Romy asks, “How do airplanes work?”
I want you to try a little experiment. Really, you should try it — it’s super easy!
Find a piece of paper. Pinch two adjacent corners between your thumbs and pointers, with your thumbs on top. Now press that edge of the paper up against your lower lip. (Don’t get a papercut!) Breathe all the way in, as far as you can go… and blow out.
What happened?
The reason the paper defies gravity is actually pretty simple. You just need to know two things:
- Air sticks to air, just like water sticks to water when rain droplets bead together and run down a car window.
- Any time there’s a vacuum — totally empty space, without even air in it — something has to fill it up.
When you blew air over the piece of paper, here’s what happened. The air behind the paper stuck to the air you were blowing, so it also moved forward. This left a vacuum behind the paper.
So the paper and the air compromised, and both filled in part of it.
This is called the Coandă effect (pronounced QUAN-duh). And it’s also how airplanes work. Airplanes seem totally magical, but they’re really just following this simple rule.
An airplane wing is shaped to take advantage of the Coandă effect. As the plane is flying forward very quickly, a lot of air has to make its way around the wing. The air that rushes over the wing is just like the air you blew over the piece of paper — just way, way faster.
The wing is rigid, so it can’t bend up like the paper. Instead, it has to move up to fill the vacuum… and it pulls the entire plane with it. The plane is also pushed up from the bottom by the air going under the wing.
When the wing is tilted more, both of these effects are stronger. (Try to think about why.) When the plane takes off, the wing is tilted enough that the “lift” is stronger than the weight of the plane, so it rises. In the air, the wing tilts back a little until the lift balances out the weight, and the plane stays steady. On the way down, well, you get the idea.
Does this still seem a little magical? It certainly does to me. Well, you can use the Coandă effect right now to make something hover in mid-air. All you need is a ping pong ball and a straw. (This actually works — I just tried!)
All you have to do is blow through the straw at a slight angle from directly up, and put the ping pong ball in the line of the straw. If you do it just right (you might have to try a few times) the ping pong ball will hang in the air until you run out of breath.
Okay, I’ll be honest: it seems even more magical now. I can understand why the ball is floating in midair, but it’s still crazy to see it hovering there. Sometimes understanding how something works doesn’t make it any less incredible.
More on this: Marshall Brain, How Airplanes Work
More from Romy Asks:
Originally published at milobeckman.com on April 8, 2015.
