I would much appreciate any critique to this line of thinking. Draw a circle around the airplane to see it as a free body diagram. The airplane engine provides horizontal force to move the plane. Force (F=ma) is a vector quantity with a horizontal direction. The wing lift is a force in the vertical direction. These two forces are 90 degrees apart. From an energy point of view, what is the energy source for the vertical lift force? Is this energy being extracted from the surrounding compressible gas? Theoretically from a thermodynamics view, is the atmosphere gas behind the airplane being cooled slightly? Possibly the example of a glider plane instead of a powered plane would be better.