This was kind of a fun exercise. I have no idea if embedded images will work but this is worth a try. I modeled an air/raft lifting off of an Earth analogue (same atmospheric model, same gravity, etc). The lifter is presumed to be able to exactly counteract the force of gravity out to 3 planetary radii at which time it no longer functions. The forward thruster provides what would be 0.98 m/s² acceleration in a vacuum. I have an atmospheric drag model (one of my hobbies is back-computing the path of meteors to solar system orbits) which will work well enough for this. The air/raft is presumed to apply the forward thrust at an angle of π/36 radians over the horizon. At the time the drive cuts off, the air/raft has not entered orbit (where q>planetary radius). Approximate orbit is: 

(imgur version https://i.imgur.com/v47PBTg.png ) 

With a more appropriate gravity turn it probably could enter orbit given that thruster but care must be taken by the pilot. I'm not sure this is modeled in a Traveller-appropriate way, though, I can't find the actual rules for air/raft in T5, it's just mentioned that Z-Drive (Lifter) can provide forward motion of about speed-5 (50 km/h)