German Explosives
German Rockets
Introduction
General
The value of the rocket as a weapon of war has been proved during the conflict of the past 5 years. Even with the vast amount of work that has been done on the rocket during this war, there is a great deal of work still to be done in perfecting it. During the past few years research work in this field has brought about the following improvements over the old types:
1. The accuracy has been increased by rotating the projectile. This is effected by using skew venturi. The rotations developed range between 1,000 and 1,500 r.p.m. and considerably reduce the deviations of the projectile due to the influence of the wind.
2. The range has been increased by using a greater weight of propellant in addition to the development of a new powder: Nitrodiglycol. This new powder is more efficient than black powder and results in greater range and less smoke formation on firing.
3. Multibarrel projectors carrying up to 42 rounds have been developed by the Germans to effect a greater rate of fire. Reloading these new projectors is carried out mechanically.
When these first new efforts proved successful, great new exertions were made on the part of the Germans to develop more effective rocket weapons: rocket-propelled depth charges, anti-tank weapons, anti-aircraft rockets, flares, and aircraft bombs with rocket propulsion were tried out; and at the peak of the research program came the radio-controlled long range rocket which was still under development at the end of the war in Europe.
Solid Fuel Rockets
The following is a brief resume on the construction of the rocket at the beginning of this war. The rocket motor consists of the combustion chamber sealed at one end and the base plate which threads into the open end of the combustion chamber. The base plate has a series of holes in it, some of which are parallel to the axis of the rocket and some of which are inclined 45 degrees to the axis.
Propellant. The propellant used at this time is the solid nitrodiglycol type. Its advantage lies in the high calorific value and smokelessness, also in the slow rate of burning. Its density is 1.5 kg/m^3, which is less than black powder, but this is compensated by the higher calorific value. The range for an 8.6 cm rocket using this type of propellant is 1,200 meters. Maximum velocity is 200 m/sec with a burning time of 5 seconds. This is not considered very good performance and so the rocket is used only against low level attacks.
As long as long range is not required, powder may be used for rocket propulsion. It must, however, be remembered that powder rockets are heavy (heavy combustion chamber) and that the charge/weight ratio is small. An attempt might therefore be made to develop powder rockets o flight construction, by using some arrangements for reloading the combustion chamber so that a larger weight of propellant may be carried. This should increase the range. Experiments on these lines have been carried out in Germany, but it was found that in order to insure reliable operation, the constructional complications became very great. This reduces use of the main advantages of rockets - less weight and simple construction.
Stabilization. The foundation for the method of stabilization was the spinning shell. By placing the ventureis askew to the main axis of the rocket produced a sufficient spin. This action gives rise to a gyroscope effect and tends to resist all external disturbing forces. This method has given very good results and is greatly superior to the fin stabilization, which is inherently subject to wind errors.
Liquid Fuel Rockets
The liquid fuel rockets are superior to power rockets as regards to:
1. Weight ratio of the propellant carried.
2. Greater energy available in the liquid propellant.
Liquid Propellant. For example, when 5 gm of powder is required for an impulse of 1 kg/sec, only 0.3 to 0.4 gm of hydrogen-oxygen mixture is required for the same impulse. It will be seen that there is, in this case, a vast difference in the energy content of the propellant, moreover, the density of the liquid fuels is far greater than that of powder. The time of burning is increased, greater velocity is reached, and altogether the advantage lies in much lighter construction, i.e., deadweight of the rocket, since the fuel and oxygen containers can be made of thin steel sheet. The combustion chamber also becomes lighter.
However, the load on the combustion chamber becomes a problem, because of the greater energy and therefore higher temperatures; but this problem was solved. Combustion temperatures for powder rockets are approximately 980 to 1,000 degrees Celsius; they are 3,000 to 4,000 degrees Celsius for oxygen-hydrogen mixtures, and in addition there is the boiling point of the mixture, the boiling points for hydrogen and oxygen being 253 and 183 degrees Celsius respectively. These temperatures make severe demands on the material, and it is necessary to look for new alloys which can withstand these demands.
It is, of course, possible to consider other fuels than a hydrogen-oxygen mixture, e.g., petrol, benzol, methyl alcohol, petroleum, spirit, etc., together with liquid-oxygen. These fuels have the advantage of a high boiling point and do not require special materials for the tanks; these are only needed for the oxygen.
Fuel Tanks. For the hydrogen and oxygen containers, for example, it is possible to use an alloyed steel, covered with a thin lead coating; if the rocket is to be used only once. At low temperatures (-183 to -253 degrees Celsius), all metals except copper become hard and brittle; however, copper remains ductile even down to such temperatures, and is therefore the best material to use for the fuel tanks.
The containers for liquid fuels at temperatures lower than -160 degrees Celsius are best made spherical (e.g., V-1), since this form offers the greatest strength. They must be insulated, but this offers no difficulties.
PC 1400 FX Radio-Controlled Glider Bomb
Overall Length: 130 inches
Length of the Control Unit Housing: 16 inches
Length of Fins at the Root: 31 and 5/8 inches
Length of Fins at Outer Edge: 18 and 1/4 inches
Length of Fin Leading Edge: 18 and 5/8 inches
Max. Width of Tail Unit: 48 inches
Min. Width of Tail Unit: 33 and 3/4 inches
Span of the Fins: 58 and 3/4 inches
Weight of Filling: 270 kilograms
Total Weight: 1,650 kilograms (approx.)
General Description: The PC 1400 FX is a radio-controlled glider bomb designed for attack against capital ships or similar targets. The complete missile consists of three distinct units: the H.E. armour piercing warhead, the control unit housing, and the tail assembly. There are four aluminum alloy fins secured ot the missile at approximately the center of gravity. The purpose of these fins is to give the bomb sufficient lift so that the control surfaces in the tail unit can exercise adequate influence.
Warhead: The warhead is an ordinary PC 1400kg bomb to which four above-mentioned fins have been attached. It has one transverse fuze pocket located aft the H-type suspension lug. Two horizontal exploder tubes are centered in the warhead to insure high order detonation on impact. The usual filling for the warhead is 50/50 amatol.
Control Unit Housing: The control unit housing, made of cast magnesium alloy, is attached between the base of the H.E. warhead and the tail unit. This space contains the gyroscopes, radio receiver, power source, and a small demolition charge for destruction of the control unit.
There are two gyroscopes mounted 90 degrees to each other in the after section of the control unit. These two gyros control the stabilizing flaps on two of the tail surfaces.
The directional apparatus consists of the radio receiver and the servo motors which take the impulses from the radio. The power source is a 24-volt battery. This equipment operates four control surfaces measuring 8 cm by 1 and 1/2 cm, which are located on the trailing edge of each of the four fins. These control surfaces are actuated in pairs; two of them control the lateral direction of the bomb, and the other two, its trajectory.
The demolition charge consists of approximately 1 and 1/2 pounds of penthrite wax. It is fuzed usually with the VZ 80 "all-ways action" fuze. The main purpose of this charge is to destroy the directional equipment in case the fuze for the main charge in the warhead fails to function.
Tail Unit: The tail unit consists of an inner cast magnesium alloy tail cone fitted with two long and two short case magnesium alloy struts.
Operation. Bombing with the PC 1400 FX is carried out in conjunction with the Lotfe 7D bomb sight. The only extra duty of the operator being to switch on the gyroscope of the bomb some 2 minutes before the moment of release. The aim of the bombardier is taken the same way as in ordinary bombing. AS the bomb is released, the aircraft is throttled back and put into a climb with the flaps down. This action is to insure not overshooting the missile. Once the requisite reduction in speed has been effected, the pilot flattens out.
At this time, corrections in the course of the missile can be taken if necessary. At the moment of release, the bombardier starts a stop-watch going. The bomb cannot be controlled during the first 15 seconds after release. On the 16th second, the operator takes control of the missile. It has been estimated that the missile can be guided with a margin of error of only 50 meters from an altitude of 7,000 meters.
The bomb takes 42 seconds to reach the ground from 7,000 meters, and 38 seconds from 6,000 meters. The lowest possible height for satisfactory release is 4,000 meters. At the moment of impact, the bomb, dropped from 7,000 meters is said to have a velocity of 270 meters per second.
Next Time: Rockets (Part 2)
Source: German Explosive Ordnance Vol. 1: Bombs, Rockets, Grenades, Mines, Fuzes & Igniters
