The Viability of Hot-air balloons as travel

While the Zeppelin of war making the victorian /pre-WWI world a smaller place is a common cliche in AH, are hot air balloons able to be used/made/designed in a way that makes it practical for their use in the 1800s?
 
A "balloon" as opposed to an "airship" by definition is not propelled; it drifts with the wind. That's an obvious huge drawback; you can only travel downwind. Of course in principle one might be very clever, rising to various altitudes until one finds a favorable wind, but in practice of course one's range of altitude is limited; then too 19th century meteorology wasn't up to predicting much about the profile of high altitude winds, nor is it very likely that one will find the right wind--some variation leads to some control of direction, but one can hardly expect to rely on a wind blowing dead opposite the direction it's going near the ground!

Then, despite the apparent simplicity of the hot air balloon, the fact is the great age of their use is today, not a couple hundred years ago. Modern hot-air balloons use fairly advanced materials, strong, heat-tolerant, yet lightweight, and advanced burners that very efficiently use hydrocarbons like propane; neither of these would be available to early hot-air balloon pioneers.

This is one reason why hot-air ballooning gave way early on to hydrogen balloons; the lift is much more concentrated so rather inferior materials could be concentrated to hold the gas--also, there wasn't the challenge of the materials having to put up with high temperatures.

If we ask, can we make dirigible airships based on hot air, the answer is, well sort of, but they are even more marginal than a hydrogen airship. When making a structure that must not only suspend a load but handle well in fairly strong air currents as an airship hull must, the poor concentration of lift and consequent huge volume requirement penalizes hot-air airships badly. Not to mention that shapes that are good for moving through the air are not so good for retaining heat nor for using the available lift with maximum efficiency, and moving the ships through the air requires more structural strength in some form (either pressurizing the hull to get a blimp, or some kind of framework, internal or external) and the motion through the air will tend to accelerate the cooling of the lift gas.

Anyway in the mid-19th century, there were no good power plants for an airship; attempts to use steam engines gave way quickly to electric batteries, which were pretty awful by modern standards and yet better than anything else available at the time. The modern airship waited for Alberto Santos-Dumont's successful mating of an internal combustion engine to a hydrogen blimp hull, in the decade of the 1900s. (Others had tried using IC engines with hydrogen gas bags and met disaster--at that Santos-Dumont was probably very lucky, for one thing the weather in the Paris area (I think maybe all of Western Europe, this favored Zeppelin in south Germany too) was unusually calm, I've been told).

Once again I offer this link. Tom Goodey is quite serious. Unfortunately in addition to being hot, water vapor is going to tend to be chemically aggressive toward almost any plausible balloon material you can dream up. Modern hot air balloons achieve temperatures comparable to steam, and if early 19th century ones did so as well I guess there's a chance that their materials might work OK to hold steam. The advantage, if you can make it work at all, is that steam lifts a lot more per cubic meter than hot air does, about three times as much in fact. Then too you can sidestep the issue of how to make an efficient burner by concentrating on making an efficient boiler instead! In fact as you might learn by perusing Goodey's pages, the initial generation of steam to inflate a gas bag is really more of a task than you'd want to attempt to enable with an airborne boiler--practically speaking steam balloons would be inflated by ground-based boilers; in that way they are more like hydrogen balloons. But you might want an auxiliary boiler to boil ballast water, thus shifting weight into lifting volume, and compensating for the inevitable condensation and precipitation of the initial steam charge.

Remarkably, he found that a square meter of his small test balloon condensed about 2 kg (IIRC, check what he has written there) of water in an hour; at that rate a decent-sized balloon capable of lifting a good fraction of a ton might last many many hours airborne.

A steam airship would still be a marginal affair compared to a hydrogen-inflated one; in correspondence with me Goodey pointed out many problems. Still, it does allow an ingenious solution to a problem that plagues other steampowered aircraft proposals--how to condense the exhausted vapor from a steam engine so as to reuse the water? (Using the lift bag as a condenser is a solution Tom Goodey has patented; whenever I mention it I feel obligated to point that out). If we have a hydrogen airship that has an auxiliary steam lifting cell and power it with a sufficiently light and powerful steam engine, we at least know how we can get the water back, and meanwhile by varying the flow of cooling air around the steam cell, we can probably vary the rate of condensation considerably, thus giving a nice range of trim control. So when I think of steampunk airships, I definitely give thought to designing it so at least some lift comes from a steam cell!

If you want to avoid hydrogen completely, a steam airship will again be slow and bulky compared to a hydrogen one, but then again in a low state of the art there's less power available anyway. The trouble with slow airships is, they need enough speed capability to deal with contrary winds; OTL the 60 knot cruising speeds of the later rigids and better blimps was just barely adequate.

Of course if we are comparing them to free balloons, even an airship capable of only a mediocre 30-40 knots might come off looking pretty good! It would still have to be operated mainly as a free balloon, seeking favorable winds to speed it along, but you'd have a bit of dynamic lift capability to offset variations in static lift to a modest degree, and climb or descend under control when properly trimmed to static neutrality.

I'm thinking right now of something 100 meters long, 25 in diameter; allowing for a 10 percent volume expansion to allow for a kilometer or so vertical range before it becomes necessary to vent gas, if it can attain a maximum airspeed of 40 knots and has drag comparable to the big rigids (implying pretty poor streamlining but that seems likely at this state of the art) then maximum drag force should be something like a quarter what those big rigids could handle; structural stresses would be, well, a fifth or so and allowing for a poorer state of the art across the board, maybe the basic structure comes in the 20-25 metric ton range, whereas static lift is about 40 tons, so there's some room there for engine, payload, and fuel. Power requirement is about 1/10 the 6000 hp or so installed in the big rigids, around 600 hp. How light can a mid-19th century steam engine and boiler combination be made to meet that spec?

Slow it down to say 30 knots and the ship is that much more helpless in adverse winds, but power goes down to less than half of 600 HP and the structural requirement gets cut down a lot too--a portion of it is fixed by the need to suspend the weight, so it doesn't go down to 9/16 as we might expect but we ought to get the all-up structural requirement including engine and boiler down well below 20 tons anyway.

By even early 20th century aeronautical standards it's a slow pig, but it might accomplish something usefully impressive in the mid-19th.
 
Another approach...

Would be Dr Solomon Andrews's Aereon. The Wiki article has a criticism of the explanation, which is well taken--the article should mention that the propulsive method is simply that of a glider. Andrews would begin with the craft having an excess of static lift (hydrogen)--clearly then it would "fall" up, and just as a glider can, by the right choice of angle of attack, prolong a fall down and parley it into forward motion, so can an excess of static lift be manipulated into forward flight while rising. It's the opposite, or rather reversal, of the airship practice of controlling deviations from perfect equilibrium with dynamic lift while under propulsive thrust. When the craft is in danger of rising to excessive heights (either those where human beings suffer from insufficient air or excessive cold, or where the gas has expanded to the limits of the structure and must either be vented or cause ruptures) gas is vented; with normal balloon practice one seeks equilibrium; with the Aereon Andrews would vent more gas and the ship would then sink; again providing leverage for forward flight on the same principle, now more obviously the same sort of thing as a glider. Approaching the ground he could then drop ballast, again becoming light, and thus extend the flight another pair of legs, and so on until the gas lift fell below his minimum structural weight, at which point he would have to land--or crash, if he vented too much gas!

Dr. Andrews demonstrated Aereon I to President Lincoln and Congress by flights over Washington DC, and offered the craft and his services in building more to the Union cause during the Civil War. He was observed to have some success in making headway against the wind.

Obviously, this is no means of making progress against really significant contrary winds, but it certainly does offer a certain amount of maneuvering capability.

Using steam for lift obviously has some possibilities here; start with excess steam, perhaps instead of venting it simply allow it to condense until the ship first comes into equilibrium at altitude and then starts to sink; before hitting the ground reboil some of the condensed water, and so on.

Of course this is rather different because most of the time, the ship is pretty close to equilibrium and thus the propulsive force available is pretty feeble. Using alternating excess and deficient hydrogen lift involved constant positive or negative weights; alternating slow condensation with gradual build-up of vapor would be more gradual and result in being basically a free balloon between the extremes. But it avoids the obvious limit of venting lift gas and dropping ballast--replacing that depletion with depletion of fuel.

I'd think that this mode of achieving some control might be more attractive in combination with a steam engine that might in itself be too feeble for the job but use clever manipulation of steam aerostatics to enhance its effectiveness. Progress over land might be made, particularly if fuel supplies could be laid in reliably. Over the open ocean of course one must design for sufficient range and given mid-19th century limits, realistically the trip is heavily dependent on predicting the prevailing winds. And obviously a risky stunt rather than something one could base any sort of economical transport (or military strategy!) on.

However other roles, such as a military scout, might be envisioned. Warships in the WWI era and before did sometimes carry "kite balloons" which were tethered hydrogen balloons with some aerodynamic shaping, to lift observers far above the ship to see over a wide horizon. An untethered very high rising variable-lift Aereon type craft might, at some daredevil risk to the observer (of the weather changing beyond his capability to maneuver back to the ship) extend that range considerably more. This is doubtless the sort of service Andrews meant the Union Army to derive from his invention, though I believe there was some hyperbolic speculation about being able to fly over enemy lines and drop bombs.
 
It should be noted that there are some questions among aviation historians regarding the Andrews' Aereon airships. As I understand, most of the primary sources are contemporary newspaper articles (and newspapers then often carried fanciful stories of progress in developing airships and airplanes). The account was popularized in a mass-market history of airships written by the journalist John Toland in in the 1950's or 1960s. Like many mass-market books written at that time, it is a well-written and very entertaining book based largely on secondary sources that is replete with inaccuracies and exaggerations to make the history more interesting.

To my knowledge, there are no official government records that would absolutely verify the supposed test flights for Lincoln ever really occurred.

Another problem with the story is that, if the unpowered Aereon worked as well as it did - and if was actually demonstrated for the President in the midst of a Civil War where aerial scouting would be of great value - why was the concept not further developed, since it supposedly provided dirigibility at least as effective as early Santos-Dumont airships in the early 1900's, entirely without a motor.

Regarding the basic question that started the thread I certainly can't add more than Shevek23 did.
 
The Steam Walrus lurking in my brain

It should be noted that there are some questions among aviation historians regarding the Andrews' Aereon airships. As I understand, most of the primary sources are contemporary newspaper articles (and newspapers then often carried fanciful stories of progress in developing airships and airplanes). The account was popularized in a mass-market history of airships written by the journalist John Toland in in the 1950's or 1960s. Like many mass-market books written at that time, it is a well-written and very entertaining book based largely on secondary sources that is replete with inaccuracies and exaggerations to make the history more interesting.

To my knowledge, there are no official government records that would absolutely verify the supposed test flights for Lincoln ever really occurred.

Another problem with the story is that, if the unpowered Aereon worked as well as it did - and if was actually demonstrated for the President in the midst of a Civil War where aerial scouting would be of great value - why was the concept not further developed, since it supposedly provided dirigibility at least as effective as early Santos-Dumont airships in the early 1900's, entirely without a motor...

You might well be right--I suppose it's possible the whole story of the amazing Aereon was exaggerated or even had parts made from whole cloth. I frankly have never considered this.:eek:

But one reason I accepted it was that the physical mechanism whereby such a craft can work is pretty straightforward. Airships in practice rely on dynamic lift all the time; it's how they can keep a course in a side wind, how they can stay airborne when heavier than their gas lift alone can support; how they can avoid rising uncontrollably up to pressure height when lighter. The USS Akron and Macon, the aircraft carrier naval scout rigids that were nearly as big as the Hindenburg, often flew as much as ten tons overweight (their static lift being somewhat less than 200 tons). Clearly the mechanism can be reversed, and a static imbalance can be leveraged into thrust.

But I wouldn't expect much thrust! It's all very well for maneuvering in light winds; they could hardly prevail against a strong headwind. (To be fair, neither, sometimes, could even such big and powerful ships as Akron or Macon!:eek:) Then too the range would be rather limited; an aerostat might possibly be designed to rise to say 10,000 feet, 3 kilometers--to do so you have to either vent a quarter of the lifting gas you started with at sea level or start out with less than 75 percent full to allow for such a pressure height. (A ship that starts out full has a pressure height of zero; it needs to begin valving gas immediately, or else the pressure of the gas will burst the necessarily light structure, however that structure is laid out). Actually airships, and still more balloons, have risen a lot higher than that--I threw that height out because that's the altitude where human beings start to suffer from low air density and pressure. Press on much above that height without supplemental oxygen or pressurized living spaces and more and more people would start to suffer various problems; much higher than 3 kilometers and everyone begins to suffer from the insidious effects of anoxia. Some people are acclimated and won't, that low, but everyone has a limit. And beyond that limit, as with drunkenness one of the first things to go is judgement, so people are quite likely to get far into the danger zone before they realize they have a problem, and by then their ability to solve it is seriously impaired...so it doesn't pay to make an unpressurized vessel go a whole lot higher than 3 kilometers.

But 3, 5, whatever--clearly an Aereon type system can only take you so far before you have to vent whatever excess lift you have left and begin the sinking leg of the trip. Then you have the same limit, where you better drop ballast or else hit the ground. I can't see these iterations taking a craft much more than say 100 miles, in good weather, and doing so involves loading the craft up with lots of extra lift gas and lots of ballast--much more than the payload I'm guessing.

I do know that there have been thermal (i.e. hot air) balloons that have attempted to exploit the same principle; I don't know with what success. It looks like getting something for nothing, but of course a hot air (or steam) craft is using fuel to heat the air or steam, and a hydrogen version like Andrews's is using hydrogen that has to be synthesized at some trouble and expense, and casting these resources literally to the winds.

I think that designing a craft to use it to advantage at opportunity would on one hand be better than no powered propellors at all (or, given 19th century limits on power/weight ratios, practically none), and on the other help out a craft that has marginally adequate prop/engine systems.

Once the latter were available, serious inventors tended to focus on them and the Aereon approach was pretty much relegated to a stunt.

One reason I've been thinking of Andrews, and the relation of thrust to dynamic lift in general, is that this thread has revived a sleeping monster in my brain, the cargo airship that uses a significant amount of steam for variable lift. The steam volume can be used much more efficiently if it is not necessary to vent the steam, but rather it could be condensed and converted to ballast.(Here, my concept is, an airship whose fixed weight is borne by helium, nearly as efficient as hydrogen and much safer, and hopefully we never have to vent any helium, while the cargo and perhaps fuel weight is borne--partially, I'm hoping--by steam). Then, if that were practical, a much smaller steam volume suffices to leverage a given payload.

At sea level for instance, if we have steam kept at just boiling temperature (as would happen if there were any liquid water in the cell, because it would stabilize the temperature of both phases at the transition temperature) of 373 degrees Kelvin, in air of a nominal standard temperature of 288 K, then the steam, whose molecules already mass significantly less than air--18 AMU versus air's average around 28.8--is further lowered in density by being hot, so a cubic meter of steam would mass 48 percent what air does, or 590 grams versus air's 1225 grams, and thus that 590 grams of water vapor lifts 634 grams of load. So one kilogram of steam by mass lifts 1.07 kg of payload--if we plan on simply venting it.

But if we can take the time to condense that steam, then--there are several ways of looking at it--condensing a cubic meter of steam draws in 1.225 kg of air that wasn't in the system before. Or, if we condense a kilogram of water and keep it aboard we need to lift it with helium, and meanwhile we've lost another 1.07 kg of static lift--since that kg of steam formerly occupied 1.7 cubic meters and the air that fills it masses 2.07 kg we see the numbers come out the same. Bottom line, if you have any substance that you can shift between a gaseous and condensed state, you change the lift by 1.225 kg for every cubic meter you fill or vacate. So to lift say 1000 tons of cargo with steam you plan to vent, you need to vaporize 933,000 kg of water--then dump it overboard, and at sea level that steam occupies 1,577,666 cubic meters approximately. (If you want to do this at greater altitudes, actually steam becomes somewhat more effective there, so you need somewhat less water, but still the volume you need to set aside is much greater due to the lower pressure). But if we can expect to conserve the steam and store it as liquid ballast, then we only need 816,326 cubic meters at sea level, massing 482,573 kg. That steam itself only lifts a bit over half the cargo's weight, the rest of the cargo is lifted by the fixed lift of helium--but the weight of the water ballasts that helium when we condense it, so the ship can be brought into balance without venting anything but heat. (And we only need to design in half the volume for steam we would otherwise need!)

The trouble is, it takes a remarkably long time to condense steam!

One might wonder, why I am even talking about such extravagantly huge cargo masses as 1000 tons! Well, there was a grandiose project, or conceptual contest, put out by the Department of Defense and called "Walrus" in the early 2000s, when I was participating in a listserv devoted to airships. The challenge was to come up with a way to deliver IIRC 1000 tons of cargo to an unprepared forward site (presumably in a combat, or at any rate only barely and recently controlled, zone) without imposing on the recipients in any way. Taking on water or sand ballast (or any sort of ballast the ship could not provide itself directly, in any environment) was ruled out explicitly. This is the context in which I was thinking of how to create 1000 tons variable lift! I'm once again trying to work out, if say 150 tons can reasonably be borne on an airships propellors (turned mostly upward, with a reserve of thrust forward to maintain a modest airspeed until arriving at the destination), can the ship afford to retain 850 tons of lift until there is time to condense the steam? I figure such a static-lift steam Walrus might be designed to cruise at say 5 kilometers, at which altitude air density is about 60 percent surface densities (and temperatures about 40 Celsius lower than on the surface!) and its all-up mass might be in the ballpark of say 3000 tons (with payload, 2000 once that is dropped off) so the question is, how low a rate of climb can the ship parley 800+ tons of lift into, can it buy itself time to condense the steam before exceeding that pressure height? Bearing in mind that as it condenses the excess lift will be dropping off, I think maybe it can be done.

But Tom Goodey and others could not figure out why I couldn't just reconcile myself to simply venting 1000 tons worth of steam lift upon cargo drop, problem solved. Elegance, that's why! I liked the idea of the more compact ship you could get with recondensing the steam, and the idea that it stands ready to once again boil the steam and lift another cargo, and so on--truly variable lift.

The other sticking point is, while Tom Goodey empirically learned that a square meter of his small steam balloon in a workshop condensed about 1.4 kilograms of water per meter of its surface area per hour, nobody really knows how that rate will respond to radically different ambient temperatures (desert conditions, or arctic) nor to substantially different air densities, nor to forced drafts. Trying to solve these problems is a brick wall I've battered my head on a lot!

But for now, I'd be happy to work out just how low a rate of climb 800 tons of lift or so could be limited to in such a big airship (I'm thinking, 840 meters long, 140 wide); whether one needs to add some wings on the sides to tip the odds in its favor (rather not if they can be avoided, but last time my mind went down this track I was figuring on quarter-circle wings about the same radius as the hull itself, thus doubling the greatest width--they can also provide a lot of area in a cool slipstream for faster steam condensation for what that's worth), how much lift helicopter-type rotors that can be swiveled forward to serve as big props can reasonably be expected to offer, and so on. As I say, if we can take a huge unbalanced lift and lower it by condensation before hitting the upper limit of pressure height, then we never need to actually vent and thus lose the steam, and a significant portion of the payload would actually be lifted by helium instead, helium later ballasted by the condensed steam.

So I'm looking at the other side of Andrews's problem--he wanted to get forward motion from unbalanced lift, I want to mitigate the unwanted consequences of unbalanced lift to buy time to balance it.
 
Here's a mention of one of the WALRUS contenders. If anyone considers my steam approach to variable static lift ASB and silly, well I consider a lot of the notions this somewhat funded version much worse. Trying to use compressed air as ballast is a profoundly unworkable idea!

Also my philosophy is, while dynamic lift is an inevitable reality of propelled aerostats and one should modestly use it to advantage, to try to get as much good out of pure static lift as possible. Using so much dynamic lift as to lift as much as half the aircraft mass begs the question, to me, of why not just dispense with the inconveniences static lift gases definitely do present, and just go with a purely aerodynamic approach. Doing so uses a lot of power and requires a heavy structure, but mixing static and dynamic lift on that scale seems to me to combine the worst of both worlds since you need to handle the same high stresses operating on much greater volumes, and while saving some power are still operating on such a scale you might as well trade off some fuel cost for a simpler, more compact structure.

Better to go one way or the other; since big airplanes and gigantic helicopters have their numerous proponents and fans (I'm also one!) I speak up for the advantages on the other end of the spectrum. The drawbacks are slow speed and really gigantic structures (which latter frankly is part of the romantic charm for me:p) but I do think if DARPA were serious about accomplishing the mission, they wouldn't give aerostatics such short shrift; trying to smuggle it in halfway merely discredits the whole project.

Actually insofar as the mission involves survivability in a contested combat environment, I suspect LTA must throw in the towel anyway, though a monster airplane or helicopter or Osprey-like hybrid or something landing on jet thrusters or whatever will also be a very unstealthy pig too, and probably not able to dodge reasonably modern missiles and the like either. (Arguably an airship's dispersed structure might endure battle damage better, but it's hard to argue that this offsets a faster craft's ability to dodge!) I think realistically, in any serious combat zone, anything big enough to do the job will either be just about as doomed, or be something monstrous like a sub-orbital rocket.
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Closer to the OP topic, because it would be something to consider in the mid-19th century pioneering context, I should mention, there are other gas/liquid substances than water that could do the job; the most serious contender being ammonia, which would be a possibility in the OP timeframe.

Ammonia's static lift is nearly as good as steam's--the molecule, at 17 AMU, actually weighs a bit less, but of course it isn't heated hotter than air, so that's the drawback. But since in my conserved-variable lift substance concept the main thing that matters is the volume set aside for the variable-state gas, that doesn't matter so much. It means you need the same volume for the ammonia as for the steam, but more helium (or hydrogen in the 19th century) volume because the mass of ammonia that achieves the same effect is greater. And you can't just passively wait for it to condense, you have to actively pump it and cool it once pressurized. But perhaps it is significantly better suited to condensing on the fly than steam is, on the timescale of a climb toward the stratosphere! When you want to quickly gain lift, the fact that it boils at ambient temperatures and pressures is a plus. It's rather toxic, and obnoxious if it leaks in subfatal concentrations--but in a way that's a plus since the crew will be quite quick to notice small leaks and quite motivated to stop them! It's also somewhat flammable so that's a risk, much less so than hydrogen but still a risk. (Steam of course, while non-toxic in the chemical sense, poses its own serious safety risks to anyone working close to it, though a lot less so to innocent bystanders). Since the name of the game is to conserve the lift substances and not vent them, the fact that ammonia is less readily available than water is not such a drawback in my variable-lift scheme. While less cheap than water, it still is pretty readily available--the cost of the helium will still be far greater. So there's ammonia. I still need to learn more about the power cost of compressing it, to judge whether powered compressors can reasonably condense it a lot faster than steam can be made to cool by reasonable means.

For that matter, in principle even heavier-than-air gases like say Freon can do the job--the fact that the gas volume is heavier than air rather than lighter just means you need even more helium to handle the condensed weight--but when it vaporizes, the air it displaces still creates buoyancy lifting a portion of its weight and relieving some of the helium, and that's your variable lift. I suspect it's dumb to go that way, but if a lower power cost and possible speeds of variation of volume justify it, it might be worth looking into after all.
 
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