4 ms·

I think they just messed up what side is flat, right?

by giarc 9y ago

DubiousPusher 9y ago
That's part of it but it's also incorrect to say "the air above moves faster than the air below, and the wing rises." The air speed is not necessarily different. Lift is generated because air is deflected from moving over the top of the wing and thus reduces the air pressure. You can create flat winged aircraft with careful orientation of the wings. Air flow is not like say a spinning disk, where the solid state of the matter forces the outer edge of the disk to move faster in order to maintain relative position.
aidenn0 9y ago
No, symmetric airfoils generate lift just fine, and if you were going to spend half your time upside-down, you'd use one. Making it asymmetrical merely makes it more efficient to generate lift in one particular direction (similar to how glasses lenses are asymmetrical to reduce distortion). Furthermore, pretty much no airfoils have flat sides, in nature or in engineering[1] The wing, when placed in airflow, disturbs the air in such a way that the pressure on top of the wing is lower than the pressure below the wing, generating net lift. This isn't a very satisfying description of lift, since it just begs the question of "how/why does it disturb the airflow in such a manner" and the short answer is "we put different shapes in a wind tunnel and measured" with the longer answer being "you don't know enough math to get a good intuition of that" [edit] After reading the article, the article did get lift right for the case of the paper though. Jets of air behave exactly as they say, and you can feel something similar by touching the back of a spoon to the stream of water from a sink; it will get pulled towards the stream of water (or just put a piece of paper on a table and blow over it). A few planes use blown flaps[2] to help get a similar effect (the introduction of a jet of air, which "hugs" the wing helps direct the airflow of the larger mass in the direction you want). 1: https://en.wikipedia.org/wiki/Airfoil#/media/File:Examples_of_Airfoils.svg https://en.wikipedia.org/wiki/Airfoil#/media/File:Examples_o... 2: https://en.wikipedia.org/wiki/Blown_flap https://en.wikipedia.org/wiki/Blown_flap
- nimish 9y ago
  The spoon in a stream is more of a surface tension thing and the classic blowing air over a piece of paper is the coanda effect. The total effects of newton's laws and bernoullis law on pressure differences need to. Be combined but the gist is that you create a force difference using the shape and angle of attack of the airfoil. The use of this is really quite neat especially in a printer!
- efraim 9y ago
  >Because the top side of an airplane wing is flat, while the underside is curved, the air above moves faster than the air below, and the wing rises. That's what the article says, but it's usually the underside that is flat and the top is curved.
  - aidenn0 9y ago
    In reality usually neither side is flat.
    - travisjungroth 9y ago
      A flat bottom wing gives you nice stall and landing characteristics. Very small, 2-4 seat, trainer airplanes have them. (Cessna 150, J3 Cub)
      - aidenn0 9y ago
        I wouldn't call the Cessna 150 flat, as it has visible lower-camber, but you are right about the J3 Cub; it's super flat on the bottom.
marcosdumay 9y ago
If you ever found yourself in a car, not driving, in a semi-desert place where it's sfe to put your hand out of a window, try that: - First, put your hand parallel to the ground, and see what the wind does to it. - Then, incline your hand so you raise your fingers, and see what the wind does to it. Lifting has no relation to the wind being flat or curved. It's the overall shape (the one you change once you incline your had) that causes it.

I think they just messed up what side is flat, right?

by giarc 9y ago

I think they just messed up what side is flat, right?

That's part of it but it's also incorrect to say "the air above moves faster than the air below, and the wing rises." The air speed is not necessarily different. Lift is generated because air is deflected from moving over the top of the wing and thus reduces the air pressure. You can create flat winged aircraft with careful orientation of the wings. Air flow is not like say a spinning disk, where the solid state of the matter forces the outer edge of the disk to move faster in order to maintain relative position.

aidenn0 9y ago

No, symmetric airfoils generate lift just fine, and if you were going to spend half your time upside-down, you'd use one. Making it asymmetrical merely makes it more efficient to generate lift in one particular direction (similar to how glasses lenses are asymmetrical to reduce distortion). Furthermore, pretty much no airfoils have flat sides, in nature or in engineering[1] The wing, when placed in airflow, disturbs the air in such a way that the pressure on top of the wing is lower than the pressure below the wing, generating net lift. This isn't a very satisfying description of lift, since it just begs the question of "how/why does it disturb the airflow in such a manner" and the short answer is "we put different shapes in a wind tunnel and measured" with the longer answer being "you don't know enough math to get a good intuition of that" [edit] After reading the article, the article did get lift right for the case of the paper though. Jets of air behave exactly as they say, and you can feel something similar by touching the back of a spoon to the stream of water from a sink; it will get pulled towards the stream of water (or just put a piece of paper on a table and blow over it). A few planes use blown flaps[2] to help get a similar effect (the introduction of a jet of air, which "hugs" the wing helps direct the airflow of the larger mass in the direction you want). 1: https://en.wikipedia.org/wiki/Airfoil#/media/File:Examples_of_Airfoils.svg https://en.wikipedia.org/wiki/Airfoil#/media/File:Examples_o... 2: https://en.wikipedia.org/wiki/Blown_flap https://en.wikipedia.org/wiki/Blown_flap

nimish 9y ago
The spoon in a stream is more of a surface tension thing and the classic blowing air over a piece of paper is the coanda effect. The total effects of newton's laws and bernoullis law on pressure differences need to. Be combined but the gist is that you create a force difference using the shape and angle of attack of the airfoil. The use of this is really quite neat especially in a printer!
efraim 9y ago
>Because the top side of an airplane wing is flat, while the underside is curved, the air above moves faster than the air below, and the wing rises. That's what the article says, but it's usually the underside that is flat and the top is curved.
- aidenn0 9y ago
  In reality usually neither side is flat.
  - travisjungroth 9y ago
    A flat bottom wing gives you nice stall and landing characteristics. Very small, 2-4 seat, trainer airplanes have them. (Cessna 150, J3 Cub)
    - aidenn0 9y ago
      I wouldn't call the Cessna 150 flat, as it has visible lower-camber, but you are right about the J3 Cub; it's super flat on the bottom.

marcosdumay 9y ago

If you ever found yourself in a car, not driving, in a semi-desert place where it's sfe to put your hand out of a window, try that: - First, put your hand parallel to the ground, and see what the wind does to it. - Then, incline your hand so you raise your fingers, and see what the wind does to it. Lifting has no relation to the wind being flat or curved. It's the overall shape (the one you change once you incline your had) that causes it.