I did some more testing over the past couple weeks. Tuft testing showed I was able to get not fully, but mostly, laminar flow on the top Kammback panel at a 9-degree decline at 65mph. I chose 65 because I only feel comfortable/safe driving 5 below the speed limit on the highway when people around you are going 5-10 over.
For the side panels, I had attached, but somewhat turbulent flow, even at a low inward angle of only a couple degrees. I added a few tufts to the car and found out that the airflow is already a little bit turbulent along the side of my car, too. The kammback at least was not making flow worse, since the turbulence was about the same...
Using my scangage, I saw no appreciable MPG difference between when I had the cardboard kammback on vs. just the stock car. I ran the same 4-mile stretch of highway repeatedly, holding constant speeds and restarting the gage tripmeter at the same points every time, for consistency.
Questions:
1) With attached but somewhat turbulent flow along the side panels, are they still providing me an aerodynamic benefit with a 2-3 degree inward angle, or is my top panel the only portion worth building?
2) Is the tuft-testing goal to maintain laminar flow or just attached flow? Can I keep increasing my panel angles until I have detached flow, then back up a little, or is there no point to increase the 2-3 degree side panel angle since I already have turbulent flow?
3) If I didn't see any change between my scangage average trip MPGs over the consistent 4-mile stretch with and without the cardboard prototype, is it even worth building at all? Or is this somehow normal to not see a scangage improvement, but to see an actual tank improvement?
I've done different types of testing with this cardboard kammback 4 times, now, and I'm unfortunately starting to get a little frustrated with it - a lot of work, time, extra miles, but no visible FE improvement. Maybe it's because I can only get down to the 30% mark on the aero template, but I assumed that would at least make some difference since I'm extending my car by 3 feet. Input and suggestions would be appreciated, thanks.