olie05 Posted October 23, 2009 Share Posted October 23, 2009 Beat me to it!! Are you a cyclist too? Im a mountain biker, but I follow all disciplines. Im a bicycle mechanic I'm a roadie... been doing the txbra races for almost a year now. Quote Link to comment Share on other sites More sharing options...
260DET Posted October 23, 2009 Share Posted October 23, 2009 Swim suits too, shark skin inspired and all that sort of stuff. On the golf ball thing, its more the shape, cars are not that shape at all. Aero can be done for cars using other more suitable devices. Quote Link to comment Share on other sites More sharing options...
garvice Posted October 23, 2009 Share Posted October 23, 2009 It would also make cleaning a pain in the but, not to mention trying to repair a damaged panel. It is hard enough getting metal straight, yet alone getting it straight and then having to re-dimple the surface. That would be a body shops worst nightmare. EDIT: not to mention Just reread my post and realised that I did mention Quote Link to comment Share on other sites More sharing options...
Valmont Posted October 23, 2009 Share Posted October 23, 2009 anyone find anything on the ratio of sizes of the dimple and the dimpled object? Quote Link to comment Share on other sites More sharing options...
Warren Posted October 23, 2009 Share Posted October 23, 2009 Not a new idea... Look up a "Corbin Sparrow"...although it only had the dimples on the fenders, the same principle is applied. Look at the rear of the front fenders in these pictures. Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 23, 2009 Share Posted October 23, 2009 Did anyone watch MythBusters on Discovery last night?! They covered a car in clay and made dimples on the car like a golf ball.. and there was a 11% increase i believe in fuel economy... Aircraft and Formula One and Nascar teams have all played with vortex generators... but why not shaping the whole body like a golf ball?! I mean the mythbusters test showed there was a dramatic increase in the reduction of drag?! From what I saw in the water tank the dimples didn't seem to be any different than vortex generators on the roof line and back of the car. I'd be willing to bet you'd see a similar reduction using them in strategic places. Lexus already does this underneath their cars so at least one manufacture is on board. With regards to racing cars if it worked and was allowed by the rules it would probably be done. And usually drag is traded for downforce, which makes a much larger difference in lap times. Quote Link to comment Share on other sites More sharing options...
Bartman Posted October 23, 2009 Share Posted October 23, 2009 I was pretty amazed as well by the Mythbusters results. I believe that not only was there a significant increase in miles per gallon, but the clay they put on the car added significant weight as well. They even took the clay that was in the dimples and put it in a bucket that was placed on the back seat! I don't know the total weight, but that car looked really weighted down. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 23, 2009 Share Posted October 23, 2009 With regards to racing cars if it worked and was allowed by the rules it would probably be done. And usually drag is traded for downforce, which makes a much larger difference in lap times. Absolutely. F1 cars and high downforce cars might have a drag coefficient of 1+ compared to an aerodynamic road car's .29 or the Z's .46. They trade the drag for downforce because going faster in the turns and in the braking zones is worth the penalty on the straights. I think as mentioned the golf ball is dimpled all over because it has no front, and a good aerodynamically designed car should not have to have the vortex generators all over. If you put them in strategic spots you should be able to get the same effect without parking your car in a hailstorm. Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 23, 2009 Share Posted October 23, 2009 I was pretty amazed as well by the Mythbusters results. I believe that not only was there a significant increase in miles per gallon, but the clay they put on the car added significant weight as well. They even took the clay that was in the dimples and put it in a bucket that was placed on the back seat! I don't know the total weight, but that car looked really weighted down. But the way the tested made weight much less of a factor. In a semi-steady state test the only factor would be an increase in rolling resistance. And from the results it appears that's a very minor factor. Now if the test would have been accelerating up to a certain speed then the 800 pounds of clay would have made a much larger difference. All that said I was pretty shocked with the result too. I'm still willing to bet you could have used a lot less dimples and gotten the same results. But it wouldn't have looked so cool. I wonder how many people are out there trying to figure out how to dimple their cars Cary Quote Link to comment Share on other sites More sharing options...
johnc Posted October 23, 2009 Share Posted October 23, 2009 I wonder how many people are out there trying to figure out how to dimple their cars Quote Link to comment Share on other sites More sharing options...
MAG58 Posted October 23, 2009 Share Posted October 23, 2009 Sailplanes and airplanes can use "zig-zag tape" along the span of the wing. It has to be placed in the right spot on the airfoil to move the separation point further back on the wing. My R/C Pylon racer gained 4mph when the monokote got a few wrinkles in the fuselage. Quote Link to comment Share on other sites More sharing options...
Chaparral2f Posted October 23, 2009 Share Posted October 23, 2009 Just park your Z out in a hailstorm. I lived in Oklahoma for a couple of years and had a Toyota Celica that went through a hail storm. Didn't improve fuel milage, and knocked the crap out of the trade in value. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted October 24, 2009 Share Posted October 24, 2009 If you start out with a poorer shaped car to begin with(aka Ford 4 door passenger car) you can see some improvement. If you started with an optimized shaped car...no. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 24, 2009 Administrators Share Posted October 24, 2009 If you start out with a poorer shaped car to begin with(aka Ford 4 door passenger car) you can see some improvement. If you started with an optimized shaped car...no. I agree 100%, as you stated, only if the car could be optimally shaped, i.e. tear drop. Due to packaging and safety constraints of production car design, the optimum shape of a tear-drop/air foil with the sharp tail is going to be tough. Due to the blunt or rounded-blunt rear end of production cars, (as compared to the sharp point of the tail of a tear drop), turbulence, i.e. drag induced from the loss of boundary layer, therefore separation of air flow across the surface and the result of drag, even as depicted on the modern, relatively speaking aero Ford 4 door. That is where the dimpling comes in to play. I’ll elaborate in the next post. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 24, 2009 Administrators Share Posted October 24, 2009 (edited) Taking the Myth busters project to the next level, and has been mentioned already in this thread regarding vortex generators, if the dimpling was applied only to the location just ahead of where the boundary layer starts to separate on the car, (roof line ahead of the rear window and back of the trunk, just like that funky Corbin Sparrow pictured above), in an effort to retain that boundary layer across the transition of the body shape for as long as possible, reducing the quantity of turbulent air flow/drag, leaving the rest of the car, smooth, should realize an even greater increase in MPG from reduced drag. Those dimples across the front, roof, and hood of the car in the Myth busters testing, (where the boundary layer of air was intact and in no need of surface mods to maintain boundary layer flow), does not need the dimpling, as such the dimples themselves in those regions are inducing a slight amount of drag. As Cary mentioned above, Vortex generators are performing the same job, using different technology and being applied only the region where separation takes place. Remember, nothing is free. This technology doesn’t 100% fix the issue, just prolongs the separation to further across the surface at the expense of drag. If we could get the boundary layer to remain intact similarly with out the dimples or vortex generators, drag would be further reduced again! Turbulence; Courtesy of AirCraftSpruce.com Here are some Vortex generators pics to help illustrate what is taking place; Courtesy of aerospaceweb.org Courtesy of microaero.com Courtesy of automotive.com Edited October 24, 2009 by BRAAP Typo's Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted October 24, 2009 Share Posted October 24, 2009 Yep. If they had just added something (like vg's) then it would have also kept the turbulence behind the sedan to a minimum. The profile and skin can almost be irrelevant at 65mph as long as you address the airflow in a rational fashion. Teardrop is also irrelevant as seen in any jet fighter, the exhaust itself controls the flow aft of the aircraft, not the profile of a pair of ROUND 38" exhaust tubes on the aft end. They kind of missed it at the end when they said the "theory" was plausible while dismissing the fact that no one seriously used it over all the more elegant designs that are in use that control airflow aft of a moving solid in a liquid. Great show otherwise... Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted October 24, 2009 Administrators Share Posted October 24, 2009 (edited) Yep. If they had just added something (like vg's) then it would have also kept the turbulence behind the sedan to a minimum. The profile and skin can almost be irrelevant at 65mph as long as you address the airflow in a rational fashion. ... Agreed. … Teardrop is also irrelevant as seen in any jet fighter, the exhaust itself controls the flow aft of the aircraft, not the profile of a pair of ROUND 38" exhaust tubes on the aft end. … Fighter jet aerodynamics have no relevance in this discussion due to the fact their design takes into account flight beyond the speed of sound, (cars just don’t go there), as such the design criteria of the shape and exterior of the air craft changes, and changes drastically with sharp points to “control” and “aim” the shock waves that are produced during trans and super sonic flight. In short, you are correct that the tear drop does not apply to fighter jets, but you are also incorrect in calling the tear drop shape irrelevant as applied to the discussion of this thread, cars traveling sub sonic. The exhaust of the fighter controlling air flow behind the aircraft, in a scenario that could be related to this discussion, only happens on such aircraft that the tail or extreme eppenage of the aircraft IS the exhaust, such as the Mig 15/17/21, F86/100 Sabre/Super Sabre, F-16, etc, or some custom Honduh's we see driving down the road, using huge by large exhaust tips mimicking the fighter jets allowing the air flow of 63 HP from a single 5” diameter exhaust tip, (or twin 12" in this picture), to reduce the turbulence found aft of the vehicle… Courtesy of urbandictionary.com They kind of missed it at the end when they said the "theory" was plausible while dismissing the fact that no one seriously used it over all the more elegant designs that are in use that control airflow aft of a moving solid in a liquid. Great show otherwise... The show is definitely fun to watch and I also would've like to see them take their testing much much further with the resources they had available. Edited October 24, 2009 by BRAAP Quote Link to comment Share on other sites More sharing options...
strotter Posted October 24, 2009 Share Posted October 24, 2009 Could this kind of effect be applied to an exhaust system? I.E., could it be possible to reduce exhaust backpressure without increasing pipe diameter? Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted October 24, 2009 Share Posted October 24, 2009 In short, you are correct that the tear drop does not apply to fighter jets, but you are also incorrect in calling the tear drop shape irrelevant as applied to the discussion of this thread, cars traveling sub sonic. Sorry, irrelevant in that I was thinking that passenger cars cannot have "pointy" rear ends for a variety of reasons. Therefore they can't be "tear dropped" so the best solution for a non-tear dropped passenger car is to control the flow (as you said) with something like VG's to fake the flow to work as if the shape was tear dropped. That's a much more elegant solution than dimpling the surfaces. I can't find it right now but there was a aero study on passenger cars that approximated what they called a "ghost tail" instead of an elongated real tail to control turbulence.That gave the cars a "virtual " tear drop.... Quote Link to comment Share on other sites More sharing options...
kiwi303 Posted October 24, 2009 Share Posted October 24, 2009 Could this kind of effect be applied to an exhaust system? I.E., could it be possible to reduce exhaust backpressure without increasing pipe diameter? You could try stuffing one of those inlet air turbulence generators down your collector, but I think the muffler would screw things up. Quote Link to comment Share on other sites More sharing options...
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