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Hydrogen-Powered Aircraft == Anti-Terrorist Device?
maladroit asks: "Today on NPR's Talk of the Nation/Science Friday , Harry Braun of the Phoenix Project said that a hydrogen-powered airplane would not have produced the fire and intense heat that brought down the World Trade Center towers. Is this true ? What are the other advantages and disadvantages of hydrogen fuel ? Details on the Phoenix Project's website are a bit sketchy, but I'm sure the Slashdot crowd has some answers (and Richard Dean Anderson jokes)." Sounds like a good theory, it doesn't account for the hostage aspect, but it would prevent the use of aircraft as cheap bombs. Would there be any drawbacks? How much would such a refit cost for your average commercial aircraft?
The Hindenburg's problem wasn't that it was full of hydrogen; it's the fabric the outer covering was made of that did it in.
Please read up on these things before spouting retardedness.
- A.P.
"Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"
Well at the very least, hydrogen is a renewable intermediate energy source, unlike the oil used to formulate AvGas these days. And presumably it would be less polluting as well. Both excellent reasons for gradually making the switch, but I don't really see how it would make a plane less of a bomb. The synopsis claims it's safer in an auto crash (presumably because it disperses rapidly), but would that necessarily apply to an airplane? Sure, it wouldn't have burned in the WTC as long, and possibly not as hot, but H2 being a gas wouldn't it have been more explosive?
---If you can't trust a nerd, who can you trust?
Whoa, someone's trying to crash a blimp into the Sears tower!
... Sheesh. This is getting boring.
*BOOOOIIIINNNGGGGGG*
Well, there he goes again...
*BBBBOOOOIIIINNGGGG*
And again
Change the channel.
; -- the corruption of government starts with its secrets. a truly free people keep no secrets. --
It's the same reason why automotive engineers are having such a big problem getting hydrogen-powered cars economically feasible (apart from the storage problem). Compared to gasoline, hydrogen has an abominally low energy density. What does that mean? To get the same amount of energy on-board, you'd need to carry many times the amount of gas in hydrogen. That means either HUGE fuel tanks, or severely curtailed range. Not being an aerospatial engineer, I can't comment about the former, but the latter just won't fly (pardon the pun) with commercial carriers. "Yes, we can get you from New York to Los Angeles. You have seven brief layovers for refuelling..."
Interesting idea, but not practical. If you're still worried about planes flying into buildings (it's been used once, if they're smart they'll now switch tactics) maybe installing fire-suppressing foam (like the systems they have in McDonalds' in the kitchen) on tall buildings to smother any high-temperature fires that break out.
A simpler method may be simply to install nose radar in *all* sizable airplanes, and automatically engage the autopilot when flying within 1000m of an object (building, mountain, etc.) to avoid it. We have the technology, folks.
Mr. Ska
Hydrogen burns very hot but (1) it requires mixing with considerable air to produce an explosion and (2) being very light it tends
to burn "up", i.e. to rise. The plane would be
fueled with liquid hydrogen at 20 degrees K
(only Helium liquifies at a lower temperature) and would evaporate quickly into a gas. Unlike the current JPx fuels, the hydrogen disipates rapidly and would stick to stuff and burn. The hydrogen would burn and disipate rapidly and
leave behind only those pre-existing materials which have been ignited.
One problem is that even liquid hydrogen is very light (very low density) and so requires very large tankage. The Shuttle's external fuel tank is mostly a hydrogen tank (something like 80% of the volume?) with a surprisingly small liquid
oxygen tank at the top. I have seen a liquid hydrogen bubble chamber being filled and marveled at the droplets of liquid hydrogen entering the chamber and just floating down (drifting really, not falling like water droplets do).
Dr. Frank J. Nagy Fermilab Computing Division Authentication and Directory Services Group
Point one: don't bring up the Hindenburg unless you know what you're talking about. The Hindenburg disaster was NOT initiated by a hydrogen explosion, it was improper maintenance and a highly flammable skin. In reality hydrogen *is* safer than liquid fuels. Think about it, if you were trapped in a wrecked car, would you rather have hydrogen leaking 10 feet from your head, or gasoline? Keep in mind that pure hydrogen in a tank can not explode, there's no oxygen. I'll take hydrogen any day.
Point two: Hydrogen is NOWHERE NEAR dense enough to use as an airliner fuel. You'd need all the room in the entire ship including the cabin taken up with hydrogen tanks, and then some, in order to fly cross country.
This might prevent some of what happened on the 11th, but you still have the kinetic energy of a 200-ton plane with 60,000 lbs of thrust hitting the target at 500 mph.
It wasn't the jet fuel that rammed the plane all the way THROUGH tower two on live TV. It might not have burned hot enough to cause the tower collapses, but having hydrogen fuel wouldn't have made the planes bounce off the towers, either...
Recursive: Adj. See Recursive.
I wrote about this the day after the attack:
Something I just thought of a little while ago, to help me gain some perspective on what happened:
A Boeing 767-400ER [boeing.com] has a maximum takeoff mass of a shade more than 200,000 kg. It has a typical cruise speed of 840 km/h.
Using our favorite formula for kinetic energy, that comes to about 5.6 billion Joules, or between one and two tons of TNT.
Or, in other words, just the force of that much mass at that speed is about the same as a WWII blockbuster bomb. Add in some twenty thousand gallons of jet fuel...and I still can't wrap my mind around that much destructive force.
And I thought cars on the freeway were deadly!
May such magnificient machines never again be used for such awful, awful purpose.
b&
All but God can prove this sentence true.
A hydrogen powered plane's fuel tanks would have blown up all at once. The reason the WTC attacked worked is that airplane fuel is sticky and burns slowly when there are massive amounts of it, so it got all over the inside of the building and generated insane amounts of heat over time, starting other fires, etc. Hydrogen would have just blown up, with a small explosion and a lot of fire at impact, but little other damage.
Hydrogen is unlikely to be seen as a viable fuel, however, because for so many years it was believed that the Hindenburg was destroyed because of the hydrogen that held it aloft. Even now that the truth is known (The Hidenburg went down because the skin was painted with powdered aluminum, AKA rocket fuel, and when the mooring line grounded arcing electricity caught the aluminum on fire.), it is rarely spoken of because so many sources still quote hydrogen as the source of the explosion.
The space shuttle Challenger had a fair bit of hydrogen. It blew up just fine.
Now, as to continued flame, that's a different matter. It is unlikely that the hydrogen would act as an effective fuel to continue the fire for much after the initial impact.
The fundamental energetics of hydrogen combustion suck compared to fossil fuel combustion.
Hydrogen comes into its own more in the context of things like fuel cells. I don't think that the high demands of take-off powering would be well met by fuel cells. Cars can take longer to accelerate on a highway for instance with less loss of functionality. Either the airplane gets off the ground by the end of the runway, or it doesn't. The ability to abort a landing and lift off again is an important safety consideration.
The reason the site is short on details is that anyone who can make hydrogen work better than fossil fuels will make billions in the first year. It's a fantasy for anything but fringe applications. (Compare the Motorola fuel cell story today. Even that is methane-based, not hydrogen.)
Looks like our journalist at NPR had to fill a slot by deadline and went with what he could get to fill it.
I've read a few things here which only help to spread the myths about hydrogen. Here are some of the common misconceptions and why they are untrue.
1. Hydrogen is extremely explosive - Hydrogen is not *extremely* explosive. It can be explosive, but it needs a certain amount of oxygen in order to explode.
2. The Hindenburg explosion was caused by the hydrogen. - It is widely believe that the explosion was caused by the flammable fabric covering of the ill-fated airship.
3. Myth#1 is why we don't have Hydrogen-powered cars - Actually, the biggest problem is that hydrogen is, for lack of a better term, sparse. (Opposite of dense). It's difficult to package a sufficient amount of it in a reasonable volume. There is ongoing work to change this by combining it / embedding it in other materials or packages, i.e. Carbon nanotubes.
4. Hydrogen is hazardous flammable substance - Because of its being the lightest (least dense) gas, a hydrogen fire will bascially burn in an upward direction. In addition, the gas will dissipate quite rapidly - imagine what would happen if you 'spilled' some Helium - it would just float straight up, even if it was on fire. Hydrogen does the same.
5. The fire was not a significant part of the tower collapse - While the kinetic energy of a fully loaded 757 / 767 cannot be ignored, if that was *all* there was, the towers would be standing today, and probably repairable as well. The collapse was caused by the extremely hot (1500+ degree) fires burning long enough to weaken the steel structure. The beams were rated for 1 hour of fire resistance. They held for at least that long, and then gave way, causing the 6 million lb. floor to fall and begin the domino effect.
Hindenburg exploded because its envelope was coated in the same chemicals that Morton-Thiakol uses in the Space Shuttle's solid rocket boosters.
It doesn't matter if I've eaten Taco bell or not, wearing boxers soaked in rocket fuel is a bad idea.
Asbestos has no chance against the heat generated by a fuel fire. Asbestos is good for things like paper fires which burn at 400-500 degrees. At the temprature the main fire was buring at asbestos, steel, and concret melts and vaporize. Asbestos coating would of just put another thing in the air.
Besides asbestos is not an environmentilst issue, its a heath issue. For what asbestos did there are better ways of doing it. If you'd like me to cover your house in asbestos than feel free. But don't come complaining when you get cancer from it, or other lung problems.
H2 falls slower that H20. H20 is heaver, so it must fall faster! Or at least Aristole said so and he's never, ever wrong. Just ask the church and Gaileo on this one.
Unfortunately, I think people forget that hydrogen-fuelled jet airliners would likely use liquid hydrogen as its fuel.
Unlike hydrogen gas (which burns relatively safely), liquid hydrogen when it ignites will do it with a force that makes a dynamite explosion seem like a minor event. If the planes that crashed into the World Trade Center were fuelled by liquid hydrogen, the initial fuel explosion would have so much kinetic force that the building would have collapsed right there and then.
If I remember from the Challenger explosion, when the solid rocket booster leak ignited the fuel in the external fuel tank the force of the explosion was equivalent to a 1 kT tactical nuclear warhead. That's why liquid hydrogen must be handled with extreme care.
> Hydrogen as safe alternative fuel... Um... Hindenburg, anyone?
Two points: the Hindenburg burned because of the envelope, not the hydrogen (see the many posts explaining this), and the Hindenburg used diesel fuel for power, and hydrogen for lift.
> No, it wouldn't burn for a sustained time, like jet fuel did,
> but it would burn even more violently, hence causing more initial
> injuries. In fact, a more violent explosion mith have collapsed
> the towers right away, and those 10,000 or so folk wouldn't have
> had the chance to escape like they did.
Not likely a problem. Most of the experts consulted believe that the sustained fire is what caused the collapse of the buildings. As the videos show, the force of the initial explosions was mostly external anyway (remember that huge fireball?) so even if the force of the hydrogen was significantly more powerful (which it wouldn't have been, for reasons below), the extra force would simply have thrown debris farther, not done much more damage. It's very likely that if the planes used to hit the WTC towers had been hydrogen powered, they'd still be standing. In addition to not having burning jet fuel all over the building (which actually trapped people in the floors directly below the impact, by running down the stairwells), the force of the explosion would tend directly out along the impact vector, then upward. The rapid expansion of the hydrogen as it escapes the tanks tends to inhibit explosive force (increase in volume means decrease in temperature and pressure), so the extra force gained by the fact that hydrogen burns very efficiently is offset.
> Then there's the issue of storage... wouldn't high-pressure
> crtyogenic fuel tanks be prohibitively heavy for an aircraft?
Yes, they are, and that's why hydrogen fuel cells aren't more popular. Once that problem can be solved (materials scientists have been working on this for a long time, mostly for space vessels) hydrogen has a chance against fossil fuels, but not until then.
Virg