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Originally Posted by trux
Interesting, I'll need to add all these photos to the weird collection too  |
Hey, Trux... talk to me before you add this photo to your collection; I'd like to be able to give you the correct information. Thanks.
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I am afraid though that this last design cannot be really efficient, because you can't really get the blade into the right angle of attack in the upward and downward kick. The angle seem to be pretty constant and the blade seems to bend only from the foot-pocket to the extremity, hence in practically 90 degrees to the swimming direction (well, it is little bit less due to the angle of the demi-lune - around 60 degrees at the extremity). On my mind, it does not really help with the propulsion a lot.
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Regarding angle of attack, I don't see the problem. The whole blade changes angle as the body undulates. The blade is pretty stiff so there's not much (although some) bending or "folding."
I guess it depends on the purpose of the monofin. If we're adding a tail to the human body, and if the purpose is endurance speed, then why not copy the champions in the natural world: blue fin tuna and swordfish? Take a look at their tail fins:
http://indian-river.fl.us/fishing/fish/sword.html
http://en.wikipedia.org/wiki/Northern_bluefin_tuna
They have a classic high-aspect ratio (span to length). As Ted C. says about his Lunocet's: "- high aspect ratio... the higher the ratio of span to chord length (chord length is the distance from the leading edge to the trailing edge), the greater the efficiency. Classic monofin designs have poor aspect ratio." I agree and my prototype reflects this. Compare my experimental fin to the drawings of the tuna and swordfish.
Now, if the purpose is slower movement and conservation of energy, maybe a lower-aspect ratio is in order. More like a whale or dolphin. Google "dolphin tail" and see top, left photo. Much lower aspect ratio. Or how about slower and lower yet: like a Grouper, see:
http://en.wikipedia.org/wiki/Goliath_grouper
The tail on this guy actually looks most like a traditional monofin.
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In our club, we have an university professor working in department of physics of fluids. We already spoke that he could let his students research some freediving fins related topics, we just did not get yet to define the jobs. Modeling and comparing different shapes of fins like these ones may be one possibility.
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Cool. What club is this? And what university? Where?
HJ
(who is not an engineer nor a physicist but just likes to think about this stuff)
