Create a script like this.

_projectile = "M_Mo_82mm_AT" createVehicle [(getPos player) select 0,(getPos player) select 1,((getPos player) select 2) + 100];

_projectile setVelocity[0,0,0]; weird result
_projectile setVectorDirAndUp [[1, 0.5, 1],[0, 1, 0.5]]; no effect

I want to create explosions(with visible dropping projectiles) without using artillery (because I don't have a place to put the artillery units).

to see if setVectorDirAndUp has an effect, add the following:
_projectile enableSimulation false;