Nick wrote: "I frequently here people talk about paddles working like wings and am prepared to accept that it is possible. Yet whenever I ask people to describe how the paddle is working like a wing, their explanations fall flat." I use my GP with a very vertical stroke. The angle of attack the blade is relatively low, like 45 degrees to the motion. A "euro" paddle is used at 90 degrees. I am quite certain that lift is involved, as I can see the water flowing over the paddle, just the way a fluid flows over a foil from leading edge to trailing edge. The leading edge is towards the boat, and the trailing edge is the outside edge. Only one vortex is formed, not two, by this stroke. I experiment with even lower angles of attack, but find that the direction of the force produced is not in the right direction to give good drive. More of the force produced is across the boat, less towards the direction of motion. The paddle is hard to hold, too, as the force produced is quite large and in a direction that does not suit the arms and hands. The blade area of my GP is quite low, as it is cut for my hands and height (5'-6") but I find my cadence to be the same or lower than that of my friends travelling at the same speed. I find I use quite a high paddle velocity through the water to achieve normal cruising speeds, that speed being defined as the speed I have to maintain to keep up with my friends, about 3 kts. I get a rest between strokes. Since the integral of the effort I put in must be roughly the same as produced by my friends (speed is equal, therefore total horsepower must be roughly equal), the peak loads must be higher, yet I find this paddle and stroke to be much easier on the body. Perhaps it is because of the rest between strokes? Before I found the 45 degree angle of attack, I used it like a "euro" blade at 90 degrees, and found the GP to be quite ineffective. Cadence was way higher than normal, like above 60 per minute, versus the usual 30 used when cruising. If this is isn't lift being produced, I don't know what to call it. It is really cool to experiment with the angle of attack, and watch (and feel!) the effect on the water flow as the blade stalls. It is also possible to see how minor dings and imperfections in the leading edge of the blade affect the flow. No wonder the Inuit used bone insets in their leading edges. I hope this explanation is clear enough? In any case, I would recommend you just build a Greenland stick and go try it. Using a vertical stroke, so you can watch the flow and see what happens at various angles of attack and so on, is worth a thousand e-mails trying to describe what is going on. 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/ ***************************************************************************
Your description is not complete enough to tell if lift is being produced in a useful direction. Does your blade move away from the boat as you stroke, or is it towards the boat? or parallel to the boat? Is your "leading" edge towards the front of the boat, or just the edge that is cutting through the water first, or is it both? One vortex indicates lift maybe produced, but it doesn't say which direction it is producing it. I've used a Greenland paddle and I can make it produce lift in a useful direction, but to do so, I must use a stroke that is different than the standard "Greenland" style stroke. Nick On Sep 7, 2004, at 3:25 PM, Robert MacDonald wrote: > Nick wrote: > > "I frequently here people talk about paddles working like wings and am > prepared to accept that it is possible. Yet whenever I ask people to > describe how the paddle is working like a wing, their explanations fall > flat." > > I use my GP with a very vertical stroke. The angle of attack the > blade is relatively low, like 45 degrees to the motion. A "euro" > paddle is used at 90 degrees. I am quite certain that lift is > involved, as I can see the water flowing over the paddle, just the way > a fluid flows over a foil from leading edge to trailing edge. The > leading edge is towards the boat, and the trailing edge is the outside > edge. Only one vortex is formed, not two, by this stroke. snip > I hope this explanation is clear enough? In any case, I would > recommend you just build a Greenland stick and go try it. Using a > vertical stroke, so you can watch the flow and see what happens at > various angles of attack and so on, is worth a thousand e-mails trying > to describe what is going on. > Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 USA Ph/Fx: (860) 659-8847 http://www.guillemot-kayaks.com/ *************************************************************************** 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/ ***************************************************************************
On 7 Sep 2004 at 12:25, Robert MacDonald wrote: > If this is isn't lift being produced, I don't know what to call it. There may be lift on the surface, but if it isn't pointed the correct direction, it doesn't contribute directly to forward motion. Only wing paddles, or more generally, paddles used with wing-like motions, will generate lift in the forward direction. It's clear to me that it is a combination of lift and drag that generates a set of forces against which I can pull to propel the kayak. But it isn't using the GP as a wing unless I use a wing stroke. 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/ ***************************************************************************
[Moderator's Note: Content unaltered. Excessive quoting (including headers/footers/sig lines/extraneous text from previous posts, etc.) have been removed. Please edit quoted material in addition to removing header/trailers when replying to posts.] Nick: The paddle moves parallel to the direction of motion. The leading edge is towards the back of the boat. If the left blade is in the water on the left side of the boat, it looks like this: \, and moves towards the bottom of the page. It is hard to say which direction the total force is directed, but there is a significant component in the drive direction, also a significant component in the cross-boat direction. This is essentially the same as the canoeist's pitch stroke, which is my favourite stern stroke. There, the cross-boat component is useful, as it reduces the amount of steering that must be done during the J part of the stroke. The J becomes a simple twist and pause, with a slight rudder action, instead of an almighty heave, shovelling water away from the boat. How do you use the paddle to get it to lift? I suspect that traditional oars also work this way. They are put in the water at a slight angle, to "bite", then drawn aft. This will produce a lifting effect that is both down (keeping the oar in the water) and forward. Pete Culler preferred narrow oars to wide. Although, he also liked spoons, that tend to work more in pure drag (according to my hypothesis, at least). The real beauty of the vertical stroke is being able to see the flow over the blade. You can really see what happens, and feel it too. Also, the experts using GP paddles use a very vertical stroke when racing, so it must give the most drive at this angle. Rob. -----Original Message----- From: Nick Schade [mailto:nick_at_guillemot-kayaks.com] Your description is not complete enough to tell if lift is being produced in a useful direction. Does your blade move away from the boat as you stroke, or is it towards the boat? or parallel to the boat? Is your "leading" edge towards the front of the boat, or just the edge that is cutting through the water first, or is it both? One vortex indicates lift maybe produced, but it doesn't say which direction it is producing it. I've used a Greenland paddle and I can make it produce lift in a useful direction, but to do so, I must use a stroke that is different than the standard "Greenland" style stroke. Nick *************************************************************************** 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/ ***************************************************************************
On 7 Sep 2004 at 14:26, Robert MacDonald wrote: > The real beauty of the vertical stroke is being able to see the flow > over the blade. You can really see what happens, and feel it too. One thing I learned in studying and working in hydrodynamics - you can't see the flow. At least not with some specific markers in the water (dye etc). I know a lot of paddlers see surface effects and then make assumptions about what's happening, but that's not the same thing as seeing what is happening. 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/ ***************************************************************************
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. 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. On Sep 7, 2004, at 5:26 PM, Robert MacDonald wrote: > > The paddle moves parallel to the direction of motion. The leading > edge is towards the back of the boat. If the left blade is in the > water on the left side of the boat, it looks like this: \, and moves > towards the bottom of the page. It is hard to say which direction the > total force is directed, but there is a significant component in the > drive direction, also a significant component in the cross-boat > direction. Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 USA Ph/Fx: (860) 659-8847 http://www.guillemot-kayaks.com/ *************************************************************************** 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/ ***************************************************************************
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/ ***************************************************************************
On Sep 8, 2004, at 1:06 PM, Robert MacDonald wrote: > > 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". Obviously the blade produces a force that has a forward direction, otherwise the boat would not move forward. This does not mean that any of that force is produced by lift. It could just as easily be produced by drag. You say the force is produced by flow, but I'm uncertain how you know this. I'm sure that the forces produced by your paddle are not perfectly parallel or perpendicular to the direction you want to go. There is almost certainly some component of "lift" type forces in the "drive" direction, but this doesn't mean it is the primary source of propulsion. Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 USA Ph/Fx: (860) 659-8847 http://www.guillemot-kayaks.com/ *************************************************************************** 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/ ***************************************************************************
I would call the force perpendicular to the blade surface "lift" Sea kayaker had an excellent article a few years ago about how a proper Greenland stroke kept the blade flying (my word) throughout the stroke by using a slicing motion that keeps water moving parallel to the blade surface. I was delighted to find that it was basically the same stroke that mine had morphed into after using a Greenland paddle for a while. Anyway, wings stall due to excessive angle of attack. The angle of the relative wind (or water flow) to the cord of the wing. This is easily felt on a Greenland paddle by just pulling the blade perpendicular to its surface through the water. Here is a really cool web page about angle of attack, including a simulator: http://www.lerc.nasa.gov/WWW/K-12/airplane/incline.html A Greenland paddle is essentially a symmetrical wing which is not known for delayed stall. Fat bladed euro paddles not only have better lift in stall due to their low aspect ratio, but the much more exaggerated asymmetrical wing shape which keeps water flowing parallel to the "wing" surface at higher angles of attack - thus delaying stall. That same shape is used on STOL (short takeoff and landing) aircraft. Here are a few web pages that shows the use of leading and trailing edge flaps to achieve the same shape and effect---> The last flap example on this page really looks like a paddle: http://www.allstar.fiu.edu/aero/Wing33.htm Figure 2 on this pages shows why a euro paddle works so much better than an Greenland when just pulled through the water: http://www.zenithair.com/stolch801/design/design.html Moveable surfaces are used for airplanes so as to have minimal drag consequences with flaps retracted at cruising speeds when high angles of attack are not required. The kayak analogy is to use a euro paddle for punching out through the surf, then to pull your Greenland paddle off the deck for cruising. Anyway, no surprise that the "wing" paddle has the most exaggerated asymmetrical wing shape of all. Paddles are wings Steve Brown -----Original Message----- Obviously the blade produces a force that has a forward direction, otherwise the boat would not move forward. This does not mean that any of that force is produced by lift. It could just as easily be produced by drag. ........ Nick Schade *************************************************************************** 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/ ***************************************************************************
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