> 1.. What causes paddle flutter in the forward stroke flutter is an interaction between flexibility of the paddle-and-arms combination and hydrodynamic forces. It generally is caused by the alternate shedding of vortexes off of opposite sides of the blade. The vortex will form on one edge and then wander across the back of the blade, causing changes in pressure "pulling" the blade to one side until the angle of incidence changes enough so a new vortex forms on the opposite edge, which then proceeds to pull the blade in the other direction. This will form a "vortex street" of opposite turning vortexes in the paddles wake. > 2.. What's the cure A number of changes will reduce or eliminate this effect. A different shaped blade. Sharper edges on the blade tend to trap and stabilize the vortex so it does not wander over the back surface. A few holes down the center of the blade could also have this effect, though I know of no one who has tried it. A stiffer shaft and firmer grip can stop or reduce it (depending on how severe the tendency of the paddle to flutter). The fastest and easiest way to eliminate flutter is to change your stroke to get some cross wise flow on the blade. This tends to keep the vortex shedding on the same side of the blade and keep it in one place. There are a number of motions that will do this, the important thing to get the some cross flow so the blade is not pulled strait back in the water. Peter *************************************************************************** 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/ ***************************************************************************
Among a very good description of the cause and cures for flutter peter wrote: >>>>>>A few holes down the center of the blade could also have this effect, though I know of no one who has tried it.<<<<<<< In 1982 Frank Goodman told me that a hole in the center of the paddle blade would cure flutter. I later put a 1" diameter hole in the center tip area of a flat paddle blade as part of a lot of other changes I put that poor paddle through looking for the ideal paddle blades. I didn't notice any effect on the flutter or anything else about the paddle from putting a hole in it. Maybe I need to drill some more holes in it (if I can find it again-a distinct possibility as I rarely throw anything away and the paddle was probably changed beyond sale-ability). What size would you suggest the holes be? Matt Broze www.marinerkayaks.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/ ***************************************************************************
Jim Syder who is a well known squirt boat designer and paddle maker also talkes about the use of holes to cut down on flutter. If i remember correctly it has something to do with breaking up the eddies on that form on the backside of a paddle during a stroke. JFF >Among a very good description of the cause and cures for flutter peter >wrote: > >>>>>>A few holes down the >center of the blade could also have this effect, though I know of no one who >has tried it.<<<<<<< > >In 1982 Frank Goodman told me that a hole in the center of the paddle blade >would cure flutter. I later put a 1" diameter hole in the center tip area of >a flat paddle blade as part of a lot of other changes I put that poor paddle >through looking for the ideal paddle blades. I didn't notice any effect on >the flutter or anything else about the paddle from putting a hole in it. >Maybe I need to drill some more holes in it (if I can find it again-a >distinct possibility as I rarely throw anything away and the paddle was >probably changed beyond sale-ability). What size would you suggest the holes >be? > >Matt Broze >www.marinerkayaks.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/ ***************************************************************************
Jim Syder a well known squirt boat designer and paddle maker also talks about the use of holes to cut down on flutter. If I remember correctly it has something to do with breaking up the eddies that form on the backside of a paddle during a stroke. JFF >Among a very good description of the cause and cures for flutter peter >wrote: > >>>>>>A few holes down the >center of the blade could also have this effect, though I know of no one who >has tried it.<<<<<<< > >In 1982 Frank Goodman told me that a hole in the center of the paddle blade >would cure flutter. I later put a 1" diameter hole in the center tip area of >a flat paddle blade as part of a lot of other changes I put that poor paddle >through looking for the ideal paddle blades. I didn't notice any effect on >the flutter or anything else about the paddle from putting a hole in it. >Maybe I need to drill some more holes in it (if I can find it again-a >distinct possibility as I rarely throw anything away and the paddle was >probably changed beyond sale-ability). What size would you suggest the holes >be? > >Matt Broze >www.marinerkayaks.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/ ***************************************************************************
> In 1982 Frank Goodman told me that a hole in the center of the paddle blade > would cure flutter. > What size would you suggest the holes > be? First thought: What about these centre holes in the first round parachutes? Or the hole in (sea) drift anchors? A paddle blade isnīt round at all, like a parachute or an anchor, but maybe you can derive from them? Only 2 cents Jochen *************************************************************************** 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/ ***************************************************************************
When experimenting with Greenland paddle designs, I noticed that a very flat paddle face had a tendency to flutter, which went away if I left more of a raised spine transitioning from the loom to the end of the blade: the blade thus had a more pronounced V-shape, especially near the loom. The tendency to flutter also disappeared for even the flat face design if I paddle with the "traditional" edge-tilting cant, although the flat blade still acts wrong in that position. TFJ *************************************************************************** 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/ ***************************************************************************
Matt wrote: >>>Among a very good description of the cause and cures for flutter peter... <clip>What size would you suggest the holes be [to prevent flutter]? thanks Matt. I would try two rows of four holes down the center, just to the side of the stiffening rib, as close to the center line as practical without weakening the blade too much. 5/8 inch diameter or so should do it, I would put perhaps four in each row about 3/4" apart at the center of the widest part of the blade. A slot would work better but would be harder to do. The idea is to allow some of the "bleed" fluid from the high pressure side to the low pressure side to help trap and stabilize the vortex on the back so it does not wander back and forth. Bleed fluid create a kind of "fence' that both strengthens and hold the vortex in plance. This is done in a number of applications and works quite well, for example if you look closely at the leading edge extensions (or strakes) on either side of the F-18 fighter's fuselage you will see similar slots. It just so happens that my first job was at Northrop right after the original development of the YF-17 fighter, which became the F-18 in co-development with McDonnell-Douglas, where they used this to stabilize the large vortexes designed to shed off these strakes. It was to make the aircraft better controlled a extreme angles of attack during a dogfight. They were quite proud of the design of this strake, it was one of the first successful application of intentional vortex formation by the flying surfaces [though all surfaces that work within a fluid do this to some extent, this was a design developed intestinally to take advantage of it]. On a paddle, it would not only prevent flutter, it could hypothetically prevent stall, allowing you to get a larger maximum thrust out of the paddle (though at the expense of slightly higher drag). this could be very useful for a WW or surf paddle where maximum transient thrust is routinely necessary and blade drag is not an issue. Though on a seakayak you do not use max thrust very often, except perhaps in surf launching or accelerating, and the drag penalty would have to be weighed against the max trust advantage. Peter *************************************************************************** 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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