FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1954
1954 - 0975.PDF
9 April 1954 443 Thermal Control Co., Ltd., Marine Works, Sackville Road, Hove, Sussex, market the Speed Develop ment Company's patented thermo electric continuous re-setting fire de tector, and a range of special pressure switches, H. I. Thompson Co., 1731 Cordova Street, Los Angeles 7, California, make "Refrasil" lightweight, re movable, tailored heat-insulating blankets for various airborne appli cations—such as insulation of the air- bleed manifolds on the Allison J35. Refrasil is made in various forms, but all are based on a heat-resistant fibre capable of maintaining a tem perature-difference of 900 deg F across a half-inch sheet. Thompson Products, Inc., Cleve land 17, Ohio, have so many differ ent products that only a few can be listed. They are probably the world's biggest manufacturers of compressor and turbine blading, and possibly of piston-engine valves as well. Fuel booster pumps are typi cal of another field, the double-ended series being capable of pick ing up fuel from either end under heavy negative-g loads at flows ex- ceding 3,000 gal/hr. Other fuel pumps are driven by the engine, elec trically, or by an air turbine. The fuel pump they manufacture for the American J65 Sapphire turbojet is the Dowty ENG.129, made under licence from the English firm. Thompson Products also have a new Tapco plant, where various cermets (ceramic-and-metal) are being de veloped. One of these, a titanium carbide/metal mix, is hoped to allow gas temperatures in turbojets to rise by as much as 200 to 300 deg F. Applied to matched turbine discs and blades, the new cermet has a ducti lity approaching that of the best metal alloys, and is better above 1,000 deg F. As hard as glass, it can be bent 90 deg over small radius, and resists impacts from foreign bodies in the engine. A year ago, this Tapco plant was delivering 250,000 compressor blades a month using a sintered method with copper as the bond metal. Tungum Sales, Ltd., Brandon House, Painswick Road, Cheltenham, Glos, supply Tungum alloys in all stan dard forms, as well as being tube manipulators and small - part machinists. Ultra Electric, Ltd., Western Avenue, Acton, London, W.3, are one of the principal British suppliers of electric or electronic control systems for turbojets and turboprops. Various systems have been specially designed for such companies as Armstrong Siddeley, de Havilland and Bristol. Most of these units continuously co-relate r.p.m., jet- pipe temperature, fuel flow and other parameters to the position of the pilot's single-lever engine control. United States Navy. At the Naval Experiment Station in Philadelphia a considerable amount of research has been undertaken towards the de velopment of thixotropic (literally "changed by touch") compounds for use as lubricants or inhibitors in stored engines. A typical prepara tion is a half-and-half mixture of a lubricating oil and an unstated formula which turns to a hard gel and sets inside the engine. Thus, it does not drain off, neither is it affected by extended storage even in high ambient temperatures. For depreservation, the engine is turned over slowly by hand and the mere act of moving, shaking or stirring the gel causes the latter to break down and revert to a liquid condition. United Steel Companies, Ltd., 17 Westboume Road, Sheffield 10, have a new gas-turbine steel combining a tensile strength of 40 tons/sq in with favourable welding characteristics. Named "Fortiweld," it is proving highly suitable for a variety of engine welded-sheet assemblies working at 450 to 500 deg C, at which tempera ture it can withstand service stresses two or three times those permissible for mild steel. Vandervell Products, Ltd., Western Avenue, Park Royal, London, W.3, are world-renowned for thin-wall within the intake, forming the first (oblique) shock at its tip. This streamlined body is an obvious place in which to put the fuel pump, controls and other paraphernalia, particularly as its drag is subsonic at all flight Mach numbers, unlike any other part of the engine, or the aircraft to which it is attached. The fuel pump is therefore inserted in the fattest part of the streamlined inner body, driven by a turbine working on ram air. The pump will be approximately 1/300 the weight of an industrial pump of the same capacity; as for the control system, this merely has to be capable of starting or stopping a 400,000 h.p. machine in approximately one second (industrial plant of this capacity, if it existed, would need half a day to bring up to speed). It can be seen, therefore, that the development problems of really useful ramjets are very great. Just to make matters worse, flexibility in operation can be obtained only if the length of the intake cone and the area of the propelling nozzle are both made adjustable. The whole unit has to be made of materials suitable for the temperatures involved and—remembering that the stagnation air temperature has been quoted above as 1,100 deg F—it appears doubtful if any cooling can be provided for longer than a few seconds' duration. Again, as the power/weight ratio of the engine is about 300 h.p./lb, the whole unit is subject to extremely violent vibration and acceleration loads. There is only one way to tackle a problem of this magnitude—crudely, to "suck it and see." Once material-testing and the development of the pump, control systems, burners and flameholders has been taken as far as possible on the ground, there is no short-cut around full-scale flight testing. Such a procedure will be expensive, even with a recoverable test-vehicle. But it has been done a thousand times across the Atlantic, and sooner or later we shall follow suit. ROCKETS. Large-scale production of rocket motors is already a requirement, both for assisted-take-off and also for use as primary or combat propulsion of various types of manned and pilotless aircraft. These motors form a propulsive jet by the dissociation or combustion of one or more liquid fuels; solid-fuel motors can be ignored for such applications as their endurance is too limited. The fuels contain everything which is needed to form the jet and consequently rockets (unlike air- breathing engines) can function independently of the earth's atmosphere; at the same time their fuel consumption is very high compared with that of engines which extract oxygen from the air. The initial requirement will state the thrust, minimum duration and probably the type of fuel to be used. A wide choice of fuels is available, although it is narrowed down considerably where the motor is intended for a manned aircraft. For the sake of argument it is assumed that an a.t.o. motor is to be developed, running on the dissociation of hydrogen peroxide, with hydrocarbon fuel added from the aircraft tanks. The original design-work is fairly straightforward, and is split among sections responsible for the mechanical design, fuel and starting system and combustion chamber. The company can, from the thrust requirement, immediately work out the necessary flow of the propellants specified, and can quite rapidly get a good idea of the combustion chamber pressures and temperatures which will be required. The characteristic length of the chamber (the length of a chamber of the same volume as that to be used but with a uniform cross-section area equal to that of the nozzle throat) is determined. Much calculation is then needed to see how slight variations in chamber shape would affect performance. It is probable that several chambers will be built, all slightly different, and initially tested with water to ensure that they can withstand the combustion pressure. The fuel system is also worked out and this is similarly examined using water as the pumped medium. This technique gives results almost indistinguishable from those which would be obtained with the correct fuel and saves a lot of expense and trouble, for it must be remembered that modern rocket fuel systems have enormous capacity and even a few seconds of rig-testing might require up to several hundred pounds of fuel. Probably most of the work will be devoted to the control system, which must be precise and foolproof. And if the motor is designed to be responsive to a throttle right down to about ten per cent of full thrust the company will have a real job on their hands. Eventually a complete motor is set up in the test bed. It will probably look rather a mess, for the components will not only be covered with test leads, but will be more spread out than in the other prototype motors which will follow. It is also likely that many of the parts will be left very rough, with plenty of metal on them, so that as the behaviour of the engine becomes known the excess can be pared off and the whole unit made much lighter and more presentable. At this stage of testing it is also possible that the fuel pump (which may be driven by a permanganate-turbine unit) will not be ready, so that fuel will have to be pumped in by a separate engine—and there are rocket fuel pumps requiring a drive power exceeding 1,500 h.p. The initial firing will be carried out cold, i.e. the peroxide will merely be pumped through a catalyst and dissociated at a relatively low temperature. These runs should give about half the design-thrust and, if all goes well, the hydrocarbon fuel will gradually be worked in until the motor is giving full thrust at top temperature. But trouble is certain to be met. Strain-gauging and thermocouples may show that excessive local temperatures are dangerously weakening the strength of the chamber. Various solutions present them selves : either increased cooling can be provided, or the heat-absorbing capacity of the chamber can be increased by thickening the walls, or the chamber can be lined with a ceramic or other refractory. The trouble is that those substances most resistant to extreme temperatures are usually poor from the heat-conductive viewpoint, so that if full
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
