Amateur Aerodynamics

In my first two posts on testing directional stability, I used first a cellphone with angle measure and then a Scangauge reporting steering angle from my car’s OBD system to try and measure changes in its stability. That worked okay but I had no way of logging data to verify that what I thought I saw on the gauge reflected a real change.   Not anymore. I bought an OBD Bluetooth scanner that connects to an app that can log hundreds of different parameters through the car’s computers. In this first test, I’ll see if I can use it to record steering angle in a crosswind as I’ve been doing. To see just what it can show, I’ll first move my car’s center of gravity around and record the differences.   How to Calculate the Position of Your Car’s Center of Gravity   Figuring out where your car’s center of gravity sits longitudinally (that is, its location between the front and rear axles) is quite simple. All you need are front and rear axle weights, something you can get at ...

After my last round of testing , I made a permanent version of the air dam extensions I tested: This brings my truck’s aerodynamic drag down to around 84-85% of what it was before I started this project:   Modification Percent Change mirrors removed, grill blocked -4.0% 9” air dam -8.6% air dam extensions -3.8% Total -16.4%   I didn’t expect to get that much with these changes, especially because I haven’t even tested anything on or around the bed, rear undercarriage, tailgate, rear wheel housings, or rear bumper.   Tailgate   Many websites claim that lowering a truck’s tailgate increases its drag. This was even explored on an episode of the popular television show Mythbusters ; the show’s hosts put a model truck in a water tunnel to illustrate the recirculation that happens in the bed (and ran some fuel economy tests with the tailgate down, removed,...

ETA 7/10/2026: For a better explanation than this (which I wrote before enrolling in an aerospace engineering degree program), and better example of test methodology and data analysis, see my most recent post on spoiler testing. Over the past several months, I’ve tested eight different spoilers on my car. I could test more, but I’ve reached a point where I would rather install something permanently and move on to other things, leaving this spoiler project behind. Hence this Spoiler Roundup. Let's meet the competitors: Straight Gurney flap Sinusoidal Gurney flap Commercial lip strip 10 ° board 20 ° board 20 ° board with slot 30 ° board Hellcat. I want this one to win only because I enjoy saying "Hellcat." Which one should I use, if any? That depends on a few things, including my goals , my design limitations, and how much I want to permanently alter the car.   Goals: I want to reduce lift and improve stability as much as possible without increasing drag or, if possible...