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Aviation History
1954
1954 - 2205.PDF
178 ARMSTRONG SIDDELEY SNARLER . . . FLIGHT, 6 August 1954 kis specially prepared display exhibit showed the Snarler in an early fprm, with the igniter screwed into the upper part of the combustion chamber. The components were grouped together for convenience. ignition by means pf a small solid charge in a steel case, screwed into the "Bucket" and fired electrically. The rig was mounted in a sandbagged enclosure with mirror vision, control being effected from a portable box removed to the safety of a hangar. Liquid oxygen and methanol were fed under nitrogen pressure from tanks of about five gallons capacity. The feed-pipes had pressure-sensitive elements, and electric break-wires were stretched across the chamber itself, so that the light-up time could t>e measured electrically. Later, the same rig was used to develop the real igniter, which was virtually a miniature rocket lit by an ordinary K-L.G. sparking plug, the aim being the production of a slim pencil of flame at all altitudes. The production-type igniter, shown in the large drawing over leaf, was finally perfected in the company's rocket test house. The erection of a proper test house was at this stage essential to further progress. The site was chosen at the company's airfield at Ansty, and the work was finished during 1947. During that year the rocket staff moved out of the main Parkside works and all rocket development has since been concentrated at Ansty. The first test-bed is shown in the plan on p. 180, and the photo graph below shows a very early combustion chamber mounted in it for a test. The bed was based on a concrete plinth and con sisted of a simple iron trolley mounted on retaining rails and constrained longitudinally by a thrust-meter. A light roof was erected over the actual test-bed, and the remainder of the build ing was roofed with heavy reinforced concrete. It was decided that the new motor, which had by this time been named Snarler, should be pump-fed; with the exception of the short-life German A-4 (V-2) missile, nearly all previous liquid-oxygen motors had been supplied with fuel by pressurizing the tanks, and it was soon apparent that the development of a suitable pump was going to be one of the most difficult tasks that the Snarler engineers would have to face. In fact, it seemed that, if full firing trials were delayed until the pump was ready, much valuable running time would be lost. A search for pressurized tanks was therefore instituted, and it was a very difficult matter to get tanks of the required size which could accept 400 to 500 Ib/sq in. Eventually, tanks for both fuels were obtained from the British Oxygen Company, and these formed the first service tanks. The feed, by compressed nitrogen, allowed a 30-second run at about half thrust, the eventual aim being full-thrust runs of three minutes* duration. During the autumn of 1947, parts of the Snarler combustion One of the very first Snarler development chambers is here seen mounted in the test house, which had then (November 1947) just been completed. chamber were manufactured from the initial drawings (the design being still very much on an experimental basis) and these were inspected, assembled, mounted on the test-bed and, on Novem ber 10th, 1947, fired for the first time. The initial trials were quite successful, and no mishap occurred. Incidentally, the Snarler produces a bright flame six to ten feet in length, and shock diamonds in the jet are visible in the heading photograph. The noise is intense. Before this stage was reached the company had already made some progress in developing a pump for the liquid oxygen. It was a trying task, and the company were almost entirely on their own. The chief troubles were in the bearings and the sealing glands; the pump of the German A-4 missile employed plain bronze bearings and bad a very short life, but this was per missible owing to the fact that the design life of this pump was les^ than two minutes. For the Snarler, a very reliable, long-life pump was required, engineered to the highest aircraft standards, and of necessity turning at high r.p.m. in order to obtain sufficient output while maintaining the smallest possible dimensions. A problem arose from the fact that liquid oxygen may com bine with all fatty materials or mineral oils when the two are brought into contact under pressure. Intense cold was another factor; the liquid oxygen impeller at less than —183 deg C was directly coupled to. the oil-lubricated ball bearings, and the latter frequently froze during development, making torque-estimation difficult. Unorthodox measures were therefore taken in the design of the pump. It was decided to employ an unlubricated roller bear ing—made by Armstrong Siddeley—separated from lubricated ball bearings by sealing glands and slinger rings. The roller bearing, a stainless-steel assembly, acted mainly as a steady, taking only limited journal loads; most of the work was done by the lubricated ball bearings. The two glands which eventually proved adequate' were quite simple rings of water-dressed bees wax leather (i.e., leather from which all natural fat was absent) axially loaded by springs. One of the most spectacular results of the many snags encountered occurred soon after pump-running was started. The first liquid-oxygen pump was of all-aluminium construction, to save weight; it was put on an electric-motor drive and the liquid oxygen was circulated through flowmeters. After a short time, the whole pump exploded with fa brilliant white flash and a dense cloud of vapour. Subsequently it was established that a bearing had failed, allowing the shaft to move axially and causing the centrifugal impeller to rub in its casing. The combination of MAIN OUTLET IGNITER VALVE STOP VALVE BY-PASS VALVE MAIN INLET There are two combined valves, one for liquid oxygen and one for the fuel- Each incorporates air- (or nitrogen-) operated poppet valves, with stream lined heads; they are so designed to minimize pressure-drop.
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