REPUBLIC OF SERBIA

MINISTRY OF DEFENCE

www.mod.gov.rs

MINISTRY OF DEFENCE

Material Resources Sector

Defensive Technologies Department

Military Technical Institute

www.vti.mod.gov.rs

Rocket dispersion reduction by the fins in the nozZle

SLOBODAN MANDIĆ

Military Technical Institute, Belgrade, msmanda@mts.rs

SAŠA ŽIVKOVIĆ

Military Technical Institute, Belgrade, sasavite@yahoo.com

SINIŠA JOVANČIĆ

Military Technical Institute, Belgrade, jovancicsinisa@gmail.com

Abstract: Dispersion of the impact points of the unguided rockets is a consequence of disturbances, such as thrust misalignments, asymmetric aerodynamic manufacturing inaccuracy, etc. Influence of some disturbances is most dominant in the initial phase of the flight when the rocket leaves the launcher due to the small velocity. This influence is minimized by rotation of the rockets in the tube of the launcher which in most cases is realized by the pins connected to the rocket which follows the  groove in the launcher tube. The rotation of the rocket in the launching tube and during flight can be also realized by stablizing fins foled in the nozzle when the rocket is in the tube which is deployed when the rocket leaves the tube. The rolling moment of the rocket in the tube and during the flight, generated by cant angle of the fins, is analyzed by CFD calculation. The CFD calculation is also used for determination of the fin hinge moment, generated by exhaust gases from rocket motor, required for deployement of the fins when the rocket leaves the tube. Influence of the of the rocket rotation to the impact point dispersion is analyzed by 6DOF numerical simulation of the rocket flight. Rotation of the rockets is verified experimentally by firing rockets and ultra speed camera record.

Keywords: Air to ground rockets, trajectory dispersion, CFD calculation, roll rate of the rocket.