How wings work in still air

Question

I was reading this when it occurred to me that - unless I'm misunderstanding it - it depends on the assumption that the fluid is moving.

http://www3.eng.cam.ac.uk/outreach/Project-resources/Wind-turbine/howwingswork.pdf

Sure, the fluid is moving relative to the wing, but that's not what the explanation is premised on. He talks about streamlines and particles with velocity, which they don't (negligible) in my office here.

Now, if I imagine a wing passing in front of my face as I sit at my desk, the wing is just separating still particles and then they come back together.

If there was a puff of smoke in front of me and a wing passed through, the smoke would mostly still all be in front of me, diffused more.

I'm an ordinary idiot off the street, so I assume I'm wrong and embarrassing myself by asking. But why?

I find the explanation unsatisfactory, its just not what happens, gas molecules are laying still and a solid body is moving through them, pushing some up and some down.

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Originally, erroneously posted here:

https://math.stackexchange.com/questions/3387491/how-wings-work-and-still-air

Answer 1

Velocity is all relative to the frame of reference.

To explain aircraft dynamics, it usually makes more sense to focus on the reference frame of the aircraft. When a plane is flying through the air, from it's point of view, you could say it is stationary, and the air is coming towards it with a velocity opposite of the velocity that the plane is moving relative to the stationary air.

So air flowing past a stationary wing in a wind tunnel at 500 kilometers per hour has the same dynamics as a wing flying through stationary air at 500 kilometers per hour (if the wings are the same size).

Answer 2

A still wing in still air provides no lift. One must move relative to the other, whether it is a fixed wing in a wind tunnel or a wing moving through air that is either still or moving at a different speed.

Answer 3

Wings will still work like normal in still air. It's just that to my understanding if the fluid is moving against the wing it will make the wing generate more lift because the air velocity would add on to the wing lift because the air is moving faster over the wing. so if the fluid is moving with the wing than it would subtract from the wings lift force because it would e moving slower over the wing I think.

Answer 4

Okay I have found the answer and its on this site.

What really allows airplanes to fly?

It's as I thought, air gets pushed down, like my hand in water. I can sleep now :)

(I've no idea what that paper I linked to was going on about, then)

Answer 5

Wings generate lift according to air speed, i.e. the relative speed of the wing to air. This is what an aircraft measures with its instruments (it can only measure relative values). If the airspeed is too low the plane will stall, i.e. not generate enough lift to stay up. The air speed relative to ground is only relevent when the plane is taking off or landing in order when one wants to be going into the wind in order to minimise runway length needed without stalling.

The same goes for all wings, eg sails on a boat.