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Aviation History
1945
1945 - 2230.PDF
NOVEMBER 8TH, 1945 FLIGHT 5°9 GERMAN LONG-RANGE ROCKET DEVELOPMENT Fig. 1. (Above) Automatic pilot for control in azimuth, pitch and roll.Fig. 2. (Right) Integrating accelero- meter for measuring velocity. Z-Z 2O 1-8 1-6 1-4 J-2 1O O-8 YAWPICK-OFF CENTRALISINC SWITCH AXES CYRO —A-B PENDULUM —C—0CIMBAL —E-F / > / / / A / / / » 0-6 18O 2OO 22O 24O 26O 28O 300 SPECIFIC IMPULSE (LB.-SEC/LB.) Fig. 3. Influence of specific impulse on range, a = 0.67. Weight = 11.24 tons Diameter = 66 inches. Thrust . 5= 2g Initial weight one a receiver transmitter, and the othera receiver for velocity measurement and range control. The velocity wasmeasured by a Doppler effect. Elaborate security arrangements were built into thecircuits to prevent influence by false iIg The radio method was soon droppedin favour of an integrating accelerometer, Fig. 2, which made the rocket inde-pendent of ground control. It consists of a pendulous gyro mounted in gymbalsand operating two sets of contacts whose angular separation can be varied. Thegyro case carries a centralising switch, the leads of which run to a reversibleinduction motor geared to the gymbal. Any deviation from the mid-position ofthe gyro axis causes a torque to be 5 6 7 13 15 A9Y A9Z applied to the gymbal to precess it backagain. Because the centre of gravity of the gyro does not lie on the axis CD,any acceleration of the system parallel to the axis EF, i.e., the rocket axis,will cause precession about this axis at a rate proportional to the acceleration.The angle of precession will be propor- tional to the integral with respect totime of all accelerations, including any component of the earth's gravitationalfield acting in the direction EF. The actual operational range variedwidely, a few rockets travelled as far as 220 miles, but most averaged 180-190miles. Since the main path is parabolic, the height reached will always be abouta quarter of the range. The total time of flight is about five minutes. The highestacceleration reached, which is at " all burnt," when thrust had risen to69,000 1b. and the weight has fallen to 8,900 lb., is just under 8g. The highestvelocity reached is at " all burnt," the rocket is then travelling at 5,000 ft./sec.and it is interesting to note that at this velocity the rocket motor is developingwell over 600,000 horse-power. Effect of a on Range In discussing rocket performance it isuseful to introduce the ratio of fuel weight to total weight, referred to as the" a " of the rocket. The a in the case of the A4 rocket is about 0.69. Varia-tions of o have much more influence, on range, than variations of size; a50 per cent, increase in weight for the same a increasing the range 10 per cent.,whereas only a 2 per cent, changein a produces the same effect. If the2,150 lb. warhead were replaced byfuel, a would have increased to 0.76,and the range to about 350 miles. Fig. 3 shows the influence of thespecific impulse on range; it will be ob- served that an increase from 215 to 298would double the range of the rocket. Improved S: of a given fuel can only behad at the expense of greatly increased working temperatures and pressures ofthe gases in the combustion chamber. The other course to improve range is thechoice of different fuels. Table III gives the specific impulse of a number of fuelscalculated on the basis of working con- ditions corresponding to the venturicharacteristics of the A4 rocket. Most practical values of the S, lies between180-240, but by using hydrogen and oxygen the value could be pushed up towell over 300. The Future The rocket motor, with its lightweight, and its very large thrust per square foot of frontal area, has madeflight at speeds well into the supersonic range possible and a few calculationshave been made to illustrate some pos- sibilities. Starting with the A4 rocket,we have assumed that the warhead is r»- placed by a pressure cabin and pilot. Inaddition, the rocket is fitted with wings; the area being arranged to provide fora landing wing loading of 35 lb./sq. ft. Three cases will be touched briefly. Inthe first, the A4 rocket with wings is fired vertically and controlled in thesame manner as a normal A4 rocket until the top of its trajectory, when the pilottakes over and glides the rocket to the Continued on p. 511) TABLE 111 SPECIFIC IMPULSE OF Ethyl Alcohol and Oxygen Petrol and Oxygen Hydrogen and Oxygen ... Hydrazine Hydrate and Hydrogen Peroxide ... Volume Ratio 1 : 1.15 1 : 1.4 1 :3.2 1 :2.03 K» Com- bustion Tempera- ture 2,780 2,240 2,560 1,750 VARIOUS FUELS h 1.3 1.2 1.2 Molecular Weight 20.0 16.5 8.4 24.0 Specific Impulse 235 224 343 200
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