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How to Think About Car Aerodynamics: A Very, Very Basic Overview

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The study of aerodynamics is complicated. If anyone tries to tell you otherwise, run the other direction—it’s a sure sign they don’t know what they’re talking about.   Over the last two years especially, my thinking about aerodynamics and appreciation of its complexity has changed dramatically—a result of my going back to school to get another bachelor’s degree, this time in aerospace engineering where a good working knowledge of airflows is required and education in not just general fluid mechanics but also aircraft aerodynamic design forms a core part of the technical curriculum. I'm in the midst of my last semester now and to clarify my thinking at this point I decided to put some things in writing in the hopes they might help someone else as well as myself, specifically focused on car aerodynamics. A word of warning: I've tried to minimize the amount of math below, but some mathematical relations are unavoidable if you want to build an understanding of fluid flows. If anyth...
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Modeling and Measuring the Efficiency of Your Car

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If you read automotive blogs, news sites, press releases from manufacturers, or mainstream news outlets when gas prices go up, you have undoubtedly seen the word "efficiency" thrown around. This is usually brought up when a manufacturer wants to tout a new engine with high thermal efficiency—e.g. Nissan’s variable-displacement engine a few years back, or Toyota's current "Dynamic Force" hybrid engines—or when people want to argue the merits of battery electric vehicles (BEV) versus internal combustion engine vehicles (ICEV), or when gas prices shoot up.   But what do we mean when we talk about "efficiency"? What is thermal efficiency, and why is it important? Are there other ways to characterize efficiency in cars that may be more useful? Can you measure the efficiency of your own car? And finally, is efficiency  different from economy ? This XL1 was reported to get more than 100  MPG  on the highway (the car was never US-certified and has no EPA ratin...
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Measuring and Improving Cooling System Performance – Part 7: Overall Performance

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Now that we have modeled cooling system performance, used math to figure out what's going on, measured a bunch of parameters to determine what it's doing in real life, and built a physical model that gave insight into what's happening under the hood, we can move on to making it better . Here's where it gets fun; you don't have to be satisfied with your car's cooling system as is. Do you need greater cooling capacity because you track your car in Phoenix in the summer? Do you want less cooling drag and can sacrifice some cooling capacity because you compete at the Green Grand Prix in New York in the cool of early spring? Do you want to reduce drag while increasing cooling capacity just a little? Do you want to rig up an actuator or system to vary outlet area so you can adjust cooling capacity and drag on the fly? Any of those, and infinitely more, are possible. You don't have to fall into the trap of thinking your car is as perfect as it can be from the ...
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