>You have to just visualize what the result of the cut is though
This is the problem working with nurbs when you are trying to model stuff that looks like the real thing and you have to define the overall shape first and then do booleans rather than doing it the way I was on the first post of this thread which is define the shape of the object with curves (get that part looking right) and then create the surfaces.

For example the fuselage of the F9F panther (see pic) is quite simple (perfect circle) but trying to define the shape of the cross section curves so that when you boolean out the cockpit opening so it is the right shape and size is a bit of geometric puzzle due to the subtle curvature extending from the fuselage up to underside of the canopy (particularily around the rear of the canopy).

>I'm not quite sure if you actually wanted a totally flat plane in there or not though.
It very slight (see photo) but thanks for showing the idea of how to address this area.