Aerial roundabout with suspended terminal for exchange of passengers and fueling whilst in-flight. The terminal platform is suspended and stabilized by the several planes that are attached at any given moment. As a result, it rotates. When one plane detaches and proceeds onto its destination, another
takes its place.

Passenger exchange is accomplished when a plane lowers its weighted zip-line, attaches to the terminal, and the terminal trolley ascends. The trolly airlock seals to the plane's exterior, the doors open and the passengers clamor on and off. The trolley then zips down to the terminal platform, is reattached to the next plane's zip-line, and hauled up. A second zip-line is used for the fueling hoses.

Planes from the ground transfer passengers, fuel, and coffee making supplies to/from the aerial terminal. Non-passenger planes can be dispatched from the ground to manage lift voids caused by flight delays.

//A second zip-line is used for the fueling hoses// An unstable platform in the sky, rotating once every 2.3 seconds*, with aeroplanes constantly linking and detatching from it can only be made safer by the presence of thousnds of gallons of flamable aviation fuel.

* - based on a diameter of 100 metres and an aeroplane speed of 600mph (268m/s).

Yes indeed! If we look at a profile of the whole system it will look like a cone. The wide upper rim of the cone will be traveling quite fast. The point of the cone, not so fast. The high speed at the edge is necessary to produce a cone wide enough to avoid crowding of the aircraft while keeping the point of the cone as close to the plane plane as possible. Otherwise, extremely long zip-lines will be needed, and the idea just becomes impractical.

I'm thinking the planes will be flying in a much greater diameter than that. Or do you mean the diameter of the platform? I guess you mean the platform. I'd think the speed of rotation of the conic section that represented the platform would depend on how wide a circle the planes were flying in and how "deep" the cone was.

The circumference of the circle is 314 meters. A
linear
velocity of 277 meters per second gives us an
acceleration of 1543 meters per second^2 or 157
times the force of gravity. Your passengers will be
paste if they can disembark in the given .18 seconds
(assuming they have 50 meters in which to do so)

If you make the air air port much, much larger in
diameter you can get the acceleration down to
something survivable at the rim and it may be
possible to get the changeover time down to
something feasible. For a 30 minute passenger
change time you'll need 500,000 meters at that
speed.

...also, I can sort of see how the platform stays aloft (although within minutes the drag from the
zip-lines would slow the aeroplanes down and pull them inwards until they, and the entire platform, plunge to the ground in a firey inferno) but how does it get there?

Thanks for grinding some of this math. Can't seem to find where I filed that know-how in my head at the moment. Time to create a new manilla and look at these numbers again. Seems a bit larger than I thought it'd be.

//drag from the zip-lines would slow the aeroplanes down//

I thought of that too, but I was hoping the rarefied air would be less of a drag. Some spiraling could be expected.

//how does it get there?//

It's built on-site by a bunch of crazy S.O.B.s in pressurized suits, dangling on wires, from planes flying in circles.

Reminds me a bit of my idea to actually get the planes
off the ground in a similar fashion. [Kansan101] also
brought up the issue of the g-force of such a design
over there.

Hey thanks for the links guys! Here's the calculations I came up with.

The airplane is subject to gravity and centripetal acceleration. The passengers on the trolley are subject to additional acceleration when the trolley starts moving but for now we'll look only at the plane. Using vector addition, and working backwards, we find that the maximum acceleration perpendicular to gravity should be about 10.96m/ss if we want our passengers to experience no more than 1.5 Gees of net acceleration. If we give an allowance of 0.5m/ss for the acceleration of the trolley, this allows us 10.16m/ss for the centripetal acceleration.

We know that the planes fly 1000km/h (277.77m/s), and we know our maximum centripetal acceleration, so we can calculate for r to see how big a circle will need to be. This gives us a radius of 7376.3 m and a circumference of 46,323 m. Using the trolley acceleration of 0.5m/ss and the radius, we can see that it will take 171s to reach the center of the disc. Probably keep it slower than that.

I was curious about how the centripetal acceleration would change as the trolley moved closer to the center so I calculated the revolutions per second and worked backwards from there to get the relationship: a=0.0014/ss * r. This means that for every meter the trolley moves closer to the center, it loses 0.0014m/ss of centripetal acceleration even though it continues to accelerate at 0.5m/ss. You'd feel like you were slowing the whole time. Keeping in mind the accelerations calculated are in the plane of the disc, and not in the context of a cone, I don't see how the math and g-forces defeat this idea... yet. The size is fine.

Where the planes fly, yes. I was hoping for a little smaller, but alas. The platform is much smaller.

The zip-lines are what I'm hung up on. I don't think we have materials that would support that length, especially under load. Even if one could do the monkey fist (in the nautical sense) thing, I don't think the plane could store the zip-line in it's retracted state. It would just take up too much space.

By "fine" I mean closer to what I'd originally imagined.

Float the central airport as a very large balloon,
with a series of tracks around the outside of
decreasing velocity. Still do the tether thing, but
the airplane can fly almost directly above the
outer ring for unloading, and the ring can extend a
jetway to the mid-ventral hatch. (which will be
slightly offcenter to allow for the continuous bank
of the plane).

The multiple rings allow the passengers to walk to
the central lounge, where they will be stranded
and charged $50 for a burger when their
connecting flight fails to show up due to the
failure of the pilot's iPod.