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Comment by hyperpape | Hacker News Reader

> You will notice that past a certain angle, the lift starts to decrease, and is replaced by a lot of drag, a force trying to slow down the wing. This is called a stall, and it limits how much lift a wing can create at any given speed. A proper airfoil geometry can generate more lift before stalling, and creates less drag for a given amount of lift, which is why most airplanes use them.

I'm a bit of a novice, so it sounds like this is the same explanation you're giving. What is the article leaving out?

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Speed. You'll always stall if you go too slow to get enough lift. Putting the flaps down increases lift and drag and lowers the stall speed.

As for why the article mentions decreased lift whereas flaps down increases lift, that's maybe a bit more complicated. Lift vs. Angle Of Attack is a curve that tops out at about 15°.[0] Flaps often go to steeper angles than that, but I'm not sure if lift actually starts to decrease again in that scenario. Certainly adding a curve to the back of the wing (flaps) isn't quite the same as changing the angle of the entire wing.

[0] https://commons.wikimedia.org/wiki/File:Lift_curve.svg

> You'll always stall if you go too slow to get enough lift.

The amount of lift needed is determined by the load factor. In a turn, or when a glider launches via a winch, the load factor is higher than in level flight.

This means that the stall speed varies with load factor.

On the other side, you can still not be stalled below the straight and level stall speed, if the load factor is low enough. In parabolic flight you can see this, and with a load factor of 0 you cannot stall.

No, flaps increase CL. https://www.researchgate.net/figure/Figure-1-4-Effect-of-fla...

You might be thinking of total lift on a 3D wing, which is something you alluded to re: wing loading. But 3d wings vs 2d airfoils are really different concepts that you seem to be mixing up. Airfoils are advantageous regardless of wing loading (which is an inherently 3d concept) because of better L/D and stall characteristics.

You are correct, I had a brain fart. Not enough sleep the last few days.

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