Join the discussion for how to make project F-Dat an aerodynamic machine!

Robbie: The cross sections need to be small due to the speeds involved AND they are relative to the inlet and outlet areas. 2inches tall x40inches wide needs to be some fraction of the inlet area (1/3 to 1/2), with the diffuser exit area being bigger than the inlet. Figure out where you are most limited on cross section and work the other numbers from there. You could add extra fences (like the side skirts) to control/define a smaller throat if needed.

Sleepyhead/Noncones: A flat floor will be easier to construct. I agree the overall layout with the separated fenders will make for some fairly weak body structure, so a simplified and easily prepared floor is going to be useful. Keeping the center of pressure near the CG will make the aero impacts more invisible with varying speeds and allows the tuning to happen at the extremities and be more effective at balance shifts.

Nice, it sounds like I can move forward with the simplicity of #1. 

I did have in my notes that the opening for the underfloor area should not be more than 2x the minimum cross sectional area of the underbody area like you say. That's easy enough. I also have in my notes that the center of pressure for the floor is usually near where the floor starts sloping back upward. It should be easy for me to get that close to the center of mass of the car. Does the 'slope' of the area in front of the flat floor matter a whole lot? (Like the difference between flat floor starts 2 ft behind the front of the car and the flat floor starts 4 ft behind the front of the car)? 

In reply to Robbie (Forum Supporter) :

No, not really. As long as the entrance is relatively smooth. You are just trying to accelerate the flow without too many losses.