I set up a 5 x 5 grid of tufts, minus 2 directly behind the exhaust. I got some video as well, which I'll post eventually.
First, below, here's how I dealt with the exhaust (2 layers heavy tin foil):
Below: 5 rows of 5 tufts, except in 2 rows behind the muffler:
Below: web cam set up, looking forward. (Not shown: I also attached it to the driver's side mud flap to capture video looking rearward.)
Observations:
- obvious separation behind the wheels (no surprise there!)
- turbulence everywhere else, but not reversed flow. It seems more turbulent toward the outsides (effect of the wheels and control arms), less worse toward the centerline
- Correction: alternating between "sometimes separated / sometimes turbulent" for the two tufts closest to the control arms
I lent my Hucho to Ben, so I'm having a little trouble remembering my definitions. I believe "separation" is characterized by reverse flow (eg. behind the wheels).
The flow down the middle 3 of 5 columns (parallel to centerline) appears turbulent, but there does not appear to be any reverse flow, so I don't think it's separated.
That's a good sign for 2 reasons: first, I believe it means the bottom angle isn't too steep. And next, it suggests that adding the full belly pan will help reduce turbulence & minimize wake off the rear. (If there
had been separation due to the angle, the belly pan wouldn't have helped.)
The outermost tufts in the last 3 rows (inline with, but furthest away from the wheels) are also in turbulence, but not separated flow.
Next in the boat tail evaluation: I'm going to reinstall the full belly pan and re-tuft test the underside.