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Aviation History
1945
1945 - 2227.PDF
FLIGHT NOVEMBER 8TH, 1945 German Long-range Rocket Development* Fuel and ContratjSystems ojJyl : Futur&^ossibilities Bj/W. G. iG, F.I <£ n 1OUS rocket development Jfras started in Germany in the yiars 1929-1930 by a few groups of gri- vate inventors. This work attract! the attention of the Army Weapons Group in 1933, and in 1937-1938 a special research and development station was set up at Peenemunde at the cost of 300 million marks. Work was started on a range of rockets which they designated Ai to Aio, only one of which, A4 or as we know it V2, ever being used operationally. The V2 rocket was the product of Prof. V. von Braun and his collaborators. He compares the present stage of develop- ment with that reached by aircraft in the 1914-18 war. Early work began in 1933, when the A1 rocket was designed. This weighed about 330 lb. and was followed in 1934 by A2, which reached a height of 6,500ft. Developments on A3 started in 1938. It weighed 1,650 lb., was 25ft. long, and about 2.5ft. diameter. Fitted with a power unit developing a thrust of 3,300 1b. for 45 seconds, it reached a height of nearly 40,000ft., while it had a range of about 11 miles when launched at an angle. Work on A4 commenced about 1940. Firings commenced in July, 1942, and the first success was in October, 1942, when the fourth to be launched flew a distance of 170 miles. Orders for the production of the A4 rocket in quantity were given at the end of 1942, and the first attacks against thi* country started in Sep- tember, 1944. Information was, however, in our hands well in advance of this date. During the development which followed, well over a hundred rockets were fired, and although at the end of this period break-ups were less frequent, failures still did occur to some 15-20 per cent, of the rockets fired. TABLE (.—LEADING PARTICULARS OF THE A4 ROCKET Lengths Overall 46ft. Warhead : ... 5ft. flin. Instrument b?.y ..." 4ft. 8in. Fuel compartment 20ft. 3.5in. Power bay (including Venturi) 14ft. 7.5in. Diameters Maximum diameter of body 5ft. 5.3in. Diameter over fins ... lift. 8in. Weights Total loaded weight 12.5 tons. Warhead (with Amatol filling) 2,150 Ib. Structure 3,865 1b. Power unit 2,235 1b. Equipment 6501b. Main fuels (tanks full) 19,310 Ib. Auxiliary fuels 400 Ib. The leading partujp^of^ set out in Table I. ^pies the nose of thp#-rocJEet and Smediately behind thg^wjfxhead/ are the plain ciiiilinj iuwlTiniii nl and radioequipment. Tiie main fuels are carried in two large light alloy tanks occupyingthe central compartment of the rocket. There are two fuels, one «, ^5 per cent,solution of ethyl alcohol in water, occupying the forward tank, and theother liquid oxygen. The rocket is propelled by a jet of hotgases resulting from the combustion of the two fuels in a chamber which formsthe front end of the venturi. The fuels are pumped under pressure into thisspace by two turbine-driven centrifugal pumps, the turbine being driven by ahydrogen peroxide-permanganate system. The performance of the turbine andpumps under operating conditions are set out in Table II. Pressurised Tanks Both main tanks are pressurised toabout 1.4 atmospheres, to assist the pumps and to prevent the tanks collaps-ing. The liquid oxygen is fed to eighteen brass roses at the base of cups formedon the end face of the combustion cham- ber. -The alcohol is pumped to a cool-ing jacket which surrounds the propul- sive nozzle of the convergent-divergenttype. Finally it is led to the burner cups, where it discharges through a ringof small nozzles and mixes with the liquid oxygen. A small amount ofalcohol is fed into the venturi through rings of small holes drilled at severalpositions along its length, thus providing some degree of internal wall cooling.Examination has shown that the skin temperatures on the inner surface havenot exceeded i,ooo° C. The fuel used in the A4 rocket has aspecific impulse of about. 220 -under ground operating conditions; conse-quently the velocity of discharge of the gases is about 7,000 ft./sec, and since275 ]b. of fuel are burnt every second, the thrust developed by the rocket willbe about 60,000 lb. The rocket is placed empty in the vertical position and thenfilled with fuels in the following order:— (1) Alcohol. (2) Hydrogen per-oxide. (3) Liquid oxygen. (4) Per- manganate. Thf filling operation takes 12 minutesand was one of the last operations, as 4.5 lb. of oxygen per minute were lostby evaporation if left standing. When the firing torch is alight, the main fuelvalves are opened and 20 to 30 lb. of alcohol and oxygen per second are fedby gravity to the combustion chamber and ignited. Combustion is maintainedfor a few seconds until an observer is assured conditions are satisfactory. Hethen starts up the flow of auxiliary fuel, * Lecture delivered before 'the Royal Aeronautical Society, November 1st, 1945. (Abstract) TABLE II.—PERFORMANCE DETAILS OF A4 ROCKET PROPULSION SYSTEM Turbine Mean diameter of blades and nozzles ... I8.5in. Main flow through turbine 3.5 Ib./sec. Working pressure 330 li./in.2 Turbine back pressure ... l.6lb./in.' Estimated power at 5,000 r.p.m ... 680 h.p. Endurance at 3.5 Ib./sec. ... 113 sees. Oxygen Pump Overall impeller diameter 10.' [.. Flow at 5,000 r.p.m 160 Ib. . --i H.P. at 5,000 r.p.m 320 Delivery pressure 350 Ib./in." Alcohol Pump Overall impeller diameter l3.4Sin. Flow at 5,000 r.p.m 125 Ib./sec. H.P. at 5,000 r.p.m 360 Delivery pressure ... 370 Ib./in.2 Assuming 5 per cent, of alcohol used inefficiently as coolant, and 5 per cent, returned by spill valve to lower pressure side of pump :— Total fuel delivered to combustion chamber 275 Ib./sec. Specific thrust 220 Ib./sec. Total thrust 60,000 1b. Capacity of main tanks ... 19,300 Ib. Endurance at full flow (approx.) ... 70 sees. the turbine is started and reaches fullspeed in about 3 seconds. The flow of the main fuels increases, thrust buildsup and soon exceeds the weight, causing the rocket to commence its verticalascent, the whole operation, from firing the torch to full thrust, taking only from7 to 10 seconds. Control For maximum range it is necessary toturn the rocket on to ita course and rotate it from the vertical until it takesup an angle of about 400 to 450 to the horizontal by the time it has reachedthe "all burnt" stage, i.e., after 60 seconds' flight. To control the motionof the rocket in azimuth, roll and pitch, J an automatic pilot was fitted. One iorra.mFig. r, comprised two electrically driven gyros, one with its axis along the axisof the rocket, and the. other with its. axis perpendicular to the axis of the rocketand to the plane containing' the target. This second gyro detects the roll andyaw of the rocket, but is unaffected by the pitching motion; the roll and yawis measured by means of two fine-wire potentiometers, and their outputs, afterpassing through an electronic amplifier, operate the control vanes. The other gyro provides a pitch con-trol, and during flight is made to precesH towards the horizontal in the roll andyaw plane. The movement is detected by means of a fine-wire potentiometer:the output from the potentiometer is fed into an amplifier and operates the con-trol vanes through their appropriate servos. The pitch control unit consistsof live independently adjustable resist- ances in series with the pitch discrimin-ator coil. Four of these resistances are initially shorted, and as they are broughtin successively, give five different rates of precession. Early rockets contained two radio sets,
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