The Mystery Behind Flight Deepens

Apparently, Viktor Schauberger is quoted as saying that fish don't swim, they're swum and birds don't fly, they are flown:

Viktor Schauberger’s comment in full, is actually: “fish don’t’ swim, they’re swum and birds don’t fly, they’re flown”.

I’ll start a “Birds Flying” topic at some point.

theartofnature.org...

a reply to: swanne

As I understand it the air above the wing has to travel that little bit further and as nature arbors a vacuum it has to speed up as it travels over the wing to keep air flow constant on both sides, which means both air flows would have to be equal on exit. Perhaps I was taught or misunderstood the fundamentals of flight incorrectly but as a paraglider pilot I like to think the experts who design the wings know what their doing and why. While a parashoot for example is designed to let us descend through the air at a safe speed, we want our wings to glide as far as possible for the most part.
Saying that I don't see how a wing is really creating lift as such with out some force applied, it's more of a descending glide in my mind, as every PG pilot knows, when there's no lift to be found we gradually go down. Unless your cheating with a motor of course

a reply to: surfer_soul

The way I understand it, the current main theory is that the shape of the wing affects the tension of the air. As the air travels along the top surface and towards the back edge (which curves down), the aerodynamic lines get "stretched" wide apart, creating a low pressure area. The exact reverse happens at the underside of the wing - the air gets compressed and pressure rises. Combined together, these two push the wing up as a reaction.

a reply to: Zaphod58

The down wash of a wing lifts it? You mean as when birds flap, bees buzz etc...?
I'm not sure how that works on gliders though? If it does I'd be interested to know thanks.

a reply to: swanne

That sounds about right, good explanation

a reply to: surfer_soul

That's still an over simplification. There's no easy way I've found to describe how lift works short of some serious math that makes my brain sit in the corner whimpering.

As a NASA page put it, there are two schools when it comes to lift. One is the Bernoulli school, that the difference in pressure creates lift. The other is the Newton school, that air acting on the bottom of the wing pushes the wing up. The truth is somewhere in between.

a reply to: Zaphod58

Air pressure can be considered a Newtonian effect, no? Unless I am missing something, the two lines of thought are pretty much equivalent. Air gets compressed under the wing (Bernoulli) and this action upon air creates a reaction unto the wing (Newton).

a reply to: swanne

That's why I say it's somewhere in between. Air goes faster over the top of the wing, and air pushes up on the bottom. So, as you say, you have to borrow from both schools to find the correct answer, along with a bunch of math that seems to think the alphabet and funny geometric symbols are fun to play with.

This page was written for younger kids but does a good job of explaining what's wrong with both schools and some interesting experiments.

www.grc.nasa.gov...

a reply to: Zaphod58

Thanks for the link, will be giving it a read when I have some battery.

originally posted by: Zaphod58
The truth is somewhere in between.

It has to be, or you couldn't do an inverted climb. As nauseating as that is.

I wonder how much the compressibility of the working fluid (gas rather than liquid) affects efficiency? At low speeds I'm not sure it'd be much, but if you're trying to eke everything out in terms of overall performance that "springiness" might matter. Vortices also seem to carry a momentum of their own, so actively moving the lifting surface into the boundary of a vortice created by a previous movement may give a bit of a boost too. Maintaining a vortice might be one of the tricks, since as long as that swirl pattern is there - it seems there should be a pocket of lower pressure air in the middle of it. I'd guess if it's effectively used there is slightly less resistance on the upstroke along with a bit of lift.

Birds also generate some amount of lift with the shape of their body too. (Its profile isn't all that far from a wing airfoil when they're in the flight posture.) It's probably small, but I'm not sure how much that's accounted for.

Aerodynamics is hard. This is why we still have wind tunnels.

The most simple and probably least satisfying explanation for lift is transfer of momentum from wing to air. Now the exact mechanism to achieve this can be rather complicated, depends on many parameters: shape, speed, density etc.

There are simple approximations that apply under certain assumptions, but they all fail at some point.