Guys: I’m pretty sure NACA ducts are going to be the next big thing on the internet. They’re neat looking. They have a cool name. The story behind them is sort of awesome. And they’re all around you as you drive, and even as you fly in an airplane. You’ve probably seen over a hundred NACA ducts and not even known it. Sneaky, interesting things, NACA ducts.
According to Wikipedia, this duct was originally developed by the U.S. National Advisory Committee for Aeronautics, or NACA. This organization was the precursor to NASA. The NACA duct was invented in the forties, by people who knew things about flying into space, meaning it was designed for freaking space travel, and you might even have one on your car!
You’ve seen this duct before. Cars that have NACA ducts include the Ferrari F40, almost every old Lamborghini, the Dodge Viper, the Nissan GT-R, the Mitsubishi Evolution, and various race-cars and rally-cars. Some performancey cars even have hidden NACA ducts, built into the aerodynamic under-pans where you can’t see them. My buddy’s 2000 BMW M5 has a whole bunch of NACA ducts underneath it. You’ll often see NACA ducts on the plexi-glass windows of rally cars, and they’re also used abundantly on airplanes.
Key characteristics? The duct is sort of triangularly shaped, fairly shallow, and submerged in the body of the vehicle, in contrast to a protruding scoop. The NACA duct is typically used for cooling purposes, effectively channeling outside air at some internal component, like a heat exchanger.
The distinctive shape is key in the effectiveness of NACA duct, since when used properly, a NACA duct allows air to flow through with virtually no interruption.
Imagine a lineup of obese tourists trying to get into the door of an all-you-can-eat buffet that’s just opened for business. Even if the width of the lineup was exactly the same width as the doorway to the delicious foodstuffs within, the tourists would tend to bunch up at the door on their way inside. In aerodynamics, this might be called a turbulent boundary layer. The gist? The viscosity of air (or a crowd of waddling tourists) changes as it approaches the immediate vicinity of a solid surface. From an air-flow standpoint, this means air begins to swirl and eddy and pile up as it approaches the body of a moving vehicle, just like tourists wondering if they’ll fit through the door, questioning whether it’s their turn to go through the door, and otherwise jamming up and shuffling about for their position in line to the buffet entrance.