Drag Coefficient wrt speed
I remember reading somewhere that drag coefficient depends on the speed at which it is measured.
And this makes sense - for example, see how airplanes are designed. The higher the speed, the less deviation away from a flat angle is allowed. Although it's indeed possible to conserve fuel by slowing down, this seems to me to be a quick fix. Better to optimize the highways we have and reduce the time it takes to get from place to place and also design around that rather than plan for congestion. https://www.speedbikebgl.de/pix/sbc04_002.jpg To this end it would be nice to see Cd/ speed curves from the auto manufacturers. I doubt that the econobubbles are going to be that good above 50mph, whereas something very low and sporty could likely have a best fuel economy at 80 mph. It's something to think about. |
the problem is not really aerodynamics. The problem is speed. Aerodynamics isn't going to help a lot for fuel economy when the car is driving 100mph. Right now freeways are getting built for 100mph speeds because in the future that is what's going to happen. We need more gears. 4 speeds and 5 speeds are not cutting it anymore.
Toyota is already working on 7 and 8 speed automatics because as the speed increases we need to increase fuel economy with it. The manufacturers are more concerned about looks than aerodynamics. It's looks that sell the car, not aerodynamics. |
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anyway the bottom line is that there is no need to try to change the subject of this thread. aerodynamics are necisary and it is very to consider the fact that a cars coefficient of drag is in fact a speed dependant variable. good food for thought, try chewing. to mira: kudos on the intreguing topic. it makes me feel that the number one concern in aerodynamics at any speed is reducing the frontal area. |
Mercedes is shipping their ML (or whatev) SUVs with 7 speeds now, WOAH, watch out 5speed autos...
That's all I'm clever enough to add. |
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Really, the greatest length that would be realistic in a car is the length of a Ford Expedition, roughly 5.2m. I don't see a workable solution to extend that during travel, although perhaps it is possible if the car was constructed properly. There would have to be an extensible shell, coupled with indicators to do it properly. It would also require a portion of the sides to be windowless to pull it off correctly. I've done a very rough plan view to give an idea. Think of it unfolding much like one of those Mercedes convertables do, at speed like the whale tail of a Porsche does. https://i5.tinypic.com/143g6t4.jpg Such a contraption could make the effective length of a car longer, perhaps bringing the 5.2m of the Expedition up to perhaps a maximum highway 7m. The other constraint is that it needs to be wide enough at the base to enable adequate cornering. So, I suppose we eventually get something that looks more and more like an elongated (and probably taller) horseshoe crab: https://www.udel.edu/PR/UDaily/2004/hcrab404lg.jpg Essentially this shape is where we are heading. After the wheels are covered, the underside is covered, the grille is basically just a tiny horizontal mouth, the wheels are as narrow and tall as possible with LRR tires, this should ultimately be our destination. https://i5.tinypic.com/143hrf4.jpg I suppose the only thing is that in most of the world, the econobubble shape will still predominate because older cars cannot easily be legislated off the road. I think that one way the government can effectively legislatively provide incentives is to target mpg AND emissions. Although now there are increasing market forces to bias us in this direction anyway. More if Bush (or his handlers) decide to invade Iran. He might ironically be the best president for the environment the US has ever produced, for all the wrong reasons! |
Another thing we will need to see is a more reclined, sportscar seating type of arrangement. Which should not be a problem because a longer car will enable a lower drag coefficient.
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i understand more gears is good but thats not what we are talking about.
remember we are not talking about acceleration. we are talking about a maintained speed. the only thing that would matter is the one gear ratio. dont tell me i wouldnt understand a concept. i understand both physics and statistics as well as the topic of this thread. back on topic: ive heard that its important to reduce the surface area as well as the frontal area. if a shape become too drawn out, it will not help much for the cd so its really difficult to strike the right compromise... man i wish i had a wind tunnel... |
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But seriously get a blower fan and setup a small tunnel. |
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