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Aviation History
1949
1949 - 1683.PDF
FLIGHT, 29 September 1949 447 JET TUNNEL High-speed Flow at Low Overall Cost THE wind tunnel was one of the first pieces of aeronauticallaboratory apparatus and since its inception has developed along classic lines. That is to say, the initial concept of usinga motor driven fan to produce the requisite airflow has remained unchanged until recent years. With the enormousincrease in flight speeds which has come about during the past decade, however, the powers required to produce tunnelwindspeeds approaching and surpassing that of sound have risen to such tremendous values that the constructional andoperating costs of wind tunnels of the traditional type have become prohibitive. For these reasons, tunnels of intermittent-flow types havebeen and are being constructed in which air stored at high pressures is released through a working section for a shortperiod (during which the flow velocities can be extremely high) after which the storage chambers must once more be pumpedup for the next run. Alternatively, a vacuum chamber can be filled with air via a working section to produce similar high-speed flows. Even the smaller tunnels of these types are by no means inexpensive. Some little time ago, however, a new approach to the high-speed tunnel problem was evolved at the English Electric Co., Ltd., makers of the Canberra. The idea was delightfullysimple, in that all that was required to generate the requisite airflow was an ordinary turbojet unit mounted inside a rela-tively short length of tunnel. A Rolls-Royce Nene with a static thrust of 5,ooolb was chosen as the power unit an.lsome idea of the compactness of the installation is given by the fact that the tunnel has been erected in an erstwhile piston-engine test-cell measuring 60 by 34 by 18ft. In form the tunnel is perfectly straightforward. The Nene ishoused in a nacelle which in turn is housed inside a bulged portion of the tunnel downstream of the working section. Theprinciple of operation is that flow through the working section is induced by the ejector action of the jet efflux, so that in thissense, the Nene can be regarded simply as an extremely powerful ejector pump. Air enters the tunnel from a settling chamber via a gauzefilter, thence flowing through an intake flare to the 3ft 8yj by 1 ft working section. It is then diffused down to the"pumping section" where one-third of the flow is passed through the jet unit, the remaining two-thirds flowing outsidethe Nene nacelle in the annular space between the nacelle and the bulged wall. A flow velocity of Mach 0.9 is reached with the tunnel empty,and with a model wing of 15m chord, this speed falls only to M 0.83, the corresponding Reynolds number being 5x10*.On most normal days of the year, operation of a straight- through tunnel of this type would induce condensation troublesif means were not taken to lower humidity at the intake. This trouble is avoided by collecting a proportion of the hot exhaustgases and conducting it forward to mix with the entering air. NEW BASIC TRAINER PLANS TWO contracts have been awarded by the Ministry of Supplyfor the building of prototypes of a new basic trainer lor the R.A.F. Handley Page (Reading), Ltd., announce that they, as one of the companies concerned, have designed a low- wing, side-by-side machine known as the H.P.R.2 to meet Service requirements. It is destined for duty anywhere in the world and, with the power of one Armstrong Siddeley Cheetah 17, will be capable of a good take-off and climb performance. It will also have the requisite low stalling speed. The Cheetah 17 gives 420 h.p. for take-off and 280 h.p. for w.m. cruising. Tail-down fixed landing-gear is specified. All-metal construction is to be employed, and the accent in design has been upon rapid and simple production (using "split construction" methods), interchangeability and easy maintenance. Percival Aircraft, Ltd., is the other company to receive a contract for two prototypes to the new specification. Thesetrainers are unlikely to go into production until the autumn of 1951. PRESSURE REGULATOR VALVE A REDESIGNED pressure regulator valve is announced byLear Incorporated, Romec Division, Elyria, Ohio. The valve, which can be operated at altitudes up to 40,000ft, re-duces pressures up to 100 lb/sq in to any constant lower pressure. Changeable conditions on either side of the valvecan be accommodated, and compensation is made for vaca- tions in liquid-fuel or water consumption by holding the outletpressure within narrow limits. For aircraft application, the unit is designed as a balancedvalve with turbo-supercharger connection, by means of which valve pressure is balanced with the air induction system ofthe engine. O. «iu —T^ U^EIIAIU- MODERNITY IN HANGARS Italian Designs with "Self-supporting" Roofs A RECENT issue of The Architect andBuilding News contains pictures of two extremely impressive hangars erected near Rome. The roof of the first (illustrated here) is cast in reinforced concrete sections and is a Lamella-type structure supported by regukrjy spaced buttresses. In the second hangar— of more advanced design—six buttresses support a 336ft x 120ft roof. The designer, P. L. Nervi, would appear to have produced a structure which fills the need for unre- stricted floor space in hangars of such dimen- sions, though there may be some doubt as to whether the cost of such a hangar would compare favourably with that of the orthodox type of building favoured in this country. F 21
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