Ok guys, I know some about aerodynamics, but i dont know EXACTLY how it works..

Maybe some of you can help me?

Cheers Theis (P.S. I couldn't find something on google, that REALLY explains it)

Well, I figured I may as well post what I know about aerodynamics, even if you already know what I'm telling you (Please discard my previous post )

Welcome to Dr. Charlie's Flight School

It is important that an aircraft is aerodynamic. If it wasn't, it would not be able to reach enough speed needed for it to fly, which leads on to the aircraft not attanining enough lift to fly.

An aerodynamic aircraft can get to higher speeds because it is not fighting as much "air resistance" (AKA "drag") than that of a not-so-aerodynamic aircraft.
But what is this "air resistance"?... I hear you ask. Air resisitance is the air particles hitting the aircraft as it flies. The faster the aircraft travels, the greater amount of air particles will hit the aircraft and slow it down.
Let's take a look at a very detalied diagram to show this effect:

http://www.simviation.com/yabbuploads/aerodynamiclesson1

The aircraft at the top of this diagram isn't as aeridynamic as that of the aircraft on the bottom of the picture. The blue arrows represent the air flowing over the aircraft as they fly. As you can see, the less aerodynamic aircraft causes a longer route for the air to travel, thus more air particles can hit it, causing more air resistance, meaning a slower speed of flight. The more aerodynamic aircraft is like a dart, slicing through the air, and causes the air to take a shorter route to travel around the aircraft, thus less air particles can hit it, causing less air resistance, meaning a faster speed of flight.

If you need more info, Dr Charlie will try to provide it.

Aerodynamics "is" (as a singular science) a pretty broad study. It simply means;  "How air moves".

Aerodynamics "are" (as in all the ways a plane is affected in flight) everything from aerodynamic efficiency (so eloquently diagrammed above) to aerodynamic mechanics (how a plane has lift, turns, banks, etc.).

You could study it all for years and still have things to learn..

Theis, just be a little more specific (eg - how does a wing work/types of drag/propulsion etc) and I'm sure we'll be able to help in some way... 

Heres something to get you started, its got the basics:

http://www.allstar.fiu.edu/aero/airflylvl3.htm

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A wing produces lift because of it's shape and how the air flows around it. A wing, looking through it, is shaped like an aerofoil. An aerofoil looks like the following:



The rounded egde of the aerofoil is the "leading edge" of the wing, and the flat end is the "trailing edge" of the wing. The leading edge is round, and splits up the airflow over the wing. The airflow underneath can go in a straight line and flow faster, whereas the airflow over the wing has to go over the leading edge and down the wing, thus flowing slower. The faster airflow causes more air particles to hit the underside of the wing, causing a higher pressure. The slower airflow over the wing causes less particled to hit the wing, causing a lower pressure. As an aircraft trundles down the runway, the pressure increases on the uderside of the wing, eventually so much pressure is caused that the aircraft is literally lifted off the runway.

Dr Charlie will try to provide more info if needed

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I see, thanks Hagar. Seems I mixed up what my Dad told me

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. Air flows down and back; wing tries to go up and forward. The ram-air (not Bernoulli-induced) pressure buildup under a tilted plane moving through the air is a factor also, but the action of the upper surface is more important.
If this were not true, then how could an airfoil with a cambered top and flat bottom be flown upside down? Sure, the region of turbulence on the upward-facing surface of the wing would cause the air above it to curve a bit, but that turbulence would create a little more drag...it's important that the air curve over that surface on its way aft (see Coanda Effect), but that's because a sufficient volume of air at a sufficient velocity must keep spilling down and back from the training edge in a coherent stream in order for the wing to produce lift.  And what about the bottom of this inverted wing, which is curved? What does Bernoulli make of that?
There are airfoils that are cambered on the top and bottom, in order to make inverted flight more efficient... how could they work with Bernoulli's priciples only if the lower side of the wing is not flatter than the top, eh? Discounting Bernoulli's theorem, you can see that with the right angle of attack, the wing, whether it's a standard or symmetrical airfoil, forces the air down and back as Coanda illustrated, and this action produces a lifting effect as Newton proved. Of course, thanks to the Coanda effect, the air flowing past a cambered mower surface might produce a negative-lifting effect as the curve of the wing forces it up and back, but it doesn't, generally, because of the angles involved, as well as the fact that flat or curved, and inclined plane moving through the air compresses air beneath it. There's your high pressure, which compensates for any pproblems caused by a curved wing bottom trying to throw air up and back. If it were only about pairs of molecules separating to take different paths past the wing, this wouldn't work nearly as well as it does.
  I know Bernoulli's ideas are gospel in many aviation textbooks, and Newton and Coanda are ignored, but ithe Bernoulli Effect, while real, I guess,  just ain't the thing that does the trick. There is in fact a pressure differential between the top and bottom of a wing in flight, but it's not the primary factor. I think the aerospace community has latched onto Bernoulli just to be different;  he is their boy, and other disciplines don't need his theorem as much.
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.

To quote Langeweische:
Trying to understand the piloting of airplanes by concentrating on Bernoulli and Prandtl is like trying to catch on to tennis by studying just exactly how the rubber molecules behave in a tennis ball when the bal hits the court and just how the catgut behaves in the racket when the bal strikes: instead of simply observing that it bounces!

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:

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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 

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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

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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.

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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.

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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!

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LOL! It has... and will... and you better not be calling me an academic- them's fightin' words, mister.


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Whew, that's a relief... I heard somewhere that you Brits have it all backwards... . I actually own a copy of the very dry but fascinating An Introduction to aeronautical Engineering, Vol.1 : the Mechanics of Flight by A.C Kermode, B.A., Fellow of the Royal Aeronautical Society (printed 1941), I was thinking I got that impression there... let's see... flip, flip... but no, he's got it right, too. Probably just one of those pernicious myths you hear hanging around airport bums.

And for what it's worth, here's an excerpt that shows an even more interesting view of how a wing produces lift, which integrates the pressure and downwash theories:
Another way of looking at it is to consider the curvature of the streamlines.  In order that any particular particle of air may be deflected on this curved path, a force must act upon it towards the centre of the curve, so that it follows that the pressure on the outside of the particle must be greater than that on the inside; in other words, the pressure decreases as we approach the inner streamlines, i.e. the ones near the top of the aerofoil. This point of view is interesting because it emphasizes the importance of curving the streamlines downwards, which is the essence of the whole matter.
Hmm. I have only skimmed this little book, mostly to admire the nice photos of vintage airplanes, but I should really hunker down and read it thoroughly some time. ..

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You're absolutely right, but the "down and back" I keep referring to describes only the air's movement relative to the path of the airplane... although when you consider how the air following the curve of the airfoil (and the zone of higher pressure ahead of its leading edge  produced by it as it moves throught the air) apparently accelerates, there's a little more to it... it all looks so simple, but man, is it complicated!!
Whatever- all I can say at this point is that if I start thinking about fluid dynamics on the molecular level while flying, I'm going to end up in a tree somewhere, but if I remember that the wing must keep that downwash going, I'll be OK.
If I ever want to design an airplane, though... 
 

I like Rotty's reconcilliation (and so does my engineering pal, as he's cursing with each email for making him think about this stuff).

My last thought is comforting and confusing at the same time. I read a formula showing the total pressure-differential lift for a Cessna at 100kias as 60 pounds.. and it makes sense. Where 60 pounds is obviously a fraction of the lift needed to keep a 2300 pound Cessna airborne.. my pal pointed out that it's like a thrust itself. It's not just 60 pounds in a single impulse.. it's like 60lbs/sec/sec.. (acknowledging the fact that mass and weight are ony interchangeable when gravity is a constant) and will have a cumulative effect storing the lift along with stored inertia (both as altitude and velocity)..  i.e.   1 lb of thrust can eventually accelerate a 1,000,000 lb object to near the speed of light when drag is anything less than 1 lb.

I need a beer too.. and I don't drink  lol

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That's interesting... what's with the vapor trail off the right stab, I wonder? Is it slipping?

Poor Theis indeed. I'm sure he will find this discussion more interesting than the average crusty lecture. It's given me something to think about too. Rotty almost had me convinced.

I'm afraid all these complex formulae make my head spin. I'm just an 'umble fitter, a practical sort of chap. I once had a brilliant maths teacher who demonstrated that maths is like statistics. A skilled mathemetician can prove almost anything depending on how it's presented & will enjoy doing so.

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Unfortunately the caption doesn't give the conditions at the time the photo was taken or the reason for the test. That break in the smoke could be something simple like a minor blip with the smoke generator. However, I think it serves its purpose by showing no significant downward movement of air (except behind the lowered flaps) which I would expect if the Newton/Coanda theory is correct.

I was looking for something to demonstrate the airflow behind the wing of an aircraft in normal flight without resorting to all this scientific gobbledegook. A picture can say more than a thousand words. Sadly I can't find the well-known photo of a B747 streaming contrails or the B-17 formation I was looking for. If I recall correctly both conclusively show the airflow behind the wings being deflected upwards rather than down. Then I suddenly realised I've seen the proof many times over the years at various air displays. I've even taken photos myself. I think this one of a B-17 streaming smoke from the engine exhausts demonstrates that there's no significant downward deflection of the air below or behind the wing in normal straight & level flight.


I'm not sure what these prove but thought I might as well post them anyway. Despite the attitude the aircraft was moving horizontally under full control.

Hagar has definitely rattled me with those pictures, but I'm still on my feet.
Gimme a minute...
Okay, have a look at these:

I was trying to find a pic of a plane passing through smoke or mist; I think part of the reason so little deflection is seen in your pix is because of the forward movement of the plane, and the plane being the source of the smoke or vapor. It's not like the downwash effect is going to produce a pronounced S-curve in smoke trailing from a plane... it's more subtle in that case. But ag planes  provide a good study, as they are moving fairly slowly and in a level attitude...granted, the nozzles point downward a bit, and of course the spray is heavier than air, but...I think these pictures show downwash. Maybe I'm wrong.
This pilot could not have just been flying lower- is it just the spray settling, or does it seem to also be flattened behind the plane? This pic really shows the lateral component of airflow along the wing, something that just complicates this debate... But I will say that the obvious energy of the tip vortices indicates a much higher-than-ambient pressure situation below (and just aft of?) the wing...


This pic shows that the spray may not just be settling, causing it to be lower than the flight path (although it obviously will, eventually- Newton again). Look at the streams of spray nearest the vortice off the right wing. Is the vortice "carrying" it upwards, or what? It looks like the spray is actually higher than the plane well beyond what could be the "downwash zone" but this front view makes it hard to say.


this one supports my case pretty well, I think. If that downward trail of spray is due only to the velocity of the spray as it exits the nozzles, that would be some pressure in that system! I don't know how high the pressure would be, but... I'll grant also that the spray is expanding in a conical shape, so again this doesn't prove very much.


Here's a closer look at the spray exiting the nozzles. It's really not spraying downward much, but look at its path immediately after. It goes down. Not much; in fact, it's  as if it's only being deflected just beyond the flight path... which would make sense in level flight, as all that's required for that is, well, enough lift for level flight. Brett's earlier post about the forces required helps explain this. I can't find a pic of a plane starting to climb in a relatively flat attitude (yet! ); I think that might tell the tale. And look again at this one: about a plane-length behind the agplane, the mist is still fairly coherent, but hasn't sunk much due to gravity... from the trailing edge of the wing to the edge of the picture, you see a long , gentle curve followed by a flat area several feet below the flight path (assuming it didn't climb at all). Of course I'm reading a little into this , but... if it was all about a high forming above the wing due to air accelerating on a curved path, would gravity  alone bend the mist this way?



Now, everybody's seen this nice picture; often used to illustrate wingtip vortices (another thing we could discuss forever). But it shows something else... look closely at the trough carved by the plane. If there were no downwash, wouldn't the vortices just be flung up over the level of the cloud deck? And if the air were just slipping under the wing, practically undisturbed, would there be such a deep trough in the cloud? Of course, the plane is just flying off the edge of the cloud, and possibly descending slightly, but I believe that the part of the cloud nearest the camera, where the cloud top is sloping down and not providing much vapor for good vortice-viewing, shows the dimensions of the depression left by the downwash before the cloud moves in to close the gap as the vortices dissipate. Not proof of anything, really, but...

You two just WONT give up a good fight, huh?

Now I'm trying to picture a venturi-like tube attached to an aircraft and trying to explain to myself that because the air leaves the tube faster than when it entered, there's at least enough thrust created to cancel the drag that the tube creates.. let alone have some left over to do any type of work,, such as lift.. It aint addin' up   

I think you're talking about wake turbulence and/or wing-tip vortices. There's no disputing that they travel downward. And it's not just heavies..

I can tell you first-hand about it, and turning a low base-leg just after a Citation had touched down after a long, straight-in final.

I was going to respond.. but anything I'd say is already in this thread

Summary: Getting enough mass, to move quickly enough to act as thrust simply by redirecting it (the act of RE-directing it would have to consume as least as much energy as any thrust generated) tickles with perpetual motion.. I can't sell myself on this theory anymore than I'd believe the wake a boat would create can help guide or propel it.

Uh OH.. I just had a mental break-through !

There is no horizontal component as the air isn't moving, the wing is. So....... the only redirection of the air IS downward..

HOWEVER... that still doesn't satisfy my perpetual motion problem (or does it ?)

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Okay; call it a draw. You have the formal training; I don't expect you to yield to a layman's observations. I'm not trying to change anyone's view so much as argue the case for downwash as best I can. As a pilot, I "feel" that downwash plays a role as well as pressure differential due to fluid dynamics, and without hard data about nozzle pressure and how much of an angle the deflection needs to be for a given weight and airspeed, blah blah blah, we're not going to really prove anything.
I think "aerodynamics" should be a sticky; these fact-and-theory-filled discussions seem to pop up every time some young innocent asks one of those "what does it all mean?" questions...
And in that spirit, I want to stir the pot with another something from Mr. Kermode... we are all probably familiar with the first four airfoils, and their specialized purposes are pretty obvious.... but how about the last one? Unfortunately, it's not explained anywhere in the book, as far as i can tell so far.
I figure if Hagar doesn't know, we're all stuck on this one. I've never seen a wing like that, as far as I can remember... and it definitely wreaks havoc with my ideas about downwash, although it seems unlikely to work well by anybody's reckoning. This type of wing must usually be mounted at a high angle of incidence, I think. Or maybe it's one of those shapes that never got off the ground (pun intemded!).

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Very interesting. I must hunt out my old modelling books that explain many of these things in detail. My immediate thought is that the reflexed section would be used on delta-winged aircraft. Not sure if there was such an animal in 1941 when your book was published.

I have a high-performance slope soarer designed by my old friend Chris Foss who is also a full-sized glider & power pilot. Not much this chap doesn't know about flying. The Phase 6 is still regarded as THE competition sloper & many championships have been won with it over the years. http://www.chrisfoss.co.uk/Phase6.htm
It comes in two versions, the fully-symmetrical 'pro' model & a 'sports' model with semi-symmetrical wing section. I have the pro version & remember he told me to make sure I sanded a reflex in the upper & lower surfaces (similar position as the upper surface in your example) as this makes all the difference to the performance. It flies extremely well & actually out-performs the sports version in low lift conditions. I put this down to carefully following his instructions on that reflexed aerofoil as he knows what he's talking about.

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Most deltas won't fly at all well without that reflexed trailing edge. I imagine the same applies to all tailless aircraft, not just gliders. The reflexed trailing edge can also be used near the wingtips of conventional aircraft to prevent tip-stall instead of washout.

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Ah, that old chestnut. If you understand the difference between airspeed & groundspeed I don't see what there is to debate there.

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I wasn't referring to a tailless glider; I'm thinking that because of the lesser surface area of a glider fuselage behind the wing (compared to the average light single, for example), it needs a little help for lateral stability. In that department, a glider is a little more like a tailless airplane.Still a little vague on how the reflex curve helps, though...

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Now that you mention using that upturned trailing edge in lieu of washout, i think I understand how it works. Or do I? I'm at a loss as to how to put it into words. Maybe I'm better off "understanding" it intuitively...not very logical, but ... (shrugs) 

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Yep. I think a lot of people are confused by the brief changes in "feel" and airspeed associated with windshear... but of course, the most stubborn proponents of the "tailwind will stall you" concept are non-pilots, based on what I've heard and read.

Nah.. no worries..  I read 1/2 dozen posts about it on other boards and there's nothing to debate. If you consider the loss in lift/airspeed that you get any time bank the wings and use up some of that lift (no matter where it comes from     )  to "turn" the plane...  The plane's airspeed doesn't differ at all whether your in dead-calm air, or wind from any direction.

Throwing gusts or shear into the mix is a non-related complication to the "debate"..

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You have no idea how refreshing it is to hear that from an engineer...

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Oh no, not me... I just wanted to bring it up and see what happens.

If you want to know a bit about aerodynamics I suggest "The Illustrated guide to aerodynamics" by H. C. "Skipp" Smith. It has just about everything you need to know about aerodynamics as a pilot.
(IBSN 0-8306-3901-2)

Thats an old trick when trying to explain lift, jeph 
The problem is...while your hand is getting "lift" from the air being that's being pushed down, the wing of an airliner doesnt get its primary lift component from the air it pushes down, but from the air streaming over the wings.

So it's not really the same, but it works in theory for the common man, but not much more.

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Not to mention it's highly inefficient at creating lift...

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Or airbrake...

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LOL    no flaming, but I didn't think you'd take me seriously and actually bump this back up  

This is like a religious debate.

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That's curious, because in order for the air to be redirected and accelerated, the path HAS to be different AND has to be longer.

The whole idea of "thrust" and Newton's third law explaining a wing's lift is still something like this to me:





It's like trying to push yourself away from a wall that isn't there (and if it worked, sailboats would be able to sail directly into the wind). And.. if you could generate a thrusting force by simply redirecting air; there'd have to be a horizontal component too, as the air is accelerated over the top of the wing, and you'd be getting a magical speed-aiding, forward push.

And what about the action/reaction to the air's initial, upward redirection at the leading edge ? Wouldn't that create an action/reaction component pushing the wing down; counteracting it all.

Achieving lift by Newton's third law can be accomplished (as shown in the lower diagram) and I'm sure it's part of what's happening in flight , but it's Bernoulli's pressure differential that makes a wing, a wing... and gives you the magically efficient, low drag lift, at zero (or near zero) AoA.

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.

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.

Ok..I'll try this angle on how this Newtonian stuff is like trying to push yourself away from a wall that isn't there..   

Picture a musket barrel with a ball loaded. Now, picture pointing it slightly downward...  As the ball is allowed to roll (be redirected) down the barrel; would it create a mathematically defineable recoil, acting on the barrel ?


NO !

Tell your wife I'm sorry for distracting you      And an early congrats.. to you both  


I read that link.. What we need are some data/diagrams at a pure zero AoA ..  Once you get into the positive AoA (looking at all those pressure patterns), you venture into what I like to call, "balllistic lift" (like the skipping stone).

I understand that there's always going to be some of that going on.. there'll always be some Newtonian stuff too.. because as Rotty pointed out.... just about any winglike surface can be held airborne with enough velocity.

It's all about accepting drag for lift.. and when all the laws are balanced out.. it's pressure differential that makes a wing, a wing.

Maybe I'll just have to go on being wrong (but not alone and in good company) until some expert can convince me that simply redirecting air over the TOP of the wing can not only create a net vector sans outside energy, but that that vector can act ON the wing (ala the musket ball) from above and "pull" it up.. They'll also have to tell me why a vector opposite the lift isn't created when the air is redirected UP as it first passes over the wing.

As for downwash.. Hagar posted some interesting pictures/links on page 3 of this thread....

Months ago, when this thread was first active; I did some research that rattled my faith in Bernoulli, but it really didn't surprise me that pressure differential alone could not produce enough lift to hold a plane aloft... And along that line of thought, neither could the lifting force created by redirecting air, if conservation of energy means anything.


For now, I'll let all the complex, aerodynamic goings-on be a black box and go on believing Bernoulli makes the end product, lift... because I just took a shower.. and we all know what the shower curtain did  

I love the Internet!! I think it has actually surpassed sliced bread!

I was searching for some info on the Coanda Effect and found this very intertaining article by Jef Raskin (that name might sound familiar to you Mac guys).

Since nobody seems to think that NASA is that bright, maybe the guy that got Mac's up and running will sway you.


Seriously, it's fairly brief and this guy has an excellent sense of humor (which makes reading this kind of stuff much less tedious). 

http://jef.raskincenter.org/main/published/coanda_effect.html

Three items that really made me chuckle: the UnderCambered Wing, The Lumpy Wing and the fact that even Einstein got it wrong and eventually "came around".

Footnote:

"Thingy"   ( delta india charlie kilo)  finally said, "you wanna know what makes an airplane fly ?"  as he took a bill out of his wallet.. shaped it roughly into an airfoil, blew over it and made it lift (I was about to say, "aha.. you're a convert")...  "MONEY"..