I'll keep posting...see if what I find is helpful.
It may be redundant ...but where I have found the EcoModder Forum Link(s) I'll include them.
I did a quick read thru the Orbywan's RV mods(Boattail & belly pan), very nice builds, a true craftsman.
https://ecomodder.com/forum/showthre...d-e-18151.html
...surprised that the underside smoothing didn't have more impact.
https://ecomodder.com/forum/showthre...n-s-18427.html
Being familiar with racecar aerodynamic history, and changes from the early 60s(if it LOOKS aerodynamic) to Jim Hall's Chaparrals of the late 60s...and then the crazy downforce numbers of the late 80s(Nissan blowing tires & Spice collapsing suspension components)
Mulsanne's Corner: Road Atlanta 1992, Rough and Tumble, attributed mostly to the underbelly's relationship with a diffuser. Today's endurance motorsports, is designed for "enough" downforce, and more efficiency(limited fuel capacity) than ever.
https://www.racecar-engineering.com/...ta-ts050-2019/
How to connect any of this to a rounded corner big box/brick is a challenge.
We are working with something that is not <3" off the ground, or moving at over 75mph. ...but efficiency is what the goal is, not making the vehicle aerodynamically heavier.
Regarding the BellyPan: "pulling" air thru the underside with a <15*(degree) angled diffuser at the rear, with strakes ...extended into the(now revised bottom) boattail?. The other issue IS the "in the way" straight axle & rearend.
Mulsanne's Corner: 1991-1993 Toyota Eagle MkIII
Don't you wish you could afford carbon fiber?
Regarding the Boattail addition, nice, clean, updated... obviously functional. Again Orbywan, a real craftsman.
It would be interesting if a measurement of the constructed angle from the sides & top is available. For reference... the NASA data:
https://www.nasa.gov/centers/dryden/...ain_H-2283.pdf
...doesn't reference a "best" boattail angle from the side or top. I did a little more checking and found:
https://doi.org/10.1155/2020/7580174
and
https://www.vortaflow.com/consulting...0reduction.pdf
The angle needs to be around 16* before separation of airflow. Funny there's that 15-16* again. I saw Aerohead had mentioned this number. 20-22* is too much but maybe less important at <75mph? Question: Does a curved side/top "inflated" boattail basically compound that 15* to a point? Has the group found more info about this?