awe - shucks- you apparantly don't fly models so none of what I said makes sense to you
If I wanted a plane to cross the channel in a self stabilizing mode - I think I could do that -- I have one rc setup I take out once a year - and fly to about 200 ft then turn off the system -it holds , due to a thing called PCM HOLD in the RX design
the plane will circle - and does gain and loose altitude (self corrects for speed ) till I get tired of watching it -
My foamy design does not fly crazy - tho it will do maneuvers which -apparantly you are not familiar with.
I hoped to explain why - but if you are looking for something from a text book - I can't help you.
Technical explanations are a waste of time if they are not clearly applicable to situation at hand.
as for zero weight - -it is a hypothetical example .
This means that IF the plane was of zero weight - how would that ZERO wingloading affect flight.