So, this is a marvelous, completely impractical flying machine demonstration. Someone bolted a seat to a jet engine. It's a wonderful demonstration of where automated control is at.
The key issue here is simply the exhaust from the jet. This thing is riding on the thrust from the jet. There's no lift of any kind here, and it's clearly doing a lot of work. As you can see from the debris this kicks up, this isn't going to be near people (or much anything else) at any point in the future. (We won't go into the sounds and such of this machine.)
But it brings up how grav vehicles work in Traveller.
in CT, there's not a lot of detail how AG works. Is there a "gravity force vector" pushing against the gravity of the planet? But how does the residual of that force work? If you're flying around in an air/raft, is there any external effect? Air pushed aside? Dust kicked up? Objects in the gravity field also adopt the AG force vector? Like, maybe as the air/raft is flying, may it collects a cloud of debris. Papers, plastic cups, maybe rocks or whatever, all things that happen to be in the AG field, adopting "AG" properties.
Then there's TNE, with contra-grav. Here, it negates the effect of gravity, negates its pull. But it's not a thrust (well, it is, it's just fixed). Contra-grav can't "push", it cancels/negates. Like standing behind a wall in the wind. The wall resists the wind, but it's not pushing back, per se. It pushes back "just enough".
So, you can't lift on contra-grav alone. You still need an external force to move the vehicle. But you don't need as much. Specifically, contra-grav eliminates (mostly) the "friction" of gravity. You still need 1G of thrust (based on your weight), but you just need it for an instant to get moving. But you will also need 1/100G to maintain that movement (or I should say to counteract the G vector). Because CG reduces gravity 99%.
Back this this jet bike, we can hand wave and say that it weighs 200kg with the rider. That suggest 2kg of downforce thrust to keep it up. Not a whole lot.
But a loaded Free Trader? At 2000 tons, 2Mkg. 20,000kg of force to keep it aloft. Now a Free Trader is roughly 280m in area, so that about .7kg of force per cm^2. THAT isn't too awful. But person, at, say, 2m x .6m, 1200 cm^2, thats 840 kg. I don't think I'd want to be underneath that ship when it took off.
An Air/raft, at 4 tons, 4000kg, 40kg to keep it aloft. Not bad, I wouldn't want it running over my foot. I wonder how close to the front door one of these could land. Because it's going to take more force to slow it down.
