Subject: Re: [baidarka] Superiority of Native paddles
From: Joe Street (jstreet@venus.uwaterloo.ca)
Date: Wed Jun 20 2001 - 17:42:54 EDT
Way to go Hendrik;
Nothing like throwing a little confusion on the subject! I think the US
government refers to this technique as dis-information???
Actually a HIGH L/D or lift to drag ratio is the object of the long skinny (high
aspect ratio) wings you refer to, which are most notably seen on the most
efficient sailplanes. Of note here is also the interesting shapes at the tips of
those wings (for example what the poles introduced with their radical 45 degree
tip sweep-back) and winglets etc. All of these techniques are aimed at reducing
induced drag which is the drag that comes as the penalty of creating lift. The
more the lift for the less drag is the higher efficiency.
Incidentally the induced drag comes about as a result of the 'fluid' on the high
pressure side of the foil trying to find its way to the low pressure side.
Generally this takes the form of a span-wise flow which results in some of the
fluid migrating toward the tip where it is suddenly accelerated through a curved
path around the tip giving rise to a vortex. It is the energy wasted in
accelerating the fluid here which is felt as induced drag and kills the
efficiency.
The question is whether a paddle should be modeled as a lift producing device or
a drag producing device. There are those on the list who believe in either side
of the argument. I myself am undecided until I try one of these greenland style
paddles and slicing stroke technique. If it does indeed work as a lifting
section then I'm sure the paddle could benefit from all of the modern knowledge
that comes from the field of high efficiency aerodynamics as well. Reducing tip
losses could result in a significant improvement in paddle efficiency. If on the
other hand a paddle works best as a drag producing device then there are probably
significant improvements that can be made in that case as well. Lets face it the
good old paddle hasn't benefited much from modern techno-how aside from some
materials science, the shapes have been pretty much standard.
I guess I better get off my butt and make a paddle before I say more....
Joe
Hendrik Maroske wrote:
> > From: "Peter A. Chopelas" <pac@premier1.net>
> >
> > Hi all,
> >
> > Since things have been a bit slow I thought I would give you all something
> > to chew on.
> [...]
> > Therefore just for grins I have listed a mathematical proof that you
> > technical types might find interesting. If the rest of you just read my
> > text you should be able to follow the idea of the math without having to do
> > it, at the very least if you may find the conclusion very interesting.
>
> Huh?
>
> [...]
> > Most of this I have pulled from "Theory of Flight" by Von Mises, and from a
> > few other books if you are so inclined to verify the equations.
>
> Aaaaahhhhh, I knew the equations were familiar to me. Okay. This looks
> promising.
> Well, there are different opinions on how these equations can be used for
> calculating an airplane. I hnow of some guys who really are earnestly
> convinced
> that all this does not apply for their type of plane, so if there are
> differing
> opinions about how to use this for aircraft, how can we try to use this for
> something else?
>
> > There will be a quiz next week.
>
> Hmmm on the other hand, this looks like a very good experiment. Just don't
> think
> I can come up with a solution in the next seven days. Give me more time for
> this
> for a good answer.
>
> One first thought is this: on a typical wing, a high aspect ratio is good
> for
> a low lift to drag ratio; less lift means less induced drag; so if we want
> to
> increase total drag (that is, need maximum push), we will want to reduce
> aspect
> ratio.
>
> On a paddle, the "wing" is rotated 90 degrees... high aspect ratio now will
> mean... hmmm...
>
> feeling triggered :-)
>
> Hendrik
> -
> Baidarka Mailing List - All postings copyright the author and not to be
> reproduced outside Baidarka or Baidarka archives without author's permission
> Submissions: baidarka@lists.intelenet.net
> Subscriptions: baidarka-request@lists.intelenet.net
> Searchable archive: http://rtpnet.org/robroy/baidarka
-
Baidarka Mailing List - All postings copyright the author and not to be
reproduced outside Baidarka or Baidarka archives without author's permission
Submissions: baidarka@lists.intelenet.net
Subscriptions: baidarka-request@lists.intelenet.net
Searchable archive: http://rtpnet.org/robroy/baidarka
This archive was generated by hypermail 2b27 : Sun Jul 01 2001 - 01:30:01 EDT