See http://www.popularmechanics.com/science/air_space/4242974.html

Okay for surveillance and lifting things, but not for fast transport.

All air vehicles are designed with aerodynamics in mind. In the case of airships, designers have to account for the volume of low-density gas used to carry the ship. Craft of such necessarily large sizes have low maximum speeds (due to wind resistance) compared to wing-borne vehicles (that depend on speed to stay aloft).

I believe there are equations that can determine the best diameter to length ratio based on the predicted required speed vs. the weight penalty. Obviously, a longer blip needs more structure than a spherical one.

Another interesting question is whether there is a use for lighter-than-air gases in regular aircraft. I understand that fully pressurized, a 747 weighs about 2200 lbs more than an unpressurized one at altitude.

Also, most airplanes have a large empty area in the tail necessitated by the cg-position for balance. If you could fill it with a helium bladder would it help or just be a risk?

The fastest airship travells at about 95 mph. A airship which travells atabout 200mph will find a lot of takers. Most of the aerodynamic designshinge around the traditional shape. If someone could revolutionize thedesign which take into the speed aspect into account, airships could become quite popular. If these could land and take off from existing airports it would further enhance their popularity.

I disagree that airships could ever be popular. They're impossible to handle in the air and to park and protect, requiring dozens or hundreds of people to pull one in and massive hangers to protect them from the weather.

The US helium reserve has also made the news recently in that it is depleteing.

I don't know about the world helium supply, but I'd hate to make a product that relied on a known-depleting supply of anything.

And like you said, 95mph. 200 would be a doubling of it. I never thought they could go nearly that fast, but planning to just double it is unlikely.

Finally, the size of airship vs. the number of people they carry is the final nail in the coffin of airships.