Re: [Paddlewise] Greenland paddles

Julio and Nick,

I do not understand why the lift generated by Greenland paddles must
necessarily be small. My fluid dynamics is pretty weak, but if someone
wants to give me the calculations of the lift force vs. the drag force, I
would be very appreciative.

I tend to think of the so-called "lift" force as this...

-- Consider pulling the greenland paddle straight back, with no lateral
motion whatsoever, and therefore no lift force will be generated. There is
a very noticeable slippage through the water.

-- Now consider paddlingg with proper technique and plenty of lateral
motion. The paddle feels like it is planted in cement. 

-- The difference in power between the two scenarios is very remarkable
indeed, and the difference in physics is that the latter has laminar flow
across a foil while the former does not.

-- I interpret this difference as the lift force. I call it lift because
whatever force causes the "cement" effect, it appears to be derived from
the laminar flow of water across the foil shape of the paddle, and in
general, laminar flow across a foil always produces lift. 

I guess as a scientist-type, lift seems the most plausible explanation,
and I will not change my theory until I see proper quantitative evidence
otherwise, or until a more plausible theory appears. Now also let me say
that my book on swimming technique gives me a lead on a possible
alternative theory, and I might investigate a little bit, although my
initial appraisal says that it probably applies to a different physical
mechanism than the one currently in question. 

I hope that we can paddle together sometime. Cheers,
Kevin

/--------------------------------------------\ /---------------------------\
|Something there is that doesn't love a wall  |       Kevin Whilden        |
|That sends the frozen-ground-swell under it  | kwhilden_at_u.washington.edu  |
|And spills the upper boulders in the sun     | Dept. of Geologic Science  |
|And makes gaps that even two can pass abreast| University of Washington   |
|			-- Robert Frost	      |(206)543-1975(w) 632-5140(h)|
\--------------------------------------------/ \---------------------------/



On Thu, 23 Jul 1998, Julio MacWilliams wrote:

> Yes, there is lift. However, Nick is saying that the lift contribution
> to forward motion is very small, which seems to be a valid claim.
> 
> The effects of the lift are dramatic when doing rolls, braces, and sculls,
> but even though one can feel the lift also when paddling forward, 
> that lift is much smaller than when doing rolls.
> 
> There has to be something else going on that makes the Greenland
> stroke so powerful, as it is hard to believe that such a thin stick
> would move you forward at all.
> 
> Maybe the combination of foil shape and narraw blade creates a fast
> eddy around the paddle that provides the mass*velociy factor necessary
> to provide a good momment of inertia to the kayak (m*v = M*v')
> 
> Whatever it is, the Greenland paddle works incredibly well, but
> the real reason why remains a mystery.
> 
> If there is ever some serious scientific study aimed at improving or
> refining Greenland paddles, then we might know.
> 
> - Julio
> 
> K in response to Nick wrote:
> 
> > > This concept has been brought up before. The idea that the greenland paddle
> > > uses lift to propel the boat just makes no physical sense. The paddle just
> > > does not move far enough laterally through the water to provide significant
> > > lift. It, like most paddles is being used primarily as a parachute, not a
> > > wing.
> > > 
> > 
> > This is simply not true. I have a degree in physics as well, and it makes
> > perfect physical sense to me. The greenland paddle in its three main
> > varieties of strokes has a high lateral component of velocity at the ends
> > of the paddle. With the proper angle of attack and with a well constructed
> > foil shape, there is laminar flow across the paddle, and lift is generated
> > in the opposite direction of which the paddle is being pulled. Learning
> > how to make the lateral velocity of the paddle fast enough to generate
> > lift takes a fair bit of practice -- I can do it reliably in two of the
> > three kinds of strokes. Come to Seattle and I'll show you. Greenland
> > paddles generate lift.
> > 
> > 
> 
> 

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