As i just wrote in another tag here...

It's the 'Vertical'-tag that makes the bomb drop horizontal. If you use the Vertical=yes in a projectile that is fired from a unit that uses the aircraft-locomotor it'll make the projectile move horizontal out of some wierd reason. Either use a hovering unit (like the blimp or the jumpjet) to fire the projectile or remove the 'Vertical'-tag.
I'll give an example:
[NapalmBomb]
Damage=75
Burst=5
ROF=20
Range=7
CellRangefinding=yes
Projectile=NapalmBombP
Speed=1
Warhead=NapalmWH
Report=KirovAttack
OmniFire=yes
[NapalmBombP]
Image=ZBOMB
Arm=2
Shadow=no
Acceleration=1
Proximity=yes
Ranged=yes
This is my napalmbomb that i use to drop out of an A-10 plane in my mod.

It works like a charm! Just give the NapalmBomb to the planes Primary weapon (Primary=NapalmBomb) and see for yourself.
B.T.W. have a lookout for my mod if you like, i'm about to release it soon.