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#1
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Why don't wings have dimples 2
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 |
#2
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Why don't wings have dimples 2
Dancing Fingers wrote:
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? The Mythbusters tested an automobile that wasn't aerodynamically shaped at the tail end. They showed wind tunnel flow lines that indicated the reduction in drag was due to keeping the flow separating a tiny bit farther downstream. A wing, unlike most autos, is already shaped so that the flow separates as far down stream as reasonably possible. Since dimpling causes extra friction, at some point the gain from delaying flow separation equals and then exceeds the loss due to the extra dimpling friction. (There are vortex generators that do something similar to dimpling for STOL wings. Basic idea is to help keep flow from separating as far down the wing as possible at high angles of attack.) |
#3
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Why don't wings have dimples 2
The thing of it is that the car they used, as I remember, also had a
very aerodynamic shape and it still helped. |
#4
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Why don't wings have dimples 2
Dancing Fingers schreef:
The thing of it is that the car they used, as I remember, also had a very aerodynamic shape and it still helped. Hm. Define "very aerodynamic"? Perhaps "more aerodynamic than most cars" which would still be far from the average aeroplane? |
#5
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Why don't wings have dimples 2
On Oct 22, 12:38*pm, jan olieslagers
wrote: Dancing Fingers schreef: The thing of it is that the car they used, as I remember, also had a very aerodynamic shape and it still helped. Hm. Define "very aerodynamic"? Perhaps "more aerodynamic than most cars" * which would still be far from the average aeroplane? I recall a salesman trying to sell a bunch of hail damaged airplanes by saying they went faster because the dents produced a "golf ball effect". I don't think he got many buyers. Aerodynamisists have been trying to create "surface treatments" to improve laminar flow for a century. So far, the mirror smooth surfaces of sailplanes are best. There is a guy, a Dr. Sinha, (http://sinhatech.com/) claiming to have something called a "deturbulator" which is a sort of flexible tape stuck on wing surfaces. If it works, and survives the rigors of actual flight operations, it might be a big deal. I wouldn't hold my breath. |
#6
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Why don't wings have dimples 2
"bildan" wrote in message ... Aerodynamisists have been trying to create "surface treatments" to improve laminar flow for a century. So far, the mirror smooth surfaces of sailplanes are best. There is a guy, a Dr. Sinha, (http://sinhatech.com/) claiming to have something called a "deturbulator" which is a sort of flexible tape stuck on wing surfaces. If it works, and survives the rigors of actual flight operations, it might be a big deal. I wouldn't hold my breath. Actually turbulator tape is fairly common stuff on sailplanes In comes in a zig-zag pattern or with dimples. Scroll halfway down this page to see the stuff: http://www.wingsandwheels.com/page29.htm Google "sailplane turbulator tape" for more info. Vaughn |
#7
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Why don't wings have dimples 2
On Oct 22, 11:35*am, 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. That may be so. But a "very aerodynamic" car is like a lightweight brick or a comfortable electric chair. It's all relative. Thanks, Bob K. |
#8
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Why don't wings have dimples 2
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." |
#9
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Why don't wings have dimples 2
"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 |
#10
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Why don't wings have dimples 2
I'm just wondering if any aero student, for their senior or masters
project, ever built a model with dimples and put it in a wind tunnel. Remember the Mythbusters didn't expect this results based on the dirty car which got worst mileage. This would suggest that a deliberately designed airfoil, with certain embedded geometric shapes, could effect drag under certain conditions. Chris |
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