FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1952
1952 - 1293.PDF
SECONDARY AIR PRIMARY AIR SECONDARY AIR PRIMARY AIR uit<j.-t ////<<<,< XZZZZ /,///// //// ,,'/,•;,>> .^.' .• . -rr~-r-7-r-> ^ST B*r~is /-/-ft ^v,,,, .^<^" i—fr y /- ' / / x H^*> / ,• s s >;//.'S/s>/ss.'/s>s PRIMARY AIR Section and plan of one half of the test-bed building for large capacity turbojets. The cascades and diffusers ensure a low noise-level. THE QUEST FOR POWER . . . Hytor compressors each of 450 cu ft/min capacity. Another flow rig which has proved invaluable is an adaptation of a normal (piston engine) supercharger test rig. A Centaurus hack super charger is driven by a 600 h.p. electric motor to supply air to a scale model turbine with precision cast blades—another variant of the cold-flow rig. The turbine is coupled to a Hercules super charger acting as a dynamometer in that load on the turbine is varied by controlling the quantity and back-pressure of air passing through the Hercules blower. The primary purpose of the rig is to study the characteristics of various forms of turbine exhaust duct, and for this purpose the model ducts are made of wood, the delivery temperature of the air being reduced by means of water- circulation heat exchangers. There are, in addition, two rigs which offer some considerable attraction to the primeval appeal of destruction which seems to lie not far beneath the surface of most of us. They are for over- speed testing. Of the two rigs, one is designed especially for the research testing of components to destruction. The test cell can be exhausted so that the power required to spin the component is reduced, and in order to mitigate the effects of component failure, the walls of the cell are lined with wooden beams and hung with "propeller netting." Drive is by a 300 h.p. motor through a pair of gearboxes, the first of which offers alternative gear ratios giving final drive speed-increase ratios of 12.5:1 and 16.3:1; the maximum speed is limited by the rating of the second gearbox to 17,000 r.p.m. As is only to be expected, an overspeed test to destruction is conducted only after full data have been obtained on the elastic and permanent deformation of the component over the speed range. An interesting tool which has been developed especially to measure the radial growth of a component under centrifugal load is an optical dilatometer. A light beam is projected across the rim of the component (e.g. a turbine wheel), the resulting shadow being magnified through a prism and lens system and projected against a scale which can safely be read through a window in the steel door of the cell. Any diametral growth of the com ponent being spun can thus be accurately discerned without risk. Of the test beds for full-scale engine running, by far the largest and most modern are an identical pair housed in a single building, the design merit of which, like that of the Turbine Research Sta tion, is of a high order. These beds are each capable of accom modating turbojets of up to 15,0001b static thrust, and in that the mass flows associated with powers of this order are enormous, the chief considerations monitoring the design were recognised as being acoustic in character. To this extent, the building must be regarded as particularly efficient, for an unusually high degree of silencing is obtained. Appreciation must be accorded Cementation (Muffelite) Ltd., on these grounds, for in addition to making and supplying the silencing equipment, they also advised on the essential design of the building. The building comprises "mirror image" halves about an imag inary north/south longitudinal centre-line, the south front of the building being approached by a long concrete ramp, the landing of which gives directly (through massive steel doors) into the engine rooms. South-extending wings flank the head of the ramp, and each incorporates grilled openings for air entry : the control room spans the full width of the building at "first-floor level," that is to say, above and behind the engine rooms, and although a single apartment, is furnished in duplicate halves each of which serves one bed. At the ends of the control room, and above it, is an additional pair of grilled air-entries. As may be seen from the sectional drawing of one half of the building, the engine under test derives its air from the upper side aperture in the south wing, the lower front aperture serving the diffuser chamber as does the top entry above the end of the control room. The diffuser chamber walls are lined with corrugated light alloy over a 2-in thick lagging of glass-wool, the primary purpose of which is to provide thermal protection for the concrete structural skin of the chamber. The diffuser itself consists of a divergent circular-section trunk fabricated in |-in mild steel plate, and is mounted on rails whereby axial movement is facilitated. At its downstream end, the diffuser terminates in a spreader drum with perforated walls and angle-iron baffle-bars. On emergence from the spreader drum, the diluted gases pass through walls of vertical splitters arranged as "dog-leg" passages giving on to the base of a vent stack where horizontal turning vanes direct the stream up ward and so out to atmosphere. Insofar as the test cradle and control arrangements are con cerned, one of the chief points of interest is that the cradles are arranged so that the observer in the control room looks down on and axially along the engine from the front: a not inconsiderable safety measure. The cradles are of cast steel, the engine carriages being supported in the mounting structure by four steel laminations which permit movement of the cradle for thrust measurement, yet incur negligible friction. Thrust is measured by an Avery weighing machine operated through a straightforward mechanical linkage from the cradle. The control panels and desks form a neat installation and, unusually, arrangements are made for automatic film recording of dial readings. Another refinement is that all engine services run down in a duct from the control room to ter minate in a manifold panel alongside the cradle. At the beginning of this article it was observed that novelty is the most transient of qualities. It is, however, worth remembering that it is on the technical novelties of today that the text-books of tomorrow are based. SPEEDING-UP AMONG the most pressing problems facing the aircraft L industry, commercial operators and airfield owners today is the saving of time and manpower in handling their materials, products and freight. It is for this reason that executives of such concerns will welcome the holding of the Third Mechanical Handling Exhibition and Convention at Olympia, London, from June 4th to 14th. There will be plenty to interest them. Many of the exhibitors have for some time past supplied mechanical handling appliances —not in ones and twos, but in batches—to aircraft manufacturers and to airports. The latest types of mobile crane, particularly suited to work on airfields, will be shown. One is equipped with a hydraulic ram for raising and lowering the jib. Finger-tip control is provided, giving easy and safe control of derricking operations. Tractors for hauling aircraft will be exhibited—one for handling 60 tons' gross weight. There will be also specially designed trailers for use at airports, and included among these is a trailer that can be lifted by fork-lift trucks. These fork-lift trucks, coming into increasing use in aviation, will be well represented among products of a number of exhibitors. In addition, there will be on view many handling appliances suitable for aircraft construction and maintenance, such as an hydraulic elevating working platform rising to 31ft.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
