EP0884554B1 - Method for controlling the lateral dispersion of projectiles stabilised by means of gyroscopic effect - Google Patents

Description

The present invention relates to a method for controlling the lateral dispersion on the ground of artillery ammunition stabilized by effect gyroscopic as, for example, those described in document WO-A-8100908, as well as a munition applying this method. She applies in particular to improving the effectiveness of artillery ammunition especially in the context of ammunition with increased range.

Improving the accuracy of the point of impact of ammunition artillery is justified by the fact that it allows the treatment of targets in requiring a reduced number of ammunition but also due to the currently envisaged increase in range of future munitions which goes hand in hand with a degradation of the precision of the points of impact.

To meet these needs, it is known to provide ammunition with devices capable of locating them. These implement systems of navigation, like the system known by the abbreviation Anglo-Saxon GPS of Global Positioning System or low inertial units cost. These systems allow, as a first step, to correct the aiming angles for future shots from trajectory measurements first shell fired, without the need to place advanced observers on the points of impact and secondly, directly correct the real trajectory, using adapted controls, loaded in the ammunition. The second process is more complex, but offers the advantage of avoiding adjustment shots, which is doubly interesting from an operational point of view by the effect of surprise obtained which does not allow the target to leave the target area and by the reduction of the time required to take a shot on goal which allows the shooter to leave the shooting position quickly, and greatly decreases the probability of location of the shooter by counter-battery radars.

The ammunition trajectory correction is carried out according to two steps :

A first step is to correct only the errors by scope. All you need is an action in the vertical plane, which can be performed from relatively simple way, by deliberately aiming beyond the target, and by controlling aerodynamic drag by an air brake system. Curvature of the trajectory is thus modulated. During this action, the control of the range involves purely axial forces, and requires only ammunition location information.

The second step, more difficult to reach, consists of correcting also lateral errors by implementing for example actuators developing forces perpendicular to the speed of displacement of the ammunition, that is to say substantially perpendicular to the axis of revolution. In this case, knowledge of the angular position actuators with respect to a terrestrial reference, vertical for example, is required.

The trajectory correction is in principle in one direction relatively unchanging compared to a terrestrial reference, at the most less as long as the amplitude of the requested correction is sufficient important.

When the ammunition rolls, the actuators must, in case they are linked to the ammunition, switch to a double frequency of the roll frequency in order to achieve a "straightening" of the force generated, to obtain an average value of the non-zero resultant force. The direction of the average force is adjusted by playing on the instants of switching.

The operating mode described above is possible for ammunition with moderate roll up to 30 turns / s per example. On the other hand, it seems difficult to apply to ammunition stabilized by gyroscopic effect because their roll speed is then too high, it is around 300 rpm for 155 mm ammunition and the expected dynamic performances of the actuator appear in this incompatible cases of conventional aeromechanical control systems for example.

Currently, two processes exploiting principles conventional actuators, as described above, appear to be able to be considered.

The first method may be to use organs piezoelectric which allow switching frequencies to be reached high. However, these may not satisfy the amplitudes of deformations required.

The second method can consist in using organs of correction decoupled in roll from the rest of the ammunition. But such a process encounters problems in making decoupling bearings which must resist initial acceleration at the time of firing and exhibit low friction.

The object of the invention is to overcome the aforementioned drawbacks.

To this end, the invention relates to a method for the control of lateral dispersion of stabilized gyroscopic ammunition characterized in that it consists in modulating the acceleration of bypass horizontal due to the gyroscopic effect by varying the center of thrust aerodynamics of the ammunition.

The subject of the invention is also a munition making application of the above method.

The method and the device according to the invention have the advantage that they require a simple arrangement of the ammunition stabilized in rotation by gyroscopic effect requiring no rapid switching actuators, no decoupling of actuators and above all no means of vertical reference measurement.

• la figure 1, la trajectoire d'une munition relativement à l'horizontale,
• la figure 2, les dispositions relatives sur l'axe longitudinal du centre de poussée et du centre de gravité d'une munition,
• les figures 3 et 4, l'évolution de l'accélération latérale en fonction d'un paramètre de stabilité u,
• la figure 5, un graphe montrant une dérivation de munition en fonction de la distance du point d'impact,
• la figure 6, un exemple de dépointage de tir pour centrer les corrections,
• les figures 7 et 8, un exemple de déplacement des centres de poussée après correction,
• la figure 9, un exemple d'implantation d'ailettes radiales de correction sur le corps de la munition,
• la figure 10, les ailettes de la figure 9 en position déployée, et
• les figures 11 et 12, un exemple de calage d'ailettes selon l'invention sur un culot de munition.

Other characteristics and advantages of the invention will become apparent with the aid of the description which follows given with reference to the appended drawings which represent:

• FIG. 1, the trajectory of a munition relative to the horizontal,
• FIG. 2, the relative arrangements on the longitudinal axis of the center of thrust and the center of gravity of a munition,
• FIGS. 3 and 4, the evolution of the lateral acceleration as a function of a stability parameter u,
• FIG. 5, a graph showing a diversion of ammunition as a function of the distance from the point of impact,
• FIG. 6, an example of shot firing to center the corrections,
• FIGS. 7 and 8, an example of displacement of the centers of thrust after correction,
• FIG. 9, an example of installation of radial correction fins on the body of the ammunition,
• FIG. 10, the fins of FIG. 9 in the deployed position, and
• Figures 11 and 12, an example of wedging fins according to the invention on an ammunition base.

The gyroscopic shunt of shells with high roll speed is a physical phenomenon resulting in a continuous lateral deviation of the trajectory, which can reach several hundred meters at the end of path. For example, the lateral deflection of a 155-millimeter shell range 27 km, depending on the horizontal distance traveled is around 800 m.

a) La pesanteur provoque la courbure de la trajectoire, c'est-à-dire la rotation du vecteur vitesse vers le bas.

b) Les conditions de stabilité gyroscopique étant supposées remplies (vitesse de rotation autour de son axe longitudinal suffisante), la munition suit son vecteur vitesse avec un certain traínage, mais à la même vitesse de rotation.

c) La vitesse de rotation de la munition autour de son axe longitudinal encore appelé SPIN, induit par réaction gyroscopique un couple autour de l'axe vertical (couple gyroscopique).

d) Le couple gyroscopique fait apparaítre un angle de dérapage entre l'axe du projectile et son vecteur vitesse. Cet angle s'établit à une valeur d'équilibre telle que le moment aérodynamique qu'il induit compense le couple gyroscopique.

Qualitatively, the phenomenon can be analyzed in the following way:

a) Gravity causes the curvature of the trajectory, that is to say the rotation of the speed vector downwards.

b) The conditions of gyroscopic stability being assumed to be fulfilled (speed of rotation around its longitudinal axis sufficient), the ammunition follows its speed vector with a certain drag, but at the same speed of rotation.

c) The speed of rotation of the munition around its longitudinal axis also called SPIN, induced by gyroscopic reaction a couple around the vertical axis (gyroscopic couple).

d) The gyroscopic couple shows a skid angle between the axis of the projectile and its speed vector. This angle is established at an equilibrium value such that the aerodynamic moment which it induces compensates for the gyroscopic torque.

The skid angle corresponds to a rotation around the axis vertical and therefore lies in a horizontal plane. Lifting force associated is itself horizontal, and produces the trajectory derivation.

The gyroscopic bypass phenomenon leads to a horizontal deflection which is the natural response of ammunition to the vertical stress of gravity. The derivation is to the right of the line firing, for a projectile rotating in the positive direction around its spin axis.

Given the order of magnitude of the gyroscopic derivation compared to the amplitude of the lateral dispersions, it is possible according to the invention to correct these by modulating the bypass amplitude.

g : accélération de la pesanteur

A : inertie de la munition autour de son axe longitudinal (axe de spin)

m : masse de la munition

V: vitesse de la munition

γ : pente de la trajectoire

p : vitesse de roulis de la munition

x_F : abscisse du centre de poussée aérodynamique F par rapport au centre de gravité G de la munition.

The gyroscopic derivation results in a horizontal lateral acceleration Γ _D , which is expressed from the quantities defined below:

g: acceleration of gravity

A: inertia of the ammunition around its longitudinal axis (spin axis)

m: mass of the ammunition

V: speed of the ammunition

γ: slope of the trajectory

p: rolling speed of the ammunition

x _F : abscissa of the aerodynamic center of thrust F relative to the center of gravity G of the ammunition.

The speed vector V is as shown in Figure 1 tangent to the path and its direction relative to the horizontal defines the slope of the path.

For ammunition stabilized by gyroscopic effect, the center of aerodynamic thrust F is located in front of the center of gravity G as shown in Figure 2 which shows ammunition in the form of a shell composed of a cylindrical body 1, a conical head 2 and a base 3.

By analogy, with stabilized ammunition stabilized by aerodynamic effect, the parameter x _F is hereinafter called "static margin".

The spin speed being assumed to be large enough to ensure stability, the acceleration Γ _{D is} established after stabilization of the transient movements of the projectile at the following value: Γ D = gcosγ Ap mvx F 1+ Ap mvx F

For a given slope trajectory γ, Γ _D depends only on the following parameter: u Ap MVX F and is expressed by: Γ D = gcosγ u 1 + u 2

The condition of stability of the ammunition imposes more than the essential stability coefficient s, given by s = AT 2 p 2 2Bρv 2 SCzαx F

Checks for inequality: s ≥ 1

B représente l'inertie de tangage/lacet

ρ est la masse volumique de l'air

S est la surface de référence ( = ΠD² / 4 avec D=calibre)

et Czα est le gradient de portance

In which

B represents the pitch / yaw inertia

ρ is the density of air

S is the reference surface (= ΠD ^2/4 D = caliber)

and Czα is the lift gradient

Depending on the parameter u, the necessary stability condition becomes: u ≥ 2BρVSCzα Map

B = 1,715 m²kg

A = 0,159 m²kg

m = 46,95 kg

S = 0,01886 m²

Vo / po = 0,5 m/rd

Czα = 2,78

et ρ = 1,225 kg/m³

Usually, the most severe condition of stability is located at the start of the flight of the munition ρ, V / p and Czα being maximum at the outlet of the launch tube of the ammunition. For a 155 mm projectile, the orders of magnitude are as follows:

B = 1.715 m ² kg

A = 0.159 m ² kg

m = 46.95 kg

S = 0.01886 m ²

Vo / in = 0.5 m / rd

Czα = 2.78

and ρ = 1.225 kg / m ³

Hence the condition of stability: u ≥ 0.0147

The evolution of Γ D = gcosγ u 1 + u 2 is shown in Figures 3 and 4. Figure 3 is an overall representation of the function. With the numerical values used above (155 mm projectile) the parameter u changes during the flight in the following range: 0.026 ≤ u ≤ 0.041

The range of variation therefore only concerns the start of the curve Γ _D = f (u) which is represented in FIG. 4.

Examination of the curve shows that Γ _D is almost linear as a function of u and that the lateral acceleration can be easily modified provided that the parameter u is varied.

It is better to increase u, which offers more possibility of variation and in addition, strengthens the stability of the ammunition.

According to equation (3) and for a trajectory whose slope profile γ is given, it appears that the acceleration of derivation depends only on the parameter: u = Ap MVX F , defined by the relation (2) which itself is expressed as a function of the angular moment Ap, the momentum mV and the static margin x _F.

The momentum mV and the angular momentum Ap essentially result from the initial conditions given by the tube launch immediately.

It is not possible to modify the amount of movement of ammunition as this would have a profound effect on its range.

On the other hand, it may seem possible to modify its moment kinetic. There are two ways to do this: or increase the roll speed.

A decrease in roll speed can be achieved by example by aerodynamic brakes. However these decrease the ammunition stability margin. In addition, this results in a decrease of parameter u, and therefore offers little room for correction.

An increase in the roll speed can be obtained by an energy process of the impeller type. For example, to double the diversion acceleration at mid-trajectory, it is practically enough to double the value of u, that is to say to increase the roll speed by a factor of 2. At mid trajectory, the variation of p to be communicated is then approximately: Δρ = 200 turns / s. Given the roll inertia and assuming that the acceleration torque is obtained by nozzles located at the periphery of the projectile, the impulse to communicate is of the order of: I = 2600 Ns

However, this solution has the disadvantage that it requires a powder mass of approximately 1.3 kg which taking into account the coefficients filling the impellers may be prohibitive vis-à-vis the architecture of ammunition.

A third solution implemented by the invention consists in modifying the static margin x _F.

• centre de gravité à 2,16 calibres (335 mm) du culot.
• centre de poussée variable en fonction du nombre de Mach M :
  

La correction de trajectoire se situe dans la phase descendante de la trajectoire, c'est-à-dire plutôt aux alentours de M = 1.The method according to the invention consists in directly varying the position of the center of thrust F which results from the distribution of the pressures due to the flow of air over the surface of the munition. As an indication, for a 155 mm projectile, the following orders of magnitude can be used:

• center of gravity at 2.16 calibers (335 mm) from the base.
• variable center of thrust depending on the Mach M number:
  

The trajectory correction is located in the downward phase of the trajectory, that is to say rather around M = 1.

An exploitable variation of the gyroscopic derivation can be obtained by reducing the static margin x _F by approximately 1 to 1.5 calibers. Simulations show that it is then possible to increase the bypass from 200 to 300 m compared to its normal value of 800 m (see Figure 8: lateral bypass by reducing the static margin by 30% from t = 30 s ). This gives a correction potential of 300 m maximum which is however flexible, by triggering the variation of static margin sooner or later, by implicitly assuming that the variation of the static margin x _F is of the "one shoot" type. , in English, that is to say unique, by all or nothing and not reversible. The correction is always in the same direction, to the right of the line of fire. In order to refocus the correction, and to be able to catch any sign errors, a priori symmetrical around 0, it suffices to shift the pointing in azimuth of the launch tube to the left so as to systematically compensate for half of the correction maximum possible.

Thus, by designating by Δ _c the amplitude of correction achievable (for example: Δ _c = 300 m) and X _max the target range, the firing site angle must be offset by: Δs = Δ vs 2X max

To modify the point of application of the result of the forces of pressure on the ammunition, it is sufficient according to the invention to deploy, as the show Figures 9 and 10, at the desired time for the start of correction, 4 airfoils whose lift combined with that of the ammunition provides the desired static margin.

Unlike the classic control systems which must be oriented in order to bend the trajectory in the direction of the target, the airfoils 4 used here remain fixed after deployment. Their role is only to modify the aerodynamic center of thrust F in order to vary the static margin x _F.

The airfoils 4 must also be angularly wedged, as shown in Figure 9, so as to maintain the roll speed of the ammunition.

For example, for a 155 mm projectile, the center of which thrust is located very in front of the projectile especially during the phase where the correction is likely to be ordered, Figure 10 shows the location of the aerodynamic force F for Mach = 1 and shows the range in which it should be positioned. The latter is obtained in the example by moving the point of application of the force F from 1 to 1.45 calibers to obtain sufficient lateral deviation modulation.

Examination of Figure 8 shows that to obtain the desired distance for the center of thrust, the only realistic solution is to deploy the wings 4 behind the center of gravity.

In order to maximize the effect of the sails 4 and to reduce maximum dimensions while retaining a certain modularity to the corrected ammunition, the airfoils 4 are placed at the level of the base 3 of the projectile.

F₀, le centre de poussée de la munition sans ailettes

F₁, le centre de poussée de la munition avec ailettes

x_F0 , la marge statique de la munition sans ailettes

x_F1 , la marge statique de la munition avec ailettes

Pc, la portance du corps sans ailettes (appliquée en F₀)

Pa, la portance des ailettes

et La, le bras de levier de la portance ailettes (La < 0).

By designating by:

F ₀ , the center of thrust of the ammunition without fins

F ₁ , the center of thrust of the ammunition with fins

x _{F 0} , the static margin of the ammunition without fins

x _{F 1} , the static margin of the ammunition with fins

Pc, the lift of the body without fins (applied in F ₀ )

Pa, the lift of the fins

and La, the lever arm of the wing lift (La <0).

The static margin with fins is calculated by considering the moment of the resulting force. We obtain according to the force distribution diagram of Figure 8 x F 1 = pcx F 0 + PaLa Pc + Pa

With eight radial fins of unitary surface Sa located as in FIG. 9, the lift Pa is approximately given by the relation: Pa = 4Sa q VS N / A or q is the dynamic flow pressure and C _Na is the lift coefficient of a fin.

Given the interactions with the cylindrical body of the ammunition, we can consider that: VS N / A = 8α where α is the incidence of the body.

The bearing capacity of the munition is expressed by: Pc = q Sc C Nc where Sc is the area of midship ΠD ^2/4 and C _{Nc is} the lift coefficient of the body.

Practically: C _Nc = 2α

The area required for a fin 4 is then expressed: Sa = Sc C Nc 4C N / A . x F 0 - x F 1 x F 1 - The

x_F0 = 2,8 calibres

x_F1 1,3 calibres (recul de 1,5 calibres)

La = 2,1 calibres

Taking as an example:

x _{F 0} = 2.8 calibers

x _{F 1} 1.3 calibers (1.5 caliber drop)

La = 2.1 calibers

Sa = 5,2 cm²

The relation (10) gives:

Sa = 5.2 cm ²

Which corresponds to relatively large fins modest, easy to integrate at the level of the base 3 by a radial mounting as shown in figure 10.

In this case, the deployment of the fins 4 can be obtained naturally by centrifugal effect.

In order not to interfere with the rolling speed of the ammunition, the fins are wedged angularly with respect to the axis of the projectile, as shown in Figure 11.

The calibration checks the relationship: tgη = pd V where d is the distance between the axis of the projectile and the center of gravity of the fin.

p = 200 t/s

V =350 m/s

d = 0,09 m

For example, for:

p = 200 t / s

V = 350 m / s

d = 0.09 m

The relation (11) gives: η = 17.9 °.

Claims (6)

1. Method for controlling the lateral dispersion of gyroscopically stabilized munitions (1), characterized in that it consists in modulating the horizontal drift acceleration due to the gyroscopic effect by varying the aerodynamic centre of thrust F of the munition (1).
2. Method according to Claim 1, characterized in that it consists in placing retractable fins (4) at the rear (3) of the munition in order to modify, at a defined instant on the trajectory, the pressure distribution on the munition by displacing the centre of thrust towards the rear of the munition in order to apply the required dispersion correction.
3. Method according to Claim 2, characterized in that it consists in setting the fins (4) radially to the munition (1) at a defined angle of inclination relative to the longitudinal axis of the munition (1) in order not to interfere with its roll speed.
4. Munition rotationally stabilizable by a gyroscopic effect for implementing the method according to any one of Claims 1 to 3, of the type comprising a cylindrical body (1) placed between a nose cone (2) and a base (3), characterized in that it includes retractable fins (4) placed radially on the base (3) so as, when they are deployed, to correct the horizontal drift of the munition due to the gyroscopic effect.
5. Munition according to Claim 4, characterized in that the fins (4) are inclined relative to the longitudinal axis of the munition at an angle η such that tgη = pd / V where p is the roll speed, d is the distance between the axis of the munition and the centre of gravity of the fin (4) and V is the speed of the munition (1).
6. Munition according to Claim 5, characterized in that each fin (4) has an area Sa defined by the equation Sa = Sc CNc 4CNa . x F 0 - x F 1 x F 1 - La in which Sc is the area of the master cross section of the munition, C_Nc is the lift coefficient of the munition body, C_Na is the lift coefficient of the fin, x_F0 is the static margin of the munition without fins, X_F1 is the static margin of the munition with fins and La is the lever arm of the fin lift.

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