US2941470A - Self-propelled projectile - Google Patents

Description

June 21, 1960 J. R. JASSE SELF-PROPEILLED PROJECTILE Filed Feb. 29, 1956 A Herr/nay United States Patent 9 i SELF-PROPELLED PROJECTILE Joseph Raymond Jasse, Paris, France, assignor to Societe Nouvelle des Etablissements Brandt, Paris, France, a 7

The present invention relates to a self-propelled projectile in which the axial longitudinal thrust for propelling the projectile is exerted by one or more gas jets issuing from the rear of the projectile through an axial nozzle or through several nozzles disposed about the longitudinal axis of the projectile.

Self-propelled projectiles of known type are stabilized on their trajectory of flight by either a rear fin arrangement or gyration.

Self-propelled projectiles having a rear fin arrangement are generally given a very slight rotation which, as is well known, is usually between 10 and revolutions per second in order to compensate for the effects due to dissymmetry in the construction of the projectile and the rotational velocity is so low that it has in itself no stabilizing effect, this being obtained solely from the fin arrangement. The latter in effect shifts to the rear of the center of gravity of all the masses of the projectile the center of pressure or aerodynamic focus which is, as is known, the point of application of the resultant of the forces due to the pressure of atmospheric air on the outer surface of the projectile for small incidences of the direction of the wind velocity relative to the longitudinal axis of the projectile, and the latter has an equilibrium which is the more stable as said center of pressure or aerodynamic focus is farther to the rear of the center of gravity.

In the fin-less selfpropelled projectiles the center of pressure is, on the other hand, situated very much forward of the center of gravity since the projectile comprises generally a forward ogive and the center of pressure is situated at a distance from the point of the ogive equal to substantially two thirds of the length of the latter, whereas the center of gravity is much more to the rear. The projectile has an unstable equilibrium and stability is only obtained by rotating the projectile at high velocity about its axis. Now, a gyroscopic stabilization at high speed is not compatible with certain types of, projectiles.

Briefly, in the two known types of self-propelled projectiles and in the conventional non-self-propelled projectiles the center of pressure is disposed at a considerable distance from the center of gravity either rearwardly (the case of a finned projectile having a lowvelocity rotation) or forwardly of the center of gravity (the case of gyroscopically stabilized fin-less projectiles). Thus all these projectiles are defective in respect of their ability to remain on their trajectory. Under the effect of the lateral component of the wind all projectiles are subjected to a torque which tends to tip them. Now this torque is proportional to its leverage, that is the distance between the center of gravity and the center of pressure, and therefore increases with this leverage.

But if the disturbance due to the aerodynamic effect of the transverse component of the wind is small in the case of a conventional non-self-propelled projectile such Patented June 21, 1960 as a shell fired from a gun, this is not so in the case of self-propelled projectiles. Indeed, the torque due to the lateral wind inclines the axis of the projectile, that is the axis of thrust, relative to the axis of the launching or firing barrel and the transverse component of this thrust imparts to the projectile a transverse velocity which is the higher as the proportion of impulse imparted to the projectile outside the guiding device is the greater.

In the two known types of self-propelled projectiles, stabilized by a fin arrangement or by gyration, the displacement due to the action of the lateral wind becomes very great, this displacement afiecting above all the direction of a finned projectile and the lift of a gyroscopically stabilized projectile.

The object of the present invention, which takes into account the above-mentioned considerations, is to provide a self-propelled projectile which is much less sensitive to the tipping effect of lateral wind and thus permits a more accurate fire.

This projectile is characterized in that the distribution of all the masses of the projectile and the shape of its body are such that the distance between the center of pressure and the centre of gravity is between 0 and 0.3 times the calibre of the projectile and, furthermore, the latter is provided with means which impart thereto on its trajectory a low-velocity stabilizing rotation As the center of pressure is substantially coincident with the centre of gravity, the leverage of the disturbing torque due to air pressure on the outer surfaces of the projectile is very small and in the extreme case, if the center of pressure coincides exactly with the centre of gravity, this disturbing torque does not exist. By construction, the projectile is therefore, if not in a state of neutral equilibrium with respect to the surrounding air, at least very near this state. If this state of neutral equilibrium is completely obtained and permanently held in the course of firing, the projectile would automatically be in a state of equilibrium but, as it is never possible to be absolutely certain of an exact coincidence between the center of pressure and the center of gravity and as, moreover, this coincidence even if it existed upon departure of the projectile would never last, since in the course of the travel of the projectile along its self-propelled trajectory the centre of gravity moves forwardly, an exact coincidence cannot be ensured along the entire trajectory of the projectile. Furthermore, other causes of disturbance such as percussion upon release, off-centre thrust caused by the propelling gases, the fact that the projectile is out of true, cannot be eliminated. For these reasons the projectile of the invention is so adopted that it has on its trajectory a low-velocity stabilizing rotation which, although small, is sufficient, since in any case the projectile is and will remain near the state of neutral equilibrium.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawing to which the invention is in no way limited.

In this drawing, Figs. 1 to 5 are longitudinal sectional views of projectiles embodying the invention.

In the embodiment shown in Fig. 1 the invention is shown applied to a self-propelled projectile having a fin arrangement and a grooved band or bourrelet.

The projectile comprises a cylindro-ogival body 1 of calibre b. The forward ogive 2 is provided with a fuse 3 adapted to ignite a useful charge which may conveniently be hollow as shown. This charge 4 bears either directly, or in the known manner through the medium of a central pivot (not shown), against a transverse partition or Web 5 which forms in the rear part of the projectile a chamber 6 in which is disposed the propelling charge 7. This charge, which is of any known type, comprises for example a central passageway for evacuation of the gases produced in the course of combustion, these gases issuing from the projectile through a rear nozzle 9 in the form of an axial jet providing the propelling thrust.

The body 1 is provided at the rear with a number of fins or blades 10 each of which may, as shown in Fig. 1, be mounted for pivotal movement about a longitudinal axis 11, which permits, when launching the projectile, maintaining these fins applied in the known manner against the nozzle 9 so that the outer size of the fin arrangement is not greater than the calibre b of the projectile.

The nozzle 9, which in the direction from the forward end to the rear of the projectile is firstly convergent and thereafter divergent, has its axis, in this embodiment, exactly coincident with the longitudinal axis XX of the projectile.

The latter is completed by a ribbed bourrelet or band comprising a number of studs 12. These studs have an inclination y relative to the generatrices of the cylindrical portion of the body 1. This inclination, which will be explained hereinunder, is for rotating the projectile in the course of launching by the displacement of these studs in rifling or grooves in the barrel of the guiding or launching device.

This projectile, Whose general shape and arrangement described above are conventional, differs from known projectiles in respect of a first important feature. The aerodynamic focus or center of pressure F, that is the point through which passes for an incidence of the Wind which is less than 10, the aerodynamic resultant of the actions of this wind on the entire outer surface of the projectile unit including the fin arrangement, is a very short distance x from the centre of gravity G of all the masses of the projectile including the charges 4 and 7. This distance x, which in the extreme case may be zero, is in any case less than 0.3 b, b being the largest crossseetion or calibre of the projectile.

It will be noticed that, if the center of pressure F does not coincide exactly with the centre of gravity G, it could be situated either forwardly of the centre of gravity, as shown, or rearwardly thereof.

As the position of the centre of gravity G is determined by the distribution and values of the masses inherent in the construction, the position of the center of pressure P may be ascertained approximately by calculation followed by tests.

The position of the center of pressure P is given with good approximation by the following Formula 1:

n (3c;12d) (1) 8a: e in which:

n is the number of fins 10.

S is the surface area of one fin.

a is the distance between the center of gravity G of the projectile and the centre of thrust P of each fin.

b is the calibre or largest cross-section of the projectile.

c is the distance between the center of gravity G and the tip of the ogive 2.

d is the length of the ogive.

e is the variation in the lift, that is the vertical component of the aerodynamic reactions on one of the fins 10 of the fin arrangement for a variation of 1 in the angle of incidence.

k is a coefficient or parameter depending on d/ b.

In practice, k may be taken to equal 6 X 10- 6.5 X 10- or 6.8 X 10- if db equals 1.5, 2 or 2.5 respectively.

In the above-indicated Formula 1 all values of the second term including e which depends on the shape of the fins, are known from the construction of the projectile and, in the first term, a is also known. Thus the formula permits calculating S when n is known and vice versa.

To obtain finally the surface area S of the fin arrangement, the center of pressure of the projectile could be ascertained in a wind tunnel. To this end, the centers of pressure of a series of projectiles or projectile models could be determined, some of these projectiles having fin surface areas smaller than S and others fin surface areas greater than S. Alternatively, a series of tests could be carried out on a single projectile or projectile model provided with oversize fins which are progressively trimmed off as the tests progress.

Thus in both cases a curve could be obtained giving for the various values of the surfaces area plotted as abscissae the corresponding positions of the center of pressure F plotted as ordinates. It is then merely necessary to mark the position of the centre of gravity on the line of the ordinates to ascertain, at the point where a straight line drawn through this position and parallel to the axis of the abscissae intersects the curve, the value of the surface area for which there is coincidence between the center of pressure and the centre of gravity.

Obviously this curve is a function of the velocity of the wind in the wind tunnel. The surface area S is determined at a wind velocity equal to the mean estimated velocity for the projectile on its propelled trajectory.

By using the Formula 1 and carrying out the aforementioned tests, it is therefore possible to determine the surface area of the fins necessary to ensure that the center of pressure F occupies the required position relative to the centre of gravity G so that the distance x therebetween is less than 0.3 b.

There now remains to be determined the means for obtaining the required velocity of rotation. This is governed by the inclination of the studs or projections 12. Let y be the inclination of these projections, the angle y in Fig. 1 being supposed that corresponding to the stud situated above the plane of the figure. A calculation permits verifying that the rotational velocity is suitable, on condition that the Formula 1 is satisfied, if the inclination y of the projections relative to the axis XX is obtained by the following expression:

In this formula, the values k, b, c, d are those given above and:

g is the acceleration of gravity.

1, is the pitching moment of inertia, that is the moment of inertia of the projectile relative to an axis perpendicular to the longitudinal axis XX passing through the centre of gravity G.

I is the rolling moment of inertia, that is the moment of inertia of the projectile relative to the longitudinal axis XX.

D is the density of the air in kg. per cubic meter.

fectly stabilized even before the opening of the fins in mid-air, whatever the setting of the fins relative to the longitudinal axis XX of the projectile, on condition that this setting is such that the fins brake the rotation.

A particularly advantageous result is obtained by so setting the fins that the setting angle i of each fin relative to the longitudinal axis XX has a value equal to the angle between this axis and the resultant ow of the axial velocity v of the projectile and the vector on corre- Spending to the velocity of rotation of the projectile at the instant when three quarters of the propelling charge has been consumed. It will be noticed that in Fig. 1 the angle i is that corresponding to the nozzle situated above the plane of the figure.

By means of this arrangement, the velocity of the projectile initially slows down, passes through a minimum and then slightly increases, but always remains in the neighbourhood of the value chosen for the departure of the projectile from the launching tube, this value being determined by the value of the angle y given by the Formula 2.

Fig. 2 shows a projectile similar to the above-described embodiment but provided with inclined studs or projections 12 adapted to impart thereto a rotation, the inclination of these projections being given by Formula 2 and the relative positions of the centre of gravity G and the center of pressure F being determined by means of Formula 1. This projectile differs from the above-described projectile in that the fins 10 of its fin arrangement are fixed and disposed within the geometric cylinder containing the largest cross-section b of the projectile. Their setting could be advantageously determined in the abovedescribed manner stated with respect to the embodiment of Fig. 1.

Fig. 3 shows another projectile comprising an explosive charge 4' which, in the illustrated example, is not a hollow charge, and, by way of modification, the centre of gravity G has been shown slightly forward of the center of pressure F. However, its distance from said center of pressure is and always remains less than 0.3 b. Further, this projectile has retractable fins 10 and does not include studs for imparting rotation thereto, this rotation being obtained by means of nozzles 9 whose longitudinal axes such as YY are inclined relative to the longitudinal axis XX of the projectile (the axis YY is shown to correspond to the nozzle situated above the plane of the figure). To ensure that the obtained rotational velocity is suitable, it is necessary that the angle z between the axis YY and the axis XX be given by the following formula:

in which:

M is the mass of the projectile. r is the distance between the nozzle and the axis XX of the projectile.

Fig. 4 shows a fin-less projectile whose body 1 is substantially reduced to an ogive. The propulsion of this projectile is obtained by means of a central nozzle 9. The projectile is caused to rotate by studs 12, whose inclination is provided by the Formula 2, whereas the position of the centre of gravity G is determined by the condition that the distance x between the centre of gravity and the center of pressure is less than 0.3 b, since in such a projectile the position of the center of pressure F is perfectly known. As is known, this center of pressure is positioned a distance from the tip of the projectile equal to substantially two thirds of the length of the ogive.

Fig. 5 shows another projectile similar to that shown in Fig. 4, in which the rotation of the projectile is ensured by inclining the nozzles 9 in the manner described with reference to the embodiment shown in Fig. 3, the inclination z being given by the Formula 3.

'Although specific embodiments of the invention have been hereinbefore described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a self-propelled projectile of revolution having a calibre b, an outer projectile body; a forward hollow useful charge in said body; the distance x between the center of pressure of said projectile, that is the point at which the resultant of the forces caused by atmospheric air pressure on the total outer surface of said projectile is applied when said projectile travels on its trajectory, and the center of gravity of said projectile being between zero and 0.3 b; at the rear of said body, a plurality of fins inclined relative to the axis of said projectile and projecting outside the portion of said body having said calibre when said projectile is on its trajectory, said fins being adapted to aid the mass of the projectile in maintaining said distance x between zero and 0.3 b; a plurality of means intermediate the length of said body and projecting outwardly therefrom, said means being inclined relative to the axis of said projectile for imparting thereto on its trajectory, the projection and inclination of said fins being taken into account, a low-velocity stabilizing rotation.

2. In a self-propelled projectile of revolution having a calibre b: an outer projectile body; a forward hollow useful charge and a rear propelling charge, both disposed in the body; at the forward end of the body, a device for igniting said useful charge; a the rear of said body, a nozzle for the ejection of the propelling gases; the distance x between the center of pressure of said projectile, that is the point at which the resultant of the forces caused by atmospheric air pressure on the total outer surface of said projectile is applied when said projectile travels on its trajectory, and the center of gravity of said projectile being between zero and 0.3 b; and at the rear of said body, a plurality of fins inclined relative to the axis of said projectile and projecting outside the portion of said body having said calibre when said projectile is on its trajectory, said fins being adapted to take part with the mass of said projectile for maintaining said distance x between zero and 0.3 b; and a plurality of means carried by said body, located intermediate the length of said body and projecting outwardly from said body, said means being inclined relative to the axis of said projectile for imparting thereto on its trajectory, the projection and inclination of said fins being taken into account, a low-velocity stabilizing rotation.

References Cited in the file of this patent UNITED STATES PATENTS 1,459,198 Dunajeif June 19, 1923 2,246,429 Brandt June 17, 1941 2,412,266 Hoagland Dec. 10, 1946 2,470,489 Hopkins May 17, 1949 2,579,323 Kessenich Dec. 18, 1951 2,793,590 Brandt May 28, 1957 2,793,592 Kroeger May 28, 1957 2,804,823 Jablansky Sept. 3, 1957 2,821,924 Hansen et al Feb. 4, 1958 2,835,199 Stanly May 20, 1958

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