Always interesting to read the comments on such things as flutter. Some might find this interesting. Some years back while tank testing paddles I tried a number of techniques for reducing or eliminatiung flutter. The one that worked best involved glueing a 1" wide band of driveway de-icing salt along the perimeter of the power face of the blade. For some reason nothing else I tried worked as well. The paddle had an interesting "soft" feel to most paddlers that some did not like. It also looked strange. Harry Roberts (editor of Canoesport Journal) called it the "Gravel Paddle" A few years later some fellows at the Air Force Academy tank tested a paddle with a series of holes around the perimeter. This also worked and, depending on the hole size, did not seem to reduce drag. They did not test the blade at an angle of attack. Many years ago during my sailboat racing days many stock boats experienced rudder and centerboard vibration (or flutter if you prefer). Some boats actually hummed a tune depending on the speed. The cure most often used was to file off the trailing edge on an angle. I seem to recall it was 80 degrees but would not swear to it. At the time I was testing paddles it occurred to me that the observed degree and existance of flutter varied between paddlers using the same paddle. Some casual testing suggested that the smaller the shaft diameter relative to the paddler's hand the greater the perceived flutter. An ergonomics engineer explained that there exists an optimal shaft size for every hand size and that the smaller shafts probably reduced the effective grip force. The ideal shaft size appears to be that which fits the hand in its natural repose. I have read this same comment (the optimal size) in several ergonomics texts. I also did some experimentation based on the observation that flutter seemed to increase as the shaft rigidity decreased in the region of the shaft/blade junction. I started with a paddle that had a narrow and "whippy" shaft at the blade top. It fluttered enormously. I then began adding carbon fiber reinforcement until, eventually, the perceived flutter disappeared. These experiments may explain why two paddles behave differently even if they look very much alike. A "soft" or less rigid shaft may increase the flutter by reducing the damping effect of the shaft. Similarly the "to small" shaft may increase the sensation similarly by reducing the damping effectiveness of the hands. I suppose it might pay to examine such simple things as paddle rigidity and shaft size if you experience flutter. You could spend a lot of time tinering with your stroke only to discover the problem in the paddle. Cheers, John Winters *************************************************************************** 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/ ***************************************************************************
John Winters wrote: > Some years back while tank testing paddles I tried a number of techniques > for reducing or eliminating flutter. The one that worked best involved > gluing a 1" wide band of driveway de-icing salt along the perimeter of the > power face of the blade. For some reason nothing else I tried worked as > well. The paddle had an interesting "soft" feel to most paddles that some > did not like. It also looked strange. A lot of research on flutter has been done by aircraft makers for over 100 years, the focus and cause on aircraft parts are similar as on paddles (except fortunately on paddles it is seldom life threatening). Even with a century of research and massive supercomputers it is still something difficult to predict reliably, the difficulty with it on aircraft is it comes on very suddenly and can become very large and violent to the point of actually failing structure or losing control of the aircraft. It is a complex interaction of the shape, dynamic fluid pressure, the flexing of the structure (in the case of the paddle, it would include the shaft, the blade and the amount of "give" in the paddle's hands and arms) which causes both the speed and angle of attack of the surface to change relative to the fluid. A more stiff surface will not allow as much pressure change, and greatly reduce the risk of flutter, hence the reason a tight grip on the paddle shaft helps. Also the shape of the edge of the blade is very critical, a sharp 90 degree edge that would make a "clean" break for the fluid would help too so the point the fluid flow detaches does not wander over the back of the blade. By putting turbulators on the edge of the surface can also work well. You are putting more energy into the boundary layer which would stabilize the flow (by keeping it attached to the surface) reducing separation and thereby prevents stalls and the rapid pressure changes across the surface. Which causes the rapid changing directions of the blade. You can see the turbulators on many commercial airplanes, little blades or pins out on the wing or tail in front of the control surfaces. They could work on a paddle the same way. This can actually reduce drag, improve controllability and safety, but at the expense of the slightly higher drag of the turbulators. So a careful and proper design theoretically would prevent flutter without the turbulators, but even with big budgets and computers, we are not that good yet. So we live with vortex generators and turbulators in sensitive areas of flow. Another interesting way to stabilize flow and prevent flutter is by putting slots or vents in strategic locations the would both energize the flow and trap the vortex so it does not wander over the surface. this is part of the reason the slots on used on the leading edge of aircraft wings, and on some modern swim fin designs. Properly shaped and carefully placed slots on the surface of a paddle blade could also help prevent flutter too, but also the expense of other aspects of the paddle performance, not to mention adding cost. So to prevent flutter on a paddle, you could hypothetically: 1) make it stiffer and hold it tighter, which would and weight or be tiring, 2) add turbulators to the edges 3) cut strategically located slots on the blade 4) change the shape of the paddle blade (but these last tow would require go though a lot of trial and error blades before you could find optimum configuration). On an existing paddle trying different ways to hold the blade (i.e. at an angle to the direction of movement, a la Greenland technique), or try the turbulators. This could be done with temporary attachment of sand paper or grit with rubber cement or wax to try it. What I would try, which is MUCH less obvious, is to take a triangle file or a hack saw blade and cut very tiny, shallow "teeth" around the edges of the blade at the widest part for about 8 or 9 inches on each side. This too you can test with some think tape over the edge that you cut little notches in with a sharp exacto knife. If it helps, remove the tape and file tiny notches in the blade edge. They would be most effective if the were more pronounce on the high pressure ("power") face of the blade. If you do not like them you can always sand them off, or try reshaping the edges at the same time. Good luck, 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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