Fin deployment mechanism for projectile and method for fin deployment

1. A fin deployment mechanism for a rotationally stabilized projectile, the fin deployment mechanism comprising:

at least one fin;

at least one balance weight; and

at least one actuator configured to actuate the at least one fin, wherein the fin is arranged in a deployable and retractable manner on the projectile, and wherein the fin and the at least one balance weight are mechanically arranged so that, when the fin is deployed by the actuator, the balance weight is displaced in towards a center of the projectile, and when the fin is retracted by the actuator, the balance weight is displaced out from the center of the projectile, and a displacement of the fin is a translation in a radial direction of the projectile, and an opposite displacement of a balance weight is a translation in the radial direction of the projectile, and

wherein a radial deployment force acting on the fin is compensated with an equally large and equidirectional radial force acting on the balance weight.

2. The fin deployment mechanism for a rotationally stabilized projectile according to claim 1 , wherein a total mass of the at least one balance weight increases when a number of balance weights increases, since the at least one balance weight is displaced in a direction towards the center of the projectile at a same time as the at least one fin is deployed from the projectile.

3. The fin deployment mechanism for a rotationally stabilized projectile according to claim 1 , wherein a total mass of the at least one balance weight decreases when a number of balance weights decreases, since the at least one balance weight is displaced out from the center of the projectile at a same time as the at least one fin is retracted into the projectile.

4. The fin deployment mechanism for a rotationally stabilized projectile according to claim 1 , wherein a number of balance weights is three, the fin deployment mechanism further comprising:

a slide again which one balance weight is fixedly mounted, wherein a second balance weight, and thereafter a third balance weight, are displaced when the slide is displaced in towards the center of the projectile.

5. The fin deployment mechanism for a rotationally stabilized projectile according to claim 1 , further comprising:

a rotatable disc to which the at least one fin and the at least one balance weight are fitted, in which the fin is arranged on a first mounted shaft journal, and the balance weight is arranged on a second shaft journal, wherein the first journal and the second journal are moveable in semi-circular grooves, and the fin and balance weight are moveable in opposite radial directions,

wherein rotation of the disc in a first direction causes the at least one fin to be deployed from the projectile and the at least one balance weight to be displaced in towards the center of the projectile, and wherein rotation of the disc in a second direction, an opposite direction to the first direction, causes the at least one fin to be retracted into the projectile and the at least one balance weight to be displaced out from the center of the projectile.

6. The fin deployment mechanism for a rotationally stabilized projectile according to claim 5 , wherein the semi-circular grooves comprises a first semi-circular, milled-out groove arranged on a first side of the rotatable disc and a second semi-circular, milled-out groove arranged on a second side of the rotatable disc.

7. The fin deployment mechanism for a rotationally stabilized projectile according to claim 6 , wherein the first shaft journal is moveable in a first semi-circular, milled-out groove on the first side of the rotatable disc.

8. The fin deployment mechanism for a rotationally stabilized projectile according to claim 6 , wherein the second shaft journal is moveable in the second semi-circular, milled-out groove on the second side of the rotatable disc.

9. The fin deployment mechanism for a rotationally stabilized projectile according to claim 6 , wherein the first semi-circular, milled-out groove for the first shaft journal for the fin and the second semi-circular, milled-out groove for the second shaft journals for the balance weights are configured to balance forces during retraction and deployment of the fins.

10. The fin deployment mechanism for a rotationally stabilized projectile according to claim 5 , further comprising a lower mounting disc arranged with at least one lower groove and an mounting disc arranged with at least one upper groove.

11. The fin deployment mechanism for a rotationally stabilized projectile according to claim 10 , wherein the first shaft journal and the second shaft journal is arranged to run in the lower groove on a lower mounting disc and the upper groove on an upper mounting disc, respectively.

12. The fin deployment mechanism for a rotationally stabilized projectile according to claim 11 , wherein the upper mounting disc is disposed on the rotatable disc, and the rotatable disc is disposed on the upper mounting disc around the center of the projectile.

13. A method for energy-efficient deployment and retraction of fins on a rotating projectile, the method comprising:

arranging at least one fin in a deployable and retractable manner on the projectile, and

fitting the at least one fin to at least one balance weight,

wherein when the at least one fin is displaced out from a center of the projectile, upon deployment of the at least one fin, the balance weight is displaced in towards the center of the projectile,

wherein when the at least one fin is displaced in towards the center of the projectile, upon retraction of the at least one fin, the at least one balance weight is displaced out from the center of the projectile, and the displacement of the at least one fin comprises a translation in a radial direction of the projectile, and an opposite displacement of the at least one weight is a translation in the radial direction of the projectile,

wherein a radial deployment force acting on the fin is compensated with an equally large and equidirectional radial force acting on the balance weight.

14. The method for energy-efficient deployment and retraction of fins according to claim 13 , wherein a deployment force acting on the at least one fin is compensated with an equally large and equidirectional radial force acting on the at least one balance weight by virtue of an increase of a mass of the at least one balance weight when the at least one balance weight is displaced in towards the center of the projectile and the mass of the at least one balance weight decreases when the at least one balance weight is displaced out from the center of the projectile.

15. The method for energy-efficient deployment and retraction of fins according to claim 13 , further comprising:

fitting the at least one fin and the at least one balance weight to a rotatable disc comprising grooves, in which the grooves displace the at least one fin and the at least one balance weight when the disc is rotated,

compensating the deployment force acting on the at least one fin with an equally large and equidirectional radial force acting on the at least one balance weight by balancing a torque contribution on the rotatable disc from the at least one fin and the at least one balance weight, when the projectile is subjected to centrifugal acceleration, with the groove which displaces the at least one balance weight and the grooves which displace the fins.