> It is unfortunate that in the public mind, hydrogen as a lifting gas is associated with the Hindenburg disaster. Actually, hydrogen filled airships were extremely difficult to set alight. Just ask the Brits in WWI.
> The RAF could easily hit the German airships with gun fire, but couldn’t get them to ignite until they developed special phosphorus filled ammunition. They used sustained machine gun fire to rip a section of the gas bags to get the hydrogen to mix with air at their surfaces. Then, the small number of phosphorus burning bullets could ignite this hydrogen air mix. Even then, the RAF brought down very few of them.
> Because of this knowledge of how difficult it is to get a hydrogen filled airship to burn, there has been much speculation that the Hindenburg was sabotaged, set to burn deliberately, in a very public act of terrorism / economic / public relations warfare against the NAZI regime (and who could blame them?).
I had no idea that there were controversies regarding the cause of the disaster, nor that hydrogen was (arguably, at least) dangerous more in the public eye than in reality. I'd be interested to hear other modern engineering perspectives on the hydrogen issue...
I don't know much about the Hindenburg disaster, but the fact that it is difficult to set something alight with bullets traveling through a thin fabric and then (flammable) air (as opposed to having sparks generated by bullets hitting e.g. metal and even then, there's not a lot of sparks) is not really evidence of hydrogen's safety. It's really really hard to make even normally flammable things catch fire with normal bullets or even tracer bullets. You could shoot at a gas tank all day and it won't explode. Even absolutely riddling a gas tank with tracer rounds often won't set it alight. It is far far far easy to set something alight with a single match than it is even with full magazines of bullets, all the more so if it's a patch of air that the bullet goes straight through.
Hydrogen is still widely acknowledged to be extremely flammable (see all the references here https://en.wikipedia.org/wiki/Hydrogen_safety). We have had many many disasters with hydrogen explosions pre and post-Hindenburg.
> to having sparks generated by bullets hitting e.g. metal and even then, there's not a lot of sparks
Just wanted to chime in on this - it's impossible for most bullets to cause a spark, unlike what TV and movies show. Most projectiles (including the .303 round the British were using back then!) are lead with a copper plating, which are both non-ferrous metals.
Some Soviet era and US military ammunition (specifically m855 rounds) have a steel core, and those can cast sparks, but almost all handguns, and most rifles, aren't using ammunition capable of doing do.
Sparks no, but a spall can be hot. Fabric will not spall but whether by spark or spall, bullets hitting solid objects can generate enough heat to ignite things they touch.
Note that regardless of what you do, a container of fuel (without its own oxidizer) would never successfully light/sustain fire without first having displaced the majority of the fuel with atmospheric air to provide the necessary oxidizer. That’s why you can’t light a full container even with tracer rounds.
Otherwise, you are only be able to light the part of the fuel that leaked into the atmosphere.
I think people have done experiments with gasoline exposed to open air or with a chamber of air and even then it is quite difficult to ignite, especially if the bullet has nothing to impact against, but travels through the vapor.
This is interesting to contrast with my experience as a former tank commander doing range gunnery with wooden targets and dry brush. Range fires due to machine gun fire happened all the time. They were not remotely uncommon or difficult to cause.
I know next to nothing about chemistry or materials science, so offer no explanation of why this would be the case but a gas tank is difficult to ignite. The only layman intuitive answer I can think of is that a high speed projectile traveling through wood generates a lot more friction than one traveling through a liquid or gas, and something has to happen to that energy.
Yeah as soon as you have a solid chunk of something to hit it's a lot easier to start a fire. E.g. it's actually quite easy to start a fire by shooting a lot of bullets into a gas station pump rather than a thin barrel.
I read (I forget where) that the Hindenburg's skin is where it started burning. The skin was fabric, painted with flammable shellac, and the shellac contained a lot of aluminum powder.
This is a major plot line in the kids series "Pendragon". One of the books centers around the blowing up of the hindenburg. I guess the author was onto this as a conspiracy and decided their own explanation! (If your child liked Artemis Fowl, they might like this series)
if you go down this rabbit hole on google, just be wary that while the hindenburg sabotoge conspiracy theory actually seems fairly plausible, most of the people you'll find talking about it are right at the top of this chart:
A bit off topic but I'm a little sad to see "Covid-19 made in lab" in the "dangerous to yourself and others" tier, especially with how much public view has evolved. Very few people will ever know for certain, it seems, but it could very well have naturally mutated from an existing virus in captivity and then escaped accidently. We have to be careful how we approach framing conspiracies because you risk to alienate and smother valid discussion.
(Scientist chiming in, albeit not working in a relevant field for this discussion)
In fact, several well-respected scientists are calling for a scientific and unbiased debate on the origin of covid, as it is now almost impossible for scientists to simply mention lab origin as a possible origin to study.
Here is one of the last papers I've seen on this subject:
I'd say right on the speculation line. It's far-fetched to say he can totally see, but he may very well experience some limited optical sensation, albeit one of such limited utility that we can't really call it sight.
The story about him seeing Shaq is an interesting example. If you already know that Shaq lives in your apartment building, how much visual acuity do you need to make an educated guess that the large form waiting for the elevator is probably Shaq? There's also no one to tell us if he ever stood there talking to thin air thinking it might be Shaq ;)
It also seems like the kind of thing that would be difficult to give a satisfactory description of, so being coy about it is probably for the best.
NOVA did an episode recently that demonstrated how the Hindenberg could have burned based on a confluence of the weather and coincidences. No sabotage or conspiracy is necessary.
If your hydrogen-filled airship is flying through heavy anti-aircraft fire, you likely have bigger problems.
This scenario also fails to address the numerous failure modes of airships, including but not limited to the extraordinarily wide range of explosive mixes of hydrogen and air, as well as the rapidity and violence of hydrogen combustion and explosions.
I read about the early history of the Hindenburg, Graf Zeppelin. Fascinated that as passenger aircraft, they stayed relatively close to the ground during their flights. I don't know why I assumed they flew at 25K feet like modern jets — I guess I had not thought it through.
But the idea of air travel where you watch the trees, rivers, pass as though you were on some "elevated train" is fascinating to me.
> But the idea of air travel where you watch the trees, rivers, pass as though you were on some "elevated train" is fascinating to me.
I did a hot-air balloon flight in Southern England several years ago and this low-level aspect was an unexpected bonus. The hills and rolling countryside seemed much more three-dimensional than I have seen from light aircraft, for whatever reason, especially in the low early-morning sun angles. It was also possible to hear ground noise (e.g. dogs barking at the balloon). You could also see the slow reaction of flocks of animals (e.g. sheep) that moved in their fields away from the balloon.
In WW1, once Britain developed effective means for shooting down airships, the Zeppelin company built lightweight airships that could climb as high as 20,000 feet, at the cost of being too fragile to handle rough air. Outside of the exegencies of war, these were not viable designs.
Being limited to low altitudes means that practical airships cannot fly over the weather, and their low speed limits alternative destinations. Three of the four helium-filled rigid airships operated by the US were brought down by bad weather. These days, we have much better materials and weather forecasting, but I think operations would still be quite frequently constrained by the weather in most parts of the world.
On the other hand, if the stream of powered sightseeing aircraft over the Grand Canyon could be replaced by a few electric airships... Well, we can dream.
Lifting capacity of rigid airships is proportional to air density. In order to fly at higher altitudes they would have to drastically reduce passenger load. And above about 10K feet the cabin would have to be pressurized, which further increases weight. The big disadvantage of flying at low altitude is more exposure to storms and air turbulence.
There's a common misconception that the Hindenburg failed because of hydrogen. That's not the case (he said confidently.)
The Hindenburg burned - it didn't explode. Hydrogen doesn't burn, it explodes. What burned on the Hindenburg was the skin, a mixture of all kinds of inflamable things including silver, dope and cotton. The same materials that made WW1 airplanes somewhat risky. When you watch footage of the Hindenburg you see the skin burning, the hydrogen escaping, and it falls to the ground, because, well, gravity.
Even then it happens really slowly - some people on the airship escaped by just waiting till it reached the ground then running away.
These days we regularly use flamable materials in transport - think Avgas, petrol, and to a lesser extent diesel and jet fuel (kerosene). The "hydrogen vs helium" issue is overrated in my opinion.
>The Hindenburg burned - it didn't explode. Hydrogen doesn't burn, it explodes
If it doesn't contain its own oxygen it can't realistically "explode".
(edge cases involving novelty chemical reactions that go solid/liquid -> gas by some other means notwithstanding)
You need precise fuel and oxygen ratios to burn things. Burning is basically just runaway oxidation. Burn enough stuff fast enough and you get an explosion. Contain a fairly rapid burn and you can fudge the same pressures as an explosion (this is what happens in a spark ignited combustion engine). Both these require the fuel any oxygen to be in sufficient proximity and mixture to each other.
Airships, propane tanks and other sources of fairly pure gasses can't explode until after you break them and let the contents mix them with the atmosphere. Now, a trashbag full of pre-mixed oxygen and acetylene. That will go bang real good.
>When you watch footage of the Hindenburg you see the skin burning, the hydrogen escaping,
You see the hydrogen burning as it mixed with the atmosphere in the presence of an ignition source. The airship casing on its own doesn't have enough fuel to burn that energetically.
> The "hydrogen vs helium" issue is overrated in my opinion.
I agree but for totally different reasons that boil down to "people overrate risks they don't understand".
Something had to bring the skin up to ignition point. That may very well have been hydrogen, either above or below explosive mixes.
Static electricity (from a potential difference with the ground, St. Elmo's fire, or other sources) likely also contributed. Forensic analysis strongly supports leaking hydrogen from the aft part of the airship, given the nose-high, tail-low attitude and handling difficulties.
A myth has taken hold that the “paint” on the Hindenburg’s skin — rather than its flammable hydrogen lifting gas — was somehow responsible for the Hindenburg disaster at Lakehurst, and this myth somehow persists even though it has been debunked by photographic evidence, scientific analysis, historical research, and even the TV show MythBusters.
Helium is quite expensive right now. The US has stopped giving away the helium in its strategic reserves, and so the cost is now based in the reality of the cost to produce it.
The cost of helium is the reason you don't see the Goodyear blimps just floating around anymore.
As for the Hindenburg vs. Titanic: The titanic wasn't filmed going down. And the footage of a huge ball of fire with "Oh the humanity!" is a bit more dramatic than even the film representation of the Titanic sinking.
Back when the first ships failed causing the death of all the occupants , human lives were just not worth much , so humans kept building ships.
And also mass media wasn't there yet, so there could be no way to massively distribute content of a ship sinking and all the bodies floating around.
Same thing with planes, had we discovered flight in the Middle Ages we would have loaded 100+ people in wooden planes as fast as humanely possible because of the enthusiasm for the new technology would have vastly surpassed the fear of being harmed by it.
> The cost of helium is the reason you don't see the Goodyear blimps just floating around anymore.
What are you talking about? The Goodyear blimps are still out and about providing video for major live TV broadcasts. It's not like they drain the helium and fill it back up each time it goes out.
For what it's worth, I see six scheduled appearances in two cities, all in January and February of next year. That's not a lot, especially when I used to see them about 3-4 times a year out in Montana (AKA, the boonies).
> It's not like they drain the helium
No, but they naturally lose helium at a fairly regular rate, since there's no blimp envelope systems that can prevent all helium loss. RC blimps, as an example, lose about .5% to 1% of their helium daily. Commercial blimps appear to have a couple of months until they've lost their bouyancy.
EDIT: A single Goodyear blimp requires approximately 300 mcf (1mcf = 1,000 cubic feet) of helium, and helium prices are around $700 per mcf when sold in bulk. That puts a blimp's helium costs alone in the $200,000 range for a blimp that can carry 14 people.
Back in 2000, the price per mcf was in the $40 to $50 range.
They don't keep the schedule up to date on the website. Two of the three Goodyear blimps were up for TV broadcasts this past weekend, and every weekend since at least the beginning of September.
I've for years fantasised about being able to go on an airship cruise in my twilight years. I'm genuinely surprised it's not been seriously mooted by any companies.
The Zeppelins were not squalid or horrible, but they were incredibly spartan and not at all Luxury compared to what a cruise ship can do with a lot of mass. Here's a reproduction Hindenburg passenger cabin[1], compare with a cabin on a luxury cruise ship[2]. They're optimised for low mass more than comfort.
Then a reproduction lounge on the Hindenburg[3], compare with any of these on a cruise ship[4]. Ships are roughly as luxurious as you want to spend money to get, rivalling any hotel. (Water is ~750x denser than air, does that mean it can buoy up 750x more luxury per passenger for the same displacement vessel?)
> Put a few hundred well off people in luxury and slow air ship them to locations hard to reach by ships
The problem is that the infrastructure required for a blimp to land and takeoff might be significantly less expensive than a port but it's still many times larger than what an helicopter would need.
VIP services are banking on the new AW609 Leonardo[0]
Put a flat section on top of the airship, and land helicopters (or tilt-rotors) on it. Take the passengers (and fuel + supplies) to the airship, don't take the airship to the passengers.
Is much known about the safety of this aircraft? As I understand it, V-22 Osprey can neither auto-rotate, nor land in emergency like an airplane (because the rotors would hit the ground). Seems a bit like worst of both worlds.
> As I understand it, V-22 Osprey can neither auto-rotate, nor land in emergency like an airplane (because the rotors would hit the ground). Seems a bit like worst of both worlds.
"The V-22 is a tiltrotor and does not rely on autorotation for a survivable power-out landing. The wide separation of the engines and the ability to drive both rotors with one engine make a power-out landing extremely unlikely. However, if required, the V-22 can glide for a predictable run-on landing in airplane mode, much like a turboprop"
>As I understand it, V-22 Osprey can neither auto-rotate, nor land in emergency like an airplane (because the rotors would hit the ground). Seems a bit like worst of both worlds.
Tradeoffs.
It's worth it to them to plop a bunch of marines down with helicopter speed faster/farther than you normally can with a helicopter.
The military generally doesn't uncritically accept "but muh safety and liability" arguments like private industry does because the cost of doing things less efficiently (trying to refuel helicopters in hostile airspace, airborne operations, etc) comes with a statistical body count as well and they have some degree of sovereign immunity.
In a non-military context the pros and cons would weigh differently.
Yeah, I see that the calculus is very different for the military. I was specifically curious about civilian case. I’m already conscious of how fragile helicopters can be, hence my curiosity re this.
But from other responses it seems that these aircraft can in fact auto rotate and glide in an emergency.
>> when you could promenade the deck while watching the world pass silently from 500 feet or so?
I don't know where this assumption comes from. Airships were not silent, nor would you ever want to promenade the deck. These things moved very quickly. The wind/engine noise was considerable. If you opened a window you would be hit with a 50+mph blast of wind. Only during takeoff (liftoff?) and landing would there be any sense that you were floating as opposed to flying.
>> I think a modern Zeppelin could be built for less than ten million dollars.
No. Just no way. There is no possible scenario whereby one could develop a new over-ocean passenger-carrying aircraft for 10mil. Talk to Boeing/Airbus. You probably need to double that number and add at least one zero.
I recently moved to Bedford in the UK, where the R100 / R101 were built and the hangars are still standing and in use for the Airlander: https://www.hybridairvehicles.com
I can't wait to see this thing in the air, even just the hangars are quite an awe inspiring sight.
Unfortunately the Shortstown sheds are not in use for Airlander. HAV no longer have a presence there. They couldn't afford the rents while they recover from the crash and work towards building their next test vehicle.
Mostly movie studios and similar rent them now. A developer is hoping to build on the airfield which would stop any future airship use if they can't be stopped.
Climate change and the need to end the use of fossil fuels may force the return of the airship. People are working on making electric airplanes feasible, but the weight of batteries makes it a tough problem. Airships are much more doable, although for any kind of frequent route, ground/sea travel is probably better. Heavier than air flight would probably need to use fuels synthesized from waste biomass, and be relegated to high-priority use.
I'd also love to see more long-distance shipping move to advanced clipper ships using modern materials, computer-controlled rigging, highly optimized sail and hull designs, etc.
It seems far more likely that jet flights would migrate to a synthetic fuel, taking yesterday’s CO2, making jet fuel today, and emitting that CO2 back tomorrow.
There exist already very efficient turboprops like ATR, but they don't sell well in the US since fuel is cheap and a faster jet plane can make more trips per week. Even in cargo usage.
Absorbing co2 at ground level and emitting it high in the atmosphere is equivalent to emitting fossil co2 at ground level -- at higher altitudes the green house effect is stronger, see radiative Forcing.
Also, the overall energy efficiency is very poor. A plant creating synthetic cerosene just opened in Germany, and the reporting said the electricity->h2->cerosene->aircraft movement efficiency is 10-15%. Ouch.
Why do that h2->kerosene at all? Why not using the compressed h2 or something like https://en.wikipedia.org/wiki/Slush_hydrogen to drive a fuel cell(or an array of them) or a micro gas turbine, to power hyper efficient electromotors built with something like https://en.wikipedia.org/wiki/Rare-earth_barium_copper_oxide
superconductors in a holistic concept which is using the h2 to cool the superconductors? I think I've read something like that not too long ago, maybe even here on hn.
The idea for synthetic fuels is that they can act as a drop-in replacement for fossil fules, so you don't have to adapt the vehicles. I wouldn´t call using H2 a synthetic fuel, because it would require a different aircraft design (its probably more reasonable appraoch overall, although access to truly carbon free h2 is limited right now).
> at higher altitudes the green house effect is stronger
Good thing the CO2 doesn't stay there forever.
> Also, the overall energy efficiency is very poor.
And energy efficiency is a good proxy for economic viability when you are comparing similar things, but completely useless when you comparing it with something. Why does the 10% efficiency matters?
(By the way, expect that to increase. It always does.)
I double checked. The co2 effect seems to be around 1.3 compared to the effect on the ground, but there are other factors that increase the greenhouse effect beyond that. There seems to be a fair bit of uncertainty on the numbers:
The 10% combined efficiency of the three energy conversions matter because energy itself isn't 100% green. With the current energy mix, there are more emissions from synthetic fuels than fossil ones.
Oh, nobody on that thread is talking about doing it today. No doubt, today it's much better to just use fossil kerosene on our airplanes than synthesize it.
Nicely done. I enjoyed it. One even had the airstrip on top I suggested elsewhere. Hurr!
I also didn't know someone seriously considered giant nuclear airships? Did this come straight out of Hollywood, or was it the other way around?!
But there is something in these concepts I don't get. In the depictions of the 'promenade' there is always solid ground where you stand on, and then have to lean over to look down through angled windows. Why not make at least parts of the promenade fully transparent, like it is on some observation decks in tourist destinations? Also the cabins seem to be a waste of room. I think something between a capsule hotel and https://sleepbox.com/ would suffice. In this mode of transport everything should be about maximizing the special viewing experience. The rest for lounge, bar, restaurant, salon, maybe selfcleaning toilets and washrooms. If tired? Sleep. Why would I need so much room for sleep? Given a travel time of some days to maybe two weeks? Just watch, watch, watch and relax :-)
Well, remember, the limitation is weight not space. You could give each person a very large bedroom upstairs, with a view out the side. However, windows would still be heavy!
But a glass bottomed ballroom would be a nice touch, if you ask me.
That's awesome. I mentioned Bucky's "Cloud Nine" on a comment of yours ten days ago, it seems you're all over it, eh? Have you seen Alexander G. Bell's cellular geodesic kites? I feel like a cellular system makes sense because it would be easier to manufacture and assemble large systems out of collections of smaller systems.
Yes! The cellular approach, with a combination of kite power and hydrogen… seems like a lot of force.
I’ve wondered about a sea anchor turbine, where the lifting power changes from day to night would spin the turbine, and provide enough power to keep the airship or platform in place (eg, to do cloud seeding duties)
Despite having worked on aircraft software for most of my career, my knowledge of aeronautics is weak.
I have often wondered why no one has tried to design and build an airship with an envelope in the shape of a lifting body. The structure might have additional weight to hold the desired shape, and it would have to take off like an aircraft, but wouldn't the added lift provide significant advantages? I know I must be missing something fundamental.
Can someone more knowledgeable tell me what it is?
Airships would have greatest utility on long trans-oceanic travel. Virtually all continental travel would be far better suited to rail. But could trains tackle the oceans? Maybe. I'm increasingly thinking that an intercontinental rail network would be more viable than trying to resurrect airships.
It's possible to build a continuous rail link from the south of Africa to the British Isles, Siberia, and Malaysia.
Tunelling across the Bering Strait would be within reason for an Asian-American link.
Crossing the Atlantic is appealing as population centres are closer to both coast, though sea distances are greater. One possible answer might be a "floating tunnel", of the type envisioned for use in crossing Norway's fjords. Suspended from buouys and anchored to the seafloor, at a depth of about 30m, muliple bores could carry passenger and freight rail traffic. One possible route might extend from Scotland via Iceland and Greenland to the Labrador coastline.
Transit times might range from 15 hours (at about 240 kph / 150 mph) to as little as 2.5 hours in a hyperloop-like evacuated tube at 1600 kph / 1,000 mph. The former is about a quarter the speed of present-day jet airliners, making short day excursions between continents infeasible but allowing for an overnight "hotel train" or working daytime trips. At higher speeds, service is comparable to present aircraft, and at the (admittedly unlikely) extremes, several times faster.
Similar crossings could be reasonably be made to Indonesia and on to Australia, crossing from Singapore, then to West Java and Timor Leste, and across the Timor sea to Darwin. A southern Atlantic crossing between Recife and Monrovia might also be possible.
There are of course formidible costs and risks. But the technology and routes are at least within the realm of possibility.
A north-Atlantic rail crossing was amongst the concepts mooted in a BBC piece some years back:
I like your thinking. Let me explain mine. From a purely logical point of view, maybe something like playing Sim City, Civilization, or other infratructure building Sims this would make sense. In peace time, and if all players were like Spock, or of the same hive mind. Because like the BBC and Popular Science articles you linked this could be much more by co-bundling pipelines of all sorts (DATA!) with it, maybe even part of a global HVDC smart grid. The costs shouldn't really matter, compared to the money the military (No matter which) burns. It could also be the enabler of (environmentally responsible?) aquafarming, seasteading, nodes of wave- and offshore wind energy farming which would branch off from it. You'd need many platforms for security, emergency and maintenance reasons along the way anyways.
But it would be very vulnerable and probably protested for all sorts of business and political reasons. Just look at what happens with proposed pipelines, high-speed rails, the bitching about where to put stations, the NIMBYism about where not, and so on.
In this case there could be less NIMBYism, because open-seas, but think of the ship builders, and the giant complex of companies operating the built ships. Wouldn't you think they object to that? Just look at what ferry operators did when some tunnel or bridge opened, making them obsolete.
So we have them, and their interests, against a potential network of submerged floating tunnels enabling all sorts of nice things, making them almost obsolete, too. Similar for Aerospace. 500kph seems doable without vacuum. Half the speed of air-traffic. 350 to 400 kph even more so, and already IS in operation at 350. Now imagine freight trains running at 250 to 300kph on separate tracks. Which you would want to have anyways, if only as reserve/backup for maintenance reasons. And now imagine a grid of these. Criss-crossing the seven seas, and having transport-hubs/nodes, switching yards, resort cities, free towns, permanent in-situ sensors, whatever, out there.
Can't have pirates though, or war.
What do you think about that?
edit: I'd opt for smelting all the container giants, bulk carriers, and similarly obsolete stuff to build this. With nuclear power, if need be. I don't care. The same for most airplanes, because less noise.
I am absolutely fascinated with airships. Im imagining a future where most building construction is moved into large factories (preferably near harbors) and lifted on site in house size chunks by a fleet of airships. Imagine the environmental and cost gains.
I'm guessing the author and most of HN missed the memo that Zeppelin is back and producing a modern semi-rigid design called the Zeppelin NT, which has been in use notably for the newest Goodyear fleet starting in 2014: https://en.wikipedia.org/wiki/Zeppelin_NT
The author definitely missed the Zeppelin NT. One flew over Silicon Valley for several years, from 2008 to 2012. They had the misfortune of launching a luxury experience during a recession. The ship worked great.
It had three steerable propellors, two steerable. This made it far more manuverable than classic airships. No more needing an army on the ground to tie the thing down.
DARPA and Lockheed's Skunk Works built a airship in 2017 or so with even more steerable fans. That thing could fly itself out of a hanger, take off, return to base, land on a short runway, and taxi to the hangar.
High winds on the ground remain a problem. Just too much sail area.
The Zeppelin NT is great. I got to ride on one of their last California flights. One of the best things was being right there with the pilots. They showed us how the controls work and were happy to take little detours if we wanted to see something.
Here's a comment from a couple of years ago with links to some Zeppelin information and my photos from the flight:
> It is unfortunate that in the public mind, hydrogen as a lifting gas is associated with the Hindenburg disaster. Actually, hydrogen filled airships were extremely difficult to set alight. Just ask the Brits in WWI.
> The RAF could easily hit the German airships with gun fire, but couldn’t get them to ignite until they developed special phosphorus filled ammunition. They used sustained machine gun fire to rip a section of the gas bags to get the hydrogen to mix with air at their surfaces. Then, the small number of phosphorus burning bullets could ignite this hydrogen air mix. Even then, the RAF brought down very few of them.
> Because of this knowledge of how difficult it is to get a hydrogen filled airship to burn, there has been much speculation that the Hindenburg was sabotaged, set to burn deliberately, in a very public act of terrorism / economic / public relations warfare against the NAZI regime (and who could blame them?).
I had no idea that there were controversies regarding the cause of the disaster, nor that hydrogen was (arguably, at least) dangerous more in the public eye than in reality. I'd be interested to hear other modern engineering perspectives on the hydrogen issue...