explanation of air over wing is wrong!! so this guy says

[Daveroo]

wow...http://www.physorg.com/news/2012-01-wings.html

[beana51]

Must say its interesting!...however I will stay with The "STICK AND RUDDER" concept ,by Wolfgang Langewiesche....his Theory's stood well with me for so long.

I guess we still have never yet learned from the "PTERODACTYLS or the BUZZARDS!"...So I guess the answer is still for the birds!!....Thanx!!<label for="rb_iconid_24">http://www.sim-outhouse.com/sohforums/images/icons/icon23.gif</label>

[aeromed202]

I remember other arguments like this. This one seems to start with a not-so-true-from-the-start statement, that air particles being split by the foil (symmetrical here) must reach the trailing edge at the same time to generate lift. I don't think anyone really believes that, although it would be close depending on various factors. The vid also exaggerates the statement by inducing a near stall to show turbulence. This high AoA plus the foil symmetry depicts more what happens to an aerodynamically shaped boat rudder than typical asymmetric foil designed to induce lift. Just take an 8x11 piece of paper, hold an edge near your mouth letting the paper fall away from you, then gently blow across the top of the paper surface and it will lift. There's lots of physics at work to generate wing lift and I can't say I disagree entirely with this guy, but basic wings get lift primarily from the pressure differences between above and below them and clearly, by the fact that we make things that do fly, having air particles not precisely meet at a trailing edge just doesn't seem a big impediment. I think I'm on good ground with this but it's been a long time since school. All those mind-mushing physics classes finally paid off.:isadizzy:

[Wing_Z]

I've never understood all that air-over-the-wing-goes-further-and-so-must-go-faster-so-by-Bernoulli-the-pressure-must-be-lower-due-to-higher-velocity-and-so-we-get-lift stuff.So it must be wrong... I mean, how does that explain induced drag?
Mind you, the aerospace engineers also had some difficulty designing to that theory, and so spent eons developing the NACA aerofoil sections (http://en.wikipedia.org/wiki/NACA_airfoil) so mortals could build aircraft.
When computers arrived they used computational fluid dynamics which couldn't care less about wrong high-school theories.

Babinsky is a scientist not an engineer, and so can't live with this misconception.
Good on him, hope the next-gen school-kids appreciate it too .

[OBIO]

I'm with aeromed on this one....the "wing" was nearly symmetrical in shape and set at a high angle of attack...not really an ideal set up to show the speed differentiation over and under the airfoil. Use a nice asymmetrical airfoil set at a neutral angle of attack...and then repeat this experiment.

Does it matter that the air flowing over the wing and the air flowing under the wing do not reach the trailing edge at the same time? I have no idea. All I do know is that for 100 plus years, heavier-than-air aircraft have been leaving ground, soaring into the sky, and flying around up there over our heads. Do I pretend to know all the science and physics and mathematics behind the flight of aircraft...heck no. Does that lack of absolute understanding lessen the awe I feel each and every time I see a plane fly overhead...nope!

OBIO

[Whitehawk]

All he's really disputing here is equi-transit time, i.e. the air moving over the upper and lower surfaces MUST arrive at the trailing edge at the same time causing the airflow over the upper surface to move faster. Which is rubbish. There is nothing happening to MAKE the air flowing over the upper surface arrive at the trailing edge at the same time as the air flowing over the lower surface. That is not to say that the airflow over the upper surface does not move faster, in fact his video proves that it not only moves faster, it moves so much faster it arrives at the trailing edge BEFORE the corresponding airflow along the lower surface. Bernoulli's theorem stands in the sense that the faster flow over the upper surface causes a lower pressure and it is this pressure differential that causes Lift. Of course, that is not the ONLY reason the wing creates lift, otherwise we would have big problems at speeds in the greater than 250KIAS (ish) range where the compressibility of the air causes significant errors to occur in a pure Bernoulli's Theorem calculation. (Bernoulli assumes that air is, as a fluid, incompressible).

At least, that's how I understand it lol! (Flight Instructor in training)

[hawkeye52]

As Whitehawk stated, Babinsky is only disputing "the air (particles) above and below the wing need to arrive at the T.E. simultaneously". In fact, Babinsky clearly states that the introduction of curvature (i.e., an airfoil) causes a pressure differential. But I'll go him one further: stick a piece of very flat plywood out of an automobile window at, say, 35 mph...and watch that puppy L I F T away! The mere introduction of A-o-A creates the pressure differential and thus the lift. There are many aero vehicles that in fact have no curvature in their airfoils; missiles come to mind. I believe the Zipper (F-104) has a diamond cross-section airfoil.

Wing also brings up a point which I suspect is key in understanding the origins of the classical explanation. Physicists and mathematicians are scientists, and scientists are big on things such as Continuity and Boundary Conditions, which require that the air particles arrive simultaneously at the T.E. for theories to work.

I too grew up with the classic explanation of lift, but years ago I read that it was bunk. That author made a statement that has always stuck with me: attach enough thrust and you can make anything fly.

- H52

[aeromed202]

I love this, lots of fun isn't it? There was this neat demo I saw as a kid in a science museum. Picture a square tube 3' long, an "airfoil" made of plastic with a classic foil top surface and a flat lower surface. This foil lies flat on the floor of the tube with a short stick extending down through a small hole that connects the foil to a simple hinge arrangement allowing the foil to move exactly up and down. You push a button that starts a fan that blows air through the tube, across the TOP of the foil only, and voila-it rises. AoA plays a part in lift but at rapidly big costs of drag, and if you think of a foil moving straight and level through air, and for explanation think of that air as being in horizontal layers, the air touching the foil going over the top gets compressed enough against higher layers of air that are less and less disturbed by the foil the farther you look vertically, thus the compression/speed increase/lower air pressure/lift. So a symmetric foil straight and level at speed X would fall from gravity since the pressure forces are equal. Increase the AoA and it will start to lift but drag will increase dramatically. Take my foil in a box shape straight and level at speed X and the pressure forces are not equal therefore you get a net lift without need for increasing the AoA. I remember some profs saying that the air diverges then comes back together but it just never made sense, at least not precisely. But like I said, by golly those things fly anyway.

[Whitehawk]

Certainly is fun trying to understand it all!

All lift produces Induced Drag, and AoA is a fundamental part of the Lift formula:

L=CL x 1/2p x V² x S

Where CL = Co-Efficient of Lift, 1/2p is 1/2 the air density (p being roe, the Greek symbol representing air density), V² is our airspeed squared and S is the plan-form area of the wing.
CL can be broken down into Angle of Attack and the shape of the wing.

Now out of those factors we as the pilot can only control two, Airspeed and Angle of Attack. If we want Lift to remain constant for example in Straight and Level flight, an Increase in Airspeed requires a Decrease in Angle of Attack, and vice versa. Now for a symmetrical airfoil with an AoA of 0 there will be no lift produced, increase AoA in either direction and we get a net result which resolves into Lift (positive or negative) and induced Drag. The same is true for a non-symmetrical airfoil however the zero lift angle occurs at -2 degrees AoA (because of the curvature of the upper surface lift is still generated at 0 degrees AoA).

Increasing AoA at a given speed will Increase Lift, (and therefore Increase Induced Drag as the byproduct of Lift) up to 16 degrees AoA where the airflow separates and the Wing has stalled. Of course, there are some airfoil designs and modifications that can increase the critical angle, everything in aviation is a compromise or a generalisation lol! One other thing to note is that AoA is between the Chord Line of the wing and the Relative Air Flow, that is the air flow experienced by the aircraft relative to it's forward motion through the air, which is why it is possible to stall the wing at any attitude, even pointing straight down! (been there, done that lol!)

Apologies for being long winded, and hope I don't come across as lecturing! Now that I have to be able to teach this stuff I figure might as well engage in a discussion on it! (And hope I haven't gotten something wrong lmao!)

[Wing_Z]

Blowing smoke in a wind tunnel is fine, if you're examining the wing itself.
But when you want to look at the air, and how it behaves, it's a different tale.

From the perspective of the air: There is a huge difference between
A wing passing through an infinite compressible and stationary airmass, vs
Blowing a jet of compressible air over a stationary object in a finite wind-tunnel.

It's so totally different, only a deeply theoretical scientist would think it might be the same thing.
And why wind-tunnel calibration is such a dark art.

I've just made this up, tell me if I'm wrong:
By ramming an asymmetric airfoil through stationary air, the particles are shoved up over the wing, and given vertical momentum, simple as that.
There's a wing between them and their mates down below, so the air is separated momentarily and creates low pressure above the wing as the particles rush upward.
Nature abhors a vacuum, so the wing tries to fill the hole left in the air (=lift)
When the wing has passed, they come back down again.
A good wing separates them smoothly, and brings them together without turbulence (and drag)

AoA is a second, different, component, and is simply pushing air out of the way.
The vertical component = lift, horizontal = drag.
Stick your hand out of a car's window, and rotate your wrist, you'll see how lift/drag change.

How's that? and my wind has only just started getting longer... ;)

[aeromed202]

I like it. That's pretty much it. Several components to be balance to get flight. But I wouldn't go much with the separated bits of air visual. I just used it because it often helps with the explanation. There obviously is no connection like strings or texting between parcels of air sliding around a wing. The top parcel does what it does same as the bottom parcel and the wing moves toward the lower pressure side, that being the more curved, in straight air flow. I also don't think there is a big difference between the tunnel display and open air. The tunnel was more to exclude possible errant forces than devilish intent. If I took that set up and did the same thing in open air it would still work, like planes do every day. But free air has all the trimmings like turbulence, density gradients, speed, weather and debris. However, I agree that true wind tunnels have to be employed with great care as to what exactly is going on for reasons like what you said. Still, they seem to be of great service so people must be doing something right.
For a little aside I use to teach advanced sailing theory which uses all the same physics in both air and water. Sail shape was more picky because it isn't enough to have "lift" pulling the boat over, sails are designed to get that vector sum pointing as close to the bow as possible by tweaking the chord line depth percentage to 35% to 40% or something. There is always a trade off somewhere but the principles are the same. That's probably why lots of my boat friends were pilots too. Ok, I'm upping the ante with a diagram I found where the force vector sum is loosely represented by an arrow. That is affected by where the maximum depth of curve is placed along the chord. Jeez it's been many years but I hope I got the vernacular right. But wings don't have to lift forward, they want to lift up as much as possible.


Oh no, I just found a place to fidget http://www.mecaflux.com/en/plan_site.htm

[pfflyers]

It's funny to see this guy's presentation considered "news."

Thirty-some years ago in A&P school they showed us the neat diagram in our text, then explained that the idea that perfectly matched pairs of air molecules travelling around opposite sides of the wing would meet up again in a perfect pair was bunk, just a simplisic way to illustrate the difference in velocity of the airflow above and below the wing.

[BPbobafett1982]

And thirty years later it's still in my A&P Textbook and the instructor said the same thing. It's an easy explanation to give someone who may not be overly concerned with the exact physics of aerodynamics of a wing in flight. But it gets the basic point across.

[Prowler1111]

Dang!..so that´s why my aero-car prototype does not lift from the ground....:icon_lol:

Prowler

[beana51]

Explain This??......Is it overwhelmingly power?..Or the principles of lift?.......How does the lawn mower seem to perform like a wing??...The Stall landing??....PERPLEXING???<label for="rb_iconid_24">http://www.sim-outhouse.com/sohforums/images/icons/icon23.gif</label>

http://www.youtube.com/watch?v=qn7hRT8Xu4E&feature=related

[hurricane3]

If a symetrical airfoil with a neutral angle of attack meets the onrushing air , does it just drop? I thought a lot of aerobatic planes had symetrical airfoils ,although the angle of incidence might come into play, giving it a positive angle of of attack.And what about a nonsymetrical airfoil flown in inverted flight?I know the AOA has to be increased but if it flys,whats the point of airfoil shape?

[pfflyers]

You are correct about angle of incidence and angle of attack determining lift on a symmetrical airfoil, most helicopter rotor blades are (were) symmetrical back when I worked on them.

As for inverted flight, it's angle of attack again that generates lift. Most aircraft that spent a lot of time inverted have symmetrical airfoils.

[pfflyers]

The RC flying "lawnmower" is pretty cute. Just shows that with enough thrust anything will fly.

[aeromed202]

I want one of those deere-igibles!!:applause::applause: Hurricane, some aircraft, like aerobatic ones, have nearly symmetrical wings precisely so they can do all the things they can do. They have horsepower to spare so they can bull their way around the clouds and force the wing to do those stunts. They just loose on fuel consumption. A non-symmetrical winged aircraft may fly inverted but would need to have a high AOA with respect to direction of flight to make up for the poor lift capability. Look at some vids and you'll see an upside down aircraft pointing the nose skyward just to maintain a level flight. For the typical aircraft though, efficiency is desired so you can lift a decent payload, for the least cost, and go as far as you can on the fuel you carry. So the point of a good airfoil is to get the most lift for the least drag penalty, while flying right side up.