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#31
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Dimples On Model Aircraft Could Greatly Extend Range
On Nov 7, 9:35*am, "Ken S. Tucker" wrote:
On Nov 6, 1:44 pm, wrote: On Thu, 6 Nov 2008 01:54:20 -0800 (PST), in sci.engr.mech "Ken S. Tucker" wrote: On Nov 5, 2:40 pm, wrote: On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker" Not quite. *As far as riblets go, it is my understanding that the height and spacing of the riblets is specified according to the boundary thickness such as to prevent the growth of turbulent bursts which causes an exchange of low momentum fluid near the surface with higher momentum fluid from above. This momentum exchange being a loss/drag mechanism. The other point of importance is the orientation of the riblets along streamlines. Yes, that's seems clear...but NOT simple :-). That's a lot different that your original point that it was not well understood. Well I think we're nit-picking sematics, my quote, "My understanding is the theory is NOT _well_ understood, but is evolving, along with applications, by experimental feed-back, aka trial & error, (I'm using SM board). " Note the word "theory" Also after the original riblet research was performed similarities to shark scales/skin were observed. http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&... Yes! Thanks for those links. Those papers are experimental results and testing, AFAIK, there is NO generally accepted theory of the "riblets effect", though it appears to be evolving. (If you have a ref to a General Theory of Riblets, I'd would appreciate a link). I'm guessing: At a molecular level the riblets control the turbulent interfacing between fluid and surface and inhibit the integrated formation of macroscopic turbulence, such as Eddy's. That micro control is certainly a quantum relation between molecules in the fluid and the interacting solid surface, whereby the micro turbulences are quantized. Setting aside sharks skin, we may want to have a look at penguin swimming, that also has very low resistance. Regards Ken Riblets aren't the only way; hair and feathers have a similar effect. "With Robert Brodkey, professor of chemical engineering, Koeltzsch has now turned his attention away from sharks, to penguins and seals. He hopes to determine whether hair makes these aquatic mammals more hydrodynamic. Initial studies by other scientists have shown that natural and artificial fibers can reduce drag by amounts that vary from 1.5 to 50 percent. Continued research could show whether hair would improve the design of boat hulls and even airplanes, Koeltzsch said. "Wouldn’t it be something if, in the future, airplanes had hairy surfaces?" he asked. " |
#32
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Dimples On Model Aircraft Could Greatly Extend Range
"Bret Cahill" wrote in message ... Have they tried dimples on radio controlled aircraft? The size and speed could designed around the magic Reynolds number = 100,000 where the coefficient of drag drops precipitously. Dimpling could vastly extent the range of large and slow as well as small and fast radio controlled aircraft. A competitive cyclist is the right size and speed for Nre = 100,000 so dimple suits can work. Same for golf balls. Nre = 100,000 for widebodies going 0.5 knots so dimples won't work except on the runway. From fluid mechanics the Reynolds number is the ratio of inertial forces/viscous forces. N re = Diameter X velocity X density of fluid/viscosity of fluid. Bret Cahill Do her dimples make her faster? http://underscorebleach.net/content/.../p2/arched.jpg -- Gregory Hall |
#33
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Dimples On Model Aircraft Could Greatly Extend Range
Hi Eunometic and guys.
On Nov 7, 2:59 am, Eunometic wrote: On Nov 7, 9:35 am, "Ken S. Tucker" wrote: On Nov 6, 1:44 pm, wrote: On Thu, 6 Nov 2008 01:54:20 -0800 (PST), in sci.engr.mech "Ken S. Tucker" wrote: On Nov 5, 2:40 pm, wrote: On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker" Not quite. As far as riblets go, it is my understanding that the height and spacing of the riblets is specified according to the boundary thickness such as to prevent the growth of turbulent bursts which causes an exchange of low momentum fluid near the surface with higher momentum fluid from above. This momentum exchange being a loss/drag mechanism. The other point of importance is the orientation of the riblets along streamlines. Yes, that's seems clear...but NOT simple :-). That's a lot different that your original point that it was not well understood. Well I think we're nit-picking sematics, my quote, "My understanding is the theory is NOT _well_ understood, but is evolving, along with applications, by experimental feed-back, aka trial & error, (I'm using SM board). " Note the word "theory" Also after the original riblet research was performed similarities to shark scales/skin were observed. http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&... Yes! Thanks for those links. Those papers are experimental results and testing, AFAIK, there is NO generally accepted theory of the "riblets effect", though it appears to be evolving. (If you have a ref to a General Theory of Riblets, I'd would appreciate a link). I'm guessing: At a molecular level the riblets control the turbulent interfacing between fluid and surface and inhibit the integrated formation of macroscopic turbulence, such as Eddy's. That micro control is certainly a quantum relation between molecules in the fluid and the interacting solid surface, whereby the micro turbulences are quantized. Setting aside sharks skin, we may want to have a look at penguin swimming, that also has very low resistance. Regards Ken Riblets aren't the only way; hair and feathers have a similar effect. "With Robert Brodkey, professor of chemical engineering, Koeltzsch has now turned his attention away from sharks, to penguins and seals. He hopes to determine whether hair makes these aquatic mammals more hydrodynamic. Initial studies by other scientists have shown that natural and artificial fibers can reduce drag by amounts that vary from 1.5 to 50 percent. Continued research could show whether hair would improve the design of boat hulls and even airplanes, Koeltzsch said. "Wouldn’t it be something if, in the future, airplanes had hairy surfaces?" he asked. " I did read the link you posted previously thanks. I thought about tennis balls (hairy balls :-) too. Regards Ken |
#34
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Dimples On Model Aircraft Could Greatly Extend Range
On Nov 7, 3:59*am, Eunometic wrote:
On Nov 7, 9:35*am, "Ken S. Tucker" wrote: On Nov 6, 1:44 pm, wrote: On Thu, 6 Nov 2008 01:54:20 -0800 (PST), in sci.engr.mech "Ken S. Tucker" wrote: On Nov 5, 2:40 pm, wrote: On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker" Not quite. *As far as riblets go, it is my understanding that the height and spacing of the riblets is specified according to the boundary thickness such as to prevent the growth of turbulent bursts which causes an exchange of low momentum fluid near the surface with higher momentum fluid from above. This momentum exchange being a loss/drag mechanism. The other point of importance is the orientation of the riblets along streamlines. Yes, that's seems clear...but NOT simple :-). That's a lot different that your original point that it was not well understood. Well I think we're nit-picking sematics, my quote, "My understanding is the theory is NOT _well_ understood, but is evolving, along with applications, by experimental feed-back, aka trial & error, (I'm using SM board). " Note the word "theory" Also after the original riblet research was performed similarities to shark scales/skin were observed. http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&... Yes! Thanks for those links. Those papers are experimental results and testing, AFAIK, there is NO generally accepted theory of the "riblets effect", though it appears to be evolving. (If you have a ref to a General Theory of Riblets, I'd would appreciate a link). I'm guessing: At a molecular level the riblets control the turbulent interfacing between fluid and surface and inhibit the integrated formation of macroscopic turbulence, such as Eddy's. That micro control is certainly a quantum relation between molecules in the fluid and the interacting solid surface, whereby the micro turbulences are quantized. Setting aside sharks skin, we may want to have a look at penguin swimming, that also has very low resistance. Regards Ken Riblets aren't the only way; hair and feathers have a similar effect. "With Robert Brodkey, professor of chemical engineering, Koeltzsch has now turned his attention away from sharks, to penguins and seals. He hopes to determine whether hair makes these aquatic mammals more hydrodynamic. Initial studies by other scientists have shown that natural and artificial fibers can reduce drag by amounts that vary from 1.5 to 50 percent. Continued research could show whether hair would improve the design of boat hulls and even airplanes, Koeltzsch said. "Wouldn’t it be something if, in the future, airplanes had hairy surfaces?" he asked. " None of this is new. When I was into waterskiing way back in the '80s the best slalom skis had varied textures along the bottom. Toward the rear the surface was just a little rough, like 1000 grit sandpaper, which reduced drag on the water. Nearer the front, the surface was much smoother so that the skier, just by flattening the ski on the water, could slow down quickly. I've noticed that when we paint an airplane with the really shiny smooth urethane paints, it seems to lose a little cruise speed. Dan |
#35
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Dimples On Model Aircraft Could Greatly Extend Range
wrote in message ... On Nov 7, 3:59 am, Eunometic wrote: On Nov 7, 9:35 am, "Ken S. Tucker" wrote: On Nov 6, 1:44 pm, wrote: On Thu, 6 Nov 2008 01:54:20 -0800 (PST), in sci.engr.mech "Ken S. Tucker" wrote: On Nov 5, 2:40 pm, wrote: On Wed, 5 Nov 2008 13:59:27 -0800 (PST), in sci.engr.mech "Ken S. Tucker" Not quite. As far as riblets go, it is my understanding that the height and spacing of the riblets is specified according to the boundary thickness such as to prevent the growth of turbulent bursts which causes an exchange of low momentum fluid near the surface with higher momentum fluid from above. This momentum exchange being a loss/drag mechanism. The other point of importance is the orientation of the riblets along streamlines. Yes, that's seems clear...but NOT simple :-). That's a lot different that your original point that it was not well understood. Well I think we're nit-picking sematics, my quote, "My understanding is the theory is NOT _well_ understood, but is evolving, along with applications, by experimental feed-back, aka trial & error, (I'm using SM board). " Note the word "theory" Also after the original riblet research was performed similarities to shark scales/skin were observed. http://ntrs.larc.nasa.gov/search.jsp...de%20matchall&... Yes! Thanks for those links. Those papers are experimental results and testing, AFAIK, there is NO generally accepted theory of the "riblets effect", though it appears to be evolving. (If you have a ref to a General Theory of Riblets, I'd would appreciate a link). I'm guessing: At a molecular level the riblets control the turbulent interfacing between fluid and surface and inhibit the integrated formation of macroscopic turbulence, such as Eddy's. That micro control is certainly a quantum relation between molecules in the fluid and the interacting solid surface, whereby the micro turbulences are quantized. Setting aside sharks skin, we may want to have a look at penguin swimming, that also has very low resistance. Regards Ken Riblets aren't the only way; hair and feathers have a similar effect. "With Robert Brodkey, professor of chemical engineering, Koeltzsch has now turned his attention away from sharks, to penguins and seals. He hopes to determine whether hair makes these aquatic mammals more hydrodynamic. Initial studies by other scientists have shown that natural and artificial fibers can reduce drag by amounts that vary from 1.5 to 50 percent. Continued research could show whether hair would improve the design of boat hulls and even airplanes, Koeltzsch said. "Wouldn’t it be something if, in the future, airplanes had hairy surfaces?" he asked. " | None of this is new. When I was into waterskiing way back in | the '80s the best slalom skis had varied textures along the bottom. | Toward the rear the surface was just a little rough, like 1000 grit | sandpaper, which reduced drag on the water. Nearer the front, the | surface was much smoother so that the skier, just by flattening the | ski on the water, could slow down quickly. | I've noticed that when we paint an airplane with the really | shiny smooth urethane paints, it seems to lose a little cruise speed. Depending upon the size of the aircraft paint can add a considerable weight burden. However, when the paint is really smooth it can drag along with it an increasingly thicker layer of turbulent air building toward the aft end of the aircraft. Dragging this thick turbulent boundary layer causes increased drag which seems counter-intuitive to smoothness. This is why various small surface patterns (seems to me somebody should try fractals) often decrease drag - they decrease the extent of the turbulent boundary layer thus the drag caused by it. -- Gregory Hall |
#36
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Dimples On Model Aircraft Could Greatly Extend Range
Dear Gregor Hall:
"Gregory Hall" wrote in message ... Depending upon the size of the aircraft paint can add a considerable weight burden. The external tank of the space shuttle used to be painted. They stopped for exaclty this reason. However, when the paint is really smooth it can .... [increase] ... drag along with it an increasingly thicker layer of turbulent air building toward the aft end of the aircraft. .... better to say that it allows for earlier boundary layer separation, essentially increasing the cross sectional area of the shape. Dragging this thick turbulent boundary layer causes increased drag which seems counter-intuitive to smoothness. It sure does. This is why various small surface patterns (seems to me somebody should try fractals) often decrease drag - they decrease the extent of the turbulent boundary layer thus the drag caused by it. NASA had an aircraft where they sucked air into the upper surface of the wing, to try and create a "laminar" boundary layer. I think it took more power than they got extra-lift / reduced-drag. David A. Smith |
#37
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Dimples On Model Aircraft Could Greatly Extend Range
"N:dlzc D:aol T:com (dlzc)" wrote in message ... Dear Gregor Hall: "Gregory Hall" wrote in message ... Depending upon the size of the aircraft paint can add a considerable weight burden. The external tank of the space shuttle used to be painted. They stopped for exaclty this reason. However, when the paint is really smooth it can ... [increase] ... drag along with it an increasingly thicker layer of turbulent air building toward the aft end of the aircraft. ... better to say that it allows for earlier boundary layer separation, essentially increasing the cross sectional area of the shape. Dragging this thick turbulent boundary layer causes increased drag which seems counter-intuitive to smoothness. It sure does. This is why various small surface patterns (seems to me somebody should try fractals) often decrease drag - they decrease the extent of the turbulent boundary layer thus the drag caused by it. NASA had an aircraft where they sucked air into the upper surface of the wing, to try and create a "laminar" boundary layer. I think it took more power than they got extra-lift / reduced-drag. David A. Smith Probably reduced lift as well. Seems to me sucking air into the upper surface of the wing would degrade the low pressure caused by the Bernoulli effect because it would tend to slow down the sped-up air traveling across the top surface of the wing. http://www.av8n.com/how/htm/airfoils.html -- Gregory Hall |
#38
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Dimples On Model Aircraft Could Greatly Extend Range
"N:dlzc D:aol T:com (dlzc)" wrote NASA had an aircraft where they sucked air into the upper surface of the wing, to try and create a "laminar" boundary layer. I think it took more power than they got extra-lift / reduced-drag. I was reading about that one, just a few days ago. It said one of the largest problems was keeping the vent holes open, from bugs and stuff, and rain changing the laminar flow. -- Jim in NC |
#39
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Dimples On Model Aircraft Could Greatly Extend Range
"Gregory Hall" wrote in message ... snip | I've noticed that when we paint an airplane with the really | shiny smooth urethane paints, it seems to lose a little cruise speed. Depending upon the size of the aircraft paint can add a considerable weight burden. However, when the paint is really smooth it can drag along with it an increasingly thicker layer of turbulent air building toward the aft end of the aircraft. Dragging this thick turbulent boundary layer causes increased drag which seems counter-intuitive to smoothness. This is why various small surface patterns (seems to me somebody should try fractals) often decrease drag - they decrease the extent of the turbulent boundary layer thus the drag caused by it. -- Gregory Hall During WWII they decided to repaint the Spitfire with a flat matt finish paint so it would be harder to see at night. It worked, they were harder to see at night. They lost 20mph because of the increased drag of the matt finish paint. If you noticed a loss in cruise speed with a slick paint job, I would suspect your data collection procedures. Paint can add considerable weight to the aircraft. What in the world makes you think a smooth surface causes the thickness of the boundary layer to increase? Have you been mislead by the installation of Vortex Generators to stir up the boundary layer? Highflyer Highflight Aviation Services Pinckneyville Airport ( PJY ) |
#40
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Dimples On Model Aircraft Could Greatly Extend Range
"Gregory Hall" wrote in message ... | | "Bret Cahill" wrote in message | ... | Have they tried dimples on radio controlled aircraft? The size and | speed could designed around the magic Reynolds number = 100,000 where | the coefficient of drag drops precipitously. | | Dimpling could vastly extent the range of large and slow as well as | small and fast radio controlled aircraft. | | A competitive cyclist is the right size and speed for Nre = 100,000 so | dimple suits can work. Same for golf balls. | | Nre = 100,000 for widebodies going 0.5 knots so dimples won't work | except on the runway. | | From fluid mechanics the Reynolds number is the ratio of inertial | forces/viscous forces. | | N re = Diameter X velocity X density of fluid/viscosity of fluid. | | | Bret Cahill | | | | Do her dimples make her faster? | | http://underscorebleach.net/content/.../p2/arched.jpg | No, I think it is more likely her dimples would make you faster. |
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