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Why don't wings have dimples 2
On Oct 23, 5:22*am, "Anyolmouse" wrote:
"Jim Logajan" wrote in message .. . Dancing Fingers wrote: The thing of it is that the car they used, as I remember, also had a very aerodynamic shape and it still helped. Disagree - it was not "aerodynamic" on the downstream side. Do you recall when they showed the wind tunnel and water tank tests? Do you recall seeing that there was an area behind the car with turbulent air? Well if the car had been elongated so that the body tapered off such that it filled that area of turbulence, then I suspect they would have gotten different results. Check out the following site: http://www.grc.nasa.gov/WWW/K-12/rocket/shaped.html Notice that the prism has a slightly lower drag coefficient than the flat plate. As that web site states "Comparing the flat plate and the prism, and the sphere and the bullet, we see that the downstream shape can be modified to reduce drag." I wonder if they would have gotten the same results by attaching a foil to direct some of the air down from the trunk to make the turbulent area smaller. Back in the '70s an uncle of mine attached one to the rear of his station wagon to keep the rear window cleaner. He swore it helped his gas mileage as well. -- We have met the enemy and he is us-- Pogo Anyolmouse- Hide quoted text - - Show quoted text - Yeah, in the ?50s? the 'Kamm back' was tried on several makes. Hope that "kamm" is the correct spelling. Harry K |
#2
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Why don't wings have dimples 2
On Oct 23, 5:22*am, "Anyolmouse" wrote:
"Jim Logajan" wrote in message .. . Dancing Fingers wrote: The thing of it is that the car they used, as I remember, also had a very aerodynamic shape and it still helped. Disagree - it was not "aerodynamic" on the downstream side. Do you recall when they showed the wind tunnel and water tank tests? Do you recall seeing that there was an area behind the car with turbulent air? Well if the car had been elongated so that the body tapered off such that it filled that area of turbulence, then I suspect they would have gotten different results. Check out the following site: http://www.grc.nasa.gov/WWW/K-12/rocket/shaped.html Notice that the prism has a slightly lower drag coefficient than the flat plate. As that web site states "Comparing the flat plate and the prism, and the sphere and the bullet, we see that the downstream shape can be modified to reduce drag." I wonder if they would have gotten the same results by attaching a foil to direct some of the air down from the trunk to make the turbulent area smaller. Back in the '70s an uncle of mine attached one to the rear of his station wagon to keep the rear window cleaner. He swore it helped his gas mileage as well. -- We have met the enemy and he is us-- Pogo Anyolmouse- Hide quoted text - - Show quoted text - Ooops that was not a foil, it was a 'chopped' off back. And I think it was in the 60s. Harry K |
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Why don't wings have dimples 2
"Dancing Fingers" wrote in message
... Last night the Mythbusters put about a 2 inch layer of clay a a sedan and drove it at 65 mph and recorded their mileage. They put dimples in the clay, like a golf ball, and repeated the same test and got 11% better mileage. This again begs the question why don't wings have dimples, especially for STOL type aircrat, where you still have laminar flow? Heck, hexagonal dimples might reflect radar better for all I know? For conversation Chris Because wings aren't shaped like golf balls or cars. The dimples in a golf ball help reduce drag by making the boundry layer turbulant which helps it flow just a little further around the back side and reduce the area behind the ball where the air flow is seperated (compared to a laminar boundry layer). Also, the dimples work only across a limited range of Reynolds numbers (less than 3*10^5). The airflow around a wing isn't generally seperated (except near a stall) so it just ain't a gonna help. I would question the results they got with the car as well, but that's just me. -- 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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Why don't wings have dimples 2
Delve into the aerodynamics of blunt bodies, as automotive
aerodynamics is called. Actually, dimples on the wings might actually help in certain conditions. So would tapering the thickness of the skins(!). But both of these are impractical from a manufacturing stand point. Might check into "vortex generators" for more insight into current approaches as to getting the boundary layer energized. |
#5
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Why don't wings have dimples 2
"Dancing Fingers" wrote in message
... Last night the Mythbusters put about a 2 inch layer of clay a a sedan and drove it at 65 mph and recorded their mileage. They put dimples in the clay, like a golf ball, and repeated the same test and got 11% better mileage. This again begs the question why don't wings have dimples, especially for STOL type aircrat, where you still have laminar flow? Heck, hexagonal dimples might reflect radar better for all I know? For conversation Chris Something along this line has been discussed here from time to time, and we did not all agree at that time. However, even ignoring the possibiliyt of measuring errors in the Mythbusters tests, an automobile does not need to produce lift in order to operate--and may work best if all lift can be eliminated. The most classic case of dimpling, of which I am aware, is a golf ball. There, the dimples provide a relatively clean breakaway of the airflow--so that, even thought the cross section of the wake appears larger, the total energy level of the wake is reduced. There have also been some potentially interesting experiments involving propellers, although I have never personally seen the sort of conclusive and complete data that a really well designed experiment should be able to provide. For example, there was an initially interesting article in Experimenter several years ago--but the experiment was not sufficiently well planned, and the aircraft was not sufficiently instrumented, to provide really conclusive findings. (Actually, changes in the relationship of engine RPM to airspeed without accurate monitoring of manifold pressure and fuel flow can be extremely misleading--but that is a subject for nearly endless future threads.) So, the bottom line is that the results of dimpled wings could be interesting--and there has been some successful experimentation of gliders. But seemingly small changes in the installation be better or worse, might have a softer or more abrupt stall, etc. Peter |
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