RE: [Paddlewise] PaddleWise [wing theory]

On 10 Jun 2003 at 10:43, Dave Gorjup wrote:

> That said, I'm having a terrible time trying to relate the operation
> of an aircraft wing or helicopter blade to the functionality of any
> kind of paddle. In my mind, wings generate lift by orienting them to
> present the least planform to the medium it's moving through, in most
> cases. Paddles must present the maximum planform to generate the most
> resultant force to the kayak and paddler.

The paddles that most match a wing or propellor model are the wing 
paddles.  These are shaped like a wing section (cambered, with a 
blunt, rounded leading edge, fine trailing edge etc).  The section is 
open underneath in most cases, so are a little more like a wing with 
flaps down and leading edge devices deployed, rather than a 
traditional NACA foil with a closed cross section (I can't help but 
think they'd be a tad more efficient if they were closed like the 
Schleicher  from Nimbus, but I digress.)

The motion of the paddle (as demonstrated to me by Greg Barton last 
year an the East Coast Canoe & Kayak Festival) is to plant ahead and 
sweep the paddle out (primarily) and back - relative to the paddler.  
The paddle is planted initially with the shaft as vertical as 
possible.  Hence the motion of the blade is a curved path out and up 
toward the surface and the leading edge is outward through the entire 
stroke.  Hence the wing paddle generates lift like a wing and the 
direction of the lift is nominally forward (i.e. direction of kayak 
motion).

Conventional paddles use a mix of drag and lift, though the 
proportions are more open to debate than established (on these fora) 
in fact.  Many discount the idea that it is overwhelmingly drag that 
produces the force and there are compelling reasons to think this 
way.  We know that avoiding flutter necessitates the use of a 
slightly canted paddle blade, but whether this results in a nice, 
unstalled flow is subject to debate.  

The cant in the Greenland paddles (GP) (as some paddles use them) is 
sufficient to suggest that it does not stall and therefore some form 
of lift is imagined to dominate.  However, Nick Schade has presented 
convincing reasons for believing that the lift on a GP doesn't 
actually contribute to the forward motion as such (this discussion is 
achived in QajaqUSA's web site) or at least not in the way that wing 
paddles do.

Peter's analysis (aside from its problems) is a scalar, not vector 
analysis and we've not had much luck in getting him to identify the 
meaning of the results in terms of what actually happens to the 
paddle generating forces that move the kayak.  My feeling, looking at 
his work but without doing any detailed analysis, is that his results 
(if corrected) would represent an efficiency that does not result in 
a meaninful contribution to forward motion (i.e his efficiency is in 
the generation of both useful and useless forces).  By analogy, the 
results that Nick talked about in a recent post on "work = change of 
energy" were correct but confused a couple of people because it 
didn't take into account the work done in moving the kayak forward 
versus the work done in moving water around without moving the kayak 
(i.e the work wasted).  Such is the problem with working with scalars 
instead of vectors.

Hopefully this presents a precis of the multiple discussions 
pertaining to the mythical lift characteristics held on Paddlewise, 
Baidarka and QajaqUSA so far.

Mike

***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************