Beneficial Aerodynamic Modifications for your 8
12-21-2010, 07:58 PM
#51
Power!!
Yeah ...
However,
(2) 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.
However,
(2) 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.
I think you are talking about incompressibility above not liquid vs. gas. Air and most gases are fluids and act like them regardless of state. the math doesn't change if it's all considered incompressible.
The real differentiator that we need to rule out is whether or not we're in a compressible regime. Which is determined by Mach number using (temperature and velocity) more often than pressure as it's more convenient to measure. In this case we are very subsonic M<<0.3 (unless it starts getting really hot) and can assume incompressible and use the same formulas for liquids and gases in this case.
Calculating mach number:http://en.wikipedia.org/wiki/Mach_number
Calculating speed of sound in air for mach number without requiring pressure:http://en.wikipedia.org/wiki/Speed_of_sound
12-22-2010, 02:47 AM
#55
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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.
The Reynolds number is used to determine how similar a scaled down model is to a full sized one. Shouldnt be an issue here as Jkrupa is running a full sized test. The Characteristic Length that you mention is chosen just as a convention...if you remember correctly, the Reynold's number is unitless...
The drag reduction in golf ***** and cars is fundamentally similar in that they turbulate the boundary layer causing a reduction in pressure drag. The physical mechanism to cause this turbulation (dimples vs a lip to "trip the flow) is different.
We've already established that wings and spoilers dont work the same. A wing works using attached laminar (smooth) flow, a spoiler creates turbulant but still attached flow. Wings dont 'like' turbulant flow, thats why you'll see wings on racing cars mounted so high (to avoid interference with the airflow of the body of the car).
I dont wish this thread to devolve into a pissing match like many often do, so i'll refrain from adding fuel to the fire. Jkrupa, when is testing going to begin?
12-22-2010, 04:01 AM
#56
12-22-2010, 07:46 AM
#60
Momentum Keeps Me Going
Here you go guys....it's all dimpled and ready to be put to YOUR OWN testing...since they already have the results....
www.fastSkinz.com
"FastSkinz, Inc. has created a drag reducing technology for vehicles through a patent pending, vehicle wrap material, called MPG-Plus™. MPG-Plus™ significantly reduces a vehicle's drag by altering the distribution of air pressure surrounding the vehicle. The improved fuel economy of a vehicle wrapped in MPG-Plus™ as compared to the identical vehicle not wrapped is 18%-20% for traditional internal combustion engine vehicles (ICEVs) and 20%-25% for gasoline hybrid vehicles (HOVs), plug hybrid vehicles (PHOVs) and battery electric vehicles (BEVs). The base film for MPG-Plus™ is considered by the industry experts to be one of the best vehicle wrap materials on the market. The base film can be converted within hours into MPG-Plus™. MPG-Plus is designed to work with all types of vehicles and is applied like a vehicle wrap. "
www.fastSkinz.com
"FastSkinz, Inc. has created a drag reducing technology for vehicles through a patent pending, vehicle wrap material, called MPG-Plus™. MPG-Plus™ significantly reduces a vehicle's drag by altering the distribution of air pressure surrounding the vehicle. The improved fuel economy of a vehicle wrapped in MPG-Plus™ as compared to the identical vehicle not wrapped is 18%-20% for traditional internal combustion engine vehicles (ICEVs) and 20%-25% for gasoline hybrid vehicles (HOVs), plug hybrid vehicles (PHOVs) and battery electric vehicles (BEVs). The base film for MPG-Plus™ is considered by the industry experts to be one of the best vehicle wrap materials on the market. The base film can be converted within hours into MPG-Plus™. MPG-Plus is designed to work with all types of vehicles and is applied like a vehicle wrap. "
12-22-2010, 07:59 AM
#61
Momentum Keeps Me Going
...or not...lol...apparently Discovery Channel and uh.. Popular Mechanics got opposite results.
http://www.greencarreports.com/blog/...r-fuel-economy
http://www.greencarreports.com/blog/...r-fuel-economy
12-22-2010, 09:13 AM
#63
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"Aerodynamic and fluid engineering" is not an available concentration in either the Masters of Science or Masters of Engineering program at Duke. See here:
http://www.mems.duke.edu/MS-PhD-program
http://www.mems.duke.edu/mems_meng
http://www.mems.duke.edu/MS-PhD-program
http://www.mems.duke.edu/mems_meng
12-23-2010, 01:23 PM
#65
"Aerodynamic and fluid engineering" is not an available concentration in either the Masters of Science or Masters of Engineering program at Duke. See here:
http://www.mems.duke.edu/MS-PhD-program
http://www.mems.duke.edu/mems_meng
http://www.mems.duke.edu/MS-PhD-program
http://www.mems.duke.edu/mems_meng
Such questions arise however, when one's introduction to the forum is in the general form of 'I am a certified expert and here to answer all your questions'. With some exceptions, the true experts on this and most other forums I've come across are almost the opposite (thinking Paul @ Mazmart, and Eric Meyer, for example). If one plays with technology in a serious manner long enough, one realizes how easy it is to get fooled along the way by good ideas that just don't pan out. It adds a certain humility (which perhaps only come with age, if it comes at all). Discussions with such people are a delight. One feature of them is when questions/dissents come up, it's not "you're wrong" it's "I think this idea is wrong, I tried it, and this is what happened." Otherwise, it does end up a pissing match.
I would rather discuss the ideas than the people. Picking on the OP's "qualifications" is the latter. However, what ever those qualifications are or are not, does not dissuade me from questioning his statements when I find some of them questionable. What I, and most others here would welcome much more than announcements of 'this is what I'm gonna do' are statements of 'this is what I've done'. In other words, data, along with the methodolgy used to obtain it. (I even suggested a couple of possible measurement methods).
12-23-2010, 01:53 PM
#66
Size Scaling
For those interested in ideas, here's a properly worded article of what I was imperfectly trying to get at:
http://en.wikipedia.org/wiki/Dynamic_similarity
Physical laws generally come with their own range of applicability. Lessons learned from one scale applied ad hoc to another scale can be quite inaccurate without a lot of fudging. In the given example, a very simple form is used (submarine), and mathmatical post processing of the data can give accurate results. The fact that auto makers and race car teams build or rent expensive time in full-sized, moving roadway wind tunnels hints that data from small models can't be accurately scaled up to full-sized vehicles.
http://en.wikipedia.org/wiki/Dynamic_similarity
Physical laws generally come with their own range of applicability. Lessons learned from one scale applied ad hoc to another scale can be quite inaccurate without a lot of fudging. In the given example, a very simple form is used (submarine), and mathmatical post processing of the data can give accurate results. The fact that auto makers and race car teams build or rent expensive time in full-sized, moving roadway wind tunnels hints that data from small models can't be accurately scaled up to full-sized vehicles.
12-24-2010, 05:46 AM
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Wikipedia is a good source to get an idea of what is going on. If you're interested in getting more technical, "Introduction to Flight" by john anderson is a good read.
12-26-2010, 08:40 PM
#70
I understand that the S1 has more lift at the nose than the S2; but I am not certain how much lift the S1 and S2 exhibit in their natural form at the front and rear axles, relative to one another.
I have been contemplating using the S2 rear shocks on my S1 in order to slightly increase clearance at the rear because of the beating my car takes over the maniacal speed bumps (at speeds lower than 2mph, if my car is laden with luggage, myself, my wife, and my daughter, the car scrapes ahead of the rear wheels and I am getting tired of fixing the undercoating) at the condo where I live; but it occurs to me that this will also slightly increase my angle of attack as well.
12-26-2010, 11:04 PM
#71
My guess is that the lowered hood put less air under the car. Someone else mentioned a similar improvement with a similar change. But, there are people a lot smarter than I am in this thread who can say for sure.
As for the shocks, not sure if S2 shocks would help. Springs would. You could test by getting the little rubber spring helpers from an auto parts store or putting a spacer under the spring. The little rubber things can go in with just a jack. The spacers are harder. I had this problem with an old mustang/capri. I used air-shocks to adjust the ride height when I needed it. I have never seen a performance air shock though, not sure I would recommend here. It was nice to hit a switch on the dash to raise the rear end when I filled the car with people or crap though.
As for the shocks, not sure if S2 shocks would help. Springs would. You could test by getting the little rubber spring helpers from an auto parts store or putting a spacer under the spring. The little rubber things can go in with just a jack. The spacers are harder. I had this problem with an old mustang/capri. I used air-shocks to adjust the ride height when I needed it. I have never seen a performance air shock though, not sure I would recommend here. It was nice to hit a switch on the dash to raise the rear end when I filled the car with people or crap though.
12-27-2010, 05:32 AM
#72
My guess is that the lowered hood put less air under the car. Someone else mentioned a similar improvement with a similar change. But, there are people a lot smarter than I am in this thread who can say for sure.
As for the shocks, not sure if S2 shocks would help. Springs would. You could test by getting the little rubber spring helpers from an auto parts store or putting a spacer under the spring. The little rubber things can go in with just a jack. The spacers are harder. I had this problem with an old mustang/capri. I used air-shocks to adjust the ride height when I needed it. I have never seen a performance air shock though, not sure I would recommend here. It was nice to hit a switch on the dash to raise the rear end when I filled the car with people or crap though.
As for the shocks, not sure if S2 shocks would help. Springs would. You could test by getting the little rubber spring helpers from an auto parts store or putting a spacer under the spring. The little rubber things can go in with just a jack. The spacers are harder. I had this problem with an old mustang/capri. I used air-shocks to adjust the ride height when I needed it. I have never seen a performance air shock though, not sure I would recommend here. It was nice to hit a switch on the dash to raise the rear end when I filled the car with people or crap though.
