Definitely Lift Demons - as described originally by Mary Shafer at NASA.
To abstract from the
full paper:
According to Shafer "Lift is caused by Lift Demons. These little, invisible demons hold on to the leading and trailing edges of the aircraft and lift it into the air by flapping their wings (so, in a reductionist sense, lift is actually caused by feathers). Some of the demons are a little confused and they hold on backwards, causing drag. The reason that planes stall at high alpha is that the leading edge demons get scared and let go when they can't see the ground anymore. Lift demons have good taste and don't like to look at ugly aircraft, so they hold on backwards on ugly planes. That's why gliders have so much lift and so little drag and why F-4s have lots of drag." This, however, did not address what gives lift to the Lift Demons' wings. Again, according to Shafer "Feathers. The multiple filaments on feathers trap the air molecules and they struggle to escape, which causes the action-reaction that we call lift. Bat wings don't have feathers but they're hairy and that works just about as well (air molecules are a little claustrophobic)."
Because Lift demons hold on backwards on ugly planes to avoid looking at the planes, drag can be calculated using CDU (Coefficient of Drag due to Ugliness) used in correlating aircraft ugliness against Lift Demons' unwillingness to hold on forwards and provide lift.
It was originally believed that Lift Demons got their lift from smaller Lift Demons whose lift was, in turn, produced by even smaller Lift Demons leading to the "Infinite Demons Theory" as proposed by the great Greek philosopher-scientist Miasma. However, with the revival of scientific knowledge that eventually ended the Dark Ages, it was realised that this situation unresolvable according to Zeno's paradox. The "Infinite Demons Theory" works in many problems of engineering significance, however, real understanding requires that the ether be introduced into the analysis at some point. The "Ether Concept" explains why planes fly more efficiently at higher altitudes. This is an absolute necessity when studying orbital and interplanetary travel where, it is believed, many of the Lift Demons are unable to breathe.
HTH,
PDR