I mentioned a study that proved that the skin of the Hindenburg was _not_ a firetrap, but was actually quite difficult to set afire at all, and burned with only a mild flame.
Clearly the Hindenburg burned by hydrogen fire, and the skin was almost totally irrelevent, as all common sense and the best expert minds gathered immediately to analyze the disaster have always agreed.
Are you aware of the many other hydrogen lifted airship fires? Ever heard of the US Army's semirigid Roma? The R-38 that the US Navy was buying from Britain that we designated the ZR-2? The deaths by fire of almost the entire complement aboard R101 _after_ it gently crashed, with no known injuries of anyone aboard, near Beuvais, France? The Dixemude, which apparently exploded in mid-air one day over the Mediterranian, probably because the French Government would not pay for new gas cells or an adequate hydrogen supply to maintain minimal necessary gas purity? There are many others. It is quite true that many hydrogen lifted airships did _not_ burn, but this merely shows that care was taken, not that the ships were safe.
In what way can helium's "risks" be said to be comparable to hydrogen's? Helium does not burn under any circumstances! In what way could hydrogen possibly be prevented from posing any risk of fire?
Here's a freebie for you. Possibly the Hindenburg disaster might have been prevented if there were better forced draft circulation of air from the interior to the outside. The ship "prevented" fires in part by flushing the air inside in case there were small leaks--but the system relied on motion through the air to drive it, and the fire occured during mooring, when airspeed had dropped to a crawl.
But by no means could you prevent all risk of those thin gas cells being set alight, and once that happened, a chain reaction burning all of them would be inevitable. All you can do is reduce the risk, and claim that the chances of disaster are acceptably small compared to the benefits offered by the airship. If I knew helium was not available, I might ride in your hydrogen lifted ship, but most people would very reasonably ask, why not take an airplane or a helicopter even, instead? And why should they risk your dream airship crashing down on them in flames?
If a helium airship is wrecked, it is kind of embarrasing--and to be honest, people have been killed. Descending helium ship wreckage _might_ do some damage. But hydrogen ship wreckage from the same disaster would be plummeting down in flames, with no lift gas to cushion the fall either.
The best way to conserve helium would be to use it airships. While the cost of helium is not high anymore compared to the overall cost of an airship, it costs enough that airship operators do what they can to retain it. Compare that to the other uses helium is put to, such as pressurizing rocket fuel tanks, or for welding. Most every other use wastes the stuff instantly into the atmosphere.
It is not just cost that is involved. An airship is in delicate balance between lift and weight. If it loses even one kilogram of lift, that kilogram of excess weight will drag it down constantly. Airship operators are motivated to keep lift and weight _exactly_ in balance. With hydrogen this was done by venting gas as fuel was burnt--this strikes me as sloppy and wasteful. Since that was unthinkable back when helium cost relatively a whole lot, American airship operators figured out ways to avoid venting it, and to avoid it getting contaminated or leaking out, and to recycle contaminated gas rather than throw it away.
Your idea that hydrogen is acceptably safe is way off base. I have replied at length on this topic elsewhere. It is true that if we didn't have helium I would rather we had hydrogen airships than none at all, but people would be _justifiably_ worried about them. By long experience accumulated with more than their share of good luck in the early days, Zeppelin company people and the German military folks they trained learned to _usually_ prevent hydrogen fires. But when their precautions failed, the destruction was rapid and spectacular--and devastating. Don't underrate it. Hindenburg had 15 tonnes of hydrogen in its hull, but that released energy equivalent to the burning of 50 tonnes of gasoline--which is about comparable to the energy released by 500 tonnes of TNT! (Explosives are not as power-packed as fuels are, they just release what they have more rapidly.) Hindenburg did not explode, but it burned all that hydrogen up in under a minute. The rate of spread of fire from one hydrogen cell to another deserves to be called "explosive" though I do avoid the term since it has only poetic accuracy. (Had Hindenburg's hydrogen been optimally mixed with enough oxygen to burn it all instantly, the resulting explosion would probably have leveled Lakehurst Naval Air Station.)
The skin by contrast--even if it were "rocket fuel," it only massed 5 tonnes. It hardly seems likely that it could match even the heat release of 5 tonnes of diesel fuel, let alone 50.
The people who claim that the skin was "explosive," or self-igniting, or even severely flammible, are irresponsible at best and at this point they ought to know they were wrong, and if they persist they are lying. An Internet friend of mine, William Appleby, went to the trouble of replicating the formula for Hindenburg's skin, as well as several variations on the theme including one that used a much more flammible dope than Zeppelin actually used on their late model airships (because it used to be used on older ones and someone might muddy the waters by claiming the Hindenburg used it, so he checked that varient too). What he found was that it took most of a minute for that fabric, ignited by a candle flame, to burn a distance of one foot. At the rate that skin burned, it would take _hours_ to burn the 245 meter length of the great airship, which actually was in flames stem to stern before it hit the ground just seconds after flames were first observed. The skin was clearly of no significance whatsoever in the disaster; it could have been pure asbestos and the outcome would have been much the same.
Or here it is; fix the space Slashdot inserts for reasons that elude me: http://www.sas.org/tcs/weeklyIssues/2004-12-1 7/pro ject1/index.html
Only if the skin _sparked_ the fire could it be said to be a significant factor, but there is zero evidence the fire started anywhere on the skin. Nor does it have the bi
You actually would not want to vary the amount of lift gas. It is in equilibrium only in one amount; more than that and you climb, until the gas has swelled to either burst its containment with relative pressure or been vented to prevent that; then you are back in EQ again. Less, and the craft sinks inexoribly under the excess weight until it drops that weight, generates some more lift gas somehow, or crashes.
Also, it is quite foolish to use hydrogen for lift gas when helium these days is widely available and costs not so much relative to the whole cost of the airship. So any power storage hydrogen would need to be kept in a separate bag, either within the helium volume or outside risking getting ignited. (Not much is likely to make that happen way up there, true.)
Since it is a hassle to liquefy hydrogen and I suppose that metal hydride storage would weigh far too much, I guess the thing to do with fuel-cell produced hydrogen is to store it as a gas under pressure in tanks. These would weigh far more than the lift of the hydrogen. Unfortunately the hydrogen gas will still produce lift, and would need to be compressed to 15 times the density of air around it to stop doing so. However at the operating altitude, 1 atm density is already 18 times ambient density there, so actually tanks that hold just 1 atm overpressure would do the job.
Someone elsewhere estimated that it would take 45 kw for the airship to keep station. I think he overestimated drag and underrated prop efficiency. Still, take that figure. About 150 MJoule per hour, times 16 hours, 2.4 Gjoule are needed. If fuel cells get 60 percent efficiency, we need 4 Gigajoules worth of hydrogen stored.
I believe the lower heating value of hydrogen is 120 MJ/kg. Therefore we would need about 32 kilograms of hydrogen stored overnight, to last 16 hours of winter darkness.
A cubic meter is a large volume, and at 12 atmospheres absolute pressure you'd need 32 of them to hold 32 kg of hydrogen gas. But how much would such a tank weigh? More than metal hydride at more modest pressures?
Anyway if we can generate 32 kg of hydrogen while also providing 45 kw of power to the motors during an 8 hour day, I think we are in business if the tank is not terribly heavy.
It takes less power to maintain a given _mass_ in a wind of given airspeed in air of less denisty, despite the fact that the _volume_ needed to lift the mass is much greater. The gas volume would have to be 18 times greater, but the cross-sectional area would increase only at the 2/3 power of that increase, while the force of the wind does decline by 18. So the force needed declines as the cube root of the density, and since airspeed is assumed the same, power declines with force. And if the source of power is _solar_, clearly the area of hull skin is greater for the high-altitude ship and sunlight is less impeded by atmospheric phenomena. Clearly with rising power available and falling power requirements, at some altitude solar power wins.
Not sure what they plan to do about nighttime however.
And as for the props--of course they do lose thrust. Now if you just turned them at a given pitch, they would also experience less drag torque as they delivered less thrust, so power demand would also fall--it follows that if you maintain power levels (and pitch the prop blades accordingly) you will drive the air much _faster_ which will partially offset the fall of density--at constant power you get declining thrust, but at a rate not as bad as the fall of density. This happens at the cost of efficiency. However if you use ordinary airplane props you probably were driving the air much faster than you should for an airship anyway even at sea level, and with this racing engine thing going on and the speed of sound _declining_ with the cooling air of high altitude, you would quickly get compressibility problems at the blade tips as they approached and cracked the sound barrier.
Clearly the thing to do is redesign the prop--increase its radius, keep its tip speed moderate. Design it for high altitude, meaning make it light but big. If you do that, it will remain as efficient as a properly sized and pitched and turning low-altitude prop, which means you can expect total power demand to decline as I said above.
Lots of people think high altitudes demand something other than props. They are thinking of airplanes, which have to move _fast_ to stay airborne in thin air--it is _speed_ relative to the speed of sound that dictates that props must be abandoned. With aircraft like airships, which can float in still air, and cannot move fast because they would come apart structurally if you strapped powerful jets on them, propellers will always be a perfectly workable method and the best known practically available way to get thrust from power.
I don' t have time to check the numbers right now, but remember the whole structure has a density of the air at its working altitude, about 1/8 the density of air at the surface, which is itself about 1/800 that of water. If it descends, even under full control and power, it will need to take air into 7/8 of its interior, but even then the overall density will be exactly that of air--this is what it means to be in buoyant equilibrium after all!
If the concentrated loads fall off, that is another story of course, but the same is true of any aircraft. Airliner toilets sometimes accumulate ice on their vents, and these "Icy BMs" crack loose when the plane descends to airports--which are near cities generally, and they often approach right over them. I don't know if any human being has ever actually been hit by one of these ice masses, or if that wa just a clever idea for a 6 Feet Under episode, but sooner or later it is bound to happen if it does not happen fairly often already.
Meanwhile--I don't suppose a downed airship is totally harmless, Mainly it would drape itself over whatever it crashed on and tangle it up. Could be a serious problem if it came down on a busy street intersection.
But there would be plenty of warning. If the ship completely loses its lift gas but otherwise keeps its integrity, it will weigh little more than air but have tremendous area, so I think your terminal velocity is very high.
Hydrogen has the greatest range of flammibility of any gas known in air, 4% to 78%. Just what sort of anti-reaction substance are you thinking of?
Flame is a chain reaction. Basic chemical formulas tell us whether a reaction is going to go forward at all, but only kinetics can tell us at what rate. If we can lower the _rate_ of reaction enough, or dilute the amount of heat released by previous reactions going into components of potential future reactions, we can lower the probability that one reaction will trigger another below 50 percent, and thus statistically the chains will die out instead of multiply to use up all the reactant at once. But how do we do this? Only by diluting the reactants with neutral gases (which includes reactants that don't have complimentary reactants to pair up with, if you can sequester these or they are all consumed.)
The trouble is, if you dilute hydrogen with anything to the point that its lift is less than helium's, what is the point of the exercise? To save money? And I think the chances are zero that _any_ substance that would weigh that little in the mix can possibly do much to lower the range of flammibility of the hydrogen it is mixed with. Some perhaps, but certainly not a worthwhile amount.
Helium costs more than hydrogen, but at modern prices the cost is only a small fraction of the cost of an airship. Why not just use helium, which is absolutely fireproof?
I just disbelieve this talk of "proprietary gas technology."
Your idea of sneaking up on the lift a high altitude system would need by only _slightly_ empyting a chamber at sea level is a new one on me, and less unworkable than the impossible idea of totally emptying out a hull on the surface. Still, the structural issues are indeed formidable. It is clearly going to be much harder to keep air _out_ of a lightweight shell than to pump some _in_, and yet the weight of blimp hulls, which need only hold pressure in, is quite high compared to the total lift.
Helium has 80 percent and more of the lift of a comparable volume of vacuum, and presents _none_ of the structural problems you acknowledge. Since clearly the shell to withstand even partial atmospheric pressure must have substantial strength, and therefore weight, it is very doubtful this approach can work at all.
There was nothing marginal about the tremendous potential heat energy that was released when Hindenburg burned. There is also no positive evidence the fire even started anywhere but the deep interior of the tail region, and very clear recent experimental evidence that the kind of material used for the Hindenburg's skin, which has been mythically compared to "rocket fuel," actually burned very reluctantly and slowly. One William Appleby has taken the trouble to simulate that material, and measure its rate of burn. It would take _hours_ for the Hindenburg to have burnt at the rate the skin would burn on its own, and actually the whole ship was consumed, stem to stern, a distance of 245 meters, before it hit the ground about 4 seconds after it started burning.
On other hand, hydrogen is by weight the most concentrated chemical fuel known to burn in air; to release equivalent energy, over 3 times the mass of any hydrocarbon fuel would be required. To be sure, as a gas it is the least dense substance known to exist at standard temperature and pressure, so Hindenburg's 240,000 cubic meters, almost all full of hydrogen, contained only about 15 tonnes of the stuff. Which however would be roughly equivalent in potential heat release to 50 tonnes of gasoline. Furthermore, gaseous hydrogen diffuses more rapidly than any other gas, and has a wider range of flammibility--from 4 percent in air to 78 percent, it will burn. The high rate of diffusion means that small leaks might dissipate quickly, but also that any leaks will establish a density gradient of flammible mix in the air around them that will fill a substantial volume. A small leak inside the Hindenburg's outer hull would mean that dangerous mixtures would exist almost instantly in a large volume near the leak, for the interior was a huge air volume with gas cells for lift floating within it. One spark inside that halo of flammible mix would ingite that whole mass almost instantly, and would indeed cause the very sort of noise that witnesses aboard heard--a sound like a gas stove being lit. This muffled explosion would bring flame straight to the leak in the cell, which would then burn like a torch, igniting neighboring cells and triggering a chain reaction. Every bit of evidence we have says this is what happened; the only argument has been about just how and why the fire _started_. Why was there a leak? Was there one, or did someone plant a small incindiary bomb? But there can be no doubt, the hydrogen released the energy that destroyed the ship in under a minute. No comparable phenomenon would happen if the ship were lifted by helium instead.
It is true that there are bozos claiming otherwise, on the Internet and even on TV. But they are clearly wrong, and I could discuss motives some of these people might have to put out false information. But most people are just flocking mindlessly behind an amusing meme, easily impressed by unsupported claims.
It is also true that a case can be made that heliums' moderate degree of inferiority to hydrogen as a lift gas lowers the margin of success of airships to a critical degree, and that therefore some accidents that have befallen helium lifted airships would not have happened to a hydrogen lifted one. I don't think that is a very strong argument at all. But all the claims for the marginal superiority of hydrogen as a lift gas, and even the fact that hydrogen is cheaper than helium, must be balanced against the simple fact that hydrogen is a very flammible gas, and many hydrogen lifted airships have been suddenly and rapidly destroyed by these flames, and nothing like that can happen with helium, and of course never has. Some helium airships have been burned up in fires driven by their fuel; this has always happened on the ground, either during a servicing accident that set the fuel alight, during disasters such as the terrible hurricane that leveled Richmond, Florida, and the blimp hangar there in late WWII, or _after_ a crash; in the latter cases, crew always had time to escape the relatively slow (though im
There can be a "move" to H2 even if another fuel is more convenient, if it is given political priority. _If_ we can anticipate a future situation where the costs of the alternatives you prefer outweigh their benefits relative to hydrogen, it would make sense to invest now in developing the hydrogen alternative.
You can make a _strong_ case that even if we have to synthesize fuels, we would do better to synthesize hydrocarbons similar to the mix found in gasoline. Even the carbon issue would be addressed that way, for if we were synthesizing fuel from scratch or biological feedstocks of course we'd be pulling CO2 out of the air as fast as we put it back in. But I see that you disbelieve CO2 emissions have anything to do with climate so this point may not matter to you.
It is quite true that gasoline is a _volumetrically_ efficient way to store hydrogen fuel. You do recognize it comes with a downside--aside from CO2 emissions, there is other pollution, and considerable hazard from burning fuel during a crash? I happen to agree that some kind of "tank" full of pure hydrogen in some form would probably pose less of a hazard, but that might be wrong.
I'd be amazed if "no one" in these hundreds of comments on a scheme to include hydrogen fuel in our repetoire of transport power sources is even _considering_ the simple, straightforward method of cooling and liquefying the gas to store it in an insulated tank. Anyway, I am. And I am not talking about cars.
My suggestion is, that if we decide to make a priority of developing hydrogen as a fuel, we should start with aviation, particularly big military transport planes. The airplanes would have to be redesigned, because you almost certainly can't put the fuel in the wings anymore. Too much surface area to insulate and too little volume left over for enough fuel, not to mention the danger that internal structure in the wings might get chilled and thus behave weirdly--snapping suddenly for instance. But a thicker fuselage with big compact tanks in it would add less drag than the smaller wings would save. Or, the planes can be desiged, for a given weight, to achieve fantastic ranges.
I don't think they would be more vulnerable to destruction by the fuel, in an attack or in a crash, than airplanes with traditional jet fuels are now.
Good for you. I'm uncomfortable with my friends who adopt Hugo Eckener's best _guess_ scenario. Which is: hard maneuvering breaks shear wire; shear wire slashes one of the rear hydrogen cells; ventilation slacks off (this is actually a certainty; by the design it would do that); hydrogen "pools" above the cell able to disperse only _through_ the skin; spark sets off mix; rest is history. We don't _know_ a shear wire broke; we don't even know a hydrogen cell had a hole in it. Possibly some saboteur did it and did not get caught (we sure _don't know_ it was sabotage, nor can we prove it was not!) Possibly something quite outlandish happened. A number of people I know insist on claiming Eckener's scenario is _true_ just because alternatives they don't like are _either_ disproved or distasteful.
But some things are impossible.
"and I consider people using pictures to model something like a large scale combustion to be naive at best."
"Pictures?" I am not sure what you mean here. Bill Appleby made actual samples of the same kind of material as Hindenburg's hull, layered in the same way, that were used on the hull. Little pieces to be sure but they do verify that _without_ the presence of hydrogen, the stuff burns slowly and needs some prodding to get started. Which was, from all descriptions, the case with Bain's authentic skin sample--he never showed it could ignite itself, and he used an intense flame to start it burning and it burnt _slowly_, with no very intense heat being produced. I suppose on a larger scale the speed of the flame propagation might pick up, but it would have to speed up by a factor of a thousand to account for the disaster.
"It's a concentrated refutation..."
Yes. Some years ago, in the late 1990s, Addison Bain stepped forward with the remarkable, revolutionary idea that _actually_ the Hindenburg fire _was in no way_ caused by the hydrogen, that the hydrogen was "unfairly condemned" as the culprit, for even if that same airship had used helium (which of course does not burn) the results would have been the same. For, as you have no doubt heard, the doped, aluminum-painted fabric was equivalent to "thermite" or "solid rocket fuel."
BTW--it is not a virtue of rocket fuels to blow themselves up in one quick blast. They burn slowly and steadily--that is part of the point, and they are typically _not_ the densest concentration of available heat energy you can attain either. That desirable feature goes a bit by the board aiming at other desirable qualities--like stable burning for instance. Thermite and rocket fuel then are very different things. And doped aircraft skin material is a third thing.
Anyway, it is the purpose of many people who are interested in airships for historical and other reasons to restore accuracy to the discussion. _Clearly_ the presence of hydrogen made a big difference. Clearly also, the Hindenburg's designers had the longest experience of anyone in the world, and with the most success, at avoiding hydrogen fires, and to do that, avoiding fires of any sort if they could help it. They couldn't always help it and had damage control strategies to prevent inevitable sparks from leading to catastrophes. They would not, and did not, fail to check out the flammibility of the material they wrapped the entire airship in. Those of us who once took Bain seriously are amazed at how _difficult_ it is to get this fabric to burn; we should not be, why would Zeppelin designers want anything less? From our point of view it is important to examine each of Bain's specific claims and see if they have any merit.
Bain wants to argue that hydrogen is safe _as a fuel_ and he thinks that the image of the fiery destruction of Hindenburg is a barrier to acceptance of hydrogen. I think that is absurd myself but I have to admit I have not been in the business of selling hydrogen fuel professionally. It is evident to me that concentrated, insulated fuel tanks are different than huge, thin-walled b
First I want to thank you--that is a useful table!
(How do you prevent slashdot from sticking random spaces into the link?)
But please look at the right column!
in terms of _gravimetric_ density, hydrogen (in any form) beats every other entry handily. 39,000 Watt-hours/kilogram, versus just over a third of that for propane, and only 12,200 for gasoline. Gasoline wins on this table hands down for _volumetric_ efficiency, but you'd be hard put to show from that that carbon bond strength has anything to do with it at all. I think it is a simple matter of the material density. Unfortunately I don't know the chemical formula of propane, but a typical gasoline molecule is made up of roughly 2 hydrogens for every carbon, or maybe a bit less. A benzene ring has 6 and 6 but it is a closed system; to form the more complex hydrocarbons there clearly can be few double bonds involved and lots of hydrogen.
Let's just assume that gasoline is 1.5 hydrogens per carbon, and that how they are bonded to each other doesn't matter much--in the end it all burns to water and CO2. OK? Carbon weighs 12 AMU, plus 1.5 hydrogens gets us 13.5 versus 2 for a hydrogen molecule. Let's multiply the hydrocarbon by 4: we get a segment that weighs 54 with 4 carbons and 6 hydrogens, that consumes 11 oxygen atoms to yield 3 waters and 4 CO2 molecules. This fuel weighed 27 times one hydrogen so we burn 27 kg of it to get 329400 Wh/kg or 8.446 times the heat of burning 1 kg of hydrogen. Now subtract 3 from that output ratio, representing three water molecules, to get 5.446 and divide that by 4; the formation of 1 CO2 by these assumptions releases as much heat as 1.36 water molecules forming. Not a dramatic difference and I rather think that hydrocarbons have more hydrogen than that. Note that propane is more punchy on a mass basis and is a simpler, lighter, more hydrogen-intense molecule. If the hydrogen ratio was as low as 1:1 which I think is impossible for something as volatile as gasoline, forming CO2 would be worth 1.533 water-formations--still pretty lame when you consider that there are 2 oxygen atoms in the reaction! If the ratio is more like 2 H to 1 C, then the output ratio drops to 1.19. Hydrogen-oxygen bonds actually seem pretty strong!
For cars or boats or trains, perhaps this doesn't signify all that much; volumetric density matters a lot. But for aircraft, where saving weight is the name of the game, hydrogen fuel delivers tremendous advantages. Even though the fuel must be stored in very bulky tanks that will cause extra drag and increase structural weight, the savings in fuel weight would be so great that the wings (a major source of drag area!) would be much smaller. If anyone here cared I could go on about how the advantages for airships would be even more decisive.
It is very overblown then to claim that "hydrogen as a fuel is not backed up by the laws of physics." Where weight is important, it is three times better than any other chemical storage medium. This is why it is used in rockets of course. (Higher specific impulse too--but that is also a funtion of its very low mass and high _mass_ energy density!)
Evidently there is not all that much energy in the double bonds of carbon as you think.
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
I'm referring to Dr. Alex Dessler's piece; John Dziadecki has links to the whole "debate." But if you read Alex's piece you'll see, Bain just makes stuff up in the vein of Imannauel Velikovsky.
If you like loading pdfs directly http://spot.colorado.edu/%7Edziadeck/zf/ LZ129fire. pdf
Is Alex's paper. But slashdot screws with URLs for some reason, you'll have to paste that somewhere and take out the extra space.
Also, for evidence that the alleged "rocket-fuel" skins are damn near fireproof:
Have fun! I can put you in touch with the authors of either of these if you have questions for them.
Bain's agenda was apparently to empower people to dismiss the Hindenburg disaster when worrying about the risks of hydrogen fuel. But liquid hydrogen, or hydrogen bound to hydrates, or even compressed gaseous hydrogen, is a very different sort of risk than a huge multi-thousand cubic meter gas bag with surface areas measured in thousdands of square meters, made of gossamer-thin stuff. The debate about whether hydrogen is risky or not is not helped by errors and falsehoods; to deny that hydrogen comes with special risks is a setup for disaster. Acknowledging and managing them (or forgoing the technology if you have alternatives) is the only way to go.
"Re the Hindenburg incident: there is now fair evidence that the whole thing happened"
No, there isn't. The Bain skin theory is based on half-baked speculation that, whenever investigated closely, falls apart.
The hydrogen gas cells were only somewhat tight--as tight as they could make them, but man, they had to have an area something like 45,000 square meters! And yet to weigh only a small fraction of the ship's total 200+ tonne lift, which was generated by the gas they contained. They were gossamer thin, and very vulnerable to cuts and holes, not to mention that all thin gas cells have gases, especially such light ones as hydrogen, diffuse right through them. Zeppelin did their very best to keep them intact but they could not always succeed.
Once a fire got going inside, the thin fabric could hardly impede it, even if their materials were not themselves flammible!
Ventilation was the key. Unfortunately, Hindenburg's ventilation depended on forward motion to create the draft. _There_ is a design flaw! They should have used fans. (But then, the power lines to them would surely have posed a spark risk...)
Cellulose acetate butyrate is far less flammible than you think,
I mean, when you say it is "highly" flammible, is that a quantified judgment? Here's a number to work with--the flames would have to progress at over 4 meters a second along the surface to set the whole length of the airship afire. The tests above show that even the very worst doped cover material investigated burns at--less than 1 centimeter/sec.
Hydrogen flames inside could account for it; never the cover.
That cover often was hit by sparks from the engine which burned little pinholes in it; it never caught. Both the experimental investigator Bill Appleby (link above) and Addison Bain's own "demonstration" of his claims used a blowtorch to light the skin afire; nothing less than incindiaries would do it. I don't know if the flame would persist or die out if left alone. But at 1 cm/sec the crew would have time to do something about it!
No one, certainly not Addison Bain, has ever demonstrated that anything like airship skin could ever set itself afire due to electric sparks, nor even that the hull of the Hindenburg or any other airship resembled the tremendous capacitator Bain alleged it was. There are clear arguments to the contrary.
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
There is no way to know that of course, as no one else was operating any airships of any kind by 1937 but the Germans--and us, and the Soviets, but they were about to abandon their little semirigid project completely. Our Navy was operating a few blimps and the Army was shutting down its blimp program. That was it.
Our blimps came in very handy during the war, but no one in officialdom prepared for that. They were very belatedly thought of and built on an emergency basis. The Navy did not want to be bothered with mundane things like convoy duty or coastal patrols! Which is what the blimps were very good for.
LTA enthusiasts in the Navy wanted great big rigid airships. I think that they--and the blimps--would have been very useful. But the LTA people were outgunned by lots of interests who wanted money to go to airplanes and other rival technologies.
It is perfectly clear that American refusals to grant access to helium were not motivated by any serious plan to actually use the stuff ourselves. I'm happy that Hitler failed to get a favor. But by no means did American decision makers, public and private, always rebuff the Nazis.
Actually letting Zeppelin have some helium for peaceful commece would not have been the same as giving it to Adolf Hitler. The Nazis were not fans of Zeppelins and they scrapped them all once they started their war. If they had had a fleet of 2 or 3 flying by 1939 and spare stocks for a couple more, that could hardly have been decisive in the war even if the Germans had put these dirigibles to the best possible miltary uses--either as naval scouts (that is, spotters for U-boats and the surface ships that broke out and took up commerce raiding when the war went into high gear-though a big Zeppelin might have carried a few airplanes to strike directly at shipping too) or as transport aircraft, just a few, with limited and dwindling supplies of helium (the stuff leaks you know) could not have done much. And so they'd either use hydrogen--risky but workable, especially if you choose missions where you can avoid being in range of being shot at--or give up on airships. Which was the Nazi inclination. I think they were idiots not to use Zeppelins more effectively but it is just as well they were that arrogant.
No doubt, if we had given the Nazis helium they would have done as much harm with it as they could.
The British _should_ have been using airships for transport to their distant colonies. If they had been, I suppose the only reason we would not sell them helium would be if the competition stimulated _American_ commercial (and sustained military) LTA. Even then, the more demand for the gas, once adequately diverse wells were found, the more bearable the cost of processing it--supply may well have been adequate for demand if there had been any demand. I think we'd have sold it to them.
It was anti-Nazi policy, and perhaps anti-LTA policy. Airplane based airlines were struggling to establish themselves in the 1930s--had airships existed as serious competiton there is every reason to think they would have severely cut into the business. After the war it was different, with much better and faster airplanes, with much longer ranges and higher capacities and above all a network of former military airfields all over the world. But in the 1930s airships had many advantages over airplanes for long-distance air transport. But the visionaries of aviation looked ahead to the days when airplanes would pull ahead, and lobbied their politicians to hasten that day.
"They had an actual cover sample that was preserved from the Graf Zeppelin company (no relation to Led Zeppelin). "
No, that was supposed to be an actual piece of Hindenburg's own skin! Which--think about it--survived the fire. Without burning up.
The Hindenburg was 245 meters long, and was burning everywhere from stem to stern in under 60 seconds, about as long as it took to fall down to the ground. For flame to burn along the skin so as to achieve that, it would have to burn at 4 meters per second. If you examine other comments of mine you will find I give references to someone who made his own doped skin samples modeled after Hindenburg's--they burnt at less than 1 _centimeter_ per second.
It was the hydrogen and the hull could have been asbestos--it would still have been heated to cherry red heat, and the ship would still crash, once the hydrogen cells were set aflame.
" The hydrogen inside had no oxygen and couldn't burn."
The hydrogen inside the 18 or so gas cells was pure and couldn't burn--as long as there were no holes in said cells. No one knows just what did happen. But a small hole in one cell could have released a quantity of hydrogen adequate to start a fire, and the ship's ventilation (rigid airships were the opposite of airtight--they had to let their pressure match that of the air outside, and hydrogen ships were designed to flush the air continually) depended on _motion_ to drive it. All that would be needed then was a spark; given that,there was quite a bit of air inside the hull. And the flames would soon burn themselves some more ventilation!
Look, the heat content of the 18 tonnes of hydrogen contained, if set afire, was equivalent to about 50 tonnes of diesel fuel. Whereas all the airship's fabrics put togehter weighted just 15 tonnes. I suggest to you, if 15 tonnes of doped fabrics can release more energy than 50 tonnes of diesel fuel (or its equivalent, 200,000 cubic meters of hydrogen) then the designers should have devised engines to burn swatches of fabric instead of diesel fuel. Weight is critical on aircraft, you know. (A steam engine could do the job by the way.)
It was the hydrogen, not the skin.
It is a funny thing--the guy, Addison Bain, who started this skin nonsense doesn't care about airships, he wants to promote a hydrogen-based fuel economy. He thinks he has to prove that the hydrogen was blameless in _every_ airship disaster (there were many other cases of hydrogen ships burning up) to set at rest "irrational" fears about hydrogen as a fuel. But that is nonsense. Hydrogen is dangerous in airships because a very flammible substance is contained in huge volumes with enormous surface areas, that need very thin skins if they are to be light enough to be lifted by buoyancy. If we had liquid hydrogen stored in tanks, they would be bulkier than gasoline tanks, but still far denser than air, with much thicker skins--liquid hydrogen has to be kept in a thermos after all! The danger is much more comparable to that posed by _any_ fuel, and less in some ways that familiar ones. Airship fires are irrelevant to the fuel question.
Is that even supposed to make sense? Why would any designer opt for the _most flammible_ skin when less dangerous designs were available?
Actually the Hindenburg's skin was less dangerous than any prior design. These Zeppelin engineers were _not_ idiots. (Not even to use hydrogen--they had no other choice but to abandon airships, and they had good reason to think they could manage the risks. But clearly not by deliberately choosing dangerous skin!!)
One Addison Bain makes all kinds of bizarre claims, about the skin being "thermite" like or "rocket-fuel" like, but actually none of them are borne out when you make a sample of the stuff and test it. Only the hydrogen, burning inside the airship, accounts for the disaster of 1937.
This is a project whereby someone created samples of the skin according to documented reports of its composition, and measured the burn rate when he set them alight with a torch.
BTW you _have_ to use a torch; sparks do not set these things ablaze. The actual airship had pinhole burns in its skin near the engines where sparks sometimes came out. Clearly if the skin were somehow "more flammible" than hydrogen gas, it would have gone up the first time one of them hit it!
Anyway, they burn at a rate of less than 1 centimeter/sec. The Hindenburg was engulfed in flames all along its 245 meter length in under a minute. Do the math; the skin burns at less than 1/1000 the necessary rate!
It is another story of course when there is a powerful source of heat _inside_ the skin that can only get out by burning through. That would clearly accelerate the flames! That was the hydrogen of course. It would have massed about 18 metric tons, and such a mass of hydrogen can release as much energy as 50 tonnes of diesel fuel. And if it is allowed to mix with air, clearly flames can progress very rapidly along the interface; think of how the flames race along a gas grill when you light it at one end. Once a big fire was going inside clearly the heat of the flames themselves would burn through the incredibly thin light gas cells and then through the outer skin, even if all the fabric were totally inert to fire. The heat would be enough to _melt_ them, and there would be your gas/air mix, in the presence of flame yet.
Here's where you can find another paper that goes over the erroneous claims of Dr Addison Bain one after another, by a Dr. Alex Dessler.
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. pdf
Look at http://www.sas.org/tcs/weeklyIssues/2004-12-17 /pro ject1/index.html
Bill Appleby took the trouble to create numerous samples of the sort of skin the Hindenburg might have had (there is some controversy as to the composition) and test them systematically.
They burn at about 1 centimeter/sec when ignited with a torch.
In real life, there were pinhole burns on the hull near the engines where sparks sometimes came out--evidently a mere spark did not even create a sustained flame, let alone cause the whole ship to be incinerated in under 60 seconds. Which is how fast the Hindenburg was set afire from stern to bow, over a distance of 245 meters. Which, you percieve, would take about 41 minutes or more with this fabric alone.
Gaseous hydrogen that is allowed to mix with air on the other han creates a very energetic flame and the very mobile, light molecules of the gas, agitated by this heat, clearly support very rapid propagation of flame along any interface where gas and air mix. Once a flame was going inside the hull, clearly the heat would tend to burn up the thin hydrogen cell skins, and cause the cells to expand releasing more hydrogen to the escape ventilation system--which under these conditions would become burners instead of vents. The most likely scenario (no one knows what happened for sure) is that a cell was accidentaly cut open, perhaps by a structural wire that snapped during the rough final approach to the mooring mast, and that a spark set the mix near or above the cut aflame. The heat released from one cell set afire would be plenty to set off its neighbors in a chain reaction, much more rapidly than the skin could possibly burn. And about 10 percent of the volume inside the hull was full of air, not hydrogen--plenty to start the fire and perpetuate it to the bow. The skin could have been totally inflammible and the results would have been essentially the same.
In fact lots of skin from the ship _did not burn up_; you can buy pieces of it even today. And the flames went on for many many hours, as the diesel fuel slowly burned.
Pure hydrogen flame releases heat in 2 ways--it produces a hot molecule (water of course) and it emits UV radiation. In the open, such photons are not as likely to be absorbed as readily as the IR photons that carbon fires put out.
The guy who falsely suggests that the Hindenburg did not burn due to its hydrogen (he blames the skin, but I know someone who experimentally has shown that that kind of doped fabric burns at about 1/1000 the speed it would have had to to account for the destruction of Hindenburg)
--anyway, Addison Bain makes a big deal of hydrogen flame's invisibility. Quite true. Except that the hydrogen flame inside Hindenburg was _inside_ a fabric skin that was _not_ transparent to these UV photons! All the heat released by burning hydrogen had nowhere to go until the skin burned up, and when it did that of course it emitted IR and red light like any other burning carbon substance. And more; the extra heat from the hydrogen (by far the biggest energy release around) would make the carbon glow even if it were not burning, like these hydrogen-flame detecting brooms or like the mantle of a gas lantern.
In the real world you rarely encounter pure hydrogen flames you see.
"There was a great show on The Discovry Channel I think. About the Hindenggerg."
I haven't seen this documentary but I am very familiar with these theories that allege the outer cover was the major culprit.
I think these sources can set you right. They were written by people who are very well informed about airships, and who also got off their butts and did serious research on the matter. One is by Dr. Alex Dessler, who analyzes all the claims from a theoretical standpoint and using documented data.
You can find it here, along with the "theories" of Dr Addison Bain that it refutes:
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
(note--for some reason I have never understood, slashdot inserts a space somewhere in URLs. You tell me why. Anyway, when this posts there will be a spurious space in the link; find it and delete it. Same for the next link.)
The other is by the very practical William Appleby, who made numerous samples of various types of skin fabric that closely simulate actual airship coverings of the day, complete with aluminum paint and different kinds of dopes, and measured how fast they actually did burn.
The Hindenburg was 245 meters long and was enveloped in flames in less than one minute; that means the flames had to progress at over 4 meters/sec. Let me quote his finding here"
"Conclusions
The Hindenburg burned so fast that the flames covered a 10-cm distance in less than 0.02 second. None of the burning times for cloth treated with doping paints in this study approached the time the Hindenburg was totally engulfed in flames, which was less than 1 minute (approximately 600 cm/sec). Sample 4 simulates the bottom of the airship, and sample 5 simulates the top portion. The painted cloth pieces burned slower by a factor of approximately 1000 to 3000, depending on treatment. The burning rate of the samples painted with cellulose acetate butyrate dope, the kind used to coat the Hindenburg, were especially slow."
"The outter covering of the zepplin was a fabric covered in a petrolium product to make it water proof."
Um, no, you weren't paying attention. The fabric was cotton (or sometimes they used linen) and they doped it for a variety of reasons--most airplanes had the same kind of skin in those days. To tension it, to stiffen it, to incorporate paints to ward off damaging sunlight, to reflect heat (important for airships, that are affected by thermal expansion and contraction)--lots of reasons. They didn't use a hydrocarbon. They used a lot of stuff that loose commentators said equals thermite. But look at Bill's experiment--the stuff does not explode, or even burn at any very impressive rate.
"The covering of the zepplin is what actually caught fire first. Not the hydrogen. If you watch the videos of the disaster you can see this is the case. "
Obviously if you rely on films taken outside the airship, the first thing they will see will be fire on the outside. That alone does not tell us anything about whether it started inside or outside. Clearly if it started inside it would show up first of all on camera in the form of flames spouting _from_ the inside!
Actually if you know anything about airships there are other signs to look for besides gouts of flames. I have never examined these films but I have friends who have; they tell me they see evidence of events inside the ship that are consistent with their theories, that sensibly enough suspect the hydrogen first of all. If there were no such signs whatsoever the visible flames on top of the ship might _might_ be the start of the fire or they might not.
"The disaster was a lot like gas tank fires of today. The fire started from a static discharge between the docking tower and the zepplin. "
Nobody actually knows what did happen. That the docking might have triggered a spark somewhere does not seem unlikely. But Ba
First of all that link does not work. I get an error page. I suggest you post an alternate way of finding that article.
From first principles we can see that it _can't_ be right that hydrogen is less "energy-dense" than a hydrocarbon fuel _by weight_.
At any rate, there is no way that both the claims above can be true. I can credit the ratio of energy densities _by volume_. But consider how low liquid hydrogen's _mass_ density would be. I don't have those figures handy, but a reasonable assumption is that a molecule of liquid hydrogen would occupy the same volume that a water molecule would. Possibly that understates the density since hydrogen molecules might pack more closely than water molecules, and will be less energetic since they only condense under either very low temperature or very high pressure. Here we assume low temperature--but a liquid is condensed matter; its molecules are already "touching" for practical purposes and density hardly varies over a tremendous range of pressures.
Then mass density would be in ratio to atomic mass units: 2/18 or 1/9. Gasoline I am not sure of either, but it is moderately lighter than water. Say it is 80 percent the density of water, that seems about right. To state that a liter of liquid hydrogen contains 1/3 the potential for heat release of a liter of gasoline is therefore to state that 111 grams of LH2 releases 1/3 the heat of 800 grams of gasoline, therefore the energy density of hydrogen by _mass_ must be
800/333=2.4
To claim otherswise, to claim that the ratio is reversed and more than reversed so that the gasoline releases 3.5 times _more_ heat _by mass_ would require the liquid hydrogen to be far _denser_ than water, or for liquid gasoline to be _even lighter_ than LH2! Lighter than LH2 by 6/7 in fact! We know that is not so.
Would you seriously have us believe that liquid hydrogen condenses 8.4 or more molecules in the space occupied by 1 water molecule in water? That is what it would take to make LH2 dense enough for both of your claims to be consistent with each other.
Either your source is screwed up, or you misread it.
You have found a link to the source of the now-endemic urban legend founded by these men that the doped skin of the Hindenburg was extremely flammable, liable to ignite itself under severe electrical conditions, and burned so catastrophically on its own that the combustion of hydrogen can be neglected in the destruction of Hindenburg. This is all false.
I was referring to a television show where Dr. Addison Bain, the major author and advocate of this implausible "theory" that seems to be uncritically taken for fact, proposed to show how dangerous the skin was.
However I do not watch a lot of TV and have not seen this show, nor any of the TV documentaries where Bain's claims are accepted as fact despite this embarrassing self-contradiction of a demonstration. I participate in a listserv devoted to airships and others on it, whom I trust on this, have very often repeated the story of Bain's demonstration. I have asked them to provide you with citations to this TV show or other documentation of Bain's embarrassment.
But meanwhile Dr. Alexander Dessler has written a paper that critically examines the core claims on their merits and shows that they are all invalidated by fatal contradictions with fact and logic:
Slashdot's hyperlink policies are a mystery to me! I can't make these links show here, just type in http://spot.colorado.edu/%7Edziadeck/zf/introd ucti on.htm in your browser;
The pdf can be found, with other intoductory material, at
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
Based on the descriptions I have read: Bain had a sample of fabric he said was a piece of the fallen ship's skin--and indeed a lot of this allegedly unstable skin was left lying around on the field, kind of odd when you want to claim its conflagration destroyed the ship and sucked up so much oxygen that the hydrogen could not even burn! Not so odd if you assume instead that he airship's designers, mindful of the danger of fire, did their best to create a flame-resistant skin instead of one make of "rocket fuel" (and solid rocket fuels do not actually have the spectacular combustion features Bain suggests this skin has but failed to show--read the paper!) But he said he had an authentic piece of this skin--and proposing to destroy it for a staged demonstration strikes me as a crime against historical evidence in itself, but he did. However he did not rig a form of spark ignition or demonstrate that the skin could create sparks of any kind itself as he claims must have happened. He used a powerful flame source instead, and it did not cause the skin to burst into a rapid "thermite" like combustion--instead it burned slowly and dimly, almost going out, needing to be nursed along. This would explain how come he had some skin to destroy, and also I think it shows that the stuff was carefully developed by the Zeppelin company to be as _fireproof_ as possible, but it seems to directly contradict Bain's claims, don't you think?
The idea that the skin _could possibly_ be more risky than the the hydrogen could only have two merits--one being that the skin could somehow release more heat or at a more rapid rate, which claim Bain makes. He also says the skin design and composition allowed it to _self-ignite_ but never demonstrates this and the paper demolishes all the bases of this claim. If the skin could just create occasional sparks that would be a grave matter--but there too the Zeppelin engineers did their best to avoid this and the way that Bain says it could is quite contradicted by engineering details he ignores though they are no secret (just obscure--you have to care about airship history to know about them).
It would be silly to design one that operates at both altitude and sea level. What I did not point out in showing that an airship can maintain the same speed with the same props is that when it does so up high it suffers far less force than down low--I said that but did not point out that this means the ship is way overbuilt for that high altitude then, if it can take the same speed at sea level. Therefore if the mission is to operate up high you make it far weaker and lighter and operate it very carefully, at reduced speeds, down low. You might go for constant aerodynamic force the way an airplane does, and thus like an airplane need less power down low (except planes also need extra power to take off and to climb--equilibrium airships would not!) We _choose_ not to use full power, to avoid wrecking the ship!
This is why solar power works so well for these things. Up high the air is very clear, you are above all the mist and dust and air itself is pretty transparent, and also very thin there. So there is a lot of power where it is needed and if the ship is brought down, it needs less so the fact that there is less light down here is OK.
So I don't have to get into an argument about whether internal combustion engines are even feasible up there or not--they are not the wisest choice of power plant up there anyway.
I was making a point with my example and assuming an airship that only went from sea level to some moderately less dense level, one where human beings could still breathe. Remember that the airship can only be filled with as much helium as it can retain at the highest level it reaches, which means it is underfilled down low, so it is desirable to limit the range of altitudes it is expected to operate in.
Slashdot Mirror
I mentioned a study that proved that the skin of the Hindenburg was _not_ a firetrap, but was actually quite difficult to set afire at all, and burned with only a mild flame.
4 -12-17/pro ject1/index.html
Here it is.
That's
http://www.sas.org/tcs/weeklyIssues/200
Clearly the Hindenburg burned by hydrogen fire, and the skin was almost totally irrelevent, as all common sense and the best expert minds gathered immediately to analyze the disaster have always agreed.
Are you aware of the many other hydrogen lifted airship fires? Ever heard of the US Army's semirigid Roma? The R-38 that the US Navy was buying from Britain that we designated the ZR-2? The deaths by fire of almost the entire complement aboard R101 _after_ it gently crashed, with no known injuries of anyone aboard, near Beuvais, France? The Dixemude, which apparently exploded in mid-air one day over the Mediterranian, probably because the French Government would not pay for new gas cells or an adequate hydrogen supply to maintain minimal necessary gas purity? There are many others. It is quite true that many hydrogen lifted airships did _not_ burn, but this merely shows that care was taken, not that the ships were safe.
In what way can helium's "risks" be said to be comparable to hydrogen's? Helium does not burn under any circumstances! In what way could hydrogen possibly be prevented from posing any risk of fire?
Here's a freebie for you. Possibly the Hindenburg disaster might have been prevented if there were better forced draft circulation of air from the interior to the outside. The ship "prevented" fires in part by flushing the air inside in case there were small leaks--but the system relied on motion through the air to drive it, and the fire occured during mooring, when airspeed had dropped to a crawl.
But by no means could you prevent all risk of those thin gas cells being set alight, and once that happened, a chain reaction burning all of them would be inevitable. All you can do is reduce the risk, and claim that the chances of disaster are acceptably small compared to the benefits offered by the airship. If I knew helium was not available, I might ride in your hydrogen lifted ship, but most people would very reasonably ask, why not take an airplane or a helicopter even, instead? And why should they risk your dream airship crashing down on them in flames?
If a helium airship is wrecked, it is kind of embarrasing--and to be honest, people have been killed. Descending helium ship wreckage _might_ do some damage. But hydrogen ship wreckage from the same disaster would be plummeting down in flames, with no lift gas to cushion the fall either.
What is your trip against helium, anyway?
Yes, but if they let it drift off station they are in trouble. It would not come crashing down immediately, but they'd have to chase it.
Fortunately, properly designed propellers should work just fine.
The best way to conserve helium would be to use it airships. While the cost of helium is not high anymore compared to the overall cost of an airship, it costs enough that airship operators do what they can to retain it. Compare that to the other uses helium is put to, such as pressurizing rocket fuel tanks, or for welding. Most every other use wastes the stuff instantly into the atmosphere.
It is not just cost that is involved. An airship is in delicate balance between lift and weight. If it loses even one kilogram of lift, that kilogram of excess weight will drag it down constantly. Airship operators are motivated to keep lift and weight _exactly_ in balance. With hydrogen this was done by venting gas as fuel was burnt--this strikes me as sloppy and wasteful. Since that was unthinkable back when helium cost relatively a whole lot, American airship operators figured out ways to avoid venting it, and to avoid it getting contaminated or leaking out, and to recycle contaminated gas rather than throw it away.
Your idea that hydrogen is acceptably safe is way off base. I have replied at length on this topic elsewhere. It is true that if we didn't have helium I would rather we had hydrogen airships than none at all, but people would be _justifiably_ worried about them. By long experience accumulated with more than their share of good luck in the early days, Zeppelin company people and the German military folks they trained learned to _usually_ prevent hydrogen fires. But when their precautions failed, the destruction was rapid and spectacular--and devastating. Don't underrate it. Hindenburg had 15 tonnes of hydrogen in its hull, but that released energy equivalent to the burning of 50 tonnes of gasoline--which is about comparable to the energy released by 500 tonnes of TNT! (Explosives are not as power-packed as fuels are, they just release what they have more rapidly.) Hindenburg did not explode, but it burned all that hydrogen up in under a minute. The rate of spread of fire from one hydrogen cell to another deserves to be called "explosive" though I do avoid the term since it has only poetic accuracy. (Had Hindenburg's hydrogen been optimally mixed with enough oxygen to burn it all instantly, the resulting explosion would probably have leveled Lakehurst Naval Air Station.)
The skin by contrast--even if it were "rocket fuel," it only massed 5 tonnes. It hardly seems likely that it could match even the heat release of 5 tonnes of diesel fuel, let alone 50.
The people who claim that the skin was "explosive," or self-igniting, or even severely flammible, are irresponsible at best and at this point they ought to know they were wrong, and if they persist they are lying. An Internet friend of mine, William Appleby, went to the trouble of replicating the formula for Hindenburg's skin, as well as several variations on the theme including one that used a much more flammible dope than Zeppelin actually used on their late model airships (because it used to be used on older ones and someone might muddy the waters by claiming the Hindenburg used it, so he checked that varient too). What he found was that it took most of a minute for that fabric, ignited by a candle flame, to burn a distance of one foot. At the rate that skin burned, it would take _hours_ to burn the 245 meter length of the great airship, which actually was in flames stem to stern before it hit the ground just seconds after flames were first observed. The skin was clearly of no significance whatsoever in the disaster; it could have been pure asbestos and the outcome would have been much the same.
Link here!
Or here it is; fix the space Slashdot inserts for reasons that elude me:
http://www.sas.org/tcs/weeklyIssues/2004-12-1 7/pro ject1/index.html
Only if the skin _sparked_ the fire could it be said to be a significant factor, but there is zero evidence the fire started anywhere on the skin. Nor does it have the bi
You actually would not want to vary the amount of lift gas. It is in equilibrium only in one amount; more than that and you climb, until the gas has swelled to either burst its containment with relative pressure or been vented to prevent that; then you are back in EQ again. Less, and the craft sinks inexoribly under the excess weight until it drops that weight, generates some more lift gas somehow, or crashes.
Also, it is quite foolish to use hydrogen for lift gas when helium these days is widely available and costs not so much relative to the whole cost of the airship. So any power storage hydrogen would need to be kept in a separate bag, either within the helium volume or outside risking getting ignited. (Not much is likely to make that happen way up there, true.)
Since it is a hassle to liquefy hydrogen and I suppose that metal hydride storage would weigh far too much, I guess the thing to do with fuel-cell produced hydrogen is to store it as a gas under pressure in tanks. These would weigh far more than the lift of the hydrogen. Unfortunately the hydrogen gas will still produce lift, and would need to be compressed to 15 times the density of air around it to stop doing so. However at the operating altitude, 1 atm density is already 18 times ambient density there, so actually tanks that hold just 1 atm overpressure would do the job.
Someone elsewhere estimated that it would take 45 kw for the airship to keep station. I think he overestimated drag and underrated prop efficiency. Still, take that figure. About 150 MJoule per hour, times 16 hours, 2.4 Gjoule are needed. If fuel cells get 60 percent efficiency, we need 4 Gigajoules worth of hydrogen stored.
I believe the lower heating value of hydrogen is 120 MJ/kg. Therefore we would need about 32 kilograms of hydrogen stored overnight, to last 16 hours of winter darkness.
A cubic meter is a large volume, and at 12 atmospheres absolute pressure you'd need 32 of them to hold 32 kg of hydrogen gas. But how much would such a tank weigh? More than metal hydride at more modest pressures?
Anyway if we can generate 32 kg of hydrogen while also providing 45 kw of power to the motors during an 8 hour day, I think we are in business if the tank is not terribly heavy.
It takes less power to maintain a given _mass_ in a wind of given airspeed in air of less denisty, despite the fact that the _volume_ needed to lift the mass is much greater. The gas volume would have to be 18 times greater, but the cross-sectional area would increase only at the 2/3 power of that increase, while the force of the wind does decline by 18. So the force needed declines as the cube root of the density, and since airspeed is assumed the same, power declines with force. And if the source of power is _solar_, clearly the area of hull skin is greater for the high-altitude ship and sunlight is less impeded by atmospheric phenomena. Clearly with rising power available and falling power requirements, at some altitude solar power wins.
Not sure what they plan to do about nighttime however.
And as for the props--of course they do lose thrust. Now if you just turned them at a given pitch, they would also experience less drag torque as they delivered less thrust, so power demand would also fall--it follows that if you maintain power levels (and pitch the prop blades accordingly) you will drive the air much _faster_ which will partially offset the fall of density--at constant power you get declining thrust, but at a rate not as bad as the fall of density. This happens at the cost of efficiency. However if you use ordinary airplane props you probably were driving the air much faster than you should for an airship anyway even at sea level, and with this racing engine thing going on and the speed of sound _declining_ with the cooling air of high altitude, you would quickly get compressibility problems at the blade tips as they approached and cracked the sound barrier.
Clearly the thing to do is redesign the prop--increase its radius, keep its tip speed moderate. Design it for high altitude, meaning make it light but big. If you do that, it will remain as efficient as a properly sized and pitched and turning low-altitude prop, which means you can expect total power demand to decline as I said above.
Lots of people think high altitudes demand something other than props. They are thinking of airplanes, which have to move _fast_ to stay airborne in thin air--it is _speed_ relative to the speed of sound that dictates that props must be abandoned. With aircraft like airships, which can float in still air, and cannot move fast because they would come apart structurally if you strapped powerful jets on them, propellers will always be a perfectly workable method and the best known practically available way to get thrust from power.
I don' t have time to check the numbers right now, but remember the whole structure has a density of the air at its working altitude, about 1/8 the density of air at the surface, which is itself about 1/800 that of water. If it descends, even under full control and power, it will need to take air into 7/8 of its interior, but even then the overall density will be exactly that of air--this is what it means to be in buoyant equilibrium after all!
If the concentrated loads fall off, that is another story of course, but the same is true of any aircraft. Airliner toilets sometimes accumulate ice on their vents, and these "Icy BMs" crack loose when the plane descends to airports--which are near cities generally, and they often approach right over them. I don't know if any human being has ever actually been hit by one of these ice masses, or if that wa just a clever idea for a 6 Feet Under episode, but sooner or later it is bound to happen if it does not happen fairly often already.
Meanwhile--I don't suppose a downed airship is totally harmless, Mainly it would drape itself over whatever it crashed on and tangle it up. Could be a serious problem if it came down on a busy street intersection.
But there would be plenty of warning. If the ship completely loses its lift gas but otherwise keeps its integrity, it will weigh little more than air but have tremendous area, so I think your terminal velocity is very high.
And I bet you win that bet. There is no reason not to use helium and many reasons not to use anything else.
Hydrogen has the greatest range of flammibility of any gas known in air, 4% to 78%. Just what sort of anti-reaction substance are you thinking of?
Flame is a chain reaction. Basic chemical formulas tell us whether a reaction is going to go forward at all, but only kinetics can tell us at what rate. If we can lower the _rate_ of reaction enough, or dilute the amount of heat released by previous reactions going into components of potential future reactions, we can lower the probability that one reaction will trigger another below 50 percent, and thus statistically the chains will die out instead of multiply to use up all the reactant at once. But how do we do this? Only by diluting the reactants with neutral gases (which includes reactants that don't have complimentary reactants to pair up with, if you can sequester these or they are all consumed.)
The trouble is, if you dilute hydrogen with anything to the point that its lift is less than helium's, what is the point of the exercise? To save money? And I think the chances are zero that
_any_ substance that would weigh that little in the mix can possibly do much to lower the range of flammibility of the hydrogen it is mixed with. Some perhaps, but certainly not a worthwhile amount.
Helium costs more than hydrogen, but at modern prices the cost is only a small fraction of the cost of an airship. Why not just use helium, which is absolutely fireproof?
I just disbelieve this talk of "proprietary gas technology."
Your idea of sneaking up on the lift a high altitude system would need by only _slightly_ empyting a chamber at sea level is a new one on me, and less unworkable than the impossible idea of totally emptying out a hull on the surface. Still, the structural issues are indeed formidable. It is clearly going to be much harder to keep air _out_ of a lightweight shell than to pump some _in_, and yet the weight of blimp hulls, which need only hold pressure in, is quite high compared to the total lift.
Helium has 80 percent and more of the lift of a comparable volume of vacuum, and presents _none_ of the structural problems you acknowledge. Since clearly the shell to withstand even partial atmospheric pressure must have substantial strength, and therefore weight, it is very doubtful this approach can work at all.
And what would be wrong with using helium anyway?
There was nothing marginal about the tremendous potential heat energy that was released when Hindenburg burned. There is also no positive evidence the fire even started anywhere but the deep interior of the tail region, and very clear recent experimental evidence that the kind of material used for the Hindenburg's skin, which has been mythically compared to "rocket fuel," actually burned very reluctantly and slowly. One William Appleby has taken the trouble to simulate that material, and measure its rate of burn. It would take _hours_ for the Hindenburg to have burnt at the rate the skin would burn on its own, and actually the whole ship was consumed, stem to stern, a distance of 245 meters, before it hit the ground about 4 seconds after it started burning.
On other hand, hydrogen is by weight the most concentrated chemical fuel known to burn in air; to release equivalent energy, over 3 times the mass of any hydrocarbon fuel would be required. To be sure, as a gas it is the least dense substance known to exist at standard temperature and pressure, so Hindenburg's 240,000 cubic meters, almost all full of hydrogen, contained only about 15 tonnes of the stuff. Which however would be roughly equivalent in potential heat release to 50 tonnes of gasoline. Furthermore, gaseous hydrogen diffuses more rapidly than any other gas, and has a wider range of flammibility--from 4 percent in air to 78 percent, it will burn. The high rate of diffusion means that small leaks might dissipate quickly, but also that any leaks will establish a density gradient of flammible mix in the air around them that will fill a substantial volume. A small leak inside the Hindenburg's outer hull would mean that dangerous mixtures would exist almost instantly in a large volume near the leak, for the interior was a huge air volume with gas cells for lift floating within it. One spark inside that halo of flammible mix would ingite that whole mass almost instantly, and would indeed cause the very sort of noise that witnesses aboard heard--a sound like a gas stove being lit. This muffled explosion would bring flame straight to the leak in the cell, which would then burn like a torch, igniting neighboring cells and triggering a chain reaction. Every bit of evidence we have says this is what happened; the only argument has been about just how and why the fire _started_. Why was there a leak? Was there one, or did someone plant a small incindiary bomb? But there can be no doubt, the hydrogen released the energy that destroyed the ship in under a minute. No comparable phenomenon would happen if the ship were lifted by helium instead.
It is true that there are bozos claiming otherwise, on the Internet and even on TV. But they are clearly wrong, and I could discuss motives some of these people might have to put out false information. But most people are just flocking mindlessly behind an amusing meme, easily impressed by unsupported claims.
It is also true that a case can be made that heliums' moderate degree of inferiority to hydrogen as a lift gas lowers the margin of success of airships to a critical degree, and that therefore some accidents that have befallen helium lifted airships would not have happened to a hydrogen lifted one. I don't think that is a very strong argument at all. But all the claims for the marginal superiority of hydrogen as a lift gas, and even the fact that hydrogen is cheaper than helium, must be balanced against the simple fact that hydrogen is a very flammible gas, and many hydrogen lifted airships have been suddenly and rapidly destroyed by these flames, and nothing like that can happen with helium, and of course never has. Some helium airships have been burned up in fires driven by their fuel; this has always happened on the ground, either during a servicing accident that set the fuel alight, during disasters such as the terrible hurricane that leveled Richmond, Florida, and the blimp hangar there in late WWII, or _after_ a crash; in the latter cases, crew always had time to escape the relatively slow (though im
There can be a "move" to H2 even if another fuel is more convenient, if it is given political priority. _If_ we can anticipate a future situation where the costs of the alternatives you prefer outweigh their benefits relative to hydrogen, it would make sense to invest now in developing the hydrogen alternative.
You can make a _strong_ case that even if we have to synthesize fuels, we would do better to synthesize hydrocarbons similar to the mix found in gasoline. Even the carbon issue would be addressed that way, for if we were synthesizing fuel from scratch or biological feedstocks of course we'd be pulling CO2 out of the air as fast as we put it back in. But I see that you disbelieve CO2 emissions have anything to do with climate so this point may not matter to you.
It is quite true that gasoline is a _volumetrically_ efficient way to store hydrogen fuel. You do recognize it comes with a downside--aside from CO2 emissions, there is other pollution, and considerable hazard from burning fuel during a crash? I happen to agree that some kind of "tank" full of pure hydrogen in some form would probably pose less of a hazard, but that might be wrong.
I'd be amazed if "no one" in these hundreds of comments on a scheme to include hydrogen fuel in our repetoire of transport power sources is even _considering_ the simple, straightforward method of cooling and liquefying the gas to store it in an insulated tank. Anyway, I am. And I am not talking about cars.
My suggestion is, that if we decide to make a priority of developing hydrogen as a fuel, we should start with aviation, particularly big military transport planes. The airplanes would have to be redesigned, because you almost certainly can't put the fuel in the wings anymore. Too much surface area to insulate and too little volume left over for enough fuel, not to mention the danger that internal structure in the wings might get chilled and thus behave weirdly--snapping suddenly for instance. But a thicker fuselage with big compact tanks in it would add less drag than the smaller wings would save. Or, the planes can be desiged, for a given weight, to achieve fantastic ranges.
I don't think they would be more vulnerable to destruction by the fuel, in an attack or in a crash, than airplanes with traditional jet fuels are now.
"I've never been that convinced either way..."
Good for you. I'm uncomfortable with my friends who adopt Hugo Eckener's best _guess_ scenario. Which is: hard maneuvering breaks shear wire; shear wire slashes one of the rear hydrogen cells; ventilation slacks off (this is actually a certainty; by the design it would do that); hydrogen "pools" above the cell able to disperse only _through_ the skin; spark sets off mix; rest is history. We don't _know_ a shear wire broke; we don't even know a hydrogen cell had a hole in it. Possibly some saboteur did it and did not get caught (we sure _don't know_ it was sabotage, nor can we prove it was not!) Possibly something quite outlandish happened. A number of people I know insist on claiming Eckener's scenario is _true_ just because alternatives they don't like are _either_ disproved or distasteful.
But some things are impossible.
"and I consider people using pictures to model something like a large scale combustion to be naive at best."
"Pictures?" I am not sure what you mean here. Bill Appleby made actual samples of the same kind of material as Hindenburg's hull, layered in the same way, that were used on the hull. Little pieces to be sure but they do verify that _without_ the presence of hydrogen, the stuff burns slowly and needs some prodding to get started. Which was, from all descriptions, the case with Bain's authentic skin sample--he never showed it could ignite itself, and he used an intense flame to start it burning and it burnt _slowly_, with no very intense heat being produced. I suppose on a larger scale the speed of the flame propagation might pick up, but it would have to speed up by a factor of a thousand to account for the disaster.
"It's a concentrated refutation..."
Yes. Some years ago, in the late 1990s, Addison Bain stepped forward with the remarkable, revolutionary idea that _actually_ the Hindenburg fire _was in no way_ caused by the hydrogen, that the hydrogen was "unfairly condemned" as the culprit, for even if that same airship had used helium (which of course does not burn) the results would have been the same. For, as you have no doubt heard, the doped, aluminum-painted fabric was equivalent to "thermite" or "solid rocket fuel."
BTW--it is not a virtue of rocket fuels to blow themselves up in one quick blast. They burn slowly and steadily--that is part of the point, and they are typically _not_ the densest concentration of available heat energy you can attain either. That desirable feature goes a bit by the board aiming at other desirable qualities--like stable burning for instance. Thermite and rocket fuel then are very different things. And doped aircraft skin material is a third thing.
Anyway, it is the purpose of many people who are interested in airships for historical and other reasons to restore accuracy to the discussion. _Clearly_ the presence of hydrogen made a big difference. Clearly also, the Hindenburg's designers had the longest experience of anyone in the world, and with the most success, at avoiding hydrogen fires, and to do that, avoiding fires of any sort if they could help it. They couldn't always help it and had damage control strategies to prevent inevitable sparks from leading to catastrophes. They would not, and did not, fail to check out the flammibility of the material they wrapped the entire airship in. Those of us who once took Bain seriously are amazed at how _difficult_ it is to get this fabric to burn; we should not be, why would Zeppelin designers want anything less? From our point of view it is important to examine each of Bain's specific claims and see if they have any merit.
Bain wants to argue that hydrogen is safe _as a fuel_ and he thinks that the image of the fiery destruction of Hindenburg is a barrier to acceptance of hydrogen. I think that is absurd myself but I have to admit I have not been in the business of selling hydrogen fuel professionally. It is evident to me that concentrated, insulated fuel tanks are different than huge, thin-walled b
First I want to thank you--that is a useful table!
(How do you prevent slashdot from sticking random spaces into the link?)
But please look at the right column!
in terms of _gravimetric_ density, hydrogen (in any form) beats every other entry handily. 39,000 Watt-hours/kilogram, versus just over a third of that for propane, and only 12,200 for gasoline. Gasoline wins on this table hands down for _volumetric_ efficiency, but you'd be hard put to show from that that carbon bond strength has anything to do with it at all. I think it is a simple matter of the material density. Unfortunately I don't know the chemical formula of propane, but a typical gasoline molecule is made up of roughly 2 hydrogens for every carbon, or maybe a bit less. A benzene ring has 6 and 6 but it is a closed system; to form the more complex hydrocarbons there clearly can be few double bonds involved and lots of hydrogen.
Let's just assume that gasoline is 1.5 hydrogens per carbon, and that how they are bonded to each other doesn't matter much--in the end it all burns to water and CO2. OK? Carbon weighs 12 AMU, plus 1.5 hydrogens gets us 13.5 versus 2 for a hydrogen molecule. Let's multiply the hydrocarbon by 4: we get a segment that weighs 54 with 4 carbons and 6 hydrogens, that consumes 11 oxygen atoms to yield 3 waters and 4 CO2 molecules. This fuel weighed 27 times one hydrogen so we burn 27 kg of it to get 329400 Wh/kg or 8.446 times the heat of burning 1 kg of hydrogen. Now subtract 3 from that output ratio, representing three water molecules, to get 5.446 and divide that by 4; the formation of 1 CO2 by these assumptions releases as much heat as 1.36 water molecules forming. Not a dramatic difference and I rather think that hydrocarbons have more hydrogen than that. Note that propane is more punchy on a mass basis and is a simpler, lighter, more hydrogen-intense molecule. If the hydrogen ratio was as low as 1:1 which I think is impossible for something as volatile as gasoline, forming CO2 would be worth 1.533 water-formations--still pretty lame when you consider that there are 2 oxygen atoms in the reaction! If the ratio is more like 2 H to 1 C, then the output ratio drops to 1.19. Hydrogen-oxygen bonds actually seem pretty strong!
For cars or boats or trains, perhaps this doesn't signify all that much; volumetric density matters a lot. But for aircraft, where saving weight is the name of the game, hydrogen fuel delivers tremendous advantages. Even though the fuel must be stored in very bulky tanks that will cause extra drag and increase structural weight, the savings in fuel weight would be so great that the wings (a major source of drag area!) would be much smaller. If anyone here cared I could go on about how the advantages for airships would be even more decisive.
It is very overblown then to claim that "hydrogen as a fuel is not backed up by the laws of physics." Where weight is important, it is three times better than any other chemical storage medium. This is why it is used in rockets of course. (Higher specific impulse too--but that is also a funtion of its very low mass and high _mass_ energy density!)
Evidently there is not all that much energy in the double bonds of carbon as you think.
Sources:
r e. htm
/ LZ129fire. pdf
p ro ject1/index.html
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fi
I'm referring to Dr. Alex Dessler's piece; John Dziadecki has links to the whole "debate." But if you read Alex's piece you'll see, Bain just makes stuff up in the vein of Imannauel Velikovsky.
If you like loading pdfs directly
http://spot.colorado.edu/%7Edziadeck/zf
Is Alex's paper. But slashdot screws with URLs for some reason, you'll have to paste that somewhere and take out the extra space.
Also, for evidence that the alleged "rocket-fuel" skins are damn near fireproof:
http://www.sas.org/tcs/weeklyIssues/2004-12-17/
Have fun! I can put you in touch with the authors of either of these if you have questions for them.
Bain's agenda was apparently to empower people to dismiss the Hindenburg disaster when worrying about the risks of hydrogen fuel. But liquid hydrogen, or hydrogen bound to hydrates, or even compressed gaseous hydrogen, is a very different sort of risk than a huge multi-thousand cubic meter gas bag with surface areas measured in thousdands of square meters, made of gossamer-thin stuff. The debate about whether hydrogen is risky or not is not helped by errors and falsehoods; to deny that hydrogen comes with special risks is a setup for disaster. Acknowledging and managing them (or forgoing the technology if you have alternatives) is the only way to go.
"Re the Hindenburg incident: there is now fair evidence that the whole thing happened"
p ro ject1/index.html
r e. htm
No, there isn't. The Bain skin theory is based on half-baked speculation that, whenever investigated closely, falls apart.
The hydrogen gas cells were only somewhat tight--as tight as they could make them, but man, they had to have an area something like 45,000 square meters! And yet to weigh only a small fraction of the ship's total 200+ tonne lift, which was generated by the gas they contained. They were gossamer thin, and very vulnerable to cuts and holes, not to mention that all thin gas cells have gases, especially such light ones as hydrogen, diffuse right through them. Zeppelin did their very best to keep them intact but they could not always succeed.
Once a fire got going inside, the thin fabric could hardly impede it, even if their materials were not themselves flammible!
Ventilation was the key. Unfortunately, Hindenburg's ventilation depended on forward motion to create the draft. _There_ is a design flaw! They should have used fans. (But then, the power lines to them would surely have posed a spark risk...)
Cellulose acetate butyrate is far less flammible than you think,
http://www.sas.org/tcs/weeklyIssues/2004-12-17/
I mean, when you say it is "highly" flammible, is that a quantified judgment? Here's a number to work with--the flames would have to progress at over 4 meters a second along the surface to set the whole length of the airship afire. The tests above show that even the very worst doped cover material investigated burns at--less than 1 centimeter/sec.
Hydrogen flames inside could account for it; never the cover.
That cover often was hit by sparks from the engine which burned little pinholes in it; it never caught. Both the experimental investigator Bill Appleby (link above) and Addison Bain's own "demonstration" of his claims used a blowtorch to light the skin afire; nothing less than incindiaries would do it. I don't know if the flame would persist or die out if left alone. But at 1 cm/sec the crew would have time to do something about it!
No one, certainly not Addison Bain, has ever demonstrated that anything like airship skin could ever set itself afire due to electric sparks, nor even that the hull of the Hindenburg or any other airship resembled the tremendous capacitator Bain alleged it was. There are clear arguments to the contrary.
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fi
There is no way to know that of course, as no one else was operating any airships of any kind by 1937 but the Germans--and us, and the Soviets, but they were about to abandon their little semirigid project completely. Our Navy was operating a few blimps and the Army was shutting down its blimp program. That was it.
Our blimps came in very handy during the war, but no one in officialdom prepared for that. They were very belatedly thought of and built on an emergency basis. The Navy did not want to be bothered with mundane things like convoy duty or coastal patrols! Which is what the blimps were very good for.
LTA enthusiasts in the Navy wanted great big rigid airships. I think that they--and the blimps--would have been very useful. But the LTA people were outgunned by lots of interests who wanted money to go to airplanes and other rival technologies.
It is perfectly clear that American refusals to grant access to helium were not motivated by any serious plan to actually use the stuff ourselves. I'm happy that Hitler failed to get a favor. But by no means did American decision makers, public and private, always rebuff the Nazis.
Actually letting Zeppelin have some helium for peaceful commece would not have been the same as giving it to Adolf Hitler. The Nazis were not fans of Zeppelins and they scrapped them all once they started their war. If they had had a fleet of 2 or 3 flying by 1939 and spare stocks for a couple more, that could hardly have been decisive in the war even if the Germans had put these dirigibles to the best possible miltary uses--either as naval scouts (that is, spotters for U-boats and the surface ships that broke out and took up commerce raiding when the war went into high gear-though a big Zeppelin might have carried a few airplanes to strike directly at shipping too) or as transport aircraft, just a few, with limited and dwindling supplies of helium (the stuff leaks you know) could not have done much. And so they'd either use hydrogen--risky but workable, especially if you choose missions where you can avoid being in range of being shot at--or give up on airships. Which was the Nazi inclination. I think they were idiots not to use Zeppelins more effectively but it is just as well they were that arrogant.
No doubt, if we had given the Nazis helium they would have done as much harm with it as they could.
The British _should_ have been using airships for transport to their distant colonies. If they had been, I suppose the only reason we would not sell them helium would be if the competition stimulated _American_ commercial (and sustained military) LTA. Even then, the more demand for the gas, once adequately diverse wells were found, the more bearable the cost of processing it--supply may well have been adequate for demand if there had been any demand. I think we'd have sold it to them.
It was anti-Nazi policy, and perhaps anti-LTA policy. Airplane based airlines were struggling to establish themselves in the 1930s--had airships existed as serious competiton there is every reason to think they would have severely cut into the business. After the war it was different, with much better and faster airplanes, with much longer ranges and higher capacities and above all a network of former military airfields all over the world. But in the 1930s airships had many advantages over airplanes for long-distance air transport. But the visionaries of aviation looked ahead to the days when airplanes would pull ahead, and lobbied their politicians to hasten that day.
"They had an actual cover sample that was preserved from the Graf Zeppelin company (no relation to Led Zeppelin). "
No, that was supposed to be an actual piece of Hindenburg's own skin! Which--think about it--survived the fire. Without burning up.
The Hindenburg was 245 meters long, and was burning everywhere from stem to stern in under 60 seconds, about as long as it took to fall down to the ground. For flame to burn along the skin so as to achieve that, it would have to burn at 4 meters per second. If you examine other comments of mine you will find I give references to someone who made his own doped skin samples modeled after Hindenburg's--they burnt at less than 1 _centimeter_ per second.
It was the hydrogen and the hull could have been asbestos--it would still have been heated to cherry red heat, and the ship would still crash, once the hydrogen cells were set aflame.
" The hydrogen inside had no oxygen and couldn't burn."
The hydrogen inside the 18 or so gas cells was pure and couldn't burn--as long as there were no holes in said cells. No one knows just what did happen. But a small hole in one cell could have released a quantity of hydrogen adequate to start a fire, and the ship's ventilation (rigid airships were the opposite of airtight--they had to let their pressure match that of the air outside, and hydrogen ships were designed to flush the air continually) depended on _motion_ to drive it. All that would be needed then was a spark; given that,there was quite a bit of air inside the hull. And the flames would soon burn themselves some more ventilation!
Look, the heat content of the 18 tonnes of hydrogen contained, if set afire, was equivalent to about 50 tonnes of diesel fuel. Whereas all the airship's fabrics put togehter weighted just 15 tonnes. I suggest to you, if 15 tonnes of doped fabrics can release more energy than 50 tonnes of diesel fuel (or its equivalent, 200,000 cubic meters of hydrogen) then the designers should have devised engines to burn swatches of fabric instead of diesel fuel. Weight is critical on aircraft, you know. (A steam engine could do the job by the way.)
It was the hydrogen, not the skin.
It is a funny thing--the guy, Addison Bain, who started this skin nonsense doesn't care about airships, he wants to promote a hydrogen-based fuel economy. He thinks he has to prove that the hydrogen was blameless in _every_ airship disaster (there were many other cases of hydrogen ships burning up) to set at rest "irrational" fears about hydrogen as a fuel. But that is nonsense. Hydrogen is dangerous in airships because a very flammible substance is contained in huge volumes with enormous surface areas, that need very thin skins if they are to be light enough to be lifted by buoyancy. If we had liquid hydrogen stored in tanks, they would be bulkier than gasoline tanks, but still far denser than air, with much thicker skins--liquid hydrogen has to be kept in a thermos after all! The danger is much more comparable to that posed by _any_ fuel, and less in some ways that familiar ones. Airship fires are irrelevant to the fuel question.
Is that even supposed to make sense? Why would any designer opt for the _most flammible_ skin when less dangerous designs were available?
Actually the Hindenburg's skin was less dangerous than any prior design. These Zeppelin engineers were _not_ idiots. (Not even to use hydrogen--they had no other choice but to abandon airships, and they had good reason to think they could manage the risks. But clearly not by deliberately choosing dangerous skin!!)
One Addison Bain makes all kinds of bizarre claims, about the skin being "thermite" like or "rocket-fuel" like, but actually none of them are borne out when you make a sample of the stuff and test it. Only the hydrogen, burning inside the airship, accounts for the disaster of 1937.
http://www.sas.org/tcs/weeklyIssues/2004-12-17/pro ject1/index.html
r e. htm
r e. pdf
This is a project whereby someone created samples of the skin according to documented reports of its composition, and measured the burn rate when he set them alight with a torch.
BTW you _have_ to use a torch; sparks do not set these things ablaze. The actual airship had pinhole burns in its skin near the engines where sparks sometimes came out. Clearly if the skin were somehow "more flammible" than hydrogen gas, it would have gone up the first time one of them hit it!
Anyway, they burn at a rate of less than 1 centimeter/sec. The Hindenburg was engulfed in flames all along its 245 meter length in under a minute. Do the math; the skin burns at less than 1/1000 the necessary rate!
It is another story of course when there is a powerful source of heat _inside_ the skin that can only get out by burning through. That would clearly accelerate the flames! That was the hydrogen of course. It would have massed about 18 metric tons, and such a mass of hydrogen can release as much energy as 50 tonnes of diesel fuel. And if it is allowed to mix with air, clearly flames can progress very rapidly along the interface; think of how the flames race along a gas grill when you light it at one end. Once a big fire was going inside clearly the heat of the flames themselves would burn through the incredibly thin light gas cells and then through the outer skin, even if all the fabric were totally inert to fire. The heat would be enough to _melt_ them, and there would be your gas/air mix, in the presence of flame yet.
Here's where you can find another paper that goes over the erroneous claims of Dr Addison Bain one after another, by a Dr. Alex Dessler.
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fi
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fi
Wrong.
7 /pro ject1/index.html
Look at
http://www.sas.org/tcs/weeklyIssues/2004-12-1
Bill Appleby took the trouble to create numerous samples of the sort of skin the Hindenburg might have had (there is some controversy as to the composition) and test them systematically.
They burn at about 1 centimeter/sec when ignited with a torch.
In real life, there were pinhole burns on the hull near the engines where sparks sometimes came out--evidently a mere spark did not even create a sustained flame, let alone cause the whole ship to be incinerated in under 60 seconds. Which is how fast the Hindenburg was set afire from stern to bow, over a distance of 245 meters. Which, you percieve, would take about 41 minutes or more with this fabric alone.
Gaseous hydrogen that is allowed to mix with air on the other han creates a very energetic flame and the very mobile, light molecules of the gas, agitated by this heat, clearly support very rapid propagation of flame along any interface where gas and air mix. Once a flame was going inside the hull, clearly the heat would tend to burn up the thin hydrogen cell skins, and cause the cells to expand releasing more hydrogen to the escape ventilation system--which under these conditions would become burners instead of vents. The most likely scenario (no one knows what happened for sure) is that a cell was accidentaly cut open, perhaps by a structural wire that snapped during the rough final approach to the mooring mast, and that a spark set the mix near or above the cut aflame. The heat released from one cell set afire would be plenty to set off its neighbors in a chain reaction, much more rapidly than the skin could possibly burn. And about 10 percent of the volume inside the hull was full of air, not hydrogen--plenty to start the fire and perpetuate it to the bow. The skin could have been totally inflammible and the results would have been essentially the same.
In fact lots of skin from the ship _did not burn up_; you can buy pieces of it even today. And the flames went on for many many hours, as the diesel fuel slowly burned.
Pure hydrogen flame releases heat in 2 ways--it produces a hot molecule (water of course) and it emits UV radiation. In the open, such photons are not as likely to be absorbed as readily as the IR photons that carbon fires put out.
p ro ject1/index.html
The guy who falsely suggests that the Hindenburg did not burn due to its hydrogen (he blames the skin, but I know someone who experimentally has shown that that kind of doped fabric burns at about 1/1000 the speed it would have had to to account for the destruction of Hindenburg)
http://www.sas.org/tcs/weeklyIssues/2004-12-17/
--anyway, Addison Bain makes a big deal of hydrogen flame's invisibility. Quite true. Except that the hydrogen flame inside Hindenburg was _inside_ a fabric skin that was _not_ transparent to these UV photons! All the heat released by burning hydrogen had nowhere to go until the skin burned up, and when it did that of course it emitted IR and red light like any other burning carbon substance. And more; the extra heat from the hydrogen (by far the biggest energy release around) would make the carbon glow even if it were not burning, like these hydrogen-flame detecting brooms or like the mantle of a gas lantern.
In the real world you rarely encounter pure hydrogen flames you see.
"There was a great show on The Discovry Channel I think. About the Hindenggerg."
I haven't seen this documentary but I am very familiar with these theories that allege the outer cover was the major culprit.
I think these sources can set you right. They were written by people who are very well informed about airships, and who also got off their butts and did serious research on the matter. One is by Dr. Alex Dessler, who analyzes all the claims from a theoretical standpoint and using documented data.
You can find it here, along with the "theories" of Dr Addison Bain that it refutes:
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
(note--for some reason I have never understood, slashdot inserts a space somewhere in URLs. You tell me why. Anyway, when this posts there will be a spurious space in the link; find it and delete it. Same for the next link.)
The other is by the very practical William Appleby, who made numerous samples of various types of skin fabric that closely simulate actual airship coverings of the day, complete with aluminum paint and different kinds of dopes, and measured how fast they actually did burn.
The Hindenburg was 245 meters long and was enveloped in flames in less than one minute; that means the flames had to progress at over 4 meters/sec. Let me quote his finding here"
"Conclusions
The Hindenburg burned so fast that the flames covered a 10-cm distance in less than 0.02 second. None of the burning times for cloth treated with doping paints in this study approached the time the Hindenburg was totally engulfed in flames, which was less than 1 minute (approximately 600 cm/sec). Sample 4 simulates the bottom of the airship, and sample 5 simulates the top portion. The painted cloth pieces burned slower by a factor of approximately 1000 to 3000, depending on treatment. The burning rate of the samples painted with cellulose acetate butyrate dope, the kind used to coat the Hindenburg, were especially slow."
http://www.sas.org/tcs/weeklyIssues/2004-12-17/p ro ject1/index.html
"The outter covering of the zepplin was a fabric covered in a petrolium product to make it water proof."
Um, no, you weren't paying attention. The fabric was cotton (or sometimes they used linen) and they doped it for a variety of reasons--most airplanes had the same kind of skin in those days. To tension it, to stiffen it, to incorporate paints to ward off damaging sunlight, to reflect heat (important for airships, that are affected by thermal expansion and contraction)--lots of reasons. They didn't use a hydrocarbon. They used a lot of stuff that loose commentators said equals thermite. But look at Bill's experiment--the stuff does not explode, or even burn at any very impressive rate.
"The covering of the zepplin is what actually caught fire first. Not the hydrogen. If you watch the videos of the disaster you can see this is the case. "
Obviously if you rely on films taken outside the airship, the first thing they will see will be fire on the outside. That alone does not tell us anything about whether it started inside or outside. Clearly if it started inside it would show up first of all on camera in the form of flames spouting _from_ the inside!
Actually if you know anything about airships there are other signs to look for besides gouts of flames. I have never examined these films but I have friends who have; they tell me they see evidence of events inside the ship that are consistent with their theories, that sensibly enough suspect the hydrogen first of all. If there were no such signs whatsoever the visible flames on top of the ship might _might_ be the start of the fire or they might not.
"The disaster was a lot like gas tank fires of today. The fire started from a static discharge between the docking tower and the zepplin. "
Nobody actually knows what did happen. That the docking might have triggered a spark somewhere does not seem unlikely. But Ba
First of all that link does not work. I get an error page. I suggest you post an alternate way of finding that article.
From first principles we can see that it _can't_ be right that hydrogen is less "energy-dense" than a hydrocarbon fuel _by weight_.
At any rate, there is no way that both the claims above can be true. I can credit the ratio of energy densities _by volume_. But consider how low liquid hydrogen's _mass_ density would be. I don't have those figures handy, but a reasonable assumption is that a molecule of liquid hydrogen would occupy the same volume that a water molecule would. Possibly that understates the density since hydrogen molecules might pack more closely than water molecules, and will be less energetic since they only condense under either very low temperature or very high pressure. Here we assume low temperature--but a liquid is condensed matter; its molecules are already "touching" for practical purposes and density hardly varies over a tremendous range of pressures.
Then mass density would be in ratio to atomic mass units: 2/18 or 1/9. Gasoline I am not sure of either, but it is moderately lighter than water. Say it is 80 percent the density of water, that seems about right. To state that a liter of liquid hydrogen contains 1/3 the potential for heat release of a liter of gasoline is therefore to state that 111 grams of LH2 releases 1/3 the heat of 800 grams of gasoline, therefore the energy density of hydrogen by _mass_ must be
800/333=2.4
To claim otherswise, to claim that the ratio is reversed and more than reversed so that the gasoline releases 3.5 times _more_ heat _by mass_ would require the liquid hydrogen to be far _denser_ than water, or for liquid gasoline to be _even lighter_ than LH2! Lighter than LH2 by 6/7 in fact! We know that is not so.
Would you seriously have us believe that liquid hydrogen condenses 8.4 or more molecules in the space occupied by 1 water molecule in water? That is what it would take to make LH2 dense enough for both of your claims to be consistent with each other.
Either your source is screwed up, or you misread it.
I was referring to a television show where Dr. Addison Bain, the major author and advocate of this implausible "theory" that seems to be uncritically taken for fact, proposed to show how dangerous the skin was.
However I do not watch a lot of TV and have not seen this show, nor any of the TV documentaries where Bain's claims are accepted as fact despite this embarrassing self-contradiction of a demonstration. I participate in a listserv devoted to airships and others on it, whom I trust on this, have very often repeated the story of Bain's demonstration. I have asked them to provide you with citations to this TV show or other documentation of Bain's embarrassment.
But meanwhile Dr. Alexander Dessler has written a paper that critically examines the core claims on their merits and shows that they are all invalidated by fatal contradictions with fact and logic:
The Hindenburg Hydrogen Fire: Fatal
Flaws in the Addison Bain Incendiary-Paint Theory
(3 June 2004: 480kb pdf file, 21 pages)
This is hosted at John Dziadecki's web site.
Slashdot's hyperlink policies are a mystery to me! I can't make these links show here, just type in
http://spot.colorado.edu/%7Edziadeck/zf/introd ucti on.htm
in your browser;
The pdf can be found, with other intoductory material, at
http://spot.colorado.edu/%7Edziadeck/zf/LZ129fir e. htm
Based on the descriptions I have read:
Bain had a sample of fabric he said was a piece of the fallen ship's skin--and indeed a lot of this allegedly unstable skin was left lying around on the field, kind of odd when you want to claim its conflagration destroyed the ship and sucked up so much oxygen that the hydrogen could not even burn! Not so odd if you assume instead that he airship's designers, mindful of the danger of fire, did their best to create a flame-resistant skin instead of one make of "rocket fuel" (and solid rocket fuels do not actually have the spectacular combustion features Bain suggests this skin has but failed to show--read the paper!) But he said he had an authentic piece of this skin--and proposing to destroy it for a staged demonstration strikes me as a crime against historical evidence in itself, but he did. However he did not rig a form of spark ignition or demonstrate that the skin could create sparks of any kind itself as he claims must have happened. He used a powerful flame source instead, and it did not cause the skin to burst into a rapid "thermite" like combustion--instead it burned slowly and dimly, almost going out, needing to be nursed along. This would explain how come he had some skin to destroy, and also I think it shows that the stuff was carefully developed by the Zeppelin company to be as _fireproof_ as possible, but it seems to directly contradict Bain's claims, don't you think?
The idea that the skin _could possibly_ be more risky than the the hydrogen could only have two merits--one being that the skin could somehow release more heat or at a more rapid rate, which claim Bain makes. He also says the skin design and composition allowed it to _self-ignite_ but never demonstrates this and the paper demolishes all the bases of this claim. If the skin could just create occasional sparks that would be a grave matter--but there too the Zeppelin engineers did their best to avoid this and the way that Bain says it could is quite contradicted by engineering details he ignores though they are no secret (just obscure--you have to care about airship history to know about them).
It would be silly to design one that operates at both altitude and sea level. What I did not point out in showing that an airship can maintain the same speed with the same props is that when it does so up high it suffers far less force than down low--I said that but did not point out that this means the ship is way overbuilt for that high altitude then, if it can take the same speed at sea level. Therefore if the mission is to operate up high you make it far weaker and lighter and operate it very carefully, at reduced speeds, down low. You might go for constant aerodynamic force the way an airplane does, and thus like an airplane need less power down low (except planes also need extra power to take off and to climb--equilibrium airships would not!) We _choose_ not to use full power, to avoid wrecking the ship!
This is why solar power works so well for these things. Up high the air is very clear, you are above all the mist and dust and air itself is pretty transparent, and also very thin there. So there is a lot of power where it is needed and if the ship is brought down, it needs less so the fact that there is less light down here is OK.
So I don't have to get into an argument about whether internal combustion engines are even feasible up there or not--they are not the wisest choice of power plant up there anyway.
I was making a point with my example and assuming an airship that only went from sea level to some moderately less dense level, one where human beings could still breathe. Remember that the airship can only be filled with as much helium as it can retain at the highest level it reaches, which means it is underfilled down low, so it is desirable to limit the range of altitudes it is expected to operate in.