Aerodynamics?

[Hagar]

Whichever theory is true it's all explained from the link Jake posted earlier. http://www.allstar.fiu.edu/aero/airflylvl3.htm

I'm not sure that either theory explains why this flies, and it flies extremely well.

I can't quote the mathematics here, but trust me, It's Newton and Coanda  who keep your plane in the air, not Bernoulli.  
And most importantly, as a pilot I have found it much more sensible to think of this wing that's keeping my ass in the air as simply washing air down and back while compressing it a little beneath, rather than picturing molecules racing along different paths to meet in the same place.

OK, try this practical experiment. Hold a sheet of paper out in front of you by one edge so it droops rather like the Boxkite wing section in my photo. Now blow across the top of the paper. No airflow underneath it at all yet the paper will rise. Explain that.

[Brett_Henderson]

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:

Oh dear, Bernoulli again. Like Langeweische, I agree that the pressure differential due to differences in velocity above and below the wing does indeed happen, but a wing produces lift primarily by forcing air down and back... and as Newton pointed out, there is an equal reaction for every action.

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 ?

[Brett_Henderson]

Hagar describes it very well.. That sheet of paper "lifts" into the lower pressure. Your breath isn't creating thrust at the paper's edge..

[Brett_Henderson]

AND...

[Hagar]

[quote]AND...

[Brett_Henderson]

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  ::)

[beaky]

Whichever theory is true it's all explained from the link Jake posted earlier. http://www.allstar.fiu.edu/aero/airflylvl3.htm

OK, try this practical experiment. Hold a sheet of paper out in front of you by one edge so it droops rather like the Boxkite wing section in my photo. Now blow across the top of the paper. No airflow underneath it at all yet the paper will rise. Explain that.

Easy. The Coanda  effect causes the airflow to "stick" to the curved surface, forcing it down and back. Then Sir Isaac takes over, causing the down-and-back motion of the flowing air to create an up-and-forward reaction.
Remember, it's Bernoulli's theory that requires airflow across the bottom of the wing...
I didn't mean to suggest that ram-air pressure had anywhere near as much to do with holding wings up as the effect of the upper surface...
I think "my" theory, which is not originally mine, but is, in fact, fact , accounts very nicely for the ability of that airplane to fly.
In fact, if we  were to believe that Bernoulli's racing molecules alone were responsible for lift, that "open-bottom"  wing wouldn't work very well at all, since Molecule A and Molecule B would have just about the same distance to travel, following the same arc and separated only by the thickness of that diaphanous wing.

[Hagar]

[quote]
Easy. The Coanda

[Brett_Henderson]

It's curious to me that about 9 in 10 sources on this topic state that Newton's laws do indeed provide the lift and in the same breath, admit it's an ongoing debate, even amongst experts. I'm having trouble getting my mind around this "thrust from no foundation" idea and that bothers me, 'cause if I'm wrong, I want to understand why.

I'm swapping emails with a club member (retired aeronautical engineer). He's acknowleged the problem I'm having with "give me a place to stand and I can move the Earth with a lever" theory as it applies to our Newtonian lift.. as there's no place to stand, or fulcrum for that matter, in this lifting thrust stuff. If we can makes sense out of each other and I can make sense out of what we come up with... I'll post it ASAP..

[beaky]

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.

[Hagar]

I'm swapping emails with a club member (retired aeronautical engineer).

Well, I'm a retired aeronautical engineer. I've also been designing, building & flying model aircraft since I can remember. I was taught basic aerodynamics theory over 50 years ago & see no reason to believe what I was told then is suddenly wrong. I'm not against new theories per se but not when there's no need for them.

I'll be interested in what you come up with but I'll take a lot of convincing.

[Hagar]

[quote]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

[Brett_Henderson]

My diagram of airfoil cross-sections was supposed to show that an angle of attack can be parallel to EITHER surface. Even the non-symetrical airfoils we all know can be inverted  and be airfoils in either direction at a given angle of attack...

My engineer pal is admitting his own dilema trying to visualize a wing redirecting air, resulting in a net, upward thrust. If that were possible.. sailboats could sail straight into the wind.

And yes Rotty, even a stalled (throwing Bernoulli out without a parachute) wing can keep itself airborne with enough momentum or engine thrust. But that's not lift or "flying". That's more along the lines of the stone skipping across water.

[beaky]

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. No matter what shape the bottom surface is the air will still take longer 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.

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!

[Hagar]

This will keep the academics arguing for years.

(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?).

You Colonials usually go the opposite way (I suspect just for the sake of being different) but I don't think so in this case. I see angle of incidence being the angle the wing is fitted to the aircraft. This is usually fixed. Angle of attack can be changed in flight with the elevators.

the air flows down and back off the wing.

Sorry. I still can't get my head round that. :-/

PS. Surely this is the whole crux of the argument. The wing is moving through the air, not the other way round.

PPS. Food for thought. Note the flaps are lowered. http://www.dfrc.nasa.gov/Gallery/Photo/B-747/Medium/ECN-4242.jpg