4)  The Wind Tunnel

John and I worked together, John on the large 7A machine and me on the smaller 6. Both machines could split a micron (0.001 mm) The 6 was metric and was purchased in 1970 for £25,000 (In 1969 I bought my first house for £4,300, now £500,000)

Both machines had a large (800 mm diameter) Rotoptic rotary table this could split 1 second of arc. On the top of this was very often placed a large tilting rotary table. One task of note was the cutting of a spherical bore. We started thinking about co ordinate cutting. The DO chaps tried the new MiniMop computer system but somehow it was left to my foreman, Colin Bell, digging out an old book and letting me get on with it. You had to set the tilting rotary at an angle such that the tool bit in the boring head did not quite make a 360 degree cut ie  cutting mostly metal but some air. The cut was made with the boring head rotating and me winding the rotary table a full 360. I do remember Ted calling me a cheeky young whipper snapper (A young and inexperienced person considered to be presumptuous or overconfident.)  Ok I will take that now but then I was cross because he had nearly wrecked the job with a form tool ignoring my set up and calculations completely.  Ted was on permanent nights. They would work until 02:00 or so then get some sleep. Waking at 05:00 for the last hour. Working like this errors could occur, I would know it the job had gone wrong, it often did, if I had an apple on my toolbox.  Read about my maths in the 1960's 

THE WEYBRIDGE TUNNELS

There follows text and photographs from the booklet "Test or be damned".   Published by Vickers-Armstrongs(Aircraft) Ltd. C 1962

Mach 1.4 to 3.5 is the operating range of the supersonic tunnel, the other four covering subsonic speed's. 

The 4ft. low speed tunnel, the " 4ft.” referring to the width of the working section, was built in 1916 and was the first commercially owned tunnel in the United Kingdom. Apart from Calibrating flight test equipment (eg. pitch and yaw meters), it is not in extensive use today. 

The 8ft. low speed tunnel came into use in 1931 and was modernised in 1956. It has a top speed of 130m.p.h. and the lift, drag and pitching moments are measured with an overhead balance. Most of the low speed work on the Valiant Bomber was done in this tunnel. 

The 13ft. x 9ft. low speed tunnel, together with the high subsonic tunnel formed the early post-war expansion of the wind tunnel facilities, necessitated by the rapid development of aircraft during and since the war years. 

Although described as a low speed tunnel, the l3ft. x 9ft. is one of the fastest tunnels of its size. At the maximum working speed of 240m.p.h., 75 tons of air pass through the working section per minute. The tunnel is 220ft. long, has a contraction ratio of 10.8 to l, and is driven by a single 24ft. diameter seven-bladed fan, powered by a 2,200h.p. electric motor.

The resultant forces acting on the model are broken down into six components, and measured by a balance developed by the National Physical Laboratory. 

To prevent interference with the air flow over the wing, the support struts from which the model is suspended must be as thin as possible. A compressive load requires a fatter strut than a tensile load, in order to prevent buckling. If the Weight of the model and the lift developed by its wings both act downwards, the strut will always be in tension so to this end, the models are hung upside down. This also necessitates mounting the balance, used to measure the forces acting on the model, above the Working section. 

The size of the working section enabled us to test a 

• 1/5 th scale Scimitar Naval fighter, 

• 1/10th scale Viscount 800, 

• 1/12th scale Vanguard, 

• 1/15th scale VC10,

• 1/13th scale Valiant 

• 1/10th scale One-Eleven. 

With the Vanguard model, powered flight was represented by driving its four airscrews with 3.5 in. diameter, 12h.p. electric motors. 

This tunnel is also equipped with large suction and Compressed air plants for testing modern high lift devices, such as blown flaps.

Test Reynolds Numbers of about 3 million are achieved. 

The high subsonic tunnel has a working section of 3ft. by 2ft. and utilises a two-stage fan powered by a 2,000h.p. electric motor. Test Reynolds numbers range from 1 to 2 million as the Mach numberincreases from 0.4 to 0.94(715 mph) at a working pressure of half an atmosphere.

As the air speed in the tunnel increases so does its temperature. At the higher speeds reached in this tunnel the heating effects are appreciable and cooling is by air exchange. The average running temperature of the air is about 30° above atmospheric.

Some of the work is carried out on “half models mounted on a four component balance which electrically transmits the magnitude of the forces to automatic data handling equipment.

The "half models" are used to attain a larger Reynolds Number and scale and thus more accurate results. Full models can be mounted on a “sting”-see picture of supersonic tunnel-and tested, but to obtain accurate results from the smaller scale models is very costly.

Both this tunnel and the supersonic tunnel are equipped with Schlieren apparatus which is used to demonstrate visually the air around the model.