[mikeash]

Dirigibles require huge volumes, because the lifting power of gas is small. Those huge volumes make for a relatively weak, slow, and difficult-to-maneuver craft. A big reason why airships disappeared in favor of airplanes was that airships had a really tough time handling or avoiding bad weather because of these limitations.

[jp555]

I have a blurry recollection of seeing an aircraft design that was a combination of an airplane and a dirigible. It looked like a poofy manta ray, an inflated rigid lifting body or flying wing. It wasn't quite VTOL & needed a very short runway, but it also gained more maneuverability in flight. Maybe it was too much of a compromise though.

[astebbin]

Could it be this one [0], or its predecessor [1]?

[0] http://www.latimes.com/business/la-fi-lockheed-martin-aircra... [1] https://en.wikipedia.org/wiki/Lockheed_Martin_P-791

[theophrastus]

Perhaps you're thinking of the infamous 'Deltoid Pumpkinseed'[1][2] ?

[1] https://en.wikipedia.org/wiki/AEREON_26

[2] https://www.amazon.com/Deltoid-Pumpkin-Seed-John-McPhee/dp/0...

[cr0sh]

You mean this one?

http://mashable.com/2017/05/24/airlander-butt-plane-successf...

There's actually been more than one of these types of aircraft (known as Lighter Than Air - or LTA Aircraft), either as an idea or prototype throughout history.

[sk8ingdom]

That type of vehicle is called a hybrid airship!

[1] https://en.wikipedia.org/wiki/Hybrid_airship

[DrScump]

The lifting power of helium is small, as opposed to hydrogen. Also, helium has supply problems.

Is it not possible to have a modern airship with hydrogen as its primary lifting agent?

[mikeash]

Hydrogen doesn't buy you that much additional lifting power.

Air is about 1.2kg/m^3 at STP, so that's the theoretical maximum you can lift with a cubic meter of gas bag. (And you can only get that value if you could somehow hold a vacuum, of course.)

Hydrogen is about 0.09kg/m^3 at STP, so you can lift about 1.1kg/m^3. Helium is about 0.18kg/m^3, so you can lift about 1kg/m^3. Helium is twice as dense, but that only costs you about 10% of your lifting power since both are so light compared to air.

I see no reason you couldn't use hydrogen, but I don't know if anyone would want to take the risk. (Specific flaws of the Hindenburg aside, hydrogen is explosive across a distressingly wide range of mixture ratios with air.) If you did use hydrogen, I think the main motivation would be avoiding the use of scarce helium, not the minor increase in lift capacity.

[ForHackernews]

If it's an unmanned drone-blimp, the safety issue because somewhat less critical.

[gozur88]

But still critical enough to make it impractical. How would you do maintenance on a hydrogen airship without risking the people doing the maintenance? And you'd never be able to fly over populated areas.

[petre]

It is possible but we all know what happened to the Hindenburg. Using hydrogen is asking for a fire to happen.

https://en.m.wikipedia.org/wiki/Hindenburg_disaster

[lostlogin]

Keep in mind that the Hindenburg was supposed to be helium filled, but due to import restrictions they couldn't get enough.

[DrScump]

Far more helium airships have wrecked than hydrogen airships, even counting only before the Hindenburg.

[petre]

Wrecked, yes, but they probably didn't burn like a torch with people jumping out of them to avoid burning alive.

[Nomentatus]

What you saw was the engine-fuel burning on the ground; the hydrogen went straight up in flames and burnt no-one.

[honestoHeminway]

Vacuum still has the best lifting power of them all..

[guelo]

We just need a material as light as a balloon but rigid enough to hold its shape and maintain a huge vacuum at 1 atmosphere outside pressure.

[scarmig]

Perhaps graphene aerogel, with a nonpermeable graphene casing?

I'm not sure of what its behavior would be with all its air sucked out, though.

[honestoHeminway]

like a hair full of nothing..

[acchow]

I assume huge volumes are also easily detectible?

[mikeash]

Seems reasonable. All else being equal, your radar cross section is proportional to your actual cross section. Plus it's probably easy to spot a blimp with your eyes.