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Aviation History
1952
1952 - 0347.PDF
Transferring hydrogen peroxide, by hand pump, from the main storage tanks to a refuelling trailer. The operators are wearing P.V.C. overalls and water from the hose in the foreground is allowed to flood the floor. Refuelling a bench-mounted de Havilland Sprite rocket motor. The operator is attaching the trailer hose to the filler connection under the Sprite's peroxide tank; the adjacent union it the peroxide dump valve. HANDLING HYDROGEN PEROXIDE Characteristics of a "New" Fuel: How the D.H. Sprite is Serviced BEFORE World War II, aircraft-engine fuel was invariably petrol, and quite ordinary petrol. During the last decade, however, numerous new fluids have become familiar to air craft servicing crews—first came special high-octane petrols for heavily boosted piston engines; then methanol as an anti-detonant; nitrous oxide as a detonant and oxidant; and kerosene for gas tur bines. Now hydrogen peroxide is coming into the picture, for use in rocket units. There is little published information concerning the bulk-handling of this chemical in high concentrations, since the aqueous solutions used for medicinal, cosmetic and industrial pur poses are rarely of a higher concentration than 30 per cent.The peroxide used in rocket units is generally of some 80 or 90 per cent strength, and requires special precautions in handling. Any rocket must, by definition, carry all the materials which form the jet efflux—typically, a fuel and an oxidant. Hydrogen peroxide is usually used as the oxidant, in conjunction with, per haps, petrol or alcohol. In the de Havilland Sprite A.T.O. unit, only hydrogen peroxide is used by so-called cold reaction (500 deg C), its decomposition being accelerated by the use of a catalyst. For the past two years, hydrogen peroxide has been handled in high concentration, and on a fairly large scale, by the de Havilland Company. It is a clear liquid, and is physically very similar to water, although denser (S.G. 1.35 at 80 per cent strength). Its manufacture in high purity (no easy task) has been undertaken in this country by the Laporte Chemical Co., of Luton, who, had a demand arisen in this country earlier, could have supplied high-strength peroxide as soon as their German competitors. The liquid decreases in strength, by some 1 per cent per year if it is perfectly stored, or by a greater amount in the tropics. This decomposition to water and oxygen liberates heat, but not so quickly as to cause danger or difficulty. This break-up is accelerated by contact with a number of metals, notably lead and copper. Unless specially prepared, steels and light alloys generally tend to act as mild catalysts; pure aluminium is quite inert. In this con nection, it may be stressed that the dominant factor is the effect of the metal on the peroxide, not vice versa, although hydrogen peroxide is mildly corrosive to many substances. The most suitable materials for storage tanks are pure alu minium, stainless steel, or an acceptable plastic. Tanks should generally be vented to permit the escape of the evolved oxygen, and a fine filter should be provided in the vent to trap dust and insects. Any hydrogen peroxide storage-site should always have a plentiful supply of water available, since the peroxide becomes innocuous from all standpoints when diluted below 50 per cent. A fire risk is introduced by the fact that the peroxide will decom pose rapidly, with the evolution of oxygen and heat, if allowed to drip on to organic matter; this characteristic is the more dan gerous by reason of the time-lag which may take place before lire actually occurs. The best guard against such an event is the main tenance of scrupulous cleanliness. A further practice to be recommended is the use of self-sealing hoses, in order to keep the fluid "contained" during all trans ference operations. This, as the photographs show, is the proce dure adopted in refuelling Sprite units. The peroxide is hand- pumped into a refuelling trailer, from which it is transferred to the rocket-unit by lightly pressurizing the trailer-tank; only just enough to fill the Sprite is dealt with at one time, to eliminate over filling. Splashes of concentrated peroxide can be painful to the skin, but are not dangerous. In any case, say de Havillands, use of P.V.C. plastic overalls and gloves should afford complete protec tion. In this connection, Mr. A. V. Cleaver, the company's special projects engineer responsible for the development of the Sprite, has recorded the only untoward incident that has so far arisen from the use of hydrogen peroxide at Hatfield: an assistant without overalls succeeded in setting fire to his trousers. Whether he adopted the time-honoured remedy of sitting in a bucket of water is not stated. INFORMATION, PLEASE! IT has been said that the possession of knowledge is less useful than knowing where the information may be found. Aero nautical engineers who follow this doctrine can supplement the facilities offered by the aviation Press and their own reference- books by utilizing two comprehensive information services. One is the Index Aeronauticus—the monthly review of technical articles compiled and issued by the Ministry of Supply. To quote from the introduction to each issue, "the primary purpose of Index Aeronauticus is to draw attention to articles of value in the world's technical Press in connection with aeronautical research, development, production and operation. Only notices of excep tional interest are selected. . . . Vol. 8, No. 1 (January, 1952) contains classified abstracts from some two hundred recently published reports and articles, together with an index to the issues for the preceding six months. The Technical Information Bureau of the Ministry also prepares translations and biblio graphies which are generally held available for reference or for transmission upon demand. In exceptional cases, the original abstracting publication is also on loan, for brief periods. Enquiries concerning the index should be addressed to: The Secretary, Ministry of Supply, Dept. TPA3/TIB, Thames House, Millbank, London, S.W.i. The second source of information is Aslib—the organization formerly known as the Association of Special Libraries and Information Bureau (the "Bureau," we note, is officially singular). The Department of Scientific and Industrial Research, which maintains Aslib, has recently made a special grant in order to establish a consultant service. This is now available to advise those who are considering the establishment of special libraries and information services, and to assist the development of existing facilities. Details can be obtained from the Director, Aslib. 4 Palace Gate, London W.8. GAS-TURBINE STEELS IN the third edition of their periodical publication Enchiridion, Firth-Vickers Stainless Steels, Ltd., mention their creep- resistant gas-turbine alloys. Firth-Vickers 326 and 337 steels have been used in various forms, from blade stampings to large rotor forgings. Rex 448 is a new ferritic steel, particularly suitable for aircraft turbines, where temperatures are not sufficiently high to warrant the use of an austenitic steel. Rex 467, another recent development, is an austcnitic steel with, it is stated, extremely good creep-resistance, in spite of the fact that it does not include the scarcer and more expensive alloying elements upon which high creep-resistance usually depends.
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