Subject: RE: baidarka high aspect ratio paddle blades; lanceolate shapes; drag, inerti...
From: Peter A. Chopelas (pac@premier1.net)
Date: Tue Mar 14 2000 - 22:47:17 EST
Ralph,
The idea of cataloging how everyone likes to push a paddle is interesting,
though I do know if we will learn anything instructive about it to design
paddles. Many people may changes their style depending on their age,
condition, equipment, etc over time and a random collections of styles I'm
not sure would tell us anything.
My wife for example learned to ski on some real junk skis when she was
young and developed some real bad habits. It took a lot of retaining
before she got in the automatic habit of using better, more controllable
technique with better skis. Now she is an excellent skier and can enjoy
some real challenging runs which she could never do using her old style,
even with better skis.
Though lumping paddling styles into beginner, intermediate, and expert
categories would be very interesting. There might be something important
to teach beginners if there are noticeably different styles used. The type
of paddles used may also affect this.
I do not really consider myself an experienced kayaker and I would like to
see if there is a noticeable difference from what I'm doing and others.
About using nature to design machines, fins, paddles, etc. One should
always be careful when comparing what fish, birds, whales insects, etc. do,
though it may be interesting. Animals have other very serious
environmental and biological constraints that machines do not. For example
I do not know or ever heard of a single example of a rotating part (like a
wheel, gear or rotating shaft) on a living organism, it just does not occur
in nature. Yet most mechanical devices could not be built without them.
Also, you could not build an airplane that looks exactly like a bird and
expect it to fly. If you take a stuffed bird and throw it like a glider it
will crash, the on-board stability and control flight computer (the bird
brain) is missing. Fish have to hide from predators, hawks and eagle have
to be able to attack and carry heavy prey, etc. etc. Though I have not
studied it, I would think that a good propeller is way more efficient than
a tuna tail, but the fish can not grow a rotating prop so it is a moot
point as far as the fish is concerned. But even so, what a tuna has is
pretty darn good. Human legs and feet do not and can not move the same way
a fish tail does. Putting both feet into a single large high aspect ratio
wing like device might be hypothetically more efficient, but John Winters
point is very valid: this does not take into account human ergonomics. And
as a practical matter I doubt very many people would buy such a device,
just a few odd balls like me would want to give it a try.
On the contrary, I have thought of Rube Goldberg like devices that a diver
could peddle and be propelled by an efficient propeller. It would be fun to
try (and way more efficient than fins), you could cover a lot more sea
bottom with the same size air tank. But again I doubt there would be a big
enough market for such a device to keep you in business.
Also insects and most fish operate in a totally different Reynolds number
range (a parameter that has to do with viscosity, mass and fluid velocity),
the scaling effects could make what is common place for say an insect,
impossible at "human" scale. That means you can not scale up or down
certain effects and expect them to work the same way.
Peter
Arlington, WA
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