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#21
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Why don't wings have dimples?
wrote in message
oups.com... A few years ago someone was marketing a perforated tape to stick on your propeller leading edges to act as vortex generators, improving thrust and therefore performance. I have never seen any of this stuff on a prop, and don't know if it was worthwhile or just another of the gimmicks to get a poor pilot's money. Anybody else see it? Dan I remember it, but haven't seen it since and don't recall who made it. I believe that there was also an article in "Experimenter", now renamed "Sport Pilot", regarding a gent who had drilled a line of dimples (or perhaps two) along the low pressure face of both blades of his prop at approximately the thickest point. He did achieve his goal with regard to static RPM and cruise RPM, as well as cruise speed for the particular aircraft. However, IIRC, some baseline data was not recorded and the article did not include the precise description and placement of the dimples; with the result that a general inference was not reasonable. Peter Where's John Ronz when we need him? |
#22
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Why don't wings have dimples?
"Peter Dohm" wrote in message
... I've seen a video of that, but don't recall where. However, I believe that you have it backward--the flow detaches earlier (from the non-spinning golf ball) and reduces the drag. I am not quite sure how that might relate to wings and propellers; but I suspect that they (wings and props) are two radically different, and possibly opposite, phenomena. Peter Ok, now you've done it. You are going to make me look this up... http://www.fi.edu/wright/again/wings...r/golf-01.html description and a drawing... http://www.aerospaceweb.org/question...cs/q0215.shtml with a little math and some graphs http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html plots drag as a function of Reynolds number for a golf ball and a smooth sphere - a good starting pont if you want to dimple your nosegear strut to reduce drag - just figure you your own Reynolds number... That's enough. Didn't find the picture I was looking for. But I see references to both the reduction in wake and Magnus effect that converts the spin into lift. Apparently both contribute to the increase in range. (and the drawings I've seen show the boundry layer staying attached longer as I thought.) -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#23
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Why don't wings have dimples?
In article ,
"Peter Dohm" wrote: "Alan Baker" wrote in message ... In article . com, "Dancing Fingers" wrote: Hi all, I always wanted to build my own airplane but the time and money has eluded me. So I've decided to design and build my own recumbent trike, with farings. This brings me to my question, if golf balls have dimples, to help them sail further, why don't wings -- especially for STOL aircraft? Would putting dimples in my faring reduce my wind resistance? Just curious. Chris First of all, golf balls have dimples because in order to create lift they need to influence the air passing by them with the golf ball's spin. The dimples help to make the air slow down beneath the ball and speed up above it; creating downward flow. I believe that you have the effect exactly backward. The spin, which should only be significant using the more steeply pitched irons; slows the relative speed over the "top" of the ball and causes it to remain attached longer, No. It doesn't. Golf balls spin with a rotation such that the bottom is moving forward and the top is moving rearward. while the air flowing under the bottom breaks away more quickly, which would result in a slight net lift. It also explains why a "slice" curves as it does--which is why a smooth ball would have improved my game. :-( Wings produce that downward flow with their shape. Exactly. Peter |
#24
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Why don't wings have dimples?
On Wed, 14 Jun 2006 05:20:31 GMT, Alan Baker wrote:
I believe that you have the effect exactly backward. The spin, which should only be significant using the more steeply pitched irons; slows the relative speed over the "top" of the ball and causes it to remain attached longer, No. It doesn't. Golf balls spin with a rotation such that the bottom is moving forward and the top is moving rearward. Not the way I play... :-) Ron Wanttaja |
#25
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Why don't wings have dimples?
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message ... "Peter Dohm" wrote in message ... I've seen a video of that, but don't recall where. However, I believe that you have it backward--the flow detaches earlier (from the non-spinning golf ball) and reduces the drag. I am not quite sure how that might relate to wings and propellers; but I suspect that they (wings and props) are two radically different, and possibly opposite, phenomena. Peter Ok, now you've done it. You are going to make me look this up... http://www.fi.edu/wright/again/wings...r/golf-01.html description and a drawing... http://www.aerospaceweb.org/question...cs/q0215.shtml with a little math and some graphs http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html plots drag as a function of Reynolds number for a golf ball and a smooth sphere - a good starting pont if you want to dimple your nosegear strut to reduce drag - just figure you your own Reynolds number... That's enough. Didn't find the picture I was looking for. But I see references to both the reduction in wake and Magnus effect that converts the spin into lift. Apparently both contribute to the increase in range. (and the drawings I've seen show the boundry layer staying attached longer as I thought.) -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. It looks like I misremembered as well, since all of them show the flow remaining attached further around the dimpled ball. However, the explanation of top spin under "How a Golf Ball Produces Lift" in the first link does introduce a problem, since the result of Magnus Effect seems (intuitively) reversed from the separation issue. The author's description of the direction of lift is consistent with the description under "Hook and Slice" which I know (regrettably) to be absolutely true. So all of the articles agree on a couple of points, and appear to have obtained the same photo for publication. However the Magnus Effect, while well known to be true to every golfer (usually in a detrimental way) appears to be backward in some sense. For the moment, this appears to have moved from my Solved Problems List to my Unsolved Problems List. Peter |
#26
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Why don't wings have dimples?
"Ron Wanttaja" wrote in message
... On Wed, 14 Jun 2006 05:20:31 GMT, Alan Baker wrote: I believe that you have the effect exactly backward. The spin, which should only be significant using the more steeply pitched irons; slows the relative speed over the "top" of the ball and causes it to remain attached longer, No. It doesn't. Golf balls spin with a rotation such that the bottom is moving forward and the top is moving rearward. Not the way I play... :-) Ron Wanttaja Wait. That was my line! Peter |
#27
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Why don't wings have dimples?
Peter Dohm wrote:
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message ... "Peter Dohm" wrote in message . .. I've seen a video of that, but don't recall where. However, I believe that you have it backward--the flow detaches earlier (from the non-spinning golf ball) and reduces the drag. I am not quite sure how that might relate to wings and propellers; but I suspect that they (wings and props) are two radically different, and possibly opposite, phenomena. Peter Ok, now you've done it. You are going to make me look this up... http://www.fi.edu/wright/again/wings...r/golf-01.html description and a drawing... http://www.aerospaceweb.org/question...cs/q0215.shtml with a little math and some graphs http://turb.seas.ucla.edu/~jkim/sciam/0197moinbox3.html plots drag as a function of Reynolds number for a golf ball and a smooth sphere - a good starting pont if you want to dimple your nosegear strut to reduce drag - just figure you your own Reynolds number... That's enough. Didn't find the picture I was looking for. But I see references to both the reduction in wake and Magnus effect that converts the spin into lift. Apparently both contribute to the increase in range. (and the drawings I've seen show the boundry layer staying attached longer as I thought.) -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. It looks like I misremembered as well, since all of them show the flow remaining attached further around the dimpled ball. However, the explanation of top spin under "How a Golf Ball Produces Lift" in the first link does introduce a problem, since the result of Magnus Effect seems (intuitively) reversed from the separation issue. The author's description of the direction of lift is consistent with the description under "Hook and Slice" which I know (regrettably) to be absolutely true. So all of the articles agree on a couple of points, and appear to have obtained the same photo for publication. However the Magnus Effect, while well known to be true to every golfer (usually in a detrimental way) appears to be backward in some sense. For the moment, this appears to have moved from my Solved Problems List to my Unsolved Problems List. Peter Will forward your Unsolved Problem to Mary Shafer (NASA). Maybe the Lift Demons have a clue? |
#28
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Why don't wings have dimples?
Peter Dohm wrote:
"Ron Wanttaja" wrote in message ... On Wed, 14 Jun 2006 05:20:31 GMT, Alan Baker wrote: I believe that you have the effect exactly backward. The spin, which should only be significant using the more steeply pitched irons; slows the relative speed over the "top" of the ball and causes it to remain attached longer, No. It doesn't. Golf balls spin with a rotation such that the bottom is moving forward and the top is moving rearward. Not the way I play... :-) Ron Wanttaja Wait. That was my line! Peter Oh well. The net effect is the same... |
#29
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Why don't wings have dimples?
"Peter Dohm" wrote in message news "Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message ... http://www.fi.edu/wright/again/wings...r/golf-01.html description and a drawing... ... So all of the articles agree on a couple of points, and appear to have obtained the same photo for publication. However the Magnus Effect, while well known to be true to every golfer (usually in a detrimental way) appears to be backward in some sense. For the moment, this appears to have moved from my Solved Problems List to my Unsolved Problems List. Peter Dunno, looked OK to me. If the ball is flying across your screen from right to left think of an airfoil moving from right to left, low pressure on top, circulation has to be clockwise in this view to accelrate the flow across the top and decelerate it around the bottom - "1877, British scientist P.G. Tait learned that a ball, driven with a spin about a horizontal axis with the top of the ball coming toward the golfer produces a lifting force. This type of spin is know as a backspin." That would be clockwise in a view where the ball is moving from right to left... Note: Have you ever seen a drawing or wind tunnel picture where the object was traveling from left to right or the air was moving from right to left? How did we become so consistant? -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#30
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Why don't wings have dimples?
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message
news:HvednScQQ67J5A3ZnZ2dnUVZ_oGdnZ2d@wideopenwest .com... "Peter Dohm" wrote in message news "Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message ... http://www.fi.edu/wright/again/wings...r/golf-01.html description and a drawing... ... So all of the articles agree on a couple of points, and appear to have obtained the same photo for publication. However the Magnus Effect, while well known to be true to every golfer (usually in a detrimental way) appears to be backward in some sense. For the moment, this appears to have moved from my Solved Problems List to my Unsolved Problems List. Peter Dunno, looked OK to me. If the ball is flying across your screen from right to left think of an airfoil moving from right to left, low pressure on top, circulation has to be clockwise in this view to accelrate the flow across the top and decelerate it around the bottom - "1877, British scientist P.G. Tait learned that a ball, driven with a spin about a horizontal axis with the top of the ball coming toward the golfer produces a lifting force. This type of spin is know as a backspin." That would be clockwise in a view where the ball is moving from right to left... Note: Have you ever seen a drawing or wind tunnel picture where the object was traveling from left to right or the air was moving from right to left? How did we become so consistant? oops, didn't read far enough: "The dimples also help in the generation of lift. By keeping the flow attached, the dimples help promote an asymmetry of the flow in the wake. This asymmetry can be seen in Figure 5. In this figure, the smoke shows the flow pattern about a spinning golf ball. The flow is moving from left to right and the ball is spinning in the counter-clockwise direction. The wake is being deflected downwards. This downward deflection of the wake implies that a lifting force is being applied to the golf ball." This is inconsistant with my thinking and inconsistant with the top of the ball moving towards the golfer as described earlier on the page... -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
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