Beneficial Aerodynamic Modifications for your 8
12-19-2010, 02:58 PM
#28
Hopefully I will be selling my splitters very soon. I am just slow to work on it because when push comes to shove, people dont always want to fork out the money. If someone really wants one and is ready to spend the money, PM me and I will get working on it.
12-19-2010, 03:08 PM
#29
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Not sure what brand are out there man, but for any material to use to strap on a lip I would suggest Forged aluminum or Titanium. Anything would work fine as long as it's light and sturdy.
12-19-2010, 03:30 PM
#31
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I've never used the 3M DS tape. Could would better than brackets, I was always taught in college that an object being put on to a stable, fixed body should only be removed by tools and not possible to remove by hand for safety purposes only. You could get a Z bracket, but that would require you to put 2 holes in your CF trunk, which I don't think you would want to do.
12-19-2010, 07:49 PM
#33
Early on someone mentioned the European rear lip spoiler. Supposedly it is there to improve MPG. Any thoughts? My guess is more MPG is less drag and less drag is good, I am just not sure how it would work. EE here, no aero experience at all. If it does, this is a cheap upgrade that will pay for itself. Anyone got a picture of one?
Last edited by 04Green; 12-20-2010 at 11:08 AM.
12-20-2010, 12:12 PM
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Early on someone mentioned the European rear lip spoiler. Supposedly it is there to improve MPG. Any thoughts? My guess is more MPG is less drag and less drag is good, I am just not sure how it would work. EE here, no aero experience at all. If it does, this is a cheap upgrade that will pay for itself. Anyone got a picture of one?
12-20-2010, 12:49 PM
#36
A couple of points to consider.
First, assuming a "squishy" mounting point for an aerodynamic aid does not flex enough to change its function, whether it's mounted "soft" or "hard" doesn't matter in the amount of force transmitted to the chassis. A 180 lb driver transmits 180 lb of down force whether he's sitting on a soft seat or a hard one.
Second. Cd is a coefficient. That is, the drag force goes proportional to Fd = Cd x (equivalent flat plate area) x (velocity squared). At a given speed, a Miata (Cd=.38) likely has less overall drag than a RX8 (Cd=.31) because it's size is so much smaller. In the car-like regime (roughly the same Reynold's Number), the bigger the vehicle, the easier it is to get a low Cd.
Third. Downforce is a force. Forces require energy to power. The 8 has rather limited power. Even if one were going fast enough to generate significant downforce, it's gonna cost fuel and top speed. Most all normal cars, even with vestigal spoilers, generate lift on both ends of the car with increasing speed. This is pretty much a given considering the wing-like cross section cars present to the wind. But lift also requires energy to power! The best semi-achievable deal for an 8 is to eliminate lift and simultaneously eliminate the power loss it represents. (Mazda claims their breadbasket trunk spoiler drops the Cd from 0.31 to 0.30 - downforce no, killing lift, yes). To generate serious downforce without hugely increasing drag, one would have to get within an inch or so of the pavement (ground effects), which is not very practical.
Fourth. Polishing/waxing or any other surface treatments will have no measurable effect. The only such effects I've seen are on high-performance sailplanes which can achieve true laminar flow over much of the wing.
If you have access to test facilities (or wind tunnel), you might consider the following. Years ago, the magazine Sports Car Graphic fitted chassis potentiometers to measure the displacement of the body relative to its wheels. From the displacement, they could deduce the aerodynamic lift. While sortof expensive, it's not terribly difficult to do, even on the (smooth level) street. They also deduced Cd by measuring the flat-plate frontal area, then recording the coast down speed of the car when it was shifted into neutral. To do so, they had to make some assumptions regarding the mechanical drag. However, testing an individual car for specific aerodynamic improvements would be simpler since any change in say the 80-45 mph coastdown would be due to the modification.
Overall, I think a splitter as you describe would help, as will a modest breadbasket wing. In terms of drag, an RX-7 type nose like the one sold by Racing Beat may be a noticeable improvement. Why? the upper part of the RX-8 grill is not only fake, it's indented in such a way the air is trapped there. An alternative (which is there to a degree in the Series II) is a panel to make the useless part of the grill flush with the rest of the nose. You might also look at the Series II undertray which I hear was modified to reduce front lift when compared to the Series I. Hoods? I'd love to see someone tuft-test them. Generally, there's a high-pressure area at the base of the windshield (which is why the cabin air intake vents are located there). This could "block" any air from exiting the engine compartment through vents located too far rearward on the hood. There's probably an optimal location for hood vents, but I doubt if anyone has looked at the issue in detail. Simply opening up room within the engine bay behind the radiator will likely have a more positive benefit than random hood-venting.
First, assuming a "squishy" mounting point for an aerodynamic aid does not flex enough to change its function, whether it's mounted "soft" or "hard" doesn't matter in the amount of force transmitted to the chassis. A 180 lb driver transmits 180 lb of down force whether he's sitting on a soft seat or a hard one.
Second. Cd is a coefficient. That is, the drag force goes proportional to Fd = Cd x (equivalent flat plate area) x (velocity squared). At a given speed, a Miata (Cd=.38) likely has less overall drag than a RX8 (Cd=.31) because it's size is so much smaller. In the car-like regime (roughly the same Reynold's Number), the bigger the vehicle, the easier it is to get a low Cd.
Third. Downforce is a force. Forces require energy to power. The 8 has rather limited power. Even if one were going fast enough to generate significant downforce, it's gonna cost fuel and top speed. Most all normal cars, even with vestigal spoilers, generate lift on both ends of the car with increasing speed. This is pretty much a given considering the wing-like cross section cars present to the wind. But lift also requires energy to power! The best semi-achievable deal for an 8 is to eliminate lift and simultaneously eliminate the power loss it represents. (Mazda claims their breadbasket trunk spoiler drops the Cd from 0.31 to 0.30 - downforce no, killing lift, yes). To generate serious downforce without hugely increasing drag, one would have to get within an inch or so of the pavement (ground effects), which is not very practical.
Fourth. Polishing/waxing or any other surface treatments will have no measurable effect. The only such effects I've seen are on high-performance sailplanes which can achieve true laminar flow over much of the wing.
If you have access to test facilities (or wind tunnel), you might consider the following. Years ago, the magazine Sports Car Graphic fitted chassis potentiometers to measure the displacement of the body relative to its wheels. From the displacement, they could deduce the aerodynamic lift. While sortof expensive, it's not terribly difficult to do, even on the (smooth level) street. They also deduced Cd by measuring the flat-plate frontal area, then recording the coast down speed of the car when it was shifted into neutral. To do so, they had to make some assumptions regarding the mechanical drag. However, testing an individual car for specific aerodynamic improvements would be simpler since any change in say the 80-45 mph coastdown would be due to the modification.
Overall, I think a splitter as you describe would help, as will a modest breadbasket wing. In terms of drag, an RX-7 type nose like the one sold by Racing Beat may be a noticeable improvement. Why? the upper part of the RX-8 grill is not only fake, it's indented in such a way the air is trapped there. An alternative (which is there to a degree in the Series II) is a panel to make the useless part of the grill flush with the rest of the nose. You might also look at the Series II undertray which I hear was modified to reduce front lift when compared to the Series I. Hoods? I'd love to see someone tuft-test them. Generally, there's a high-pressure area at the base of the windshield (which is why the cabin air intake vents are located there). This could "block" any air from exiting the engine compartment through vents located too far rearward on the hood. There's probably an optimal location for hood vents, but I doubt if anyone has looked at the issue in detail. Simply opening up room within the engine bay behind the radiator will likely have a more positive benefit than random hood-venting.
Last edited by HiFlite999; 12-20-2010 at 12:52 PM.
12-20-2010, 01:26 PM
#37
Here's an an article about eyeball engineering done right from the good old days:
http://www.rotaryeng.net/Car-Life-all.pdf
and this about general chassis considerations wrt aero:
http://www.rotaryeng.net/SCG-articles.pdf
(Feel free to compare the general useless of present day car magazines in comparison to stuff like this).
The hosting site itself is poorly executed, but full of interesting things.
http://www.rotaryeng.net/Car-Life-all.pdf
and this about general chassis considerations wrt aero:
http://www.rotaryeng.net/SCG-articles.pdf
(Feel free to compare the general useless of present day car magazines in comparison to stuff like this).
The hosting site itself is poorly executed, but full of interesting things.
12-20-2010, 01:42 PM
#39
First, assuming a "squishy" mounting point for an aerodynamic aid does not flex enough to change its function, whether it's mounted "soft" or "hard" doesn't matter in the amount of force transmitted to the chassis. A 180 lb driver transmits 180 lb of down force whether he's sitting on a soft seat or a hard one.
Third. Downforce is a force. Forces require energy to power. The 8 has rather limited power. Even if one were going fast enough to generate significant downforce, it's gonna cost fuel and top speed. Most all normal cars, even with vestigal spoilers, generate lift on both ends of the car with increasing speed. This is pretty much a given considering the wing-like cross section cars present to the wind. But lift also requires energy to power! The best semi-achievable deal for an 8 is to eliminate lift and simultaneously eliminate the power loss it represents. (Mazda claims their breadbasket trunk spoiler drops the Cd from 0.31 to 0.30 - downforce no, killing lift, yes). To generate serious downforce without hugely increasing drag, one would have to get within an inch or so of the pavement (ground effects), which is not very practical.
For the street my splitter comes off and I switch from the GTC-200 wing to the mazdapseed wing. Not only does MPG improve, my ground clearance improve but my car doesn't stand out so much. I dont recommend anyone install a spitter or big wing for the street, there is just no functional point.
12-20-2010, 03:20 PM
#40
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Have a look at the custom splitter made for my FD by afgmoto1978
http://www.rx7club.com/showpost.php?...&postcount=107
http://www.rx7club.com/showpost.php?...&postcount=108
When used with a similar splitter and a JKL wing this car was very fast in autox. Well, it was fast after the ancient tires were replaced.
Currently we are working (by we I mean afgmoto1978
) on installing a dual element APR wing on this FD.
I would imagine something similar could be done for an RX-8.
http://www.rx7club.com/showpost.php?...&postcount=107
http://www.rx7club.com/showpost.php?...&postcount=108
When used with a similar splitter and a JKL wing this car was very fast in autox. Well, it was fast after the ancient tires were replaced.
Currently we are working (by we I mean afgmoto1978
) on installing a dual element APR wing on this FD.I would imagine something similar could be done for an RX-8.
12-20-2010, 04:36 PM
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This is a puzzling post....
I can't find a Bridge Aerodynamic Inc in Pittsburgh, nor a Masters in "Aerodynamic and Fluid Engineering" at Duke.
Some of the claims are also puzzling for someone of this education level:
1) "Also to note that CD varies as the square of speed is de/increased." - CD the simply the drag normalized by the dynamic pressure and the frontal area. The dynamic pressure and drag vary as the square of speed, but not the CD.
2) " Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little." - There's simply no mechanism for wind noise to be affected by dirt particles on the car, considering the boundary layer thickness (and probably the viscous sublayer) on the surface is much greater than any particle size.
3) "Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard." - This simply makes no sense to me.
4) "Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps." - What in the world is "slyde", and how does it affect steering and the heating of the front tires?
I want to believe, but....
I can't find a Bridge Aerodynamic Inc in Pittsburgh, nor a Masters in "Aerodynamic and Fluid Engineering" at Duke.
Some of the claims are also puzzling for someone of this education level:
1) "Also to note that CD varies as the square of speed is de/increased." - CD the simply the drag normalized by the dynamic pressure and the frontal area. The dynamic pressure and drag vary as the square of speed, but not the CD.
2) " Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little." - There's simply no mechanism for wind noise to be affected by dirt particles on the car, considering the boundary layer thickness (and probably the viscous sublayer) on the surface is much greater than any particle size.
3) "Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard." - This simply makes no sense to me.
4) "Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps." - What in the world is "slyde", and how does it affect steering and the heating of the front tires?
I want to believe, but....
What's up everyone? I'm new to this site since about a month ago when I got my '04 GT (Grand Touring) RX-8 and I absolutely love my car. I'm posting this thread to the concerns of the people who want to actually improve the handling/speed characteristics of their RX-8 through modifying the chassis and body. I'm a Aerodynamic Engineer for Bridge Aerodynamic Inc. located in Pittsburgh, PA. I graduated from Duke with a Master in Aerodynamic and Fluid Engineering. Enough of that, let's get this started.
First, if you have a warranty on your RX-8, you may want to check with Mazda if the modifications your'e about to do will not void the warranty. You guys probably know a lot more about the warranty disclaimer and guidelines more than I, I'm just trying to look out for all of you because I know how easy the dealer can screw you over.
Q: Can/will body kits increase the Aerodynamic Efficiency on my car?
A: Yes, but VERY VERY few. The CD (Co-efficient Drag) on our RX-8's is 0.31, which is OK. Usually depending on material of the body kit (Flex strength) and how wide it protrudes from the body itself (the wider, the more wind resistance) and how many (un)necessary holes it has will tell you if it's actually helping with your CD. If the body kit has a snug fit onto your body and is either made out of carbon fiber or Poly-Urethane and doesn't have too many holes, it COULD help the CD and downforce. If you guys want me to explain this part more in-depth, PM me please.
Q: That huge spoiler HAS to give me downforce, right?
A: Depends! If your car is RWD (which all of ours is) and the spoiler is made out of a sturdy but lightweight material, and isn't higher than 3/4 of the back window and is fixed onto the body of the car (which means NOT bolted down), chances are your'e going to get better CD and downforce. But, all of our RX-8's are bolt-on spoilers. Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard.
Q: Will lowering my car improve CD?
A: Yes, sort of. It WILL minimize lift at higher speeds, hence increasing downforce. Increasing the downforce pushes the car down onto the pavement/racetrack, allowing higher cornering speed. It will also improve the stability of your car at moderate to high speeds and reduces turbulence when behind an opponent at the track. Also to note that CD varies as the square of speed is de/increased.
Q: I just waxed my car, it'll cut that air like butter now won't it?
A: Not necessarily. Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little.
Q: Just strapped on a front splitter, will this do anything?
A: Sure will. This will make the most improvement to the aerodynamic characteristics on your RX-8. It will not only give you better downforce, CD, stability, but it will also curve the incoming air into your radiator and oil coolers. Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps.
That is just a simple guide to understanding a small amount of how aerodynamics work and a little modification tips. I could get way more in-depth (Relationship to velocity, Slipstream, Fluid dynamics through engine coolant jackets/oil motion, noise emission, ETC.) If you guys have any questions please PM me and i'll be sure to get back to you ASAP! Thanks for your time. I will post another fully in-depth thread with charts and graphs, as I will be taking my car into work and will do some research on it. I will be testing different body kits, lips, spoilers, width of different size rims/tires, and bolt-on chassisand/or body modifications. Have a nice day
First, if you have a warranty on your RX-8, you may want to check with Mazda if the modifications your'e about to do will not void the warranty. You guys probably know a lot more about the warranty disclaimer and guidelines more than I, I'm just trying to look out for all of you because I know how easy the dealer can screw you over.
Q: Can/will body kits increase the Aerodynamic Efficiency on my car?
A: Yes, but VERY VERY few. The CD (Co-efficient Drag) on our RX-8's is 0.31, which is OK. Usually depending on material of the body kit (Flex strength) and how wide it protrudes from the body itself (the wider, the more wind resistance) and how many (un)necessary holes it has will tell you if it's actually helping with your CD. If the body kit has a snug fit onto your body and is either made out of carbon fiber or Poly-Urethane and doesn't have too many holes, it COULD help the CD and downforce. If you guys want me to explain this part more in-depth, PM me please.
Q: That huge spoiler HAS to give me downforce, right?
A: Depends! If your car is RWD (which all of ours is) and the spoiler is made out of a sturdy but lightweight material, and isn't higher than 3/4 of the back window and is fixed onto the body of the car (which means NOT bolted down), chances are your'e going to get better CD and downforce. But, all of our RX-8's are bolt-on spoilers. Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard.
Q: Will lowering my car improve CD?
A: Yes, sort of. It WILL minimize lift at higher speeds, hence increasing downforce. Increasing the downforce pushes the car down onto the pavement/racetrack, allowing higher cornering speed. It will also improve the stability of your car at moderate to high speeds and reduces turbulence when behind an opponent at the track. Also to note that CD varies as the square of speed is de/increased.
Q: I just waxed my car, it'll cut that air like butter now won't it?
A: Not necessarily. Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little.
Q: Just strapped on a front splitter, will this do anything?
A: Sure will. This will make the most improvement to the aerodynamic characteristics on your RX-8. It will not only give you better downforce, CD, stability, but it will also curve the incoming air into your radiator and oil coolers. Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps.
That is just a simple guide to understanding a small amount of how aerodynamics work and a little modification tips. I could get way more in-depth (Relationship to velocity, Slipstream, Fluid dynamics through engine coolant jackets/oil motion, noise emission, ETC.) If you guys have any questions please PM me and i'll be sure to get back to you ASAP! Thanks for your time. I will post another fully in-depth thread with charts and graphs, as I will be taking my car into work and will do some research on it. I will be testing different body kits, lips, spoilers, width of different size rims/tires, and bolt-on chassisand/or body modifications. Have a nice day
12-20-2010, 05:50 PM
#43
12-20-2010, 06:04 PM
#44
This is a puzzling post....
I can't find a Bridge Aerodynamic Inc in Pittsburgh, nor a Masters in "Aerodynamic and Fluid Engineering" at Duke.
Some of the claims are also puzzling for someone of this education level:
1) "Also to note that CD varies as the square of speed is de/increased." - CD the simply the drag normalized by the dynamic pressure and the frontal area. The dynamic pressure and drag vary as the square of speed, but not the CD.
2) " Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little." - There's simply no mechanism for wind noise to be affected by dirt particles on the car, considering the boundary layer thickness (and probably the viscous sublayer) on the surface is much greater than any particle size.
3) "Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard." - This simply makes no sense to me.
4) "Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps." - What in the world is "slyde", and how does it affect steering and the heating of the front tires?
I want to believe, but....
I can't find a Bridge Aerodynamic Inc in Pittsburgh, nor a Masters in "Aerodynamic and Fluid Engineering" at Duke.
Some of the claims are also puzzling for someone of this education level:
1) "Also to note that CD varies as the square of speed is de/increased." - CD the simply the drag normalized by the dynamic pressure and the frontal area. The dynamic pressure and drag vary as the square of speed, but not the CD.
2) " Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little." - There's simply no mechanism for wind noise to be affected by dirt particles on the car, considering the boundary layer thickness (and probably the viscous sublayer) on the surface is much greater than any particle size.
3) "Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard." - This simply makes no sense to me.
4) "Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps." - What in the world is "slyde", and how does it affect steering and the heating of the front tires?
I want to believe, but....
However,
(2) The dirt or surface finish has minimal effect on cars, but not at all for the reason you give. Air at normal temps and pressures behaves much like a liquid than a gas. Air molecules at these densities tend to "stick" together which creates "fluid" behavior. At about one millionth of atmospheric pressure it's fully a gas and the rules of aero/fluid dynamics are suspended and particle like behavior comes into play.
(3) What he's getting at is a well-known effect for RWD cars. A car can be perfectly neutral handling at normal slow speeds. This means in a corner that the buildup of slip loads occurs evenly F/R. However when the engine is putting out significant power just to drive the rear wheels, the driven tires are already significantly loaded. In a turn, they will now slip more than the fronts which don't have that preload. Result = oversteer. Adding weight aerodynamically to the rear is a common way to combat the problem. Unloading that weight suddenly can indeed result in an instant spin.
12-21-2010, 07:40 AM
#45
Hmn... dont 'quote' me on this but I think that a well designed lip spoiler does reduce drag to an extent. As a car moves through the air it creates a low pressure area behind it. This low pressure area results in a large amount of 'pressure drag'. The spoiler works in a similar way to the way dimples work on a golf ball, converting the otherwise smooth, laminar flow just off the skin of your car's trunklid to turbulent, but attached flow. Disrupting the flow of the boundary layer does result in an increase of parasitic drag, but decreases the OVERALL drag because the decrease in pressure drag is so great...
12-21-2010, 09:19 AM
#46
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I wrote a rebuttal that was far too long, and was punished by the internet gods as rx8club signed me off.
Ill keep this one short. You are wrong. This is why:
Size has nothing to do with the "stickyness" of the air. Skin drag is what you are refering to, it exists, but its overall effect on the golfball (or a car) is much less than the drag force of the golfball due to pressure drag. If size were a factor, aerodynamicists wouldnt make models of airplanes/boats/cars etc. because thier results would not be accurate. By the way, olympic bicyclist (many of whom are larger than golfballs) wear dimpled clothes and ride bicycles with dimpled wheels and frames...
Relative hairyness" of flies/birds has nothing to do with the Reynolds number...
the reason airplanes dont have hair like flies or feathers like birds probably has more to do with evolution than anything else...Additionally the extremly complex flight analysis of things with articulated wings has no place in this discussion.
But i digress...
I was trying to simplify by making a comparison to something common as most members arent aerospace engineers. Dimples in golf ***** reduce the pressure behind a golfball in a similar manner to how a spoiler reduces the pressure behind a car.
Check this out http://www.aerospaceweb.org/question...cs/q0215.shtml
Ill keep this one short. You are wrong. This is why:
Size has nothing to do with the "stickyness" of the air. Skin drag is what you are refering to, it exists, but its overall effect on the golfball (or a car) is much less than the drag force of the golfball due to pressure drag. If size were a factor, aerodynamicists wouldnt make models of airplanes/boats/cars etc. because thier results would not be accurate. By the way, olympic bicyclist (many of whom are larger than golfballs) wear dimpled clothes and ride bicycles with dimpled wheels and frames...
Relative hairyness" of flies/birds has nothing to do with the Reynolds number...
the reason airplanes dont have hair like flies or feathers like birds probably has more to do with evolution than anything else...Additionally the extremly complex flight analysis of things with articulated wings has no place in this discussion.
But i digress...
I was trying to simplify by making a comparison to something common as most members arent aerospace engineers. Dimples in golf ***** reduce the pressure behind a golfball in a similar manner to how a spoiler reduces the pressure behind a car.
Check this out http://www.aerospaceweb.org/question...cs/q0215.shtml
12-21-2010, 02:42 PM
#47
Gee "you are wrong" is a substantial argument. Agreed that Reynolds number is not related to viscosity. What it is to a degree a "statement" as to the relative importance of that stickiness. Size is absolutely a factor in interpreting data from a wind tunnel - and is exactly and precisely why WW1 vintage airplanes flew so badly; they had been scaled up from models naively. In reverse, any RC-flyer who does an exact scale down of a full size plane is well aware of this. What's important in overall dynamics varies with the characteristic length of the system which is a parameter in calculating Rn. Flies and bumblebees swim through air more than they fly through it. As stated in a Wikipedia article:
"Additionally, John Maynard Smith a noted biologist with a strong background in aeronautics, has pointed out that bumblebees would not be expected to sustain flight, as they would need to generate too much power given their tiny wing area. However, in aerodynamics experiments with other insects he found that viscosity at the scale of small insects meant that even their small wings can move a very large volume of air relative to the size, and this reduces the power required to sustain flight by an order of magnitude.[30]"
I do stand corrected on the hairy part - that aspect has been shown not to be correct wrt flight.
The mechanism of drag reduction of cars and golf ***** is fundamentally different though it can be considered a similar result.
Aero Drag is generally though of as being the sum of Induced (from lifting or downforce) + Parasitic. Parasitic drag is the sum of Form (aka Pressure), Skin, and Interference drag. On the scales of cars, the dominant by far is Form, at least in terms of something that can be affected in a meaningful way. While considered kindaof independent, they aren't really and the golf ball is a prime example - using a transition layer effect to redirect airflow vs. basically using a "brick" to block the overall air path in the case of a wing/spoiler.
"Additionally, John Maynard Smith a noted biologist with a strong background in aeronautics, has pointed out that bumblebees would not be expected to sustain flight, as they would need to generate too much power given their tiny wing area. However, in aerodynamics experiments with other insects he found that viscosity at the scale of small insects meant that even their small wings can move a very large volume of air relative to the size, and this reduces the power required to sustain flight by an order of magnitude.[30]"
I do stand corrected on the hairy part - that aspect has been shown not to be correct wrt flight.
The mechanism of drag reduction of cars and golf ***** is fundamentally different though it can be considered a similar result.
Aero Drag is generally though of as being the sum of Induced (from lifting or downforce) + Parasitic. Parasitic drag is the sum of Form (aka Pressure), Skin, and Interference drag. On the scales of cars, the dominant by far is Form, at least in terms of something that can be affected in a meaningful way. While considered kindaof independent, they aren't really and the golf ball is a prime example - using a transition layer effect to redirect airflow vs. basically using a "brick" to block the overall air path in the case of a wing/spoiler.
