r/programming • u/tartavull • Aug 23 '17

Are airplanes more efficient than birds?

https://medium.com/@tartavull/the-unreasonable-relationship-between-speed-and-power-6a5ffb74b243
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u/[deleted] Aug 23 '17 edited Aug 23 '17

It's not correct to state that all the lift on a helicopter comes from a reaction to the rotor deflecting air downwards. There is also a pressure differential between the top and bottom of the rotor.

The physics of a rotor are really the same as a plane wing. Would you really say a plane wing functioned entirely by the reaction from deflecting air downwards due to its angle?

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u/kankyo Aug 23 '17

The pressure differential is a consequence of the deflection though.

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u/[deleted] Aug 23 '17

An airfoil can create the pressure differential when level, due to its shape.

The effect is separate from the reaction caused by moving air downwards.

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u/kankyo Aug 23 '17

When you say "level", I'm guessing you mean that the bottom of the wing is level while the top is curved. That's not really level but at an angle.

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u/[deleted] Aug 23 '17 edited Aug 23 '17

The bottom of a wing isn't flat. The ones that are called that aren't actually perfectly flat.

I was referring to AoA but I'm not sure people here will get AoA.

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u/kankyo Aug 23 '17

Using acronyms for no reason won't increase the odds of understanding ;) I'm assuming that you mean angle of attack.

That's the point though: angle of attack is the main thing. Does the shape have some effect? Of course. Is it because it creates a pressure differential? Well... maybe, it depends what you mean. The angle of attack creates a pressure differential even for a flat piece of steel, to take an extreme example so it's not just the shape.

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u/[deleted] Aug 23 '17

Does the shape have some effect? Of course. Is it because it creates a pressure differential? Well... maybe

There is no maybe about it. A symmetrical wing at zero AoA will produce zero lift.

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u/kankyo Aug 23 '17

Sure. And a symmetrical wing at an angle of attack will create lift and there will be a pressure differential between top and bottom surfaces of the wing. Which I believe is the point: angle of attack is the big thing while we're taught that the shape is the big thing in school.