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Aviation History
1954
1954 - 0974.PDF
442 FLIGHT A Double Mamba on a test-bed at the Armstrong Siddeley factory; the engine is mounted on a non-lifting wing in a tunnel fitted with silencing splitters at both ends. The Quest for Power ... diameter, in which the pressure of the airflow rises at the expense of velocity and Mach number. At the rear of the diffuser, pressure is sufficiently high and velocity low enough to permit the maintenance of stable combustion; the fuel is injected from a nozzle array and the flame held in the airstream—which is still roaring through the engine at high speed—by a flameholder, which is a carefully designed baffle capable of producing a local region of slow-moving turbulence without much loss in total-head pressure. The hot exhaust gases are then expelled through a propulsive nozzle, and the thrust results from an unbalanced longitudinal force on the inner wall of the diffuser. Such is the ramjet, and there is much more to it than the unfortunate appellation "stove-pipe" would suggest. It is a power unit that appears to have been sadly neglected in this country, although many well-known firms are now devoting attention to it. Its applications are widespread. It is suitable for a speed range from Mach 2 until the so-called "heat barrier" rears up at about Mach 6. Primarily of interest for guided-weapon propulsion, the ramjet is also seen as a booster and possibly even a primary power unit for manned intercepters. It is also likely to be of use in the tip-drive of supersonic helicopter-rotors, and it can also be combined with a rocket in a variety of ways, generally with the rocket mounted within the ramjet to help it take-off and to keep the flame alight at very high altitudes. The subsonic ramjet is attractive only on account of its low weight and simplicity, but has already been extensively used for helicopters and target aircraft. Assuming the requirement is for a large ramjet for a long-range missile, the company will back-up a large amount of paper work with the usual rig-testing of models and components. This work will differ from that involved in turbojet development in two main features: the enormous power required will make full-scale ground testing impossible, and an unusual amount of attention will have to be paid to the fuel and control systems. One hypothetical Marquardt ramjet, intended for a ground-to-air weapon designed to cruise at Mach 3 at 80,000ft, has a diameter of 30in and a weight of 1,260 lb. Calculations show that, at the end of the boost phase after six seconds of rocket- assisted flight, the design Mach number of 3 will be reached, and the following data apply: h.p., 370,000; airflow, about 1,000 lb/sec; fuel consumption, 45 lb/sec; stagnation air temperature, 1,100 deg F; and stagnation air pressure, 260 lb/sq in absolute. At the cruising height of 80,000ft these values become: speed Mach 3 (reduced from 2,210 to 2,000 m.p.h.); h.p., 2,000; airflow, about 6 lb/sec; fuel consumption, 0.27 lb/sec; stagna tion air temperature, 780 deg F; and stagnation air pressure, 10.5 lb/sq in absolute. The dominant factor revealed by these figures is the enormous variation in operating conditions for which the engine has to be designed; the fuel flow, for example, varies by 165 :1. A plain, open-mouthed intake with a normally attached shock-wave involves an unacceptable loss in total pressure at Mach numbers above about 1.6, and a double-shock intake is therefore designed, with a streamlined central body mounted concentrically engine-instrument systems, such as a miniaturized tachometer generator which, as it runs filled with oil, can be used in temperatures very much hotter than usual. Another Smiths product is a remote inductor pres sure gauge for liquid pressures up to 200 p.s.i. Smith-Clayton Forge, Ltd., Lincoln, are important suppliers of turbine discs and compressor wheels, which are drop-forged in heat-resistant steels. Smith's Stamping Works (Coventry), Ltd., Ribble Road Works, Humber Avenue, Coventry, turn out large quantities of steel drop-forgings, with the emphasis on high-tempera ture gas-turbine alloys. Solar Aircraft Co., San Diego, Cali fornia, have long specialized in high- temperature problems. Their Solar-amic process for the ceramic coating of metal surfaces is now in world wide use, and is employed in the manufacture of numerous piston en gine exhaust assemblies and is be coming standard in the hottest parts of turbojets—for example, the GE J47 is now able to use poorer-quality alloys owing to the Solaramic coating on the flame tubes and com bustion chambers. Sparcatron, Tuffley Crescent, Glou cester, specialize in spark-machining processes, which are showing re markable savings in the production of all manner of dies and other tool room fields. Super Oil Seals and Gaskets, Ltd., Factory Centre, Birmingham 30, manufacturers of oil seals, rubber mouldings and similar products, also hold British Empire manufacturing and sales rights for American Aero- quip flexible hosing. Taylor, Taylor and Hobson, Ltd., Leicester, are known for their great variety of optical inspection and measuring equipment. Particularly appropriate is a new turbine blade-edge microscope, which enables a 40-times-magnified view of the edge of the blade to be compared accur ately with a master profile. By this means, errors of one-thousandth of an inch are rendered visibly obvious. Tecalemit, Ltd., Plymouth and Brent ford, call themselves "the authority on lubrication," and it is certainly true that almost all our present pro duction aircraft have this company's micro-pumps, oil and fuel niters and elements. Teddington Controls, Ltd., Cefn Coed, Merthyr Tydfil, South Wales, mass-produce an immense amount of equipment directly related to aero engines. Typical examples are the oil cooler anti-surge valve for Mer lin power plants, the thermostatic oil ccoler valve for Heron Gipsy Queen 30 Mk 2s, an engine starter time switch for the Viscount Dart, a starter cartridge selector switch for various aircraft using the Avon, Sap phire and Ghost, a flamestat for the Britannia Proteus jet-pipe, and a wide range of hot-air-handling equip ment. In the last-named field, it may be noted that all of the thou sands of Avons built have Tedding- ton hot-air valves, a typical standard pattern being Type FKH/A/9 for the Swift, with temperature limits of — 55 to 320 deg F, air pressure of 150 lb/sq in, ljin bore, reversible electric actuator with built-in brake, and total weight of 5 lb. On the Canberra a 2in double valve is fitted, while the Vulcan has a big four-way valve, all outlets being of 4in bore. A particularly impressive perform ance is put up by the FKH/A/21 Proteus anti-icing valve, which accepts engine gas at no less a tem perature than 700 deg C. This gas is mixed with intake air by means of a jet pump, and the valve follows Teddington practice in being made of H.R. Crown Max, with a preci sion-fitted carbon sliding gate valve. Owing to the high temperature at which these valves work, remote actuation is used. Teleflex Products, Ltd., Chadwell Heath, Essex, make the well-known series of controls of this name, which go into every R.A.F. "super- priority" aircraft.
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