US3260045A - Propelling charge for solid-fuel rockets - Google Patents

Description

July 12, 1966 H. RENNER ETAL 3,

PROPELLING CHARGE FOR SOLID-FUEL ROCKETS Filed Jan. 25, 1963 2 Sheets-Sheet 1 3n ven for: I /erm 1 Refine/- Kan-Z 02. Wei 20w 74 fin.

y 1966 H. RENNER ETAL PROPELLING CHARGE FOR SOLID-FUEL ROCKETS Filed Jan. 25, 19s:

2 Sheets-Sheet 2 ATTORNEY5 United States Patent 3,260,045 PROPELLING CHAR E FOR SOLID-FUEL ROCKETS Hermann Renner and Karl-Otto Wehlow, Dusseldorf, Germany, assignors to Firma Rheinmetall G.m.b.H., Dusseldorf, Germany Filed Jan. 25, 1963, Ser. No. 253,883 Claims priority, application Germany, Jan. 30, 1962, R 31,998 2 Claims. (Cl. Gil-35.6)

This invention relates to a propelling charge for solidfuel rockets. It is a requirement in particular for the propelling charges of solid-fuel rockets that the rocket should exhibit a constant impact diagram or target pattern within a certain temperature range, so as to enable the projectile to be used within the required temperature range with uniformly good hitting results, independently of any temperature control system. This temperature requirement generally extends over a fairly large zone of the negative and positive temperature range.

When these requirements are taken into consideration, however, problems of interior ballistics arise, since every powder has a lower burning rate at negative temperature and a higher burning rate at positive temperature, in relation to the normal temperature, because of the physical and chemical properties inherent in it and the nature of the burning process resulting therefrom.

This property of the powder must be taken into consideration when the firing table is drawn up. This temperature dependence of the burning rate of the powder is particularly disadvantageous in rockets, since if the constriction ratio (ratio of the surface of the powder to the nozzle cross-section) is planned to be constant for the entire temperature range, there is obtained at low negative temperatures a greater burning time of the rocket which, moreover, results in a poorer specific impulse owing to the lower combustion chamber pressure developed. The firing range is thereby decreased and the dispersion of the impact diagram becomes greater.

This eliect is of even greater importance, for example, in the case of a double-base powder (Ngl-Nc powder) which, in certain circumstances, owing to various additions, for example of lead salts for correcting the burning rate, exhibits a zone of unsteadiness in the burning rate as a function of the pressure, it being possible for the burning rate above and below this zone to be very different. For this reason, the operating range of the rocket should be located either above or below the zone of unsteadiness.

If, for reasons of construction, the rocket is so designed that, by reason of the temperature requirement, the equilibrium pressure of the combustion chamber for a certain temperature range is above and, for the remainder, in or below, the range of unsteadiness, the drawbacks described make themselves noticeable to a particularly serious extent. In certain circumstances, the rocket may become totally unusable in the temperature range in which the unsteadiness lies because of too marked a dispersion.

According to the invention, the drawbacks described can be reduced in rockets having loosely inserted internally burning propelling charges in that changes due to temperature in the physical properties of the propellant (dimensions, solidity etc.) are used to compensate changes in the chemical behavior (burning) which are likewise due to temperature. The invention can be carried into effect very advantageously in that the changes in the dimensions of the propellant body are used through the coefiicient of expansion to change the construction ratio. This can be effected, for example, by changes in the dimensions of the propelling charge body varying the cross section of the nozzle directly or by way of suitable intermediate elements, whereby a change in the constriction ratio is likewise obtained.

As a further advantageous development of the inven tion, changes in the dimensions of the propelling charge body which are due to temperature can also be used to build up tensile and/or bending stresses in the wall of the body which result in deliberate breaking up of the latter and thereby enlarge the effective, i.e. burning, surface, whereby the constriction ratio is likewise aflected. This can be brought about in a very simple and suitable manner by providing the propelling charge body at its inner and/or outer periphery with one or more longitudinal grooves which, when the pressure increases inside the propelling charge body, promote, as predetermined breaking point or points, the formation of cracks.

Further details of the invention are elucidated in the description of the example of embodiment illustrated in the drawing, in which:

FIGURE 1 is across-section of a rocket;

FIGURE 2 is a partial longitudinal section thereof;

FIGURE 3 is a cross-section of the rocket showing the propelling charge after formation of a crack, and

FIGURE 4 is a perspective view of a sealing strip.

Referring to the drawings, the reference 1 designates the cylindrical wall casing of the combustion chamber in which is arranged the propelling charge 2 formed as an internal burner. Between the wall of the combustion chamber and the outer periphery of the propelling charge body 2 there is an annular gap 3, the width of which is subject to changes due to temperature, since the wall of the combustion chamber and the propelling charge body have different coeflicients of expansion. The width of the annular gap 3 is so calculated that, at normal temperature at approximately 10 C. or 15 C. as examples, the propelling charge body can easily be pushed into the combustion chamber. In the upper temperature range, the wall of the propelling charge body is then applied tightly against the wall of the combustion chamber, while at falling temperatures a widening annular gap is formed. At the ends of the propelling charge body the annular gap is sealed by means of sealing rings 4, 4' at least one of which is so movable that changes in the length of the propelling charge body can be taken up. The hollow propelling charge body has internally a star-shaped crosssection in order to obtain a large surface (burning area) and is provided, for example, with two opposite notches (predetermined breaking points) 5, S. In the region of the notch 5 there is provided at the periphery of the propelling charge body a further notch 6 into which there is provided an elastic sealing strip 7 with a V-shaped profile. When a longitudinal crack is produced in the zone of the notch 5, the burning area is increased by twice the cross-section of the crack. The sealing strip is pressed against the Wall of the combustion chamber by the pressure obtaining therein, the two sides of the seal spreading open and maintaining their bearing action against the propelling charge body. In this way, the interior of the propelling charge body continues to be kept under pressure and any entry of the combustion chamber pressure into the annular gap is prevented. Furthermore, it is made possible in this way to obtain an area increasing in size by stages for corresponding temperature ranges. By appropriate utilization of the elasticity properties of the propelling charge body in combination with notches formed in varying widths, the eflect can be so controlled that in the positive temperature range above the normal temperature mentioned no crack is formed through the body bearing against the wall of the combustion chamber, one crack, for example, is formed as from a certain lower temperature, below the normal temperature mentioned and another crack at even lower temperatures through the further embrittlement and more intensive bending open of the propelling charge body.

FIGURES 3 and 4 better illustrate particularly the elastic sealing strip 7 which has a V-shaped profile. FIG. 3 thus shows in cross-section a view similar to FIG. 1 which is a cross-section of a rocket and which illustrates the propelling charge 2 immediately after the formation of a crack in the direction from the notch 5 down into the further notch 6. The sealing strip 7 is V-shaped as clearly shown in FIG. 4 which is a perspective view of a portion of the strip and tis sealing strip has been forced in FIG. 3 against the cylindrical wall casing 1 with the side portions of the strip forced against the sides of notch 6. The inner portion of the propelling charge is held under pressure by the V-shaped sealing strip 7 and thus the sealing strip, since it is pressed against the wall of the chamber 1, will prevent the combustion gases from entering the annular gap 3. It is to be observed that the drawing as to the original FIG. 1 shows the annular gap on quite an enlarged and exaggerated scale so that it can be readily observed, but actually this gap is extremely small.

What we claim is:

1. A rocket propelling means for solid-fuel motors,

comprising a casing, a propellant charge of the internal burning solid type in the casing and spaced by a gap therefrom, a longitudinally extending notch provided on the outer periphery of the propellant charge, said notch being of suflicient radial depth so that a crack is formed due to combustion pressures between the inner and outer surfaces of the solid propellant charge adjacent the notch, and sealing means in the notch to seal off the outer surface of the solid propellant charge from the burn area, said crack providing increased burn area.

2. A rocket propelling means for solid-fuel rocket motors according to claim 1, in which the sealing means comprises an expansible elastic strip.

References Cited by the Examiner UNITED STATES PATENTS 2,816,418 12/1957 Loedding 6039.47 2,937,493 5/1960 Adelman 6035.6 3,048,968 8/1962 Hutchinson 6 )35.6 3,066,481 12/1962 George et al. 6035.6

MARK NEWMAN, Primary Examiner.

SAMUEL LEVINE, Examiner.

C. R. CROYLE, Assistant Examiner.

Claims (1)

1. A ROCKET PROPELLING MEANS FOR SOLID-FUEL MOTORS, COMPRISING A CASING, A PROPELLANT CHARGE OF THE INTERNAL BURNING SOLID TYPE IN THE CASING AND SPACED BY A GAP THEREFROM, A LONGITUDINALLY EXTENDING NOTCH PROVIDED ON THE OUTER PERIPHERY OF THE PROPELLANT CHARGE, SAID NOTCH BEING OF SUFFICIENT RADIAL DEPTH SO THAT A CRACK IS FORMED DUE TO COMBUSTION PRESSURES BETWEEN THE INNER AND OUTER SURFACES OF THE SOLID PROPELLANT CHARGE ADJACENT THE NOTCH, AND SEALING MEANS IN THE NOTCH TO SEAL OFF THE OUTER SURFACE OF THE SOLID PROPELLANT CHARGE FROM THE BURN AREA, SAID CRACK PROVIDING INCREASED BURN AREA.

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