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Underwater Aerodrome Dome

Dome holds highly pressurized air...
  (+3, -1)
(+3, -1)
  [vote for,
against]

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....

Vernon, Jan 06 2012

LØ6 - Furnace Creek http://www.airnav.com/airport/L06
Elevation: -210 ft. / -64 m (estimated) [Klaatu, Jan 06 2012]

Dive tables http://www.scubadiv...ive_tables_NAUI.jpg
[Klaatu, Jan 06 2012]

Sulfur hexafluoride http://en.wikipedia...Sulfur_hexafluoride
"It has a density of 6.12 g/L at sea level conditions, which is considerably higher than the density of air." [Klaatu, Jan 06 2012]

Suspended Animation Suspended_20Animation
This old Idea talks about using 1500 atmospheres of pressure, and nobody claimed it wasn't survivable. [Vernon, Jan 06 2012]

Something on the Hadean Era http://en.wikipedia.org/wiki/Hadean
As mentioned in an annotation [Vernon, Jan 07 2012]

Langly's Steam Craft http://www.flyingmachines.org/lang.html
As mentioned in an annotation. [Vernon, Jan 07 2012]

On Large Chinese Kites http://www.uh.edu/engines/epi340.htm
As mentioned in an annotation. [Vernon, Jan 07 2012]

Kline Fogleman airfoil http://en.wikipedia...%93Fogleman_airfoil
This type of airfoil is a LOT simpler than the standard type. How long ago might it have been discovered, if the air was denser? [Vernon, Jan 07 2012]

Drag http://en.wikipedia...wiki/Drag_(physics)
It says that the power needed to overcome drag must go up as the cube of the velocity. [Vernon, Jan 07 2012]

[link]






       [+] but "450 atmospheres" is an instant soylent-green making machine; I think the record is close to 70 atm.
FlyingToaster, Jan 06 2012
  

       Go to LØ6 on a very cold morning and you'll be at a density altitude of -2200 feet. Easier and cheaper, and without the need for Heliox. <link>
Klaatu, Jan 06 2012
  

       [FlyingToaster], only if you are exposed to it instantly. I'm confident that the human body can adapt to the pressure, if it is applied gradually. The submarine trip between the dome and the seaport will take enough time, I think, to allow sufficient pressurization and on returning, depressurization.
Vernon, Jan 06 2012
  

       LslashedO6 isn't underwater. The airpressure is not going to be 450atm.   

       The underwater record is 2,250 feet which is 69 and change atmospheres.   

       I think it would be rather easy to fly in 70 atmospheres. If that is indeed the idea; I wandered off somewhere around lasers and glass blocks.
FlyingToaster, Jan 06 2012
  

       //The submarine trip between the dome and the seaport will take enough time, I think, to allow sufficient pressurization and on returning, depressurization.//   

       But, the interior of the sub would also have to be pressurized to the same depth. They are not normally pressurized. From a depth of only 130', it takes over 2 hours to decompress after an 8 minute dive at depth. <link>
Klaatu, Jan 06 2012
  

       [Klaatu], the sub might also have to travel a thousand kilometers between the dome and the seaport. We might specifically select a seaport 5000 or more kilometers away, for all trips to/from the dome, to allow adequate compression/decompression time, while in transit.
Vernon, Jan 06 2012
  

       Why the insistence on bone-crushing depth ? 70 atm should be plenty to allow for relatively easy human-powered flight.
FlyingToaster, Jan 06 2012
  

       [FlyingToaster], the depth is related more to the chosen size of the dome than to anything else. We DON'T want ships running into it, but we DO want it to be big enough for lots of fliers and flying-room. And, actually, I see I neglected to think of an important factor (will edit main text -- 450 atmospheres can't work).
Vernon, Jan 06 2012
  

       Houston, I think we have a problem. Since the heaviest component of our atmosphere is Nitrogen, and that is the one gas we must leave behind, you lose lift by using Oxygen and even lighter Helium.   

       I have to bone this. Unless you have conceived of a new way to euthanize cats (getting a bun from 8th of 7, automatically) this idea sinks into the Challenger Deep.   

       Edit: Wouldn't it just be easier to fill a surface dome with Sulfur hexafluoride, and let people flap away?
Klaatu, Jan 06 2012
  

       //sulfur hexafluoride// what I was thinking: it's 6x(IIRC) heavier than air: replacing N2 with SF6 would make a breathable atmosphere 5x heavier than air at ambient pressure.
FlyingToaster, Jan 06 2012
  

       I'm not certain lasers are terribly effective at melting glass together at 4 km underwater.
RayfordSteele, Jan 06 2012
  

       [RayfordSteele], the laser units would be positioned adjacent to the glass, before being turned on. Where did you get the notion that the beams should travel through all that water, first?
Vernon, Jan 06 2012
  

       It's not the traveling through water / dispersion that's the problem I'm raising, it's the rapid heat loss and immediate cavitational boiling at the glass / water interface that would be difficult to work around.
RayfordSteele, Jan 06 2012
  

       Hold everything a mo.   

       We're sort of assuming that a denser atmosphere will be easier to fly in, but is that true? (I ask because I don't know.)   

       A denser atmosphere will give more bouyant lift, but this effect will be negligible for bewinged human (if the density of air were 100x higher, it would be about 100g/litre, reducing your effective weight by about 10% or less).   

       So, bouyancy won't achieve much.   

       How about the fact that the air you "throw" with your wings will be denser? This is more promising, since if a wing-flap pushes a given volume of air at a given velocity, then 100x the atmospheric density should give 100x the reaction force.   

       But then if the air *is* 100x denser, could you still push it (by flapping) as easily? Shirley not.   

       Finally there's viscosity, which should help in some respects but will hinder in others. Does the viscosity of a gas scale with its density?   

       Water is good for flying in, but mainly because it gives near-neutral bouyancy to living things; I suspect that the viscosity of water is an impediment to penguins.   

       So, my question is: will a denser atmosphere (either compressed air, or SF6) make it significantly easier to fly? If so, why?
MaxwellBuchanan, Jan 06 2012
  

       [RayfordSteele], that depends partly on how smoothly the glass blocks fit together, before trying to fuse them. Consider two ordinary lab-glass slides; a little water between them makes them stick together pretty tightly (and the water becomes a thin film). If we can duplicate that effect underwater, between adjacent glass blocks, then fusing could start in the middle of two interfacing blocks, and be worked toward the edges, pushing the (boiling) thin film of water out.   

       [MaxwellBuchanan], for your answer, see penguins. They don't swim through water; they "fly" through water (I'm quoting that "fly" only because it's slower than typical aerial flight). And their wings are stubby because water is so much denser than air. It therefore logically figures that, with respect to actually-dense air, smaller wings are needed than for thin air.   

       Now I recognize that human arms and breastbone musculature aren't adapted for flying, the way birds including penguins are adapted. So, for a human to flap wings and get airborne may be impossible in Earth's gravity (note I wrote "might" in that last sentence of the main text). Isaac Asimov once wrote a short story about how, even on the Moon, humans might not be able to master flying --but that human-style "swimming through air" should be workable there.   

       Whatever. We still have plenty-strong leg muscles, and various pedal-powered flying machines most certainly will work much more easily in thick air than in ordinary air.
Vernon, Jan 06 2012
  

       //[MaxwellBuchanan], for your answer, see penguins.//   

       That was my damned point! Penguins do indeed "fly" through water, but I am pretty sure it is because they are nearly neutrally buoyant in water. Their wings are mainly for propulsion and/or steering, not for lift, because they don't need any lift.   

       Now, if you can compress a gas to the same density as water (to make humans near-neutrally buoyant), then clearly we'll be able to fly. However, as far as I'm aware, you can't do that.   

       So, my question stands: what aspect of compressed air (or SF6) will make it easier to fly?
MaxwellBuchanan, Jan 06 2012
  

       [bigsleep], the primary background notion here is that we can use water pressure to let us play in a higher air pressure. Imagine trying to contain 250 atmospheres of pressure in a huge dome at ordinary ground-level! Thick-walled as I've described that underwater dome, it would have to be even thicker if the water wasn't outside it.   

       [MaxwellBuchanan], regardless of whether humans try to flap wings or use pedal-power to fly, thicker air will allow the wings to be smaller. Think of it in terms of Mass and Action/Reaction. At 250 atmospheres, HOWEVER you move some air, you are moving 250 times as much mass as you move (same volume) at 1 atmosphere of pressure.
Vernon, Jan 06 2012
  

       nice save.
FlyingToaster, Jan 06 2012
  

       Not necessarily so.   

       It may be true, it may not, but nobody has presented a coherent argument either way.   

       It seems fairly intuitive that the amount of air ("some air" as you put it) you can move will be inversely related to its mass and its viscosity.   

       In other words, with a given amount of muscular effort, I might expect to move a constant mass of air.   

       What you're saying, [Vernon] is loosely equivalent to saying "however much lead you can lift, you are lifting 250 times more mass than if you lift feathers."
MaxwellBuchanan, Jan 06 2012
  

       It's easier to flap a couple paddles with 1sqft surface each than if they were 350 sq.ft surface each (based on SF6/O2-mix at 5x weight, and a pressure of 70atm).
FlyingToaster, Jan 06 2012
  

       //It's easier to flap a couple paddles with 1sqft surface each than if they were 350 sq.ft surface each// Even when the stuff they're pushing against is 350 times denser and (I'm guessing) 350 times more viscous?   

       If you're talking about the mass of the paddles themselves, then yes, that is a factor. However, the added viscosity of the high-density gas is going to impede any forward motion as well (and will, equally, impede the return stroke of the wings).   

       The point is that to produce a given amount of thrust, you have to accelerate given *mass* of gas to a given amount (F=ma). That will be true whatever the density of the gas.   

       I'm not saying it won't be easier in denser air, but nobody has given any rational reason why it would be.   

       Put it another way. Aircraft can generally go faster than submarines (for comparable engine powers).
MaxwellBuchanan, Jan 06 2012
  

       OK - Google says that the viscosity of a gas is independent of its pressure (but is dependent on the size of its molecules). So, compressed air will not be more viscous than regular air, but SF6 will be.   

       So, if we stick to compressed air for simplicity, we can ignore viscosity changes.   

       You're now left with the fact that you still have to accelerate the same mass of gas with each flap, in order to produce thrust. That means that you have to expend the same energy to move the gas itself.   

       Like I said, it might go either way. But it's not true in the simple "intuitive" way that seems to be being taken for granted.
MaxwellBuchanan, Jan 06 2012
  

       Yes, but think lever-arm: flapping is much easier if you can move the x pounds of air that's 2 feet away instead of 10. And apparatus weight: smaller wings = less weight. And reciprocating motion: not as much.
FlyingToaster, Jan 06 2012
  

       // 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. //   

       Please cite a credible reference to support this statement. Here I am thinking that the problems associated with human-powered flight mostly had to do with the limitations of technology and human anatomy. Won't I be embarassed when I find out it was just air density all along.
Alterother, Jan 06 2012
  

       //Yes, but think lever-arm// That applies to the mass of the paddle (or wing), true.   

       But then you have a new problem. With big wings, you can glide between thrusts (like a bird does). With a small wing (sufficient only to move the necessary mass of denser air), you can't. Therefore you have to flap non-stop.
MaxwellBuchanan, Jan 06 2012
  

       call. That makes no sense. With a decent suit the human body could become a lifting-body, viscosity aside.
FlyingToaster, Jan 06 2012
  

       Yes, the human body can probably be a fairly good aerofoil, but will only generate enough lift at very high speeds, which have to be generated by a lot of thrust, which means...   

       It's an interesting discussion. I sort of assumed like everybody else that denser air would be easier to fly in. But, since it provides no significant buoyancy advantage (ie, by mass displacement) and has the same viscosity as ordinary air, it's not that simple.
MaxwellBuchanan, Jan 06 2012
  

       Airplanes fly better in cold air. I always assumed it was because it is denser.   

       As for the dome, bugger the glass blocks.   

       Find a flat section of sea bed, ideally with flat rock. Smooth it out good, make a rim around it. Seal the floor with cement.   

       Pump sand onto the floor to make a nice dome shape, and pour concrete onto the sand. Once the concrete sets, pump the sand out, and air in.   

       (I need to think about pressure differences.)
baconbrain, Jan 07 2012
  

       Based on the normal human terminal velocity in atmosphere of (according to WP) 120mph, and an atmospheric density of 350x normal, terminal velocity is less than 10mph.
FlyingToaster, Jan 07 2012
  

       "Density Altitude" is the term aviators use.   

       Wikipedia says, "Air density is perhaps the single most important factor affecting aircraft performance. It has a direct bearing on:   

       The lift generated by the wings — reduction in air density reduces the wing's lift.   

       The efficiency of the propeller or rotor — which for a propeller (effectively an airfoil) behaves similarly to lift on wings. .... "
baconbrain, Jan 07 2012
  

       [Alterother], it is well known that in the Carboniferous Era the atmosphere was was somewhat denser than today. And various flying insects got to be REALLY BIG, partly because the oxygen level was something like 30% --but remember the Square Cube Law --they needed that denser air in order to be able to loft their weight.   

       [MaxwellBuchanan], please recall that the flapping motion of bird wings is not simply up-and-down; there is a twisting component to it, allowing the wing to have less drag in one direction than the other.   

       Also note that I'm NOT claiming that birdlike flying for humans would certainly be possible. I'm sure it would be MORE possible than at ordinary air pressure, but that doesn't mean it would be ENOUGH possible.   

       Meanwhile, pedal-powered aircraft CAN certainly be lots smaller than currently exist, and will be much easier for an average person to use to get airborne. I would expect this Underwater Aerodrome to be used mostly by that kind of flier.
Vernon, Jan 07 2012
  

       There will be a limit to the height of a aerodrome as well, by the effect of altitude sickness. Normally 4000m is going to cause some minor problems, but that will be 250x more of an effect in the high density atmosphere, limiting the effective ceiling to around 16m...? Huh? Doesn't sound right, does it?
Ling, Jan 07 2012
  

       ^That's anoxia; won't matter.
FlyingToaster, Jan 07 2012
  

       [Vernon]: the non-existence of human beings or anything even remotely like them during the Carboniferous Era, and the noted lack of resemblance between human beings and flight-capable insects of _any_ era are also well-known facts. I am aware that air density (or altitude density) is a major factor in the mechanics of controlled flight, but I still do not agree with your claim that air density has been the primary impediment in the development of human- powered flight, so once again, I humbly request that you cite a reference. Any reference.
Alterother, Jan 07 2012
  

       [Ling], the height I specified for the dome is only 2000m. And, inside a pressurized container, the effects of gravity on air pressure are, I think, negligible.   

       [Alterother], you seem to have missed the point. Why are insects so much smaller today than in the Carboniferous? Partly because of the lesser oxygen level today, AND, crucially, partly because the air is thinner. Which means, for ANY creature with a hankering to fly --like humans-- thicker air makes it easier. Therefore, quite logically, if the atmosphere was thicker, we would have had less difficulty developing flight --we'd have put lots more effort into keeping things from blowing away in high winds, than we actually do!
Vernon, Jan 07 2012
  

       With all respect, [Vernon] (and I mean that), I'm simply taking issue with your opening statement, which seems to imply that air density is the major impediment to human- powered flight, which it isn't. A minor impediment, yes, but the thing that's been really holding us back has been the long, slow development of technology allowing us to overcome our natural inability to sustain flight. This, I believe, has much more to do with our anatomical arrangement and the relative density of our bones and tissue. The air density issues have already been solved by the development of mechanically-powered aircraft technology, and can now easily be (and are) adapted to human-powered contraptions, of which many exist, functioning to greater or lesser degrees of success. Yes, higher air density would probably help, but you're working on electronically-timed fuel injection while everyone else is still inventing the wheel.   

       Essentially, I see this as an idea based on a fundamentally flawed premise, and (in my view) your comparisons to insects large and small, from any era in Earth's history, have little bearing on human-powered flight because A) flying insects have their own wings built in and don't need to construct things like pedal-powered Ekranoplans, and 2) human beings, with rare exception, are not insects. Furthermore, this is a wonderful argument and I'm going to play with it until it breaks.
Alterother, Jan 07 2012
  

       //human beings, with rare exceptions, are not insects// marked-for-tagline.
mouseposture, Jan 07 2012
  

       //thicker air makes it easier//   

       (A) denser air isn't "thicker" - a gas's viscosity is independent of its density.   

       (B) if you mean "denser" - does anyone happen to know how dense the carboniferous atmosphere was (at sea-level)?
MaxwellBuchanan, Jan 07 2012
  

       Apparently it's a well-known fact, or at least is stated as such.
Alterother, Jan 07 2012
  

       [Alterother], with a denser atmosphere, lighter-than-air craft would have been made human-capable far sooner than actually happened. And as for heavier-than-air craft, the problem is often discussed in terms of power-to-weight ratio, but that view is simplistic, since it ignores the increased lift that can be achieved when the air is denser.   

       (I might mention kites as a form of heavier-than-air craft, and if I recall right, the Chinese built some large man-carrying kites a number of centuries ago. Note that if true, denser air would have allowed the kites to be smaller.)   

       Anyway, for free flight, denser air means that a rather lesser power-to-weight ratio would have been needed, to construct the first powered heavier-than-air craft. There's a famous incident about Samuel Langley trying to build a steam-powered airplane, and he might have beat the Wright brothers except that the steam engine that he special-ordered arrived twice as heavy as he wanted. Or something like that.   

       Next, with respect to actual human-powered flight, the focus was on the strength-to-weight ratio of materials used in constructing them, due to the fact that the available power was strictly limited --but again, if the air was denser, some of Da Vinci's designs might have gone airborne in his lifetime.   

       [MaxwellBuchanan], most people don't bother about the distinction between denser and thicker. But your point is valid, so...   

       Regarding denser air in truly ancient times, there's a Wikipedia article about the "Hadean" era, which states: "iquid water oceans existed despite the surface temperature of 230 °C (446 °F) because of the atmospheric pressure of the heavy CO2 atmosphere" --the pressure isn't mentioned. (It occurs to me that this could have been an important factor in the early appearance of Life, since chemical reactions of all types proceed faster at higher temperatures. That is, more reaction-possibilities could have been randomly "tried" in a shorter time.)   

       I've read elsewhere that Earth has had about the same amount of CO2 as Venus, which today gives Venus an atmosphere 90 times as dense as Earth's. But life on Earth sequestered this planet's CO2, mostly in the form of calcium carbonate rocks (chalk and limestone, some of which has been metamorphosed into marble), but partly --during the Carboniferous Era!-- by separating out the carbon and (eventually) making coal.   

       Well, back in the 1960s or so, I read that the world's known coal reserves could last (at then-current rates of burning) for 500 years. No hint of global-warming consequences were attached to that fact, of course. Nor was there any logical concluding about what the Earth's overall atmospheric pressure would be like, if it all was burned...but it IS indeed quite logical that when all that coal was formed, Earth's atmospheric pressure had to have diminished at least some.
Vernon, Jan 07 2012
  

       //Anyway, for free flight, denser air means that a rather lesser power-to-weight ratio would have been needed, //   

       Why? I'm not saying it's not true, but why?
MaxwellBuchanan, Jan 07 2012
  

       [MaxwellBuchanan], if you assume that all the effort needed to loft a human from the ground must come solely from engine power, then power-to-weight ratio is indeed the only factor (as in taking off from the Moon). But on Earth we can use airfoils to let the air itself provide lift. Consider a submarine and the size of its diving planes, versus the horizontal stabilizer of an equally-large aircraft.   

       And, there is a "power law" associated with the power needed to overcome wind resistance. So, the faster you must go through air to get enough lift, the much-more power you need. While you would obviously need SOME more power to push through denser air than thinner air, you can avoid the effects of the power law if you can get off the ground at a low speed.
Vernon, Jan 07 2012
  

       //Consider a submarine and the size of its diving planes, versus the horizontal stabilizer of an equally- large aircraft.//   

       Indeed so. And yet, mysteriously, the aircraft flies faster and has more comfortable seats. I think this clinches it.
MaxwellBuchanan, Jan 07 2012
  

       // the aircraft flies faster and has more comfortable seats //   

       From this statement, it is possible to deduce with a high degree of certainty that you have never made the aquaintance of the Tupolev Tu-154 (for which you should immediately fall on your knees and thank any Deity that you may subscribe to).
8th of 7, Jan 07 2012
  

       And from yours, that you have never been cajoled into following an older sibling in his quest to find the breeding ground of the Western Pacific Nugfish.
MaxwellBuchanan, Jan 07 2012
  
      
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