Lift You Up

21 June 2015

A passenger plane in flight. LAN
A passenger plane in flight.

There’s nothing like a 10-hour overnight flight from Atlanta to Santiago to get a person thinking about flying. As much as we love to complain about crowded seats and bland food, modern flight is pretty amazing. And it’s all thanks to a complex bit of physics.

Not how planes fly. Credit: Wikipedia user רונאלדיניו המלך
Not how planes fly. Credit: Wikipedia user רונאלדיניו המלך

The common view often taught in school is that planes fly due to Bernoulli’s principle. That is, the faster a fluid like air moves, the lower its pressure. A wing is curved on top, so the air flowing over the top of the wing moves faster than the air flowing below the wing. Since the pressure is higher on the bottom of the wing than the top, you get lift and the plane rises. But this isn’t actually how it works.

A more accurate model.Wikipedia user Kraaiennest
A more accurate model.

While it is true that Bernoulli’s principle comes into play, the physics isn’t so simple. For one, the air flowing over a wing doesn’t simply line up on the other side. The air above the wing does speed up going over the wing, but the air below the wing also slows down. There’s also the tilt of the wing that comes into play (known as the angle of attack). As a result, the air not only flows around the wing, but it is pushed down a bit as a result. This makes sense if you think about Newton’s third law of motion (action-reaction). If a wing is being pushed up by the air, some of the air has to be pushed down as a result. So it’s both Bernoulli and Newton.

But even this is still a basic model. Wings don’t have to be symmetrical, for example, and planes can fly upside down. There are also issues with turbulence and the viscosity of air. Aeronautical engineering is a complex field, and relies on both computer simulations and real world testing. As a result we have a way to travel the world quickly and efficiently.

It would still be nice to get a bit more leg room, though.