PA38, I'm not even an uni student yet, but I can answer that Q for you!
Consider, oh i dunno, any small plane, let's say a Yak-52, flying along straight and level. Wings are doing their job etc etc etc. Then the pilot just happens to see a crowd that had come for an airshow. As he passes them, he brings the stick to the right until the ground, to him, is where the sky was (180 deg roll). all the time, he's kept his nose at level.
One, the plane's nose will start to drop groundward, he sees the green half of the outside world coming down the windscreen and he will have to push the stick down (away from him) to counteract this.
two, he will start to drop. He sees this on the altimeter and pushes the stick even further to counteract this.
So he ends up upside down, but with the nose pointed at about 20-30 degrees or more from horizontal.
Fact is, the loss of aerofoil lift is compensated by both the downforce of the twisted aerilons and the engine prop, which is now providing a bit of upward thrust.
Keep in mind also that when the wings are inverted, while they're not providing the same amount of lift as they would right way up, they still are contributing to the net (total) forces upward.
There. that's it explained. Can I get a sponsorship for AeroEng in Cranfeild now?