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Aviation History
1954
1954 - 2203.PDF
176 FLIGHT THE combustion chamber consists of an inner ' chamber and an outer shell. The inner chamber is a mild-steel forging, machined all over and chromium plated. The outer case is cast in aluminium alloy Q.T.D.133, and is made in two portions which fit over the inner chamber. The outer case incorporates an integral scroll along which passes methanol fuel rcgeneratively to cool the inner chamber. A dump valve is also fitted to drain the outer chamber; normally in the open position, it is closed only by the application of full methanol pressure during firing. The gearbox for the pumps is driven by a shaft with two universal couplings which permit limited relative movement between the box and the source of power. The drive Is geared up by an epicyclic gear of about 2.7:1 ratio, the outer annulus of which is normally free to rotate, so isolating the pumps from the input shaft, the latter being driven at all times. When the pilot closes the master switch a nitrogen-operated piston clamps the band clutch, so arresting the rotation of the annulus gear and causing the pumps to rotate. The train of spur gears drives the fuel and oxidant pumps and an oil pump. The liquid-oxygen pump has a fully shrouded centrifugal impeller, cast in phosphor-bronze and machined all over. The case is made of aluminium alloy, with inserted stainless-steel rubbing strips beside the impeller. The seals are either of leather or else of Gaco, which offers the advantage of being proof against special lubricants. The metha- nolfwater pump has an unshrouded steel centrifugal impeller, with a separately made entry helix. PROPELLANT PUMP GEAR BOX DRIVE FLANGE LIQUID OXYGEN PUMP FUEL PUMP Delivery pressure varies between 500 and 700 Ib/sq in. The control valves are, as far as possible, grouped into two compact banks. The valves are nitrogen- operated poppet-type units, with streamline heads and a very low pressure-drop. The valves and pistons are of light alloy, and the seats are of soft aluminium. The gas-sealing packing is of leather. BY-PASS VALVE ARMSTRONG SIDDELEY SN THE term "rocket" is applicable to any device which produces a propulsive jet by the combustion or dissocia tion of one or more fuels, without the combination of oxygen from the atmosphere. Although fundamentally the simplest form of propulsion unit imaginable, the rocket can assume any of a great variety of forms. The simplest unit of all is the solid-fuel rocket of the November 5th variety, in which a rigid case is filled with a combustible mixture containing all the ingredients necessary for the produc tion of the jet. Solid-fuel motors were made by the million for unguided missiles during the 1939-45 period, and are also manu factured for take-off-assistance installations for many types of aircraft and missiles. There is also the liquid-fuel rocket which, according to the size of tank fitted, can have variable burning time—and can also be throttled and shut down. The fuel, or fuels, can conveniendy be fed into the combustion, or reaction, chamber merely by pressurizing the tanks with a sqpply of com pressed air or inert gas. If a rocket is required capable of acceptance for a piloted air craft on the same basis as are the more established forms of aircraft power unit, something more refined is necessary. For example, it is preferable that the fuels should fete fed by pumps; a foolproof control system is a "must"; aiyf it is also highly desirable that the unit should have a hfe,/at least measured in hours and not minutes. / Ignoring the take-off-assistance application, for which a short-duration, expendable unit is adequate rockets can be applied to aircraft either as boosters for limited periods when extra power is needed or else they can be the primary propulsion unit, i.e., the aircraft can be powered solely by the rocket motor. The charac teristics of all rockets are such that, unlike all other forms of aero engine, they provide thrust that does not decrease with increasing altitude; in fact, it actually increases. Consequendy, a rocket can provide an extremely effective booster unit where rate of climb and high-altitude performance are of paramount importance—as they are on all types of fighter aircraft. Rocket- thrust can provide valuable assistance, also, in rapidly accelerating a supersonic aircraft through the speed of sound. Where duration is of minor consequence, there is also a case for the all-rocket fighter; but it is still too early to discuss the applications of rocket motors which are being developed in this country, and the following account must be treated simply as a chronicle of the development of the first British aircraft rocket (except, that is, for assisted take-off units), with a security veil drawn over all that has come after it. , ft was in 1946 that the Ministry of Supply asked Armstrong Siddeley Motors, Ltd., of Coventry, to develop a liquid-fuel rocket motor with a mrust of 2,000 lb for use as a booster unit for fighters. The company began rocket work at the end of thai year, with Mr. S. Allen, the experimental engineer in charge of all combustion research, at the head of the new team. His first two recruits were Mr. D. Hurden and Mr. H. L. G. Sunley. From the outset, the company were working virtually from scratch. The only closely related work going on in Great Britain at that time was that undertaken by the M.o.S. itself, at the R.A.E. out-station at Westcott. The country furthest advanced in the rocket field was certainly Germany, and Mr. Sunley was, in fact, in Germany with the M.o.S. when he joined Armstrong Siddeley. When he returned, he brought with him numerous reports and selected items of research equipment. The company's engineers began by holding discussions with the R.A.E. and with any other organization who had any experience of liquid-fue! rocketry, and these early talks led to the abandonment of kero-sine as the proposed hydrocarbon fuel, the eventual choice being liquid oxygen and a 65/35 per cent mixture of mediyl alcohoi (methanol) and water. Gradually, the form of the new rocket began to crystallize; there was, however, nowhere that these ideas could be put to the test. The development of small combustion chambers was con-
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