Airline pilot here …
That’s a darn expensive runway. To hold a 747 the concrete is normally about 2 feet thick, and a typical runway is 150-200’ wide.
Is it possible? Sort of. Airplane tires are designed for intermitent use and will overheat if run at any kind of speed for very long. Their max speed is also limited to maybe 120% of normal takeoff speeds.
So if you got going much above 200 mph, you’d start shredding tires immediately. And even at more typical takeoff speeds of say, 175 mph, they’d start coming apart after 10 minutes tops. Shredding tires are what brought down that Concorde in Paris. There’s a LOT of energy in big chunks of rubber rotating that fast. So that’s your real limiting factor.
How hard would it be to control while almost-flying? If we ignore the tire issue and assume we’re really going to be cruising this way, it’d be pretty hard. An airplane almost flying is a skittish beast. As the speed increases the wings begin to carry the weight, which means the tires are carrying less and less. Eventually the tires are carrying zero and you’re flying.
In real flying, we hasten the takeoff process by accelerating to an intermediate speed and then pointing the airplane into the air to essentially pull it off the runway quickly. If we didn’t “rotate” the nose upwards, we’d roll a lot farther and faster, but eventually it’d lift off in a more or less level attitude.
So the issue is a little bit definitional. At, say, 100 mph, the airplane isn’t flying at all, it’s just a very complex truck. At 200 mph it’s flying in every sense of the word, and you’re trying to force it to stay near the ground. Flying near the ground for any length of time gives you lots of opportunities to bump into something, which is not good for your health.
An airplane is steered on the ground via the nose wheel(s), like a super-fast tricycle. The faster you go, the more skittish the tricycle. Who among us hasn’t (at age 10) ridden a trike down a hill & crashed spectacularly?
Steering in the air is done by banking, which then causes the airplane to turn left or right. But, rolling on the ground you can’t bank much or you’ll drag a wingtip or outboard engine on the ground.
In the transitional condition you want to operate in, both control systems are at the edge of their envelopes. In normal operations we get through that tough spot in just a few seconds; living there for hours would not be easy (or safe).
Finally, zooming along at 200mph or so, the slightest hill or valley or curve would be a major challenge, and at that speed you’d be dealing with rapidly changing crosswind coditions as you blasted across the countryside. That’d be less of a problem across a broad plain, but in hilly terrain, it’d add to your other control woes.
How dangerous? See above. In the real world you’d wreck tires in a few minutes, top, followed by either losing control or having a fuel leak, or fire, or both. In the fake world where we pretend the tires aren’t a problem, you’d still be working darn hard to not screw up. I’d give it 30 minutes before I either crunched the jet or climbed up to 25 feet or more, which I define as cheating. How long could *you (or a non-pilot professional truck driver) almost-fly on the first attempt? 3 miles = 2 minutes maybe, on a good day, if you were lucky.
How fast? As I’ve said, nobody can almost-fly & maintain control for any long duration (30 minutes plus). So we’ve got to stay below the almost-flying regime, where we’re just using it like a very fancy truck. If you leave the flaps up, you can probably make about 175 mph and still be controllable.
Fuel economy would suck bigtime. I can’t hazard a guess, not having 747 fuel consumption figures available, but you’d do a LOT better to fly at altitude, where the 747 gets around 40 miles/gallon/seat.
All in all, not a real practical idea. I’m sure you could sell the videos for a lot of money though. Just make sure your life insurance is paid up.