I had a similar discussion with an instructor fresh out of OSU's aviation-degree program, not long ago..

Conservation of energy is the problem I see with this:

Quote:


If the action/reaction of the air forced downward has more to do with lift than Bernoulli... where did the energy for enough "thrust" to apply lift come from ? Any energy used up the create the thrust had to come from somewhere and all the physics I understand say that's a losing proposition. Moving something through the air fast enough to redirect air as lifting thrust doesn't add up ('course sometimes I'm pretty dense).. It borders on calling wings nothing more than control surfaces.


As for inverted airfoils.. They aren't like a slice taken lengthwise from a cylinder:




They're more like this:




Where an angle of attack can decide if a less-efficient, inverted airfoil exists.

Some experts (even in the FAA) still insist that compressed air plays a part in ground-effect. Go figure ?

AND...  consider that thrust vector at the wing's trailing edge. If the vertical component were sufficient to be actually holding the plane up in the air.. The horizontal component would have to be pretty significant too. Now we're talking about the wing not only generating upward thrust to keep us aloft, but at the SAME time negating drag to a degree with forward thrust. I don't buy it  

I've been Googling this topic and it's reminding me more of that debate with the OSU grad (and his professor).

Just like in the debate on whether or not light has mass, it seems certain aspects (that are actually based in their very own argument) get conveniently over-looked.

If indeed the downwashed air has sufficient mass and velocity for Newton's law to explain the lift (and it can proven on paper), it seems that the initial action/reaction.. cause/effect is glossed over. What body was acted upon for that initial acceleration to have occurred ? To say that the only, resulting action/reaction is that which lifts the wing is like saying that a cart can roll down a hill without first being pushed up the hill. Or.. it's like saying you can push something with a rope  ??

Scientists can show (on paper) where light has mass and even back that theory by pointing out how black-hole gravity effects it. If that were the case.. turning on a flashlight would be pretty interesting. Instantly accelerating even the smallest bit of "mass" to the speed of light would produce one heck of a recoil 

I suppose you could model and remodel the math and come up with a whole slew of Newtonian vectors and pressure differentials, complimenting and cancelling each other, to show how lift exceeds gravity. Maybe I'm the old dog, 'cause I still see it all going back to Bernoulli and what happens when air takes different length paths to reach the same point.

I need a Tylenol 

Quote:

We'll have to agree to disagree on that. I believe "your" theory was first mooted fairly recently, in the late 1990s & goes against the conventional theories & aerodynamic research of over a century. Like Brett I'm too long in the tooth to go for these new-fangled theories. I'm sure there are other forces at work but the basic Bernoulli concept suits me fine. Here's an explanation of both theories. http://www.pilotsweb.com/principle/lift.htm#lift01

Quote:

Well, air doesn't actually move in lines like the usual diagrams. Nor is it split into molecules. It's much easier to visualise air as a fluid like water. I believe the concave lower surfaces of those wings act in much the same way as a flat-bottomed high-lift wing section would.

PS. Here's a diagram of that paper experiment I mentioned. This was first described in 1910 & is still the best demonstration of "how 'planes fly" that I know.

Alright, back up, back up, one at a time... and stand still, you...!

Let me try to adress some of the very clever points being made here in one swell foop...

Brett hit it on the head: in a sense, the wings are merely a control surface. They deflect air that would ordinarily just flow back alongside the plane (picture a plane with propeller but no wings trying to take off).
Where does the energy come from to produce lift? Well, I don't see any paradox there; why can't there be enough energy in the slipstream (the relative wind, not necessarily the prop slipstream) to create lift by reaction as it goes down off the back edge? Prove to me that that can't be, and I'll shut up... after you provide an alternative better than Bernoulli's.

 And I may have misled some of you talking about the "forward" part of the reaction... I did not mean to suggest that the camber of the wing somehow produces enough thrust (in the classic sense, meaning that which equals or overcomes drag and weight in flight) for acceleration... my feeling on this is that a good wing, properly flown, will produce a little thrust, maybe enough to keep the induced drag caused by lift from getting out of hand and spoiling the whole show... but that's really not very important in a discussion of Bernoulli and Prandtl vs. Coanda and Newton (a tag-team match that has kept pilots busy on rainy days for a long time!)

And in arguing with me about inverted airfoils, Brett has somehow agreed with me. If i may repeat myself:
If Bernoulli's effect- which requires the bottom of the wing to be flatter than the top- were the main source of lift, how would a standard airfoil- that is, asymmetric in cross-section- produce lift while inverted?
Brett's diagram of an "inverted" airfoil looks a lot like a symmetrical airfoil to me. I realize that a standard airfoil (let's picture a Cub wing, whatever NACA # that is, for argument's sake) is not symmetrical front-to-back, and yes, the bottom of the leading edge is rounded a bit, but in essence it is flat on the bottom, humped on the top, and tapers off at the training edge.

If it were solely up to Bernoulli's molecules flying in formation, that type of wing would not fly upside-down any better than a  piano., regardless of ram-air pressure, laminar flow, or anything else. The curvature, now on the bottom, would create a low pressure zone under the wing and a high above it, and no more flying that day. If an aerodynamic principle is true rightside-up, it is true upside-down, right?

And yet, I have seen such wings fly inverted, and Bernoulli be damned, it works!
Granted, a wing with a little roundness on the bottom will definitely help things while flying upside-down, but again, that type of wing also knocks Bernoulli out of the game, because a hi-perf aerobatic wing will either still be flatter on the bottom, which won't work in inverted flight according to Bernoulli, or it'll be symmetrical- a shape that, according to Bernoulli, shouldn't fly at all!The roundness helps because of the Coanda effect.

With forward speed from a powerplant or in a glide, and sufficient angle of attack, any flat, inclined plane could be made to fly, however horribly: a barn door, overstarched Jockey shorts, you name it. You all know that in your hearts, so the next question is: without that upper-surface curvature, how can lift be produced if the air molecules cannot speed up to make that longer trip in time to meet their partners at the trailing edge ? Which reminds me: who says they always meet up at the same time? What happens if one or two million of them get sucked into the pitot tube or fresh-air inlet, or carom off the fuel filler cap? Nothing... because they don't have to meet up at the same time, and probably rarely do.

Quote:

The Cub would possibly fly inverted (I've flown a model Cub inverted) but the wing would have to be at a much greater angle of attack to maintain altitude. No matter what shape the bottom surface is the air will still have further to go over than under. If your theory is correct there would be no need for different aerofoil sections for various purposes. If I understand you correctly all the lift (centre of pressure) would be concentrated on the trailing edge.

Quote:


No; I'm not explaining it right, I think. The curvature makes all the difference for various purposes, but the angle of attack is all that's needed. The most perfectly purpose-shaped airfoil won't work at all without the necessary A of A (I'm talking about mean chord line related to relative wind- I believe in the UK "angle of incidence" and "angle of attack" are opposite to the American definitions?).

BUT... I've ben hunting around for more proof of my position (which is not so much a denial of Bernoulli's pressure-centric view as a defense of the Newtonian downwash-centered view, aided by Coanda's research in how fluids cling to surfaces), and i found this very interesting take on the subject... it seems we're all right, and i like the way that it's proven here... there's even a very tidy explanation of how the plane you showed us can fly based on Bernoulli's theorem alone:

http://www.usfamily.net/web/stauffer/debate.html



I probably should have kept my mouth shut; the first link provided in this thread explained things pretty well, but it has always irked me that flight students- myself included- are still only offered fluid dynamics at the molecular level when they ask what keeps the airplane up, when all they really need to know is that- thanks to Newton and Bernoulli (and poor Coanda, who's rarely brought up in these discussions)- the air flows down and back off the wing.

Reading Langeweische's explanation, which I found on my own after putting down my FAA-sanctioned textbooks in frustration, was a major revelation for me... and it should be noted that he didn't dismiss Bernoulli completely, he just asserted that a pilot doesn't need to know more than that, whereas an engineer has to take molecular physics into account in order to build a wing perfectly suited for a particular task.

So... class is dismissed, my workday's over, time to go have a beer!