One of the biggest stumbling blocks on a car like the Challenger II is maintaining aerodynamic slipperiness while simultaneously providing the engines with sufficient air to properly ignite the fuel. To feed the front engine, we have a center mounted flush duct that sits on top of the vehicle, roughly where the hood would be on a normal car. When the car is in motion, it directs plenty of air to the front engine with minimal aerodynamic impact.
The rear engine is more challenging because it is situated behind the driver's canopy. As air travels over the canopy, it is directed upward, creating a null space in the area a top-mounted intake would normally be located. To get around that problem, my dad and his crew added NACA ducts to both sides of the vehicle adjacent to the the rear engine. But to be frank, they were one of the few parts of the original vehicle that didn't work well. The ducts directed oncoming air into a squirrel cage, where it had to spin 180 degrees before reaching the throttle bodies. The air tended to stall within the cage, which eventually necessitated the addition of small ears to the NACA ducts. This improved their function, but had significant aerodynamic disadvantages.
My original plan was to replace the NACA ducts with a rear air scoop, which is the most common solution utilized by other streamliners. I mocked it up in cardboard, but when Tim Gibson, my engineer and aerodynamicist, saw the result he deemed it aerodynamically unacceptable. Tim's a ridiculously smart guy, so after gathering and calculating all of the necessary data, he presented me with a solution that provided sufficient air intake without significant aerodynamic disadvantages.
His solution was a set of side-mounted straight intakes with specific veins that funnel air directly to the throttle bodies. While this superficially resembles the NACA duct solution, it is simpler, more efficient, and actually works. The master metal shaper Terry Hegman took Tim's drawings and spent the next three weeks hand shaping the intakes into the car's aluminum skin. I'm glad we have Terry, because there simply aren't that many people who can do that anymore. The end result, as you can see in the pictures, is gorgeous.
If you'd like more information about our project, you can find it at thompsonlsr.com <http://thompsonlsr.com> . See you next week.