The Second Age of Airships 363
The Telegraph has a story about a new generation of airships. It says "It's a new vehicle. It's a hybrid because we're combining helium lift, aerodynamic lift, a hovercraft landing system, and vectored thrust... If you can get beyond the word airship — because that has a lot of history — people think about them differently."
Re:Great, instead of peak oil ... (Score:4, Interesting)
Re:Helium (Score:3, Interesting)
Re:Forever. (Score:5, Interesting)
Vaccuum ships? (Score:3, Interesting)
If Helium rises because it is less dense, would it be possible to force a balloon open, using some sort of supports, and end up with essentially a balloon filled with nothing, and thus able to rise? Or is this beyond current material science?
Re:Use hydrogen. (Score:3, Interesting)
Parent is right - little research is being done on hydrogen as a fuel for cars because it's infeasible. GP's opinion reflects the general association people have with hydrogen - "Isn't that explosive?" - but few actually oppose hydrogen for that reason. It's all about cost effectiveness (or lack thereof).
Re:Vaccuum ships? (Score:3, Interesting)
If Helium rises because it is less dense, would it be possible to force a balloon open, using some sort of supports, and end up with essentially a balloon filled with nothing, and thus able to rise? Or is this beyond current material science?
I tried to calculate this a couple years ago, and using metal with an excellent strength/weight ratio -- Aermet 310 -- and a spherical model with stiffening ribs, I couldn't find any viable solution: no matter how large the diameter of the sphere, the weight of the metal required to contain the vacuum against the external air pressure was greater than the vessel buoyancy, and I went up into kilometer-radius ranges.
I didn't try it with composites because that's a lot harder to make valid design assumptions, and frankly my mathematics skills are rubbish, but I'd be interested in hearing anyone else's data on this.
Secondary facts re: seagoing vessles et al. (Score:4, Interesting)
The parent of my parent post brings up putting rocks in sailing vessels as argumentative support, he is wrong for at least two reasons.
(1) Many modern non-sailing vessels still use ballast. The problem isn't old-timey nor is it "solved", nor is it _really_ the same issue as buoyancy with respect to airships. In a seagoing vessel the problem is that a non-trivial amount of the vessel must remain "above" the water over which the vessel must remain buoyant. As such, to remain upright, as cargo is loaded above the waterline, one must add weight below the water line to keep the ship upright. In an airship the entire ship is "submerged" in the air, so the issues are much simpler. That is, an airship and a submarine are in the same domain, but an airship and a sailing ship are not.
[ASIDE: One of the things the boat commander of a submarine must watch for is rolling over during initial dive. In surface operation, the sub is a surface ship, and its center of gravity is below its center of buoyancy just like any other ship. In underwater operation the center of gravity must be above the center of buoyancy or it won't sink below the surface. That moment when the two must cross is tricky, as they must "cross", not "pass each other". That is, if say the port side takes on ballast faster, the center of gravity would pass to the port of the center of buoyancy and the ship would roll. The normal way to make this happen most safely is to be under-way at the time of submersion or surfacing so that the wing-like bow planes and rudder etc. can be used to counter any small tendency to roll. The single most dangerous submarine maneuver is the static (non-moving) submerge. It is virtually never done as messing it up is expensive in both lives and equipment. Surfacing is safer than submerging as "blowing" the ballast tanks can right the ship very quickly if it starts to roll, and can be done before reaching the surface. That leads to that really dramatic "breaching" thing where a significant fraction of the sub leaves the water entirely before crashing back to the surface. Dramatic, "safe", but again, hard on the men and gear. (I hear it's fun though... 8-)]
(2) Ballast was much more spoken of, and "tricker" in the age of sail as the power source (the wind) wanted to push the ship over anyway. Additionally, _letting_ or even encouraging the wind to push the ship over a little (e.g. heeling) could lead to increased speeds and efficiencies.
(3) Ballast in seagoing vessels is more important and variable because you want enough to stay upright, but each little bit more than that sinks the ship a little more, causing more of it to interface with the viscous watter instead of the less-viscous air.
(4) Water can not be meaningfully compressed. Things "denser than" water also cannot be meaningfully compressed. (e.g. compressed enough to substantially effect displacement.) Air and lifting gas is eminently compressible. Consequently airships, in issues of both displacement and buoyancy, are completely dissimilar to anything seagoing (except a scuba diver in a wetsuit 8-) so none of the natures and limits you (grandparent poster) mention really apply as such.
Re:helium shortage (Score:3, Interesting)
If there is a shortage why are we wasting it in party balloons?
Re:Vaccuum ships? (Score:3, Interesting)
A vacuum balloon is going to be very difficult if not impossible.
A vacuum aerogel, however, might be in the realm of possibility. Aerogels have been made with evacuated bubbles inside, making the whole lighter than air. [youtube.com] The record so far is apparently 1 mg/cm^3 [wikipedia.org], which is just lighter than air at 1.2 mg/cm^3. That's not great, but it's a young technology that will get better.
Alas, a vacuum aerogel airship would need to be very large -- too large to make on Earth. We would need orbital manufacturing facilities to make this concept work. But theoretically it is possible.