-----Original Message----- From: Robert C. Cline [mailto:rcline_at_onramp.net] Sent: Tuesday, August 04, 1998 8:59 AM To: K. Whilden; paddlewise Subject: Re: [Paddlewise] lift and efficiency: D 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 ************************************************************************** * I was similarly confused several years ago when George Gronseth first wrote about Greenland paddles having lift. Since Greenland paddles are symmetrical in section, they obviously can't have the kind of lift generated by air moving over the top of an airplane wing. However, lift is created when there is a difference in pressure between opposite sides of an object regardless of the means used to create that pressure difference. (John, correct me if I am wrong about this.) Despite the word, the direction of lift does not have to be up. You can also create lift by moving an inclined object through a fluid. A prime example is holding your hand outside a moving vehicle and tilting it so the wind moves it up. Other examples are when you scull your kayak paddle either on or under the surface of the water, or support yourself with a sweep stroke, or roll using a sweep or screw roll. I think this is the kind of lift most people are referring to with regard to Greenland and other paddles. If I understand them correctly, wing paddles are an exception in that they *are* shaped like airplane wings in section, and generate forward lift in the same way. However, they are specialized paddles used mostly for racing, and since they do not perform as well as standard paddles for bracing and rolling, they are rarely stocked by recreational paddling shops. I think I have seen only one ad for them in Sea Kayaker. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Aerobatic airplanes also have symmetrical profiles on their wings. That is what allows them to fly upside down. When the wing is at a positive angle with respect with the flow, the air has a longer path around the round edge to travel to the top of the wing, while the flow that goes under the wing has a shorter turn. Hence, *the key is in the round shape of the front edge*. That is why symmetrical profiles have the center of lift closer to the front than asymmetrical profiles. I know this is very hard to explain without a drawing, but if you go to a hobby shop, any book on model airplanes should have good drawings about it. On Greenland paddles, for the same reason explained above, it is very important to have the edges properly rounded. A sharp edge would make the paddle stall at even the smallest angles (tested, been there). The same principle applies to rudders, and skegs. If the leading edge is too sharp they just stall and only act as drag. - Julio > > However, lift is created when there is a difference in pressure between > opposite sides of an object regardless of the means used to create that > pressure difference. (John, correct me if I am wrong about this.) Despite > the word, the direction of lift does not have to be up. You can also > create lift by moving an inclined object through a fluid. A prime example > is holding your hand outside a moving vehicle and tilting it so the wind > moves it up. Other examples are when you scull your kayak paddle either > on or under the surface of the water, or support yourself with a sweep > stroke, or roll using a sweep or screw roll. I think this is the kind of > lift most people are referring to with regard to Greenland and other > paddles. > > If I understand them correctly, wing paddles are an exception in that > they *are* shaped like airplane wings in section, and generate forward > lift in the same way. However, they are specialized paddles used mostly > for racing, and since they do not perform as well as standard paddles > for bracing and rolling, they are rarely stocked by recreational paddling > shops. I think I have seen only one ad for them in Sea Kayaker. > > Chuck Holst > *************************************************************************** > PaddleWise Paddling Mailing List > Submissions: paddlewise_at_lists.intelenet.net > Subscriptions: paddlewise-request_at_lists.intelenet.net > Website: http://www.gasp-seakayak.net/paddlewise/ > *************************************************************************** > > *************************************************************************** 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 is being posted for a friend: Kevlar Sealution for sale including all accessories and graphite crank shaft Lendal paddle. Bob Hoffman has a couple of herniated discs and ordered this boat in an ultra light configuration. I believe it weighs 32 lbs. or so and has a clear skin coat. Bob's back has worsened and he has to give up paddling completely. He can be reached at 561-272-1324, which is Delray Beach, FL. Shipping would probably be under $150 to anywhere in the US. cya *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
You can place a free classified ad on my web page, Paddle Florida!. It's a new feature. Paddlers can post "Stuff For Sale" and "Stuff Wanted" ads. It's open to all private/non-commercial sales. http://www.paddlefl.com/classified.htm Brad Manley Paddle Florida! http://www.paddlefl.com >Date: Tue, 4 Aug 1998 14:29:32 -0400 >From: "Bob Denton" <gulfstream_at_flinet.com> >Subject: [Paddlewise] Kevlar Sea Yak for Sale > >This is being posted for a friend: > >Kevlar Sealution for sale including all accessories and graphite crank shaft >Lendal paddle. > >Bob Hoffman has a couple of herniated discs and ordered this boat in an >ultra light configuration. I believe it weighs 32 lbs. or so and has a clear >skin coat. >Bob's back has worsened and he has to give up paddling completely. > >He can be reached at 561-272-1324, which is Delray Beach, FL. Shipping >would probably be under $150 to anywhere in the US. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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