It must be a perennial embarrassment to high school physics teachers that cheap balsa gliders — to say nothing of folded-up pieces of paper, or butterflies — can fly. After all, it says right here in the official textbook that airplanes fly because air has to go a longer distance over the top of the wing than under the bottom, and so (because of some guy named Bernoulli) there is more pressure below the wing than above it.
This Bernoulli fellow, who lived several hundred years ago, was stating a simple fact of the physics of fluids (actually, fluids flowing through pipes) that he considered more or less self-evident. He would be no better known to pilots today than d’Alembert or Torricelli had his name not come to be associated with an appealingly simple — but unfortunately flawed — explanation of lift. Because in fact air particles marching past a wing are not like an ordered mass of soldiers — call them the Bernoulli Brigade — who part at the leading edge and rejoin their buddies at the other end. There is nothing to cause the upper-surface flow to arrive at the trailing edge at the same time as the lower-surface flow, and it doesn’t. Actually, it gets there sooner.
