Second World War when pilots were undergoing training. In the VST a test model was launched into a rising column of air whose speed is adjusted so that the model’s fall is just balanced by the rising air. By remotely setting its aerodynamic controls the model can both be induced into, and recovered from, a spin, thus allowing detailed study of the phenomenon. Amongst its international contemporaries the VST was unique in that it could be pressurised to 60 lbs per square inch, thus allowing a much greater accuracy of the aerodynamic data obtained.
By the time the VST became operational, the problems of spinning were much better understood and the methods of recovery better established. Thus the requirement for it as a research facility was substantially reduced and few spinning tests were undertaken. It was subsequently used as a vessel for the storage of compressed air which was piped to the other wind tunnels. Out of the other four planned conventional wind tunnels, only two were constructed in the end so only part of the accommodation of the High Speed Laboratory was used for laboratory purposes. Initially the extra space was used to house the design and administrative staff involved in the construction work underway on the tunnel site and airfield. Later, as electronic computing was introduced and a central facility to serve the whole RAE was created, the HSL became the home for an autonomous computing section and for a ‘mainframe’ computer which was a very bulky bit of equipment.
The HSL complex was put up for disposal in the early 1990s and was acquired by a company called Bodyflight who re-commissioned the VST as a wind tunnel for skydiving. The only change that needed to be made to the tunnel was the installation of a more powerful engine, and operations began in 2005. The remainder of the HSL complex is now used as a leisure centre. Many of the former offices have been converted into residential accommodation, a mezzanine has been built in the machine hall to house a wave machine, and a swimming pool has been built in the former location of one of the wind tunnels.
Vertical spinning tunnel built between 1948 and 1955.
MATERIALS: the tunnel is constructed of pre-formed steel plates.
PLAN: the vertical spinning tunnel (VST) is circular on plan.
It is attached on its south-west side to a large rectangular building which formerly accommodated the offices and laboratories. Adjoining this building on its south-east side is the former machine hall which is square on plan. Neither of these two buildings are included in the listing.
EXTERIOR: the VST consists of a vertical steel pressure-shell in the form of a cylinder approximately 24.4m high and 13.7m in diameter. It is divided into sections by regularly spaced, full-height ribs. A cylindrical column attached to the south side is the lift shaft to the motor room which also contains an emergency staircase. Two beams project from the top of the building which act as supports for an external hoist used for lifting bulky electrical equipment to the motor room. This is glazed all round with a wide horizontal band of vertical metal-framed windows.
INTERIOR: the vertically placed working section of the tunnel is approximately 9m high and, circular in cross-section, has a diameter of 4.6m, forming in effect a tube within a capsule. There is a catch net below the working section onto which the model could be landed as the tunnel speed was reduced upon shutting down, and another above to prevent an escaping model reaching the fan. The original electric motor mounted above the tunnel, accessed via the original metal open tread staircase, has been replaced in the early C21, although parts of the original laminated teak blades of the fan are kept on site. Positioned in between the outer wall of the tunnel and the working section are a series of small rooms, including the observation room, which are closed by pressure-tight doors of similar design to those used in submarines.