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XKCD: Airfoil

October 8, 2010 13:38 3,374 views 4 Comments

Are you able to answer this students question? Why *can* airplanes fly upside down if this is how an airfoil works.

Or better yet: Why does the air above the airfoil have to meet up with the air below the airfoil?

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4 Comments »

Ramiel said:

I know this is half jokingly so here’s the serious answer: I think they use symmetrical airfoils.
and the air above has to meet the air below because its just a law of conservation of mass…mass flow rate in = mass flow rate out
now that better answer: they can fly upside down because their wing is installed upside down. and it has to meet because they like each other..i dont know..that wasn’t very creative

# 8 October 2010 at 15:06

Blake said:

Ramiel,
You have the right spirit though

# 8 October 2010 at 15:07

Zhatt said:

Hum.
Well, a plane can fly upside-down because of angle of attack. If the oncoming air hits the wing at a sharp enough angle it will create lift inspite of the airfoil.

The air moves faster and has a lower pressure over the top of an airfoil because of Bernoulli’s principle (not that I know how that works).

The “conservation of mass” if an oversimplified model and the air doesn’t need to meet up at the tailing edge. In fact, I think the air moving over the top moves much faster than the air below which creates the downwash.

# 10 October 2010 at 18:46

Jennifer Bray said:

http://amasci.com/wing/airfoil.html

# 18 October 2010 at 17:33