Each tick you can add something to the Z velocity. That’s why it will help to have a velocity variable to keep track of the current speed. Then your trace will always be FROM: actor location, TO: actor location + (velocity * deltatime)
To get the gravity acceleration to be framerate independent, you’ll need to figure out the formula for acceleration. I’m not too good with the maths side of things but IIRC it’s 0.5 * gravity * (time * time).
So, Velocity.Z += 0.5 * 9.8 * deltaTime^2.
Also the Quake 1 & 3 source is available if you need to look up how they do the maths for things like this.