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Aviation History
1954
1954 - 2208.PDF
FLIGHT 6 August 1954 REDUCING VALVES 179* COOLING SWITCH IGNITER CHAMBER DUMP VALVE In purely diagrammatic form, this drawing shows the control system and fuelfoxidant supply adopted on the flight Snarler. The principle of operation is described in the text. ARMSTRONG SIDDELEY SNARLER . liquid oxygen, aluminium powder and friction heat did the rest. This was in January 1949. Bearing trouble became so acute that each new idea was tried on a rig before being introduced to the pump itself. A plastic bearing was considered at one stage, with a filling mainly of asbestos; it failed rapidly, and the heat generated sheared the heavy steel shaft clean across. However, the metal-explosion trouble was eventually cured by making the impeller of bronze and running it in a case faced with thin discs of stainless steel. These inert materials proved quite compatible, as was established when the redesigned pump was stripped after an actual firing; the bearing had failed early and had disappeared completely, all journal loads thereafter being taken by the impeller. The next milestone was the first genuine run of the rocket with the fuel pump, the date being February 23rd, 1949. The nucleus of the eventual Snarler aircraft rocket had then been developed, and most of the remaining work centred on the control system. At this point, it is worth noting that a liquid-fuel rocket is (like a gas turbine) capable of being broken down into basic com ponents, each of which can be developed on its own and matched to the remainder to form the whole, and the final aircraft installa tion is extremely flexible as a result. For example, so long as the combustion chamber is put somewhere at the tail of the aircraft the remaining units can be disposed in any convenient part of the airframe. It is, therefore, practically impossible to illustrate an actual rocket motor installation of this type, and neither can the company show one for display purposes; the best that can be done is to group all the components into a compact mass, and this has been done by Armstrong Siddeley with their display Snarler, and by our artist (p. 176-177). During all the development trials of the combustion chamber, ignition system and pumps, separate switches had been used for each control service. For an aircraft installation, a total of two control switches, or levers, was considered to be the acceptable maximum. Primarily, the system has to ensure that, in the starting cycle, nothing can happen unless the preceding opera tion has been completed. How this can be achieved can be seen quite readily, each part of the system being fitted with a pressure- sensitive switch which triggers the electrical circuit to open the valve for the next part of the starting cycle. The starting cycle is preceded (in an aircraft installation) by the pilot opening the liquid oxygen suction valve—if convenient, this can be done while the lox* tank is still being filled, so reducing loss by evaporation. Opening this valve permits lox to circulate, under gravity, from the tank to the pump, through the centri fugal impeller, to a by-pass valve near the combustion chamber, and then back to the tank. After a short period the whole lox system is cooled down almost to the temperature of the fluid, a fact rendered obvious by the appearance of frost on the lagged pipes. If this were not done, the blue-tinted fluid would * This is a convenient American abbreviation; some firms use "LOi" 2.500 2,000 1,500 1,000 10 11 NENE SPEED (r.pm 12 x 1000) (Left) Variation of thrust of the flight Snarler with pump speed and altitude. g • 4 (- FUEL-<, L02—* FUEL^i: yagf 8 < "^^ „»' 1 1 FLIGH IMPROVE 9 1 n T MOTOR D MOTOR 1 1 IFULL TTHRUST R0TTLED 2 15 ENGINE SPEED (r.p.m. x 1,000) On the fight is shown variation of propellant consumption and combustion chamber pressure with pump speed. In the upper drawing the "LO2" symbol is used for liquid oxygen. 300 200 100 0 1 1 i 1 1 3 1 THf THR0TTL 1 1 L UST •D 2 13 ENGINE SPEED(r.p.m.x 1000)
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