Kevin wrote: >Ok, now lets talk about lift... but first lets talk about drag. The >paddler is pulling backwards on the paddle (force vector points towards >the stern). The resistance of the water (drag) on the paddle resists that >pull (force vector points towards the bow). The drag force vector is >slightly smaller than the paddler force vector, which is another way to >think about efficiency. The difference in the size of the vectors >represents the energy that is lost due to turbulence and the slippage of >the paddle through the water. When lift is generated due to laminar flow, >the size of the resistance vector is slightly increased because the lift >vector points in the same direction as the drag vector. Even if further >calculations were to show that the lift generated by Greenland paddles >really is insignificant, efficiency is probably still increased because >there is a lot less turbulence created by the laminar flow. And note, >modern, non-wing paddles can significantly reduce turbulence by slicing >the paddle outwards away from the kayak, just like racers and greenland >paddlers. > >Well, the concepts above are quite clear to me, but I wonder how clear it >is to the readers. I suppose I could put it down on a web page, with force >vector diagrams, and with maybe even a bonus picture of me waving my >hands. Anyhow, I hope my definitions make sense, and maybe clear up a >little confusion. What is clear to Kevin is clear as mud to me. If Drag were less than the force...then the paddle is moving through the water. I guess the laminar flow is on the power face and the turbulent flow is on the other face... ?? But if that were true, then lift would be created on the underside of the wing. Lift... Lift on a wing is created because there is a greater greater distance on the upper surface of the wing between the leading edge and the trailing edge of the wing. Isn't this called the airfoil... corrolated with "hydrofoil?" What is a "wing paddle?" John Winters speaks of low-aspect ratio... what is that? I'm having a difficult time with this discussion not knowing the vocabulary. I've looked for ads for a "wing paddle" but haven't seen any. Perhaps that refers to the asymetrical design?? I'm reaching here. Thanks Robert *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Robert wrote; > >What is clear to Kevin is clear as mud to me. If Drag were less than the >force...then the paddle is moving through the water. I guess the laminar >flow is on the power face and the turbulent flow is on the other face... ?? >But if that were true, then lift would be created on the underside of the >wing. Lift is complex and not intuitive. Maybe this will help. Definitions: By aspect ratio I mean the mean blade width divided by the paddle length. So, rectangular blade that is 3" wide and 24" has an aspect ratio of 8:1. "High" and "low" are arbitrary. I use 2:1 and lower as low aspect ratio, 2:1 to 4:1 as middle of the road, and 4:1 and up as high aspect ratio. One could choose other cut offs. The wing paddle is the paddle most used by kayak racers. There are a number of variations on the theme but the general characteristics are aspect ratios between 2.0 and 3.5:1, maximum chord depth range between 15 and 20% of the mean blade width and the maximum chord depth location is around 40% aft of the leading edge. Don't get hung up on these ranges. There may be many outside these ranges. Most wings (but not all) are concave on what we call the power face. The chord depth can be taken as the maximum thickness measured from a line connecting the leading edge with the trailing edge of the blade. Now for the confusing part. Three basic kinds of flow occur on a blade. Steady flow (what I think Kevin is talking about when he says "laminar") where all particles move in an orderly manner in the same direction, unsteady flow, or turbulent flow where there is a randomn component, and reversed flow or what we call "stall" where the flow separates from the surface. Steady flow can exist on both faces. Unsteady flow and stall need not occur over the entire surface so part of the flow can be steady and some unsteady. For example, the mast introduces turbulence on sail boats but the flow can reattach at some point aft on the sail so the sail still produces lift. Lift can be generated by flat bladed paddles and foil shaped paddles. Some are better at generating lift than others. I believe that confusion enters the picture here because for airplane wings, rudders and keels (just some examples) one might want to the maximise the ratio of lift to drag. In other words, one wants as much lift as possible at the lowest possible drag. There are times when maximising the lift/drag ratio may be counterproductive. For instance when a plane is landing. Then the flaps are used to increase lift at teh lower speed. Drag is not less of a problem because there is ample power to offset its effects. With paddles the objective may be different and more akin to sailing where the objective can shift from the most favourable lift/drag coefficient to the most favourable total power coefficient (Ct). By total power coefficient I mean the greatest power per unit of paddle area. For example a sail when working to windward (angle of attack aproximately 10 degrees) might have a Ct of 0.4 but as the angle of attack shifts aft to the point of stall the Ct might increase to say 1.2. Then after stall the Ct might decrease to, say, 1.15. (just examples). In other words the greatest power may not be when the drag is at its lowest. I mentioned that interested readers might like to check out Marchaj's "Sailing Theory and Practice" . What I will say from here on refers to Fig 102 on page 154. Figure 102 shows the Ct for four aspect ratio foils (6:1, 3:1, 1:1 and 1/3:1. What is interesting (at least to me) is that the highest Ct is obtained with the 1:1 aspect ratio and it is higher over a wide range of angles of attack from roughly 25 degrees to 50 degrees. Above 50 degrees it is lower than the higher aspect artios but the difference is smaller (about 10% less as opposed to being as much as 60% greater at aprox. 35 degrees. This is one of the reasons why I question the claims of efficiency of high aspect ratio paddles particularly when the claim is attached to lift. I believe this also may explain why so many people find the low aspect ratio paddles to be "hard" on them. Modern low aspect ratio paddles are generally larger in area than more traditional high aspect ratio paddles and that, when coupled with a higher Ct might explain paddler perceptions. If low aspect ratio paddle A had less area (commensurate with its Ct) than high aspect ratio paddle B then the paddler perception might be reversed. The common question is, "Why is all this important?" Clearly people think how a paddle feels and functions is important or it would not surface in so many questions and discussions. The comment is frequently made that, "If you like it that is good enough" and that may be perfectly acceptable approach for some. I wonder, however, what the "Greenland paddle" would have looked like if the Greenlanders had taken that approach and were perfectly content with the first flattish piece of wood they picked up off the beach. I believe some one commented that when the high aspect ratio paddle was used in more of a lifting mode that it felt like it was "in concrete" and that is possible since the Ct could be higher. This same observation does not appear unique to high aspect ratio paddles. Nick asks a good question when asks "What is a Greenland paddle?" I wonder, however, if a more useful question would not be "What are the distinctive characteristics of a Greenland paddle?" I recall how strong the responses were to the question "What is a Greenland kayak? " People did not seem able to agree on what it was although they could agree on some of its characteristics. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Hank: > >Low aspect ratio is a short wide blade (many modern blades). A high aspect >ratio is a long skinny blade (greenland blade or a Werner little dipper). What's the advantage to each? ...and the disadvantage of each? What's the advantage/disadvantage to dihedral? Many thanks. PS Your paddle has arrived today. I'll be testing it out tomorrow. Can't wait! Thanks again. Robert *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:32:51 PDT