Real-World Aero: Wind Tunnel Testing For the Weekend Racer

Wonder no more
You hear the advice all the time from the "know-it-alls" in racing (yes, that applies to us, too): No matter how small your track or how slow your car, good aerodynamic practices can help improve your lap times.

Yes, that advice is true. As a general rule, if you have to apply the brakes anywhere on the racetrack, you need more downforce. When that downforce is achieved aerodynamically (as opposed to achieving it by weight), it is doubly beneficial because it is gained without the disadvantage of inertia trying to push you into the wall as the car turns. The problem is that wind tunnel testing is expensive, so the information provided to Saturday night racers is too often based on tests done on Nextel Cup cars or theory with no real-world numbers to back it up-until now, that is.

Noted aerodynamicist Gary Eaker has been operating his own private wind tunnel, AeroDyn, in Mooresville, North Carolina, for a few years now. AeroDyn has been quite successful with its Nextel Cup clientele because it is one of the most affordable wind tunnels in the country. That all changed with Eaker's newest innovation, affectionately known as A2. A2 is the little brother to the AeroDyn wind tunnel, and was designed for the express purpose of making wind tunnel testing accessible to race teams that may not have the support of big-money sponsorships. A2 doesn't have all the bells and whistles that AeroDyn offers, such as a simulated rolling road and yaw control, but it does offer solid, repeatable aero testing that can be greatly beneficial to a race team.

We've always wanted to get a real-world short-track car into a wind tunnel to see how it performed, but as experienced by most race teams, the cost was too prohibitive. When Eaker opened the A2 facility, we finally had our opportunity. We joined drivers Freddie Query and Preston Peltier at A2 as they ran Query's Super Late Model asphalt car through a series of tests. Query and Peltier are both savvy veterans and came prepared to make the most of their time in the tunnel with a complete list of all the tests they wanted to perform and all the hardware they needed to get it done quickly. We followed along to see what worked and what didn't. Over the course of approximately five hours, Query, Peltier, and a handful of volunteers were about to pull off 33 tests. The following are some of the most interesting tests we witnessed.

Spoiler Angle
After making a few baseline runs, the first test with the car fully taped in qualifying trim and sitting at inspection ride height involved raising the spoiler angle from 50 to 70 degrees. This was done to see how it affected front versus rear downforce balance, but the surprise was how little it actually helped downforce at all. Downforce improved by 11 counts in the front and only 8 in the rear, while drag increased dramatically. Normally, a team testing a downforce car in a wind tunnel cares very little about drag numbers. In this instance, it shows that the spoiler was already approaching its stall angle closer to 50 degrees and wasn't helping appreciably at 70.

Because the spoiler is behind the rear axle, downforce here has a mechanical cantilever effect on the car, which reduces load at the front. Raising the spoiler angle (as long as it isn't stalled) will increase rear downforce and mechanically decrease load on the front tires. Lowering the spoiler will have the opposit effect. For reference, one count in a wind tunnel is equal to 1 pound of downforce on the track at 135 mph. It does not change with the weight of the car, only speed. The second interesting thing to note from this test is that by moving the spoiler, the downforce improved more over the front wheels than the rear. Aero, it should be noted, is as much about creating pressure differentials above and below the body sheetmetal as it is about air actually hitting a surface and pushing it down. The spoiler actually causes air to dam up in front of it, and the high-pressure zone created by the spoiler can reach all the way to the hood. The car responded as much as it did at the front because the chassis is remarkably open. There is no front or rear firewall to speak of. The Super Late Model has an offset chassis, and the only area boxed off with sheetmetal is the driver's compartment. Because the area underneath the body is so open, the front and rear wheels are easily able to "talk" to each other, so a change at the rear of the car will affect front downforce much more than a car with a full firewall.