Nick Wrote: "For a paddle to create lift in a forward direction the leading edge (first through the water) must be towards the front of the boat, like the leading edge of a propeller. As you describe, the paddle may be creating lift, but it is in a direction perpendicular to the direction you want to go, so it isn't "useful" for propelling the boat forward. This isn't to say it is useful for some other purpose, but it is not contributing directly to making the boat go forward." Not entirely true. The blade produces a force that has a component in the forward direction, also one across the boat. The force is produced by flow across the blade, from one edge to another. On an airplane, with more or less horizontal foils, the components of the force produced by a foil are called "lift" and "drag", one vertical and one against the direction of motion. For a paddle, we must break the force into slightly different vector components, with new names, as we are not trying to support a heavier-than-air craft, but push a boat. I suggest we call the forces components "drive" (forward) and "cross-boat". "One "useful" aspect of the lift is it may help submerge the blade fully. By pulling the blade deep you improve the overall efficiency potential. I suspect that during the latter half of the stroke, the "leading" edge swaps and that as you bring the blade back up towards the surface, the blade has the ability to produce some lift in the forward direction, but I have yet to hear from a Greenland paddler who can confirm this." My stroke is nearly vertical. There is no downward component to the force. The depth of the blade is entirely due to my efforts to push it into the water. Having the blade deep in the water does improve the effectiveness, as the low pressure zone on the blade is deeper in the water where it can be much larger before ventilation occurs. There is some kind of push that occurs near the end of the stroke, but I am not sure what the blade is doing at that point, as it is behind me where I can't see it. I don't believe that my stroke is optimised to make use of this effect. Resources on the Web note that Maligiaq emphasizes the importance of a long follow-through, and there is anecdotal evidence of this push from related sources. People who use more horizontal strokes may benefit from the downward component to drag the foil down, as do rowers. The Greenland paddle is well designed to create a low pressure zone deep in the water to avoid ventilation. That is why the blade is wider at the bottom, and the tapers to a nearly round shape at the surface. The shape produces a blade with a high aspect ratio and which has great resistance to ventilation. Different angles of attack produce different amounts of drive and cross-boat force, also different total forces. It may not be "lift" we are using to drive the boat, but it is definitely a force produced by flow across the blade, and the drive force produced is higher with this flow regime than when the paddle is dragged through the water at 90 degrees to the motion. I suspect that playing with the variables that improve lift will increase the drive force as well. Worth testing, anyway! John wrote: "I have always considered "lift" a poor choice of words to describe the phenomenon. I like "magic" better. :-)" I have often wondered if John Winters' experiments with paddles used angle of attack as a variable? Strange things happen when the blade tilts, as he points out! Rob. *************************************************************************** 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/ ***************************************************************************Received on Wed Sep 08 2004 - 10:06:49 PDT
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