[aerohead]

*Wheelhouse drag has to do with the volume of the wheelhouse in which the wheel/tire occupies.
*You could calculate the difference in the overall 'void' attributed to the addition of the wheel covers.
*You'd want to test for the entire wheel-flop range of motion to ensure that nothing collides with the wheel arch.
*I'm unsure of what the flow over the wheel will do when the cover protrudes so far from the wheel.Technically this is a no-no aerodynamically.Some of the air will try and ride the wall of the cylindrical covers,while a portion will attempt to spill over the outer edge.Since it's spinning,the 'trailing edge' cannot be boat tailed,giving the wheel a larger overall frontal area.
*Un-skirted,having the outer face of the wheel even with the body is good only if the tire is even too.
*Would not the articulated skirts as on AEROCIVIC not be easier to deal with?