The reason why angel food cake has a hole in the middle is because angel food cake is baked in a tube pan that has a hollow center.
The tube pan that the angel cake is baked in with the hollow center allows the cake to rise evenly and also maintain it's airy structure as the angel food cake expands during the baking process.
The hole for angel food cake pans and angel food cakes also allows for proper heat distribution and ensures the angel food cake cooks through properly and also without it collapsing in the center.
To make an angel food cake upside down you bake the angel food cake as you normally would right side up.
Then after the angel food cake cools you place a plate over the upside down cake and then flip it over and remove it from the pan.
To get the cake out of the pan run a knife around the edges of the cake to help it slide out more easily.
Bake the upside down cake until a toothpick that is inserted comes out clean, about 40-45 minutes.
Rotate the cake pan halfway through baking.
The upside down cake will rise up very tall while baking.
Remove the upside down cake from the oven, then cool the cake completely upside-down set on a wire rack, about 3 hours.