Staying on topic here but veering off course a little -
I have a Civic hatch with the little mini tailgate.
Other posters here have found that opening the windows in their cars actually does not hurt the FE as much as they thought.
If I were to open my tailgate, as well as my windows, air would swoop into the cabin and find its' way out the back of the car through the opening - hopefully filling in my wake some.
What do you guys think will happen ?
A. I will die from all the fumes coming into the cabin from the stupid hole I made
B. The drag will actually be worse.
C. I'll be fine because the air ( and fumes ) will exit the cabin out the back. Possibly a very slight increase in FE.
D. Nothing. ( A wash )
Here is an example of the tailgate down ( Note that in the picture the hatch is open. For the test, only the tailgate would be open ):
