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Aviation History
1960
1960 - 2373.PDF
PLIGHT, 21 October 1960 641 New Tunnels for Warton ADDITIONAL FACILITIES FOR ENGLISH ELECTRIC AVIATION TEN years ago the British aircraft industry was pro-ducing advanced aircraft projects by the score, butlarge high-speed tunnels in which they could betested were conspicuously absent. Today the position is markedly different: projects for new high-speed aircraftcan be counted on the fingers of one hand, but in the matter of research facilities the industry has pulled upits socks in a determined manner. Every major British aircraft company now has the use of generally adequatetransonic and supersonic tunnels, in most cases paid for by the firm concerned. These facilities, most of whichare either driven by turbojets or are of the intermittent blow-down type, are backed up by tunnels of the moreexpensive continuous-running variety at the RAE Bed- ford (Flight, July 5,1957) and Aircraft Research Associa-tion (Flight, May 4,1956). On October 19 the Minister of Aviation opened a newblow-down facility in Lancashire which in many respects can be regarded as the most capable in Europe. Locatedat Warton, the flight-test centre of English Electric Aviation (member of British Aircraft Corp), and financedentirely by the company, it consists of a 4ft tunnel for Mach numbers between 0.4 and 4 and an 18in tunnelfor Mach numbers between 1.5 and 6, both served by the same air storage. English Electric's installations at Warton may well surpass incapability the wholly owned facilities of any other company in the world. The first tunnel was built there in 1948; it is a 9ft x 7ftcontinuous-runner, with a maximum speed of 170ft/sec and digitized output to facilitate immediate analysis by an EnglishElectric Deuce (Flight, April 15, 1955). The following year the company installed a pioneer turbojet-powered tunnel, built asa high-subsonic installation with a working section 3ft 8in X lft but modified in 1950 to have a slotted lft-square working sectionfor transonic operation. With this tunnel the company's staff perfected new instrumentation systems, and in particular methodsof employing straingauges, model supports and balances at Mach numbers between 0.6 and 1.1. It also enabled Mr Petter's teamto develop the Canberra. Armed with the knowledge gained with it, the company installeda larger and more advanced tunnel in 1954 in order to support the test programme on the P.I research aircraft (which later becamethe Lightning fighter). Powered by two Rolls-Royce Nene engines, this tunnel has an 18in slotted transonic working section whichcan be replaced by solid liners matched to Mach numbers of 1.4, 1.6 and 1.7. Again, the outputs are digitized. Yet another facilityis an 18in water tunnel in which separated and vortex flows can be investigated visually at up to 20ft/sec.By 1956 it was a sine qua non that the company's design staff, led by Mr F. W. Page, would have to reach out into realms beyondMach 2. English Electric had not joined the Aircraft Research Association, and in any case it was clear that their interests wereleading them into fields in which the ARA facilities, and even those at the RAE, would be inadequate. Not only was the com-pany intensively investigating advanced military aircraft—largely of the "Canberra-replacement" variety (which have since evolvedinto the TSR.2 programme);—but they were also taking more than a passing look at supersonic transports and a variety of guidedweapons. Newer, better-instrumented and faster tunnels were inescapable requirements, and in December 1956 the decision wastaken to finance the construction of a wholly new facility, of the blow-down type, with two working sections, one chiefly for air-craft and one for missiles. It is possible now to outline the characteristics of the installation, which is described by the com-pany as "meeting the requirements of the next generation of aircraft and winged missiles, and also covering re-entry conditions all times sensed by elements linked to the hydraulic system tofnr r-or» n;« v...ii:^.:. :»,,:i^., » Dnrt^,,UrUi ruitctanrtino- is rhp new Drevent overstressins the plate in the event ot maltunction. Final inspection of a delta-wing/body calibration model inside the 4ft tunnel, showing the $lotted liner of the working section 4,400 cu ft/min. The delivery is cooled by air/water heatexchangers downstream of each compression stage, and an alumina drier between the compressors and the bottles maintains thestored humidity at below 0.00031b/lb. Temperature-drop in the air leaving the storage vessels is reduced to not more than 25 °Cby heat transfer from a "sink" of mild steel made up into tubular matrix blocks inside the delivery from each bottle. 4ft-square Tunnel Flow control Primary control device is the main control valve,which has a threefold function: to establish the desired flow with minimum air consumption; to maintain constant flow duringthe test period; and to shut down the tunnel rapidly on completion of the test and seal off the air storage completely. The rapiditywith which the supply pressure can fall posed control demands beyond the capacity of any existing valve. It was finally decidedto adopt a two-component design, with a sliding piston to provide coarse control and a ported rotating cylinder governed by a closed-loop system providing fine control. Both members of the valve are automatically closed by fail-safe electrical and hydraulic inter-locks upon a signal from any of the pressure switches located throughout the tunnel. Provision is made for varying tunnelpressure during the course of a run. Flexible nozzle Located between the settling chamber and theplenum chamber, the flexible nozzle raises the Mach number of the incoming air from below unity up to the value required inthe working section. The sidewalls are fixed, but the upper and lower walls are flexible. Each is a plate of Monel measuring27ft X 4ft X0.5625in, mounted on rigid beams which run the com- plete length of the nozzle section. Each beam is hinged directlyto the plenum chamber, and the upstream ends of the beams are mounted on hydraulic screwjacks so that the vertical aperture atthe throat may be varied from 48in down to 2.5in. In order to provide correct nozzle contours, the Monel plates are secured tothe beams only at the upstream and downstream ends, the inter- mediate links being provided by 18 pairs of hydraulic jacks which,according to signals precomputed for each Mach number, position each of the 18 wall stations within an accuracy of 0.002in. Thejoints between the flexible plates and the sidewalls are sealed pneumatically, and maximum curvature of the flexible walls is at for certain ballistic missiles." Particularly outstanding is the nefacility's data-handling system. . Air Supply As the drawing overleaf shows, compressed airis stored in four cylindrical bottles, each 90ft 6in in length and having an internal diameter of 6ft. When fully charged to6001b/sq in the four bottles contain some 34,0001b of air. The bottles are pressurized by a pair of three-stage reciprocating com-pressors, each driven by an 820 h.p. motor, which together deliver preven g f malfunctionWorking section The 4ft X 4ft transonic working section is located immediately downstream of the flexible nozzle. The wallsare formed from four sheets of perforated plate of 19 per cent porosity, surrounded by a plenum chamber of octagonal cross-section. Immediately downstream of the perforated plates is a variable diffuser formed from two sections of adjustable platescontrolled by screwjacks. These plates improve pressure-recovery,
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