How would you like to fall from 5 meters height while carrying 6 lit jet engines and a bunch of flammable liquid on your back?

The answer is pretty obviously safety. That, and I doubt flying is terribly reliable either given he is doing it with muscles and his muscle memory (super impressive, by the way), so if he did it over water just to prove a point, there's a good chance he'd ruin tens of thousands of dollars worth of equipment.

He could fly to five metres attached to a safety line on a ten-metre tower, or a crane. A simple auto-descender would do fine.

My impression watching this guy's videos when they have hit the news over the past few months has been that, for whatever reason, it skims the ground and can't ascend. If he wants to disprove that, it should be possible to rig up a safe test.

As far as I can tell, they're working on a garage budget. A ten meter tower and crane is non-trivial to rent and setup.

No reason to disprove something that is disprovable with a basic understanding of basic physics and aerodynamics.

I expect the big challenge with a device like this is NOT ascending too high where you'd be at risk of breaking a leg or thousands of dollars worth of red-hot jet turbine. This isn't a drone, it's a flying person.

That fits the "lack of fine control", doesn't it?

So he's not going to fly much then, is he?

I think this takes some time. It takes 2 years of constant practice to learn how to walk well, and we evolved that capability. Learning to hover and fly might similarly take years. He most certainly could do it, but at significant risk of breaking bones and wrecking his equipment and/or starting on fire.

> Learning to hover

But if there's no ground effect in those videos, then he can already hover. So if there's plenty of footage of stable hovering at 0.5 meters "in mid air", why is there none at all of hovering at 3.0 or 5.0 meters? It doesn't entirely convince me that it can be done.

For the same reason that just because you can balance on a balance beam 30cm from the ground, you'd probably be hesitant balancing on one 5 meters off the ground.

EDIT: If you want to see him testing the concept in a bunch of iterations, you can check out the vimeo page here: https://vimeo.com/gravityindustries/videos/

Arguably, the leg-mounted jets COULD be close enough for ground effect, but they're apparently destabilizing so they switched to two backpack-mounted engines instead.

> just because you can balance on a balance beam 30cm from the ground, you'd probably be hesitant balancing on one 5 meters off the ground

I get what you're saying, but when applied to someone supposedly building flying machines, I just find it a bit of a thin rationale.