Dracorat said:
You quote speaks nothing about inversion, rather about using water for aerodynamic analysis which is a common method of testing airfoils.
However, that aside, it means nothing in relation to arguments about fly and being able to be used underwater.
1. It speaks nothing about inversion becasue it is not needed - of course it would say nothing.
2. No - that's pretty much settled, I think. You can fly underwater, but at 1/2 move and the loss of one category of manuverability. Or, if youi prefer, you cannot fly underwatewr at all
The justification for allowing it is:
1. Makes sense.
2. Fits within the rules for "hampered movement"
3 . The MotP, with applicability to 3.5e, says you fly can in the plane of water (where you are underwater always. And the rules they state fit very nicely with "hampered movement" for 3. 5.
The argument against allowing any sort of flight to work at all underwater ignores the MotP as setting any precedent except for the plane of water itself.
Basically, you can allow per RAW and, if you want, deny using RAW as justification as well.
So, in the end, so can have RAW behind you either way, as is often the case.