TLD's 747 Bus Service (Signal Driver)

Factual Questions
1

So I build a runway. A bloody long one. A couple thousand k’s of tarmac across the Australian interior.

I take a standard Boeing 747 and drive the bugger along it as fast as I can. In other words, I do not want to take off, so I set the flight control surfaces accordingly, and go nutso with the four Rolls Royce engines.

The questions:

  • Is this even possible?
  • How easy/hard would it be for an experienced pilot to do this?
  • How insanely dangerous would it be?
  • What effect would sea level operation, tyre rolling resistance, and drag from the wacky trim and lowered landing gear have on top speed and range? I’m really keen to know how fast you could go.
  • Would the tyres simply overheat and blow up before the first drinks are served?
2

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.

3

Thank you for that informed and detailed response, LSLGuy. Just what I was looking for. I suspected the transitional period of “half-flying” would be a problem. It’s interesting to see how big of a problem it is, and your post illustrates that perfectly.

4

One more comment …

You asked about how fast it could go. If we ignore the tires and the controllability problems, we’re left with the simple question of: “How fast can the engines push the plane along the ground?”

In normal operations, the engines are limited to producing max power for only a little while, with 5 to 15 minutes being typical limitations. The maximum power available for unlimited duration is only maybe 90% as much.

In flight at low altitude, that’s still enough power to push the typical airliner up to max airspeed, which is around 400-450mph. One of the reasons we fly higher is that the air pressure is less up there and as a result the same air resistance occurs at a higher actual speed. The airplane only “feels” a wind resistance of, say, 300 mph when we’re really going more like 600 mph. But down at ground level, apparent and actual speed are the same.

Now having the landing gear extended will slow that a bit, maybe 350-400mph tops, and somewhere around 300-350 mph we can expect the wind to tear off the gear doors which aren’t designed to be exposed to that speed.

For better controllability and higher speed, we’d want the flaps up; if they were extended to the takeoff or landing settings we’d expect to start tearing them up at more like 250-300 mph.

Bottom line: 400-ish mph. And making a REALLY cool noise. Can you imagine seeing THAT roar over the next hill heading at you?

In the military I’ve had fighter-sized airplanes go by at 450+ just a few feet away while I was standing on a hilltop. It was quite a sight, even for somebody used to fast machines. Something 10+ times as large would leave folks speechless, maybe even sh*tless.

Waay cool.

5

In other words, not an awful much faster than current Maglev technology - which involved far less engineering, and far less fuel.

6

But not nearly as cool. :smiley:

7

Course you could always rip the wings off, move the engines inboard, lower it, put high speed wheels and tyres on and (to save on road construction costs) run it on a salt pan. In fact … lookee here!

:slight_smile:

8

I read about a World War II FW-190 pilot who had his plane damaged and put it down about fifty miles from his airbase. The engine was fine and he had plenty of gas, he just couldn’t fly, so he taxied home on the roads. The account didn’t mention speed but I imagine it was no more than ordinary highway speeds.

DD

9

It might be safer and easier to stick with having the runway go the whole distance, but actually take the aircraft off, get the gear up and then snot along at 10’. You’d then have all the benefits of ground effect (the wings become much more efficient when within about 1/2 wingspan from the ground) and none of the disadvantages of friction, tires blowing etc. It’d still look very cool (cooler IMO).

Normally, I’d say that this is very unrealistic given that normal countries have hills and stuff, but, as much of Australia has a landscape not far removed from that of a ballroom dance floor, I reckon you’ve got real chance here :).

DesertDog, the FW190 would have been driven home much much slower than ordinary highway speeds. The tail-wheel undercarriage configuration points the nose up when on the ground partially obscuring your view ahead, and is also inherently unstable on the ground, the tail-wheel fancies itself as a nose-wheel.

10

Just want to add that in the OP’s scenario when the time came that you finally wiped out the resulting carnage would be amazing, probably the best part of the video.

Back in 1996 when I was based at Palwaukee we had a business jet - a Gulfstream IV - cartwheel on take-off. I wasn’t there for actual event, but the aftermatch alone was breathtaking, what with huge chunks of aluminum and what not embedded at all angles in the runway, scattered large debris, and a truly amazingly long and deep skid-mark/furrow plowed through the ground, some trees, a couple small hills, two roads, and a parking lot. A 747 would do a LOT more damage!

11

You mean a WIG (Wing In Ground-effect) plane. The Soviet Union built a few, and more recently Boeing proposed a military transport WIG with 5x the payload of the An-225.

12

Yes. There was also a company in Cainrs, Australia, that was developing a WIG. Apparently they underestimated the costs involved in commercialising the technology.

If I remember correctly, they did test fly the aircraft, and I think they may have crashed it, but I’m not sure.