I was listening to a news account of the troubles the British government was having with expanding Heathrow Airport, and I got to thinking that if such things continue, at some point (say 50 years from now), someone’s going to attempt to do a “Big Dig” and bury the airport and runways.
One big issue I can see with this, is that you’re not going to want a human at the controls, flying the jet into a tunnel (unless its really oversize), it’ll have to be computer controlled. Another issue would be the noise in the tunnel/underground airport, you’ll need some serious noise abatement systems in the tunnel, or it’ll be loud enough inside the plane to damage hearing.
I’m sure that there’d be other issues as well, but I don’t know enough about aircraft to even WAG what they might be. Perhaps the change in air pressure caused by having the jet enter the tunnel would cause problems. (Need to have a way to circulate fresh air rapidly into the tunnels, at the very least.)
So, what other technological hurdles would there be?
I think the runways are going to be, necessarily, open air. The taxiways are relatively small addenda. What’s the advantage for subterranean facilities?
There’s a phenomenon called “ground effect” that operates within about one-and-a-half wingspans of the ground. It works as sort of a cushion beneath the wing, giving more lift than you’d have (at the same speed and angle-of-attack) outside of ground effect. So there are aerodynamic considerations when flying in places where the airflow is constrained in one way or another. In a sufficiently narrow tunnel, where the airflow is limited above, below, and to the sides, I suspect the effects would be even more pronounced.
I just can’t see this ever happening. You may think that planes stay in narrow corridors defined by the runways, but they don’t. Not every plane uses the same amount of runway on takeoff. Pilots sometimes have to abort a landing and climb out. Climb angles are different depending on the type of plane and how heavily loaded it is. The only reason to build an underground airport is if something else is on the surface. In that case, put the airport on top and the something else underneath. What could need that airspace more than the airport?
Actually, there is another reason for a subterranean airport; security. The germans built rockets and aircraft in hollowed-out tunnels during World War II. From what I can find online, I don’t see any sort of runway. I suspect the completed planes were taken away by rail.
I suspect an A380 will displace a wee bit more air when plunging down a tunnel. Either it would have to be a truly gigantic tunnel or have the mother of all air extraction systems.
Besides that, IIRC, the normal landing approach angle is 3 degrees, so you’ll need a fairly long trench for the plane to go down into as it descends into the tunnel opening or you’ll have to build the tunnel on the face of a mountain or hill. Please note that pilots are not keen on flying into mountains.
By my calculations, if you go with the trench idea, and assuming a tunnel height of 50 meters, in flat ground you’ll need a trench 1Km long to descend into the tunnel opening.
Did you ever watch Battlestar Galactica? Accidents in tunnels tend to be bad bad things. What could have been a rough crash landing would turn into a monumental fireball.
Yes, but it would be so levely contained! a fiery inferno of destruction and death underground, while oblivious birds chirp in the prairie above.
I just remembered something related, the IJN carrier Akagi actually had two stacked decks, one on top of the other. Planes could take off from both the lower and upper decks. But not even the Japanese where suicidal enough to attempt landing on the lower, tunnel like, deck!
North Korea has apparently built a few runways that go through/under mountains. It’s not clear, though, whether they actually intend to use these for landing planes, or just as a convenient place to hide them until they take off.
This is pretty silly speculation. There is no way this’ll ever happen. Aside from everything already mentioned, you simply cannot shoot an approach down to the minimums, break out at the last second, make corrections, and zoom right on into a tunnel opening. Firstly, there’s no way to make corrections due to crosswinds and centerline adjustments. Secondly, you’d have to raise the landing mins (the height of the cloud deck above the ground) to give aircraft more time to make a precise path to the opening. Aircraft need a nice long, wide, open-field runway to make these corrections. Ever been on an airplane that’s floated for a bit down the runway before setting down? How’s that going to work with a tunnel opening?
This isn’t even taking into account the empty aircraft and soon-to-be bankrupt airlines operating out of that airport. I mean, I wouldn’t fly on that plane. Would you?
If VTOL or STOL planes ever catch on as well as their researchers would like them to, there may be a place for them in an underground, or mostly underground, facility, but I would wager that, like on an aircraft carrier, would be mostly for storage and maintenance.
I’m surprised that nobody has yet mentioned (or perhaps they have, I only skimmed the thread) that the main reason people protest about expanding airports is not the noise from the airport itself, but the noise from the additional flightpaths and the extra planes that would use these in the event of expansion. Putting the airport itself underground does nothing to solve these problems.
Airplanes, including airliners, are capable of approaches significantly steeper than 3 degrees - it’s just that such steep descents are likely to scare the hell out of a certain percentage of passengers. Some airports require angles steeper than 3 degrees, and cargo pilots fly steep approaches more often than passenger airliners because boxes don’t complain. A trench/ramp is necessary, but not as long a one as you assumed.
Flying an airplane near any object or building, let alone eveloping it in a tunnel, is unsafe. Aside from the logistical and aerodynamic problems already mentioned (say…what happens when the tunnel lights fail when you’re airborn at 100 knots…?), flying in a tunnel would be like driving a car at full speed across a mile-long suspension bridge consisting of nothing but two planks for the tires. Certain death.
But that’s something a computer specifically designed to do that would be able to do repeatedly. Flying is a much more difficult task but it might be possible to build special planes capable of doing this with special tunnels. I don’t have a cite but I was under the impression that a lot of the modern military aircraft are not even all that stable without constant micro adjustments by their flight systems.
The problem I foresee is that even if such technology were to materialize it’s still fairly stupid to make a passenger jet that can’t be landed by a human being.
