Swimming Blimps

Have I mentioned I'm a sucker for airship stories?

A group of Swiss researchers want to buld a swimming blimp -- an airship which would move through the air by undulating its body.  It isn't as loopy as it sounds -- air and water are both fluids, after all, and the same rules for moving through a fluid apply to both.

Certainly a swimming blimp would have some advantages:  it would be quiet -- much quieter than modern airships with twin aircraft engines roaring away in outboard pods.  An absence of metal engines and spinning propellors would also make them very hard to spot using radar.  And finally, a swimming blimp would just look awesome.

The big issue would appear to be weight.  Fish swim in water and stay neutrally buoyant because muscle isn't all that much more dense than seawater -- especially with fat deposits and air chambers to make up the difference.  So fish can be almost entirely muscle.

Air is a lot less dense than water, so blimps and other airships have to include large volumes of lifting gas to float.  Large large volumes:  about 14 cubic feet per pound of weight.  That means a balloon capable of carrying a single person must be a good 20 feet in diameter.

Trouble is, that doesn't leave much room for muscles (or a mechanical analogue) to make the things swim.  The electroactive polymers referenced in the New Scientist article sound promising, but it's noteworthy that so far all they've been used for in the test model is steering -- controlling the little fins at the back, not thrashing the whole body from side to side.  Even the article notes that electroactive polymer muscles failed to defeat a high-school girl at arm-wrestling in 2005.  It's likely to be some time before a swimming blimp is possible at all, and a very long time before the efficiency of aerial swimming can rival the time-tested rotary propellor.  If ever.

So if you look up in the next few months and see something swimming by, you're probably hallucinating.