John I attempted that once before and had problems. The sheet of material generated enough lift that is caused my tires to lose traction and would make the car veer off the road. I don't recommend this method as it can be dangerous.
The physics of this situation clearly says that this is nonsense. Force is force no matter what direction it's applied. If this lift conjecture were true then it is necessarily the case that a sheet of coroplast is sufficiently strong as to be able to lift an automobile without first collapsing. Moreover if you were merely holding it with your hand then your hand would also have to be sufficiently strong as to be able to lift your auto. Highly doubtful.
I have a good friend that manufactured, among other things, wings that were mounted on top of super modified round track racers. These were acute airfoils mounted upside down on the top of the car. He touted these wings as creating something on the order of 3000-4000 pounds of down thrust via negative lift. If this were true then it ought to be the case that if the wing were to be mounted upside down, I.E. airfoil up, the car, weighing far less that 3000 pounds and the lift being far more the the weight of the thing, should be able to take off and fly.
Physics is physics and is immutable.
