Unit Z orientation (getting shifted by terrain)

[Garfield1337]

I made a projectile system where projectiles travel in a line and are not affected by terrain height (height is defined by: travel height - projectile location's Z). The problem is that when projectiles fly over a bumpy terrain, their Z orientation changes so it looks ugly :\ (Unit movement type is foot)
When i tried the fly movement type, their Z orientation didn't change, but their height was varying.
Any way to fix this?

EDIT: I use quilboar's missile as projectile as it looks quite like a bullet.

 

[Pharaoh_]

By height you mean their actual flying height? E.g. GetUnitFlyHeight() would return various values? If not, then please, explain the difference between Z orientation and Height. Sometimes Pitch angle and Roll angle is they problem to that, but I still don't understand what do you mean by orientation.

 

[Frotty]

Set those to 0

 

[Garfield1337]

By height you mean their actual flying height? E.g. GetUnitFlyHeight() would return various values? If not, then please, explain the difference between Z orientation and Height. Sometimes Pitch angle and Roll angle is they problem to that, but I still don't understand what do you mean by orientation.

Visual height, they go up and down (not sure about their fly height value). By Z orientation i mean projectile's facing in Z axis (pitch).
Frotty's way worked, but thanks for posting.

Set those to 0

Thanks, that worked.