Why Planes Fly: What They Taught You In School Was Wrong

So we all know how planes fly, right? The top of the wing is rounded and the bottom of the wing is more straight. Air takes longer to travel over the top of the wing than the bottom, which results in more pressure on the bottom, hence the lift. Right?

As it turns out, no.

This is what I was taught, and it’s what I’ve always believed (it’s even in most lower-level text books), but it’s simply not true. The concept is called the Bernoulli Principle, and it accounts for very little of the lift that makes flight possible.

The main reason planes fly is far simpler: wings force air downward, which in turn pushes the wings upward.

The primary actor here is the the Coanda Effect, with the Bernoulli Principle taking a supporting role. It all starts with the air wrapping downward along the back of the wing (Coanda).

Try this: go to the sink and get a clear drinking glass. Start the water running so that it’s a very thin but steady trickle and bring an outer, rounded part of the glass slowly towards the stream. Watch what happens when you touch it. The glass grabs the stream and forcibly wraps it around itself!

On a plane this equates to grabbing the air going over the top of the wing and pulling it snug to the downward sloping wing surface. This redirects massive amounts of air toward the ground, which results in an upward force, i.e. lift.

The concept is the same as an engine that forces gas backward, which propels the plane forward. This is simply using the wings to do the same thing: forcing air downward, which propels the wings (and plane) upward.

In other words, it all really boils down to Newton’s third law of equal and opposite reactions: *air goes down, wing goes up*.

It’s astounding to me that the truth is so much simpler than accepted wisdom (Beroulli). Anyway, definitely check out this most excellent presentation below; it goes into all the detail and shows the math behind it. And as always, feel free to correct me in the comments or via email.:

References and Notes

• [ Understanding Flight, by David. F. Anderson ]

• Ask yourself why planes can hang tons of massive crap (engines, bombs, etc.) off of the bottom of their wings if the bottom of the wing is so important for flight. The answer is that the bottom of the wing isn’t doing much at all. It’s the top of the wing that’s doing the “heavy lifting” (sorry) because it’s the Coanda Effect and resulting downward push of air that allows modern flight.

• In addition to the Coanda Effect we also have the very tangible “angle of attack” issue. As a kid you no doubt put your hand out the car window in the shape of a wing. You noticed that if you angled it straight on you could hold it steady, but if you angled the front edge upward you created massive lift. The same works for kites, and planes.

• This also explains how planes can fly upside down.