US2759326A - Powder reactor including a perforated conical grid - Google Patents

Description

Aug. 21, 1956 E. w. BRANDT POWDER REACTOR INCLUDING A PERFORATED CONICAL GRID Filed March 2, 1954 ulnumuml INVENTOR MMM/ww ATTORNEY United States Patent O POWDER REACTR INCLUDING A PERFORATED .CONICAL GRID Edgar William Brandt, Geneva, Switzerland, assigner' to Anstalt fur die Entwicklung von Eriindungen und gewerblichen Anwendungen Energa, Vaduz, Liechten stein, a corporation of Liechtenstein Application March `2, 1954, Serial No. 413,537

I,Claims priority, application Switzerland March '14, 1953 Il Claim. (Cl. 60-35.6)

This invention relates to powder reactors for selfpropelled projectiles.

There are two distinct types of self-propelled projectiles viz: (a) those which undergo a reaction thrust over a considerable part of their trajectory, such as for example aircraft rockets, and (b) projectiles red with the aid of a launching weapon and propelled practically only while travelling through the tube in which they are guided.

While the rst type of projectile can attain a high speed because it is accelerated during a relatively long period, the second, without travelling at the same speeds, has less dispersion because on the cessation of the thrust at the muzzle of the weapon it complies with the same ballistic conditions as an ordinary projectile.

The present invention relates more particularly to reactors for self-propelled projectiles of the second type hereinbefore set forth, preferably utilizing double-base colloidal powders having a high speed of combustion and developing pressures of the order of 200 to 300 kg. per sq. cm.

It is known to be advantageous to select for the propulsion of such projectiles particles of powder the geometric shape of which tends to keep the combustion surface approximately constant. Numerous shapes have been proposed, 'among which preference is often given to tubular particles assembled in bundles in the reactor; use may also be made of a single (tubular or multitubular) shaped body.

For the purpose of reducing the duration of combus tion of a given powder charge, while increasing the maximum pressure resulting therefrom in the reactor, it is necessary to increase the total ignition surface of the particle or particles, and consequently at the same time their structural fragility. As the pressure may attain its maximum value in only one or two hundredths of a second, it is obvious that a shock is produced on the dilerent parts of the charge, which tends to disrupt the elements. Experience shows that, all other conditions being equal, this initial phenomenon also depends on the method of ignition and the position of the igniter in relation to the self-propulsion charge.

Moreover, the fragility of the particles increases during the combustion of the powder in parallel layers, so that iinally the powder tube or tubes are broken up in an unforeseen and irregular manner. The variation of pressure as a function of `time is therefore no longer a reproducible function and the law of propulsion is no longer constant lfrom one projectile to another.

Furthermore, the nozzle or nozzles of the reactor may be partially closed by the particles of powder, which even during a very short period, is sucient to create asymmetry of propulsion which is detrimental to `accuracy of re, if it occurs when the projectile has issued from the muzzle of the weapon. It should also be noted that particles of powder, carried by the reactor gases, are ejected from the nozzle or nozzles and that these unburnt 2,759,326 Patented Aug. 21, 1956 ICC particles which escape combustion give rise to a considerable reduction of the self-propulsion output.

Finally, the unburnt particles give rise to another no less serious inconvenience, since hitherto the operator using a tiring weapon of the Bazooka type for tiring such projectiles, at maximum speeds of the order of 200 to 250 meters per second, has been compelled to protect his face and hands specially with the aid of cumbersome accessories (shield or deflector, gloves, etc.) because in order that a self-propelled projectile may attain these speeds, its charge must burn over a few metres in front of the muzzle of the weapon.

lt has already been proposed to obviate the aforedescribed disadvantages by incorporating in the reactor a grid or" suitable shape, adapted to retain and iilter the unburnt particles. Previously known grids however only incompletely solved this problem. lf, in fact, the apertures of the grid are of too great a diameter, it fuliills its function imperfectly, allowing the ltration therethrough of particles of smaller diameter, while orifices of small diameter are liable to be obstructed on the ignition of the charge and thus to give rise to irregular combustion and asymmetrical ejection of the gases.

The powder reactor of the present invention is of the type comprising a cylindrical reservoir housing a self-propulsion charge, a pyrotechnic igniter of high caloric power, one or more nozzles at the end of said reservoir, and a metallic grid of generally conical shape widening from rear to front, interposed between the charge and the nozzle or nozzles, and is characterized in that said grid, perforated by a large number of orifices of small diameter, axially encloses at its narrowest part the igniter which is held at a distance from -said charge, for the purpose of irst heating the parts of Ithe grid which delimit its or-iiices and then to burn by contact .the particles of powder thus filtered.

The length of the igniter is preferably much smaller than that of the grid, the rear end of the propulsion charge being supported at the level of the base of said grid, which is at that point of a diameter approximately equal to that of the reservoir, so that, at the time of tiring, the gases from the igniter can expand without risking damage to the particles of powder, which they ignite by sweeping over a maximum surface of their rear section. Moreover experience has shown that the combination of an igniter having a high caloriiic power with the grid such as hereinbefore deiined, permits the retention and the lburning of particles of small diameter. ln addition, the reactor of the .present invention gives rise to additional pressure which entails an increased speed of combustion and consequently a reduction of the total duration of the reaction.

According to one embodiment of the invention, the grid has at least fifteen oriiices per square centimetre, the diameter of each orifice being smaller than two mill-imetres, Afor a reaction pressure lying between 200 and 300 kg. per sq. cm. In order to prevent hindrance to the flow of the gases, the grid must haveat least `six hundred orilices.

As 'the result of repeated tests it has been found that the particles of dimensions smaller than the diameter hereinbefore speciiied appear in negligible quantity in the propulsion gases and that they are burned during their travel between the grid and the mouth of the nozzle or nozzles, after having passed Kthe neck Where the temperature of the gases is highest.

The small aperture of the oriiices hereinbefore defined (less than 2 millimetres in diameter) prevents the deiiec- .tion of the ignition flame towards the exterior of the grid, which would not fail to occur with oriiices of greater diameter.

T-he conicity of the grid, measured by the angle of a generatrix to Vthe axis,may, in accordance with the invention be between 3 and 10 degrees, at which value the inclination tof the internal surface of the grid is particularly favorable for the combustion of unburnt particles. In fact, those particles which,` after having encountered the widened part of the grid, are too large to be consumed instantaneously, are brought, while burning, by the inclination of t-he f-ace of said grid towards a zone of smaller diameter, thus reducing the risk of obstruction of the orifices.

The active surface of the grid being a function of its conicity, of which the limits are suitable to the pressures normally -required of 200 to 300 kg. per sq. cm., could nevertheless be increased if it were found advantageous to increase the pressure with a view to making available higher acceleration of the projectile on leaving the weapon.

In order to enable the invention to be more readily understood, reference is made to the accompanying drawings, which illustrate diagrammatical-ly and by way yof example, one embodiment thereof, and in which:

Fig. l -is a diagram illustrating variations of pressure as a function of time;

lFig. 2 shows in axial section lthe rear part of a reactor in accordance with the invention.

In the diagram illustrated in Fig. 1, the curve (in broken lines) indicates the pressure of combustion plotted against time in the reservoir of a conventional powder re-actor. The second curve (solid line) shows .the corresponding variation of pressure inside a reactor of the type illustrated in Figure 2, the conditions of the experiment being the same in both cases tand the reactors differing only through their grids and ythe respective arrangements of the igniter and the propulsive charge in relation to said grid.

Itis found that the reactor of the invention gives rise in its reservoir to a maximum pressure P2 yfhich is greater than, the maximum pressure P1 of .a reactor of conventional type, fwhile the corresponding reaction time t2 is shorter than t1.

The reactor illustrated in Figure 2 comprises a cylindrical reservoir 1, a self-propulsion charge constituted by a bundle of tubular grains 2 arranged in the form of a crown (an additional central grain can, if desired, also be provided). The grains 2 are perforated transversely at 3 Y- in order to promote equilibrium of pressures during combustion.

A grid 4 `of generally conical form, truncated near its apex and widening from rear to front, is interposed between the charge 2 and a plug 5 comprising a group of t convergent-divergentnozzles 6. The narrowed part 7 of the grid 4 is held by compression in a hollow 8 of the plugl 5, while its base has anedge 9 .in the periphery of which corresponds to the internal calibre of the .reservoir 1. A part of the annular rear portion of each grain 2 bea-rs on `the edge 9, which serves as support. An axial igniter 10, the rear end of which is housed in a metallic casing 11', which itself isV screwed into the plug S, is surrounded by the narrowed part 7 of the grid 4.

The length of the igniter 10 penetrating into the grid 4 is substantially less than that of the grid and preferably does not exceedfhalf the length of said grid, The result is that the greater part of the internal lvolume of the grid is clear and that a relatively considerable free space separates the igniter 10 from the powder grains 2.

The 'orifices 13 of the grid 4, are in an actual construction on the same scale far more numerous and there will be at least l5 of them per square centimetre, the diameter of each being less than 2 millimetres. This condition is particularly satisfactory for the propulsion of a reactor operating under maximum pressures of the order of 200 to 300 kg. per sq. cm. Tes-ts carried out with a grid the internal diameter of which, at the base of the cone, measured about 40 millimetres and the height of the active part of which was twice as great, showed that it had to have at least 600 orifices such as those hereinbefore defined and preferably more than 1,000 orifices.

The conicity of the grid 4, that is to say the angle a subtended by its axis with one of its generatrices, is 6 or 7 degrees, but may vary according Ito the conditions of operation (combustion pressure, dimensions of the reservoir, ete), while preferably remaining within limits comprised between 3 and 10 degrees.

Finally, the nozzles 6 of the powder reactor are closed by an annular wad 15 adapted to yield under a determined pressure, marking the commencement of propulsion. As the reactor described is more particularly intended to propel a projectile, it also comprises a finning constituted by an assembly of fins 16. A detonating primer lf2, projecting from the rear of the plug 5, is adapted to communicate fire by mechanical percussion to the igniter 10 containing a pyrotechnic composition having a high calorifi'c power, for example an aluminothermic mixture.

On firing the shot, and as the result of the percussion of the detonating primer 12, the igniter 10 deagrates and the jet of fire issuing from it, guided by the internal surface of the grid 4, penetrates between and through the tubular grains 2, igniting each of them. by their internal and external surfaces, and also by their rear portion. This process permits the initial heating of the grid by the igniter and facilitates combustion by Contact of the unburnt particles which encounter it subsequently. The small diameter of the orifices 13 of the grid 4 prevents the jet of re issuing from the igniter 10 from penetrating, even partially, into the compartment 14 provided between the external surface of the grid 4 and the wall of the reservoir 1.

The propulsion gases issuing from the grains 2, and also the particles of powder which they may carry, encounter the grid 4, which stops the unburnt particles and permits the penetration of the gases through orifices 13 into the compartment 14. As soon as the pressure has attained a sufficient value, the wads 15 yield and the gases pass into the nozzles.

What I claim is:

A powder reactor for rockets of the type comprising a cylindrical chamber containing a propelling charge, a pyrotechnic igniter. of high caloritic power, a series of nozzles at the rear of said chamber, a metallic grid of generally conical shape, widening from rear to front interposed between the charge and the nozzles, said grid having a-large number of orifices of small diameter and enclosing said igniter axially in its narrowest part, the rear end of the propelling charge being supported on the wider front end of said grid which at that point is of a diameter approximately equal to that of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,605,607 Hickman Aug. 5, 1952

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