OTTOL wrote on Jan 9^th, 2007 at 10:52am:

I'm not sure i get the point, there... although I am clear on your postion in The Great Lift Debate ( I think)...

What's missing in the first pic is what the airflow under the "flat bottom" wing is doing... it's not like that hard corner somehow stops air from flowing under the wing.
Regardless, however, that nearly-symmetrical airfoil shown in the second picture would need a bit higher A of A to get the same amount of lift as the first shape (assuming the same A of A and airspeed). in your diagram, it'd be nearly stalled, except maybe at an extremely high airspeed. But we also don't know the loading of this wing or its aspect ratio... so whatever.


I would never say Bernoulli's theorem doesn't figure into it at all... it does, or at least it appears to, but I am convinced that Newton's law and  Coanda's (verified) effect have a lot more to do with the lifting properties of an inclined plane than path-length differential alone, with its effect on pressure.

  And I can prove it.

Let's put it this way, for the Bernoulli fans: so far, no experiment has verified pairs of molecules arriving at the leading edge holding hands, parting company with the promise to meet up at the trailing edge, then altering their respective velocities in order to keep their scheduled date.

Not saying it ain't possible; just saying I don't believe it's been verified... hence the term "Theorem", or "Theory".
Newton and Coanda, however, enjoy the status of law-definers: their theories have been verified as fact or law, without fail, over and over again.

I know there is acceleration of airflow over the top, which of course leads to a pressure differential, but it's the motion of the mass of air off the top of the wing , down, and back that makes the real difference. Tweaking camber for enhanced pressure differential, or changing the planform or length of a wing... these can help improve efficiency, but not in all cases at all speeds. Change the A of A, however, and you get results, no matter what other variables are present.

Consider turbulent air, such as you see above a stalling wing: isn't turbulent air faster still? Isn't the pressure of a volume of turbulent air much lower than still air or air that is flowing in only one direction? Sure, the non-linear nature of turbulent air keeps Bernoulli's paired molecules from meeting on schedule, but even Bernoulli would tell you it's not so much the "paired molecule" thing as it is the pressure differential... right?

Which brings us back to the bottom line: if it isn't primarily "downwash" (and by this I do NOT mean air "bouncing" off the bottom of the wing, but air forced down off the top) that keeps a wing flying, why is it that any wing can be stalled at any airspeed if the A of A is not within limits for that wing and load at that airspeed? Don't the air particles still have farther to travel over that top surface?

And talk about pressure differential!! Picture a plane in extremely nose-high, mushing flight, just on the edge of a stall: the bottom of the wing has a much greater pressure buildup, thanks to increased ram-air pressure, and with the airflow starting to break up over the leading edge, causing turbulent air to spill away from that curved top, the low-pressure zone on that side is low indeed. ..  the ratio of high to low pressure spreads out significantly...according to Bernoulli alone, the plane should now zoom backwards, still nose-high.
Right?

But we know it doesn't... it continues to mush, or descend  despite application of power (RORC), or, unless A of
A is reduced, it stalls. Because without Coanda's fluid dynamics providing cohesion of airflow to the top surface, optimized by the correct A of
A for that airfoil at that loading at that airspeed (and with that aspect ratio) there is no downwash to demonstrate Newton's law.



Thus the extreme pressure differential alone becomes insufficient to produce enough lift to support the weight of the aircraft, because air is no longer flowing in a coherent manner down and back off the top of the wing.


Conversely, you give me a plane with two flat pieces of plywood for wings, no camber at all, and with enough power and the right A of A I will make it fly. Guaranteed. It will fly better with a little hump on the top, even if the bottom is concave and Bernoulli's little friends have only a few inches' difference in their journeys, but it will fly with perfectly flat wings, showing downwash and acceleration over the top.

Sorry; couldn't help myself...

Edit: I'm not yelling; I didn't realize how large the .jpg text would appear 

How'd that little Newtonian ditty go again?.......

Oh yeah......



I hope you don't come after me for the rights to these images that I'm defacing....

Remember, one of those big blue arrows is yours.

I think (with regard to the vectors that you placed on the first drawing (the unaltered one ) that you were approaching the Newtonian portion with a Bernoullian mindset.  

note to anyone preparing for a check ride:

the correct answer to this question is the answer that your CFI told you as you would need to say it on an oral exam. end of story.

while flying along - GOD HELP YOU - if this is the stuff you think about  LOL

because if it is - you need to consider engineering airplanes instead of flying them.

remember a pilot is a technician - but an aviator is an artist.

which are you?

on an oral exam this seems to suffice...

"As air flows over the upper, more curved surface of the wing it is accelerated, this creates an area of relatively low pressure above the wing. The air flowing below the wing is flowing slightly slower and creates an area of High pressure below the wing. The high pressure below the wing seeks to equalize with the low pressure above the wing creating lift, which in turn pushes the wing and everything attached to it upward."


the worst an examiner could do is say "why?" at which point you could provide a brief explanation of bernoulli or venturi effect... BUT any examiner who digs into that answer is a down right SOB - period.

Hey Rotty.. I don't have the energy to keep this up (quoting pasting sorting posting  lol  ).. so I'll just say, " I have to admit that I CAN 'see' the Newtonian suff"..  I just can't reconcile it with conservation of energy...  I  REALLY do want to be in the right camp, but I can't fake it and honestly believe that when all the moving, redirected, sped up and swirling air stuff balances out.. it's the pressure differential that makes the difference between a wing and a barn door..   

And Ottol.. what's mine is yours     (and mine again)..

I know that I'm agreeing with (and actually paraphrasing what you've already said). The point that I was trying to make is; there actually is data disproving the whole "paired molecule" myth.

Really, really it won't hurt you. .....It's a very nice article.  

The problem is; and the "paired molecule" idea is prime example number one. People tend to search for simple answers to explain complex things. I used to teach the "paired molecule" philosophy when I was a CFI. Because that's what I was taught.

Oh geez!!! Operator?......All lines are busy!!

Sorry, I didn't expect you to slip a response in there..

That last one was for RottyDaddy...

Quote:
I think I understand that ....but.....If you are a believer in the idea of Newtonian Flow Turning, then the direction of energy would be the same as the big blue arrow that you, I'm guessing unwittingly, represented. Soooo......naturally, an equal amount of energy would be applied in the exact opposite direction. I'm not sure where you would get a lift vector 20 degrees aft and upward from the center of lift and 30 degrees forward and upward (approximately)when all Newtonian theories show the flow vector angling down and aft from the trailing edge.