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Aviation History
1955
1955 - 0827.PDF
FLIGHT, 17 June 1955 825 MACH 3 WIND TUNNEL Powerful New Research Installation at Armstrong Whitworttfs Whitley Plant ONE of the main duties assigned to Dr. William FrankHilton, D.Sc, Ph.D., A.R.C.S., D.I.C., F.R.Ae.S.,when he joined Armstrong Whitworth Aircraft, Ltd., as chief aerodynamicist in May 1950, was to design and develop their first supersonic wind-tunnel. He was respon- sible to Mr. J. Lloyd, F.R.Ae.S., at that time technical director of the company. Supersonic running of the tunnel took place for the first time in December of last year, and the completed installation was ready for formal opening by Lord Brabazon of Tara on Monday last. Early in the design stages of the A.W.A. tunnel project it wasdecided to select a continuous tunnel in preference to an inter- mittent type. The capital cost of air bottles capable of storingenough air to run a two-foot tunnel for 15 min per hour, it was calculated, would equal or exceed that of the continuous tunnelwhich came to be chosen. Special efforts were made to ensure quick starting and stopping procedures (normally the main advan-tage of the intermittent type). The use of turbojets was not favoured; their high running cost, it was estimated, would in thefirst one or two years' running swallow up the saving in first cost of a jet-driven tunnel. It was decided to house the new tunnel in the existing No. 4Hangar at Whitley—incidentally the hangar in which the com- pany's first Whitley bomber was manufactured. A suitable sourceof cooling water was here available—the River Sowe. To con- solidate all A.W.A. wind-tunnel work under one roof, the 5ft x 4ftlow-speed tunnel was moved from Baginton and also installed on the same site.Although a delivery promise for December 1952 was obtained on all items ordered for the tunnel, several manufacturers of majorcomponents were unable to meet their promised delivery dates. This was not true of the auxiliary plant for compressing, dryingand storing air, which was in working order by March 1953; and in the previous November it had been decided to design andmanufacture an intermittent transonic tunnel powered by this dry air storage. Six months later this tunnel was operational,for a total extra cost of about £3,000. This intermittent tunnel has proved useful for the rapid testing of models of aircraft at the design project stage up to speeds ofMach 1.5. Its running time of 15 to 20 seconds every quarter of an hour prevents its use for the serious development of aircraftand missiles for which many thousands of readings would be required. In the design of the new continuous tunnel one major problemwas to obtain quick starting and stopping, for supersonic flow must be established in the working section as quickly as possiblein order to reduce the loads on the strain-gauge sting when starting up the tunnel. This is accomplished by starting up themotor compressor set with the compressor inlet butterfly valves closed. By means of a switch, oil pressure can be applied suddenlyto these valves, causing them to open or close in only 3\ seconds. A small leakage past the butterfly valves ensures adequate aircooling of the compressors, which are surging during this phase of the operation. The working section was designed so that the shock-wave fromthe nose of a "standard" model (of 16in length and 10 deg half- angle conical nose), when reflected from the tunnel wall, wouldpass behind its four-inch span tail. This implied a different working-section size for different Mach numbers, and it wasdecided to employ a series of fixed working sections, machined from cast iron. From calculations of the working section sizesrequired at Mach numbers from 1.4 to 2.5 the corresponding pressure ratios were obtained and this "minimum air requirement"was issued to various compressor manufacturers. The best compromise between convenience, simplicity andeconomy was found to be two centrifugal compressors, working in parallel to supply a working section 20in wide at Mach numbersup to 1.8, and working in series to supply a working section 14|in wide at Mach numbers above 1.8. Height of the working sectionvaried between 24in and 16in. By standardizing the two working- section widths, the hinged liners in the balance section betweenworking section and diffuser were found to be reasonably simple to design and manufacture. Similarly two alternative adaptersblend the vertical walls of the contraction smoothly into the two different widths and at the same time blend the horizontal wallsinto the nozzle profiles. An initial drying period for the tunnel air of at least one hour General arrangement of the supersonic tunnel, with certain portions shown in part-section. The whole of this assembly is accommodated in the Whitley hangar which also houses the transonic and low-speed tunnels. SWINGING ELBOW COMPRESSOR COMPRESSOR INTAKE (motorcooling) IOJOOO hu MOTOR P GEAR BOX DIFFUSER BUTTERFLY VALVES VALVE COMPRESSOR INLET SCREEN SAFETY NET EXPANSION- RETRACTION JOINT ASCADES
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