Underwater Aerodrome Dome

Almost all the difficulties associated with human-powered flight can be traced to the fundamental fact that the Earth's atmospheric pressure is less today than it has been in other eras. This is mostly a Good Thing, since a thicker atmosphere holds heat better than a thinner one, and we already have enough Global Warming problems coming at us as it is.

But it is annoying for any human who wants to fly under his or her own power. The few vehicles that have been built which do allow a human to fly almost all require that that human be in most-excellent physical condition, and plenty of would-be fliers wouldn't be able to get such vehicles off the ground.

No more! In a feat of world-class spectacular/extreme engineering, it is proposed that we go down to the bottom of the ocean (average depth roughly 4 kilometers) and build a huge dome. For the purposes of describing this Idea, I'll propose that we find a flat area about four kilometers in diameter, and build the dome as a hemisphere that's two kilometers high (halfway to the surface). Very few (sinking) ships or subs are likely to collide with it.

We want to build the dome igloo-fashion of very thick and very large glass blocks --the word "cyclopean" comes to mind. The glass doesn't need to be perfectly transparent (will cost less). There are at least three reasons to do it this way.

First is that we can shine lasers through the glass and focus them at the glass joints, to fuse the blocks together. While a somewhat slow process (depends on how many lasers are employed, and how powerful they are), the joints will be stronger and better-sealed and longer-lasting than other ways to connect the blocks. So, when finished, the net result is one vast single-piece glass dome.

(Note that the bigger the glass blocks, the fewer fusings need to be made. Also, because we are underwater, we can use balloon-equivalents to support the weight of the blocks, keeping them lofted high off the seafloor, when doing the joint-fusings.)

The second reason is that glass is very good at resisting pressure. This isn't important when building it, since all the work can be done underwater. It can become important later, of course, when the dome is pumped full of air. Oh, and regarding that rare sinking ship that collides with it, we want the dome to shrug it off, of course! (And we want subs to bounce off, too, naturally.)

Third is that massive blocks simply weigh a lot, and, ideally, we want the dome-full-of-air to weigh MORE than all the water that will eventually be displaced when the dome is filled with air.

Now we are ready to pump air into the dome at sufficient pressure to push the water out of the dome. At four kilometers down, this pressure can easly be almost 400 times normal atmospheric pressure. To some extent this is a major plus, because the air will weigh almost 400 times as much as an equal volume would weigh at sea-level. It means that it will have about 1/400 the tendency to try to lift the dome to the surface of the ocean.

MORE, because the glass in this situation is at first glance not experiencing ANY significant pressure from within or without (the air balances the pressure of the deep, remember), we can increase the air pressure in the dome, perhaps by 50 more atmospheres.

HOWEVER, there is a downside to the above, simply because if the dome is 2 kilometers high, then the weight of the water at the top of the dome is far less than its weight at the base of the dome. We therefore can't actually accommodate 450 total atmospheres of pressure, throughout the interior of the dome. But we can probably have 250 atmospheres or so; the glass at the dome-base resists exterior pressure, and the glass at the dome-top resists internal pressure -- OF COURSE it needs to be very thick!

Before continuing it will be necessary to point out that we will have to use a special gas mixture; we can't simply use ordinary air at that pressure. We want people to be able to breathe this compressed gas and survive, after all! And various gases affect blood-chemistry in different ways, that can cause significant problems when the gases are pressurized. Fortunately, scientists investigating deep-sea diving have worked out the kinds of gas mixtures that can be used safely (the different blood-chemistry effects can be balanced out).

A suitable airlock system is required, of course, to allow arriving submarines to bring customers to this Underwater Aerodrome. Because, at say 250 times normal atmospheric pressure, it will be 250 times easier for the average human to power a flying machine in there! You might even be able to flap wings, and take off....