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ChazInMT · 09-01-2011, 01:51 AM

I have an “Aero” idea, coming at it from a perspective of the air itself and what it is trying to do. My main idea is that the air molecules we drive through on, let's for ease of understanding say, a calm day, pretty much just want to be where they are. Not unlike a bunch of guys standing around. The particular air molecule we are interested in is 16” off the ground and it is the one which is going to go over the top of the car, dead center, we shall name this guy Alan. Let’s have the car going 45mph or so, as Alan rises up the hood, and windscreen of the car, he is being forced up against a bunch of other guys, that aren’t too particularly thrilled to move up either, and as such, are pushing back on Alan. At the moment Alan is on top of the car, he is seeing the greatest push back from the guys above him. If he at this point is just dropped, in the case of a 0% aft body template, than he would just drop back down, trying to get to the point he was before the car came along, and he would not be able to push on the back side of the car at all, all the energy that went into raising Alan up high, would just be wasted as he drops into the abyss created by the passing car. A Scion Xd has this characteristic.

If the car is shaped right, then Alan will be able to slide down along the back of the car and push it forward a bit as he goes, picture a wheel on the end of a spring pushing down on a sloped surface. The energy put into raising Alan up would now be used to help push the car forward.

Since Alan has mass, and also is rubbing up against a bunch of other guys creating friction, he is not able to move too fast in the downward direction, so his ability to accelerate, and, maintain pressure on the surface below him has limits. As long as the shape below Alan is gradual, he will help to push the car forward as he tries to get back the his 16” high place in the world all the while being pushed by the guys above him. Cue the VW XL1.

So, simplistically looking at it, all Alan does is move up and down as the car goes by. To him he ends up where he started. So here is where the leap of logic takes place…..we look at flow as being a horizontal motion, which, relative to the car, it is. But what does Alan the air molecule see? Up & down, that’s it. So looking at it from this perspective, attached flow according to Alan, is being able to get back to where you started by riding down the back surface of the car moving under you while keeping pressure on its surface. If the shape changes too fast, Alan loses contact with the surface, and can no longer push on it, so his “spring energy” is not returned to it.

I liken this to when you squeeze a fish and it shoots out of you hand. If pressure is maintained as it is builds in at the proper pace, it will help to propel the car forward.

I hope this make sense. It sort of unifies what we are trying to accomplish by looking at the movement of air not from the perspective of the car, but by the air itself. In roofing, you make a better roof by trying to think like the water drop. I think in aerodynamics, it would help us to think in terms of the air molecules movement instead of the ocean of air rushing over the skins of our cars. Where does Alan want to go? What forces can he impart? What forces are acting upon him?

So to conclude, when thought of from the perspective of stationary “Air Drops”, Alan et all, the air primarily moves up and down. (Obviously it swirls about a bit and moves forward some, but really I doubt any air molecule is displaced by more than 50-70 feet) The learning point here is to look at this from the real perspective of the air as we drive through it, not a wind tunnel with the air passing across the car. The shape of our cars determines whether the air helps to push the car along as it moves through this stationary air, or, lets the air loose contact and therefore, waste the energy put into it to move it out of the way. Aerodynamics in our case, optimizing the drag coefficient, is trying to reclaim the energy we put into the air when we push it out of the way to move through it.

I could go on about the implications of this idea, for quite some time. I thought this to be a good intro.

So, Duh? Or am I missing something? Is this a basic fact known for centuries that I've come to on my own? I never seem to be the first one to think of something. I've never seen air discussed from this perspective, we're always debating what it looks like as it flows in primarily the horizontal direction.

09-01-2011, 01:51 AM	#1 (permalink)
ChazInMT Aero Deshi Join Date: Jan 2010 Location: Vero Beach, FL Posts: 1,065 MagMetalCivic - '04 Honda Civic Sedan EX Last 3: 34.25 mpg (US) Thanks: 430 Thanked 669 Times in 358 Posts	Up & Down Aerodynamics, Another Way To Look It. Perhaps? I have an “Aero” idea, coming at it from a perspective of the air itself and what it is trying to do. My main idea is that the air molecules we drive through on, let's for ease of understanding say, a calm day, pretty much just want to be where they are. Not unlike a bunch of guys standing around. The particular air molecule we are interested in is 16” off the ground and it is the one which is going to go over the top of the car, dead center, we shall name this guy Alan. Let’s have the car going 45mph or so, as Alan rises up the hood, and windscreen of the car, he is being forced up against a bunch of other guys, that aren’t too particularly thrilled to move up either, and as such, are pushing back on Alan. At the moment Alan is on top of the car, he is seeing the greatest push back from the guys above him. If he at this point is just dropped, in the case of a 0% aft body template, than he would just drop back down, trying to get to the point he was before the car came along, and he would not be able to push on the back side of the car at all, all the energy that went into raising Alan up high, would just be wasted as he drops into the abyss created by the passing car. A Scion Xd has this characteristic. If the car is shaped right, then Alan will be able to slide down along the back of the car and push it forward a bit as he goes, picture a wheel on the end of a spring pushing down on a sloped surface. The energy put into raising Alan up would now be used to help push the car forward. Since Alan has mass, and also is rubbing up against a bunch of other guys creating friction, he is not able to move too fast in the downward direction, so his ability to accelerate, and, maintain pressure on the surface below him has limits. As long as the shape below Alan is gradual, he will help to push the car forward as he tries to get back the his 16” high place in the world all the while being pushed by the guys above him. Cue the VW XL1. So, simplistically looking at it, all Alan does is move up and down as the car goes by. To him he ends up where he started. So here is where the leap of logic takes place…..we look at flow as being a horizontal motion, which, relative to the car, it is. But what does Alan the air molecule see? Up & down, that’s it. So looking at it from this perspective, attached flow according to Alan, is being able to get back to where you started by riding down the back surface of the car moving under you while keeping pressure on its surface. If the shape changes too fast, Alan loses contact with the surface, and can no longer push on it, so his “spring energy” is not returned to it. I liken this to when you squeeze a fish and it shoots out of you hand. If pressure is maintained as it is builds in at the proper pace, it will help to propel the car forward. I hope this make sense. It sort of unifies what we are trying to accomplish by looking at the movement of air not from the perspective of the car, but by the air itself. In roofing, you make a better roof by trying to think like the water drop. I think in aerodynamics, it would help us to think in terms of the air molecules movement instead of the ocean of air rushing over the skins of our cars. Where does Alan want to go? What forces can he impart? What forces are acting upon him? So to conclude, when thought of from the perspective of stationary “Air Drops”, Alan et all, the air primarily moves up and down. (Obviously it swirls about a bit and moves forward some, but really I doubt any air molecule is displaced by more than 50-70 feet) The learning point here is to look at this from the real perspective of the air as we drive through it, not a wind tunnel with the air passing across the car. The shape of our cars determines whether the air helps to push the car along as it moves through this stationary air, or, lets the air loose contact and therefore, waste the energy put into it to move it out of the way. Aerodynamics in our case, optimizing the drag coefficient, is trying to reclaim the energy we put into the air when we push it out of the way to move through it. I could go on about the implications of this idea, for quite some time. I thought this to be a good intro. So, Duh? Or am I missing something? Is this a basic fact known for centuries that I've come to on my own? I never seem to be the first one to think of something. I've never seen air discussed from this perspective, we're always debating what it looks like as it flows in primarily the horizontal direction.