Setvectordir / setvectorup

[SouthSaturnDelta 1]

Hi .

I drop a bomb and get it to 'wobble' until it detonates using this (crude) effort ~

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Code Sample </td></tr><tr><td id="CODE">

_n = 0

#LOOP

~0.15

_bomb2 setVectorup [(getPos AIR1 select 0)+ _n  ,(getPos AIR1 select 1),(getPos AIR1 select 2)]

_n = _n + 0.15;

~0.15

_bomb2 setVectordir [(getPos AIR1 select 0)+ _n  ,(getPos AIR1 select 1),(getPos AIR1 select 2)]

~0.15

_n = _n + 0.15;

?(alive _bomb2): goto "LOOP"

Now here the problem -

Why do I have to use alternates of setvectorup and setvectordir for the bomb to be moved.If I use either of these commands then the bomb remains stationary (while falling).

Can anyone suggest a way of creating a smoother wobble effect for ordnance?