Aerodynamics?

[Brett_Henderson]

Your artistic license on the airflow, is about the same as mine with the leading edge (it gets a point across).  

We (and many others) have discussed the balsa wing and sail structure, as to different/same length paths, and have concluded (as can be seen in a wind tunnel) that air can be "trapped" in the convex portion and act as the bottom surface... as it would have to be.. BECAUSE the air directed up (leading edge or in that convex area) would again have its own action/reaction countering the whole lift deal..

Try applying another, universal law of physics; Conservation of energy....

[beaky]

I'm feeling a little malicious tonight, so if you don't mind, I'm gonna get my Crayons out now.....



Okay, I'll admit, I took a little artistic license with the airflow but more importantly notice how easily path length is altered with a small change in relative wind.

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...

[Brett_Henderson]

[quote]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.

[Brett_Henderson]

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

[OTTOL]

the balsa wing and sail structure, as to different/same length paths, and have concluded (as can be seen in a wind tunnel) that air can be "trapped" in the convex portion and act as the bottom surface... as it would have to be.. BECAUSE the air directed up (leading edge or in that convex area) would again have its own action/reaction countering the whole lift deal..

I have to say that ya' lost me on that one.
How does air "get trapped in a convex structure." And where does a rubber-band powered airplane have a convex anything (they come in a flat package and are a stamped out of a flat piece of paper-thin balsa). The same thing applies when using a paper airplane as an example.

[quote] Try applying another, universal law of physics; Conservation of energy....

[OTTOL]

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.

[beaky]

Let's put it this way... 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.  

BH:If that does not happen (same volume of air behind the wing as there was in front).. there'd be a vacuum somewhere along the way... and we know that aint happening.

R:  Depends on what you mean by "vacuum"... perhaps a zone of lower-than-ambient pressure?

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?

BH:  Paired molecules don't meet.. it's a mass thing (same amount front-to-back)..


R:Agreed.
I am embarassed... I can't find the source of the whole "paired molecule" thing, but that is how Bernoulli was explained to me, long ago. As it turns out, his ideas make more sense as applied to Venturis: he simply showed that flowing fluid, when constricted, will accelerate, thus losing pressure. I thought Venturi first explained that, but what do I know?
That being the case, though, this diagram elegantly shows how Bernoulli's work explains how a wing works:



But I still think this action is not the main factor.

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?

BH:A stalling wing has long since transitioned into ballistic lift, akin to the skipping stone.. and any pressure-differential force is now more opposite the planes moving mass (a flying wing in level flight  is has zero inertia opposite the lift). Stalled or stalling wings take us out of this discussion..

R: But what about when it's almost stalled? Or when the root is stalled, but the tips are not? Besides, the stall is important, because a stall, the moment it happens, is an interruption of lift. It shows very well what causes lift in the first place.

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?

BH: Again.. stalling changes everything.. but if you look at my diagram, you'll see what I'm pointing out. The orange "origin" of this lift vector would be acting/reacting into/from nothingness. You can't have directions and magnitudes (vectors) yieding a final componemt in any one direction without an outside source of energy. The air came "up" from somewhere, in order to be moved "down" and those vectors cancel.

R:  With a flat plane, no camber at all, and assuming no camber shape due to laminar flow (let's lay laminar flow aside for now), how would the air be deflected down off the top? Coanda effect, that's how. Not from/to nothingness... from one velocity to another (velocity in this case meaning speed and direction). In fact, without Coanda's priciples, there'd be no laminar flow, if I'm not mistaken. But I digress..

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.

BH:It will NOT fly at a perfectcly zero AoA.. it WILL descend, albiet slower in proportion to its velocity regardless of velocity. An airfoil WILL fly at zero AoA (with enough velocity)

R: Sure, sure. Thanks to that hump and the resulting deflection/pressure drop, a cambered airfoil is more efficient. That's one reason why you don't see barn doors with empannages flying around, even thought it'd be cheaper to make planes that way.

But a cambered airfoil has an effective zero A of A, slightly negative... or consider this: your cambered airfoil still flies when its flat bottom is "level" with the horizon in part because the air is still flowing down off the upper surface.

And a barn door could fly... therefore, camber- and Bernoulli- are not required for flight... they just help.

[RitterKreuz]

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.

[OTTOL]

Dang Daddy!!! I'm glad that there is a 5,500 word limit. That's not a post it's a short Romance Novel!!

[quote]

[Brett_Henderson]

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)..

[Brett_Henderson]

[quote]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.

[OTTOL]

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.

[Brett_Henderson]

Don't think of it as paired molecules.. Just remind yourself that there can't be less air in a wing's wake than there was before it passed by..

[OTTOL]

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...

cancel.NO NO NO... That was to illustrate why the Newtonian stuff can't work out. I was showing that IF the vectors acting on/from nothingness COULD happen, they'd ..

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.

[Brett_Henderson]

Let's just talk about the purely vertical components..