Adding another article to the pile; this one about a research team examining the role that the fish’s body plays in interacting with and generating vortices that increase propulsion efficiency. In the particular velocity regime they were interested in, they found that fins were more efficient that propellers:
I suspect the answer to “which is more efficient” is going to depend a whole lot on how you set up the problem. Anyway, there’s a few cites within the article for further reading.
I vaguely remember in the past, that Discover had an article talking about fins vs propellers and legs vs wheels. I can’t seem to google it up, but IIRC, they mentioned the fins trumping propellers but that wheels were much more efficient than legs.
There was a news story just yesterday about a submarine propulsion system being developed inspired by the jellyfish. But that’s all they would say. No details at all.
H. G. Wells predicted the atomic bomb in his 1914 essay, The World Set Free.
He even coined the term ‘atomic bomb’. This isn’t the guy you were referencing in your post, but I thought it was interesting enough to extend the minor hijack.
According to this article, Deadline was written by Cleve Cartmill in 1944. It shows up in the March 1944 issue of Astounding Stories.
And yes, apparently “[f]earing a security breach, the FBI began an investigation into Cartmill, Campbell and some of their acquaintances (including Isaac Asimov and Robert A. Heinlein)”.
The source of the gas bubble doesn’t seem to matter.
"…supercavitating vehicles can achieve high velocities by virtue of reduced drag via a cavitation bubble generated at the nose of the vehicle such that the skin fraction drag is drastically reduced. Depending on the type and shape of the supercavitating vehicle under consideration, the overall drag coefficient can be reduced by an order of magnitude compared to a fully-wetted vehicle. " - http://www.aem.umn.edu/research/supercavitation/documents/thesis_eric.pdf
The supercavitating article was very interesting and led to an article about supercavitating propellors which was also interesting because it referenced partially submerged propellors which are more efficient than submerged propellors. But is there actually a way to use the supercavitating torpedo design in a partially submerged craft like a boat? Could their be a gas ‘bubble’ that completely seperates a boat hull from the water? Sort of a running indentation in the water surface maybe.
Looks like air cavity systemsare close. I was wondering about something that produced the cavity through cavitation caused by the specially shaped nose.
Would a paddlewheel be considered an analogue to a fish fluke?
In March of 1845, the Royal Navy conducted some tests, with the screw Frigate HMS Rattler competing against a paddlesteamer HMS Alecto. Rattler won, but I don’t know how accurate of a test that was, as the Rattler may have had bigger (more horsepower) engines.
Paddlewheels are cylinders, and while a single paddle may spent more than half of it’s time out of the water (and not producing thrust), there is always one or more paddles on that cylinder in the water at any one time…
I know that propellers are very efficient, but what about the big rear paddle wheels?
These were used up to the present day-Mississippi steamers using paddle wheels were made up to the 1930’s.
Of course, a river steamship has different requirements from an ocean going ship…and a paddle wheel may be less prone to damage in shallow water.
IIRC, the basic principle is that moving a small amount of air (or water, I presume) quickly is less efficient but produces higher thrust; while moving a large mass of air slowly is most efficient. Therefore jets are less energy efficient that props, while in turn props are less efficient than the wings of the plane.
I don’t believe they are that efficient. I did a senior project to construct a underwater vehicle and did some research on props. Typically they are about 50% (about 50% of the engine hp is transferred to the water, the other 50% never is produced by the engine). Also the most efficient prop configuration would be a single blade, though for balance a dual blade is the most efficient practical set up. The more blades the less efficiency though the more power you can transmit so more thrust. The reason for the loss of efficiency for more blades is that the blades are passing through the propwash of the others.
Props can be made more efficient but they are a compromise to operate over a speed range and load range. A variable pitch prop could compensate and deliver higher efficiencies.
With the above posting that a dolphin efficiency at .81 I’d say that nature has a efficiency advantage which may be quite significant. My money is still on the penguin however.
