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(11) | EP 0 210 732 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
A balistic body stabilized by flexible fins Durch nachgiebige Flossen stabilisierter ballistischer Körper Missile balistique stabilisé par empennage flexible |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention concerns the stabilization of flying ballistic bodies such as missiles, rockets and bombs, whether self-propelled or not. In the following all such flying ballistic bodies will be referred to for short as "projectiles", it being understood that this term refers to fin-stabilized projectiles.
[0002] More specifically the invention concerns an improvement in the aerodynamic stabilization of projectiles.
[0003] The aerodynamic stability is one of the main considerations in the design of projectiles, whether launched from landborne, seaborne or airborne launchers or, whether dropped from an aircraft. Conventionally aerodynamic stability is achieved by means of stabilizing fins and the larger the surface of the stabilizing fins the better the aerodynamic stability. However, there exist geometric constraints which restrict the space available for launching. For example, in the arming of fighter aircraft, the geometry of the aircraft has to be taken into account; or in case of landborne or seaborne launchers the design of the latter must be considered. In consequence of this, restrictions are put on the span of the stabilizing fins, which restrictions are incompatible with considerations of stability.
[0004] It thus occurs quite often that projectiles are developed which are insufficiently stabilized with the result that the ballistic performance of such projectiles is highly sensitive to atmospheric interferences and geometric tolerances which in turn results in inaccurate performance expressed in terms of high dispersion.
[0005] It has already been proposed to overcome these defects by means of popout stabilizing fins which emerge out of the body of the projectile after its launching but this solution turned out to be complicated and unreliable and to cause an undesired increase of the body weight of the projectile.
[0006] Another proposed solution for improving the aerodynamic stability of projectiles is to shift the centre of gravity forward. However this solution requires the addition of considerable dead weight at the front part of the projectile which reduces the payload for a given propulsion.
[0007] A further US-A-4 351 503 describes a fin stabilized ballistic projectile in which each fin is pivotably connected to the body of the projectile drawback inherent in large size stabilizing fins, whether static or of the popout type, is the fact that the larger the diameter of a flying projectile the easier becomes its detection by radar.
[0008] It is accordingly the object of the present invention to overcome the above-described deficiencies by providing a new type of fin stabilization for projectiles.
[0009] In accordance with the present invention there is provided a fin stabilized ballistic projectile in which each fin is pivotably connected to the body of the projectile characterised in that each fin is connected to the body by an in itself twistable connecting member, the location of connection of each fin being rearward of the aerodynamic centre of said fin.
[0010] It has been found in accordance with the present invention that projectiles with twistably connected fins have a significantly larger stabilizing effect than rigidly connected fins of the same size and geometry. In flight, when the projectile oscillates about its theoretical trajectory in consequence of atmospheric interferences, the twistably connected fins are deflected out of their rest position whereby the oscillation of the projectile is automatically attenuated. The extent to which the connecting members can be twisted can be determined empirically for each specific design.
[0011] The connecting members may, for example, be in form of torsion bars or helical springs and may be made of metal or of suitable plastic material.
[0012] The invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Fig. 1 is a fragmentary diagrammatic elevation of a projectile with twistably connected stabilizing fins according to the invention;
Fig. 2 shows in a diagrammatic manner the flight stabilizing effect of twistably connected fin according to the invention; and
Fig. 3 is a comparative oscillation attenuation diagram.
[0013] The projectile diagrammatically illustrated in Fig. 1 comprises a body I having at its rear a number of stabilizing fins 2 each connected to body 1 by means of a helical spring 3.
[0014] In Fig. 2 the fraction of the body 1 shown in Fig. 1 is signified by the longitudinal axis 1'. The point CGB shown on line 1' signifies the centre of gravity of the body. The point CGF on fin 2 signifies the centre of gravity of the fin and the point AC the aerodynamic centre thereof. The projectile moves at an angular velocity q and at a translatory velocity v with an angle of attack a formed between the trajectory and the axis 1' which means that the projectile oscillates about its theoretical trajectory. In consequence the angle of attack a, each stabilizing fin 2 is deflected by being turned around the spiral spring 3 by which it is connected to body 1 forming with the axis of the latter an angle 8. As a result of the deflection of she stabilizing fins 2 the oscillation of the projectile about the trajectory is gradually attenuated which means that the angle of attack a is diminished, whereby in turn the deflection angle 8 of the fins is equally diminished.
[0015] In Fig. 3 there are shown two attenuation curves of the oscillations of a fin stabilized projectile. The drawn out curve shows the attentuation of a projectile with twistably connected fins according to the invention, and the dashed curve shows the attenuation of a projectile having the same geometry and flying under the same conditions with rigidly connected fins. The curves show the reduction of the angle of attack as a function of time and while the drawnout curve shows that with a projectile according to the invention the angle of attack a diminishes rapidly and after three seconds is reduced to less than half the original, the attenuation of the angle of attack a with a conventional missile with rigidly connected stabilizing fins of the same size and geometry, is much slower.
[0016] The invention is further illustrated by the following example:
For imparting a satisfactory aerodynamic stability to a projectile weighing 200 kg. having a diameter of 40 cms. and being 4 m. long and flying at a low attitude at a velocity of 250 m/sec., conventional rigidly connected fins are required having a span of 70 cm. If, however, the fins are twistably mounted in accordance with the invention using a torsion bar of a hardness of 2,000 kg m2/sec2 and each mounted 10 cm. behind the aerodynamic centre of the stabilizer, the surface of the fins can be reduced by 20 % as compared to rigidly connected stabilizers of the same size and geometry. Such a reduction is of great value, for example, for air to ground bombs mounted on and launched from the lower face of the wings of an aircraft.
1. A fin stabilized ballistic projectile in which each fin (2) is pivotably connected
to the body of the projectile characterised in that each fin (2) is connected to the
body by an in itself twistable connecting member (3), the location of connection of
each fin being rearward of the aerodynamic centre of said fin.
2. A projectile according to Claim 1 wherein said twistable connecting member (3)
is a torsion bar.
3. A projectile according to Claim 1 wherein said twistable connecting member is a
helical spring.
4. A projectile according to any one of Claims 1 to 3 wherein said twistable connecting
member (3) is of metal.
5. A projectile according to any one of Claims 1 to 3 wherein said twistable connecting
member (3) is of plastic material.
1. Flossenstabilisiertes ballistisches Projektil, bei dem jede Flosse (2) schwenkbar
an dem Körper des Projektils befestigt ist, dadurch gekennzeichnet, daß jede Flosse
(2) an dem Körper durch ein Drehverbindungselement (3) verbunden ist, wobei der Ort
der Verbindung jeder Flosse hinter dem aerodynamischen Zentrum der Flosse liegt.
2. Projektil nach Anspruch 1, wobei das Drehverbindungselement (3) eine Torsionsstange
ist.
3. Projektil nach Anspruch 1, wobei das Drehverbindungselement eine Spiralfeder ist.
4. Projektil nach einem der Ansprüche 1 bis 3, wobei das Drehverbindungselement (3)
aus Metall ist.
5. Projektil nach einem der Ansprüche 1 bis 3, wobei das Drehverbindungselement (3)
aus einem Kunststoff ist.
1. Projectile balistique stabilisé par des ailerons dans lequel chaque aileron (2)
est relié de façon pivotante au corps du projectile, caractérisé en ce que chaque
aileron (2) est relié au corps par un élément de liaison (3) pouvant en lui-même être
tordu, l'emplacement de la liaison de chaque aileron étant en arrière du foyer aérodynamique
dudit aileron.
2. Projectile selon la revendication 1, dans lequel ledit élément de liaison pouvant
être tordu (3) est une barre de torsion.
3. Projectile selon la revendication 1, dans lequel ledit élément de liaison pouvant
être tordu est un ressort hélicoïdal.
4. Projectile selon l'une quelconque des revendications 1 à 3, dans lequel ledit élément
de liaison pouvant être tprdu (3) est en métal.
5. Projectile selon l'une quelconque des revendications 1 à 3, dans lequel ledit élément
de liaison pouvant être tordu (3) est en matière plastique.