Having trouble turning off gravity through script

I’m creating a script that launches a missile from a helicopter, and I want the missile to fall a bit and then launch. I have useGravity unchecked in inspector.

When I launch the missile, it drops (because the script sets useGravity to true), and then starts moving forward after .5 seconds (using constantForce.force and yield WaitForSeconds), but keeps falling even though I set useGravity to false after yield WaitForSeconds(0.5).

Could it be the yield that keeps it from finishing the execution and turning off gravity?

**Note: When I launch the missile, in inspector, I see Use Gravity quickly check its box then uncheck it.

You probably need to set the missile y velocity to zero after you turn gravity off to stop the motion in that direction.