It's not the 3D that kills you; it's the sudden 2D at the end.

Yup but I always thought what if we do like a 1 feet above the ground? We avoid death by plummeting from the sky.

There are other advantages like

- we don't need roads and we save a lot of energy and money on their construction and maintenance.

- we also save energy by going from point A to point B directly instead of following the road.

- No friction between tyre and ground

I guess the amount of energy required to keep vehicle above ground by 1 feet is more than all the savings combined.

You’re not going point to point a foot above the surface unless you’re over water (calm seas at that). Soviets built a concept plane that did just this, though. Airplanes are more efficient near the ground than a little bit away, but not as efficient as at normal cruising altitudes.

You're probably thinking of Ground Effect Vehicles (sometimes Ekranoplans). The Russians built lots, not just as a concept, if you own a huge lake (not an ocean) they're somewhat practical for crossing it quickly. The Americans and Canadians (who also own some large lakes) have likewise built some of these.

The Ground Effect, as its name suggests, only exists near the ground, so in one sense you're "flying" but if the surface drops away you will fall too. Hence it's good on a lake or possibly open plains, but won't work on normal ground with rises and hills and so on, never mind buildings and trees.

I'd thought that there were only a few prototype Erkanoplans built, though it seems there actually was an operational fleet.

There's a particular larger model intended for defence purposes which saw only a single prototype, now abandoned.

The Soviet Navy ordered 120 Orlyonok-class ekranoplans, but this figure was later reduced to fewer than 30 vessels, with planned deployment mainly in the Black Sea and Baltic Sea fleets.

https://en.wikipedia.org/wiki/Ground-effect_vehicle#Soviet_U...

There is one specific prototype which has seen some attention (article and videos), the so-called "Caspian Sea Monster":

https://en.wikipedia.org/wiki/Caspian_Sea_Monster

On HN a couple of years back:

https://news.ycombinator.com/item?id=24857096

For water use, hovercraft tend to be more flexible. They still experience issues in rough water, and though they can cross flat unimproved terrain (beaches, swamps, snow, meadows), they perform quite poorly on slopes, particularly laterally, and generally have poor lateral stability, notably with high winds.

Hydrofoils accomplish much the same capability on water. Tracked vehicles on land. Not having to support your mass dynamically also helps. That said, hovercraft remain useful for military marine beach landings. And eels.

I was thinking of the single giant transatlantic troop carrier they built. You’re right, there are others.

3D has the problem is that you can't just stop, wait and think if anything is totally weird. A self-driving car can pull over if it's confused, a self-flying plane can't.

Then again, self flying planes have been a thing since the early 1910s. It's far easier when you can just pick and altitude and heading and you're basically 99.9% in the clear that you won't hit anything.

In a car that approach will get you roughly a few meters forward, so it's incredibly hard to make a working car autopilot in comparison.

Well, usually it can stop, but if it gets confused during road construction where there's no shoulder to pull off to and it just stops in the road, you run the risk of a truck rear-ending you.

Empty air, a 2d empty plane would be easy too. If it was 3d tunnels it would be hard, those Descent videogames were tricky.

It is considerably more complicated. Apart from added axes of movement (not just vertical, but pitch/roll), you also have to contend with the fact that air is the only source of friction. Acceleration and breaking are much slower than something with wheels on the ground. There is a reason why flying a plane in Grand Theft Auto is much harder than driving a car, even with the simplified physics and vehicle controls.

If we could make aircraft that handle in our atmosphere like the spaceship in Descent, then that would close the gap a bit. But I'm not holding my breath.

The more axis you have to account for, the more complicated it gets.

Go play a car simulation game. Done? Now go play Descent and tell us if it's any easier.

Except when something breaks, and you need an equivalent of parking by the side of the road.

Some factors that complicate the job: Higher speed, more kinetic energy when crashing, aerodynamic lift, uncontrollable regimes...

It is definitely not easier. I mean avoiding a mid air collision might be but that’s rarely what kills a pilot.

no : stalls are deadly in 3D, send the ground at you with no control unless one recovers