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Aviation History
1950
1950 - 0242.PDF
158 FLIGHT, PRESSURE REDUCING VALVE (AIR) EROXDE AIR-DISTRIBUTOR VALVE CATALYST AR-DISTRIBUTOR VALVE AH FILLING PCUNT CATALYST FILLING POINT SPRITE ROCKET . . . petrol or paraffin, in conjunction with an oxydizer such as hydrogen peroxide (although, in point of fact, liquid oxygen was used in the V-2). The function of the oxydizer is simply to provide a source of oxygen sufficient to sup- port combustion, and in this connection the development of hydrogen peroxide at high concentrations was a valuable step toward making the liquid-fuel rocket a more practical proposition. It is perhaps apposite here to remark on the curiously laggard-like attitude of our "military scientists" towards rockets in the past and, indeed, to some extent, in the present. Certainly, the German interest in rockets was common knowledge over here from as far back as the early twenties, and much as one might have detested the V-2 from actual experience of having lived in their target area, the fact that the weapon was a major scientific achievement must be recognized and our late enemies be given every credit for pursuing their unique researches to so terrifyingly efficient a conclusion. What is not generally known is that, ironically, highly concentrated hydrogen peroxide was developed in this country before the war (concurrently with, yet quite independently of, the similar German development), but when our authorities were apprized of it they exhibited a myopic lack of interest. The Sprite owes its existence to the fact that de Havil- lands have always paid close attention to all developments which show any likelihood of attaining real significance in aviation. Thus it was that, in view of the German advances in the design of rocket propulsion, Major Halford set up a special-project section under the leadership of Mr. A. V. Cleaver, whose task was the evaluation of the various known forms of aircraft rocket and the develop- ment of units for manufacture by the de Havilland Engine Company. Initially, the special-project section concerned itself only with the most general study of the possibilities of rocket propulsion for aircraft based, in the first instance, on the extensive German data and experience. It soon became clear, however, that the hydrogen-peroxide cold rocket was simple and reliable and offered the most promising prospect for the evolution of comparatively simple units like the Sprite ; it was, in addition, an essential stage in the wider programme of rocket research upon which the de Havilland Engine Company has embarked. In a cold rocket, such as the Sprite, the oxydizer is itself the fuel and all that is required in addition to the Port (left) and starboard (above) views of valve units and control gear, showing relative dispositions and internal construction. concentrated peroxide is a catalyst. The chemical formula for hydrogen peroxide is H,Oj, which is only another way of saying that each molecule of peroxide is made up of two atoms of hydrogen and two atoms of oxygen. A catalyst is simply a substance which, when brought into contact with the main substance (in this case the hydrogen peroxide) causes the latter to undergo a molecular change, or decompose. There are a number of catalysts for hydrogen peroxide; for example, among the metals platinum, silver and lead are extremely good, and copper is fairly active; mild steel, on the other hand, has a low catalytic efficiency, whilst stainless steel is almost inert and pure aluminium is 99.99 per cent inert. It is, of course, their catalytic reactive qualities as well as mechanical properties that have determined the materials used in the construction of the Sprite. In general, stainless steel has been used throughout, the only major disparities being the air bottles, which are of high-tensile steel, and the control valves, which employ duralumin bodies and ordinary steel internal components. The catalyst used in the Sprite at the present time is either calcium permanganate or sodium, permanganate at a concentration of 50 per cent by weight with water (the peroxide concentration is 80 per cent by weight with water). The function of the catalyst can conveniently be illus- trated in the manner shown in the accompanying diagram. At A are shown two peroxide molecules, each composed of two hydrogen atoms and two oxygen atoms. When these molecules come into contact with the permanganate catalyst, the two hydrogen atoms and one of the oxygen atoms in each molecule break away to form molecules of water (as at B) whilst the spare oxygen atoms of the original peroxide molecules pair off to become a molecule of oxygen. Necessarily, this change of molecular state liberates energy and it is this energy in the form of heat that turns the molecules of water into steam. The heat generated is, however, greateV than that required merely to turn the water molecules into steam and this excess is used to expand the molecules, with the result that they issue from the reaction chamber through the outlet nozzle as a high-velocity stream, the thrust being derived in accordance with momentum laws. The pressure generated in the reaction chamber of the Sprite is approximately 300 lb/sq in, and the temperature—as already noted—is of the order of 480 deg C, whilst the jet velocity is in the region of 3,500 ft/sec. A good deal of misapprehension is current concerning the dangers and difficulties of handling hydrogen peroxide
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