Airplanes with flat plate wings

| We're talking about experience with flat-plate wings and at what point | should I consider going to imbedded spars and/or CF rod.

The best answers you're likely to get, are 1) make the wing a lot stronger and stiffer than you ever think it'll need to be, and 2) most of the measures aren't too expensive, aren't too hard to to add (at least if you do it early in the construction), and if you pick appropriate thicknesses it won't even mess up the aerodynamics of a flat wing too much, so go ahead and add it.

Actually, the second post in the thread answered your post reasonably well (and basically said #1.) | Why don't you two take this spitting-contest off-line since it's now | descended to a level I don't want to waste my time reading.

Kill files are good for that.

Thread drift happens. Deal with it. At least it's still model airplane related (though if it wasn't, I'd have stopped posting already.)

| Last warning, or I'll get this thread closed.

Good luck with that.

Hint: You may be reading this on rcgroups, but this is a Usenet newsgroup, and so things may not be run the way you're used to.

And besides, wasn't the general feeling in that other thread that discussions should happen on the newsgroup, rather than sent privately via email? (I don't completely agree, but ...)

byrocat wrote: >

LOL!!!

Please also read this:

FLAT AIRFOIL FLIGHT CHARACTERISTICS:

"...60 Minutes reported they had never received such an enormous mail response from any program they had ever produced. Most inquiries were about, how and why, the small paper gliders could be so stable and efficient in both, upright and inverted flight (always returning to level flight no matter how badly launched). Also, why didn't some modern aircraft use the designs? I'm sorry to say it but, no one could answer that question. The show had interviewed an engineer from NASA, who had honestly admitted not knowing the answer..."

-

Airfoil Lifting Force, miscellaneous discussion from the archive of the Physics Teaching list server PHYS-L, snipped-for-privacy@atlantis.cc.uwf.edu:

"...Someone recently asked me this: how can anyone say that the lower pressure above a wing explains lift properly, since we should never say that vacuums create "suction forces." Does not ALL the lifting force come from below the wing? ... Oh dear. I was afraid of this. The above explanation has the misconception in it. The major problem is that symmetrical wings (with equal pathlengths above and below), thin membrane wings, and upside down wings all generate lift, so the above explanation using pathlength differences is not correct. Take a look at:

*The truth is that there are two ways to CALCULATE lift, and both methods can be made into explanations of lift.* [bolded by me]

1. Because of the shape and tilt of a wing, when it cuts through the air it leaves an "empty" space behind its top surface and a "filled" space in front of its lower surface. Air encountering its lower surface is slowed down, so by Bernoulli's law it exerts a greater pressure on the surface there. Air passing by the upper surface is drawn into the empty space behind the wing and is sped up. By Bernoulli's law the high-speed air exerts a lower pressure on the upper surface. So, wings create lift because of pressure differential.

2. As a wing cuts through the air, it applies a downward force upon the air. This comes about because of the tilt and shape of the wing. The underside of the wing deflects air downwards. Since the airflow adheres to the upper surface, the upper wing surface also deflects air downwards. There is a downward force on the air, and as a result, the wing is forced upwards. If you measure the total mass of air being accelerated downwards, you can calculate the force between the wing and the air, and this is simply the lifting force. So, wings create lift because of reaction forces.

Which one is right? Both. Which one should be used? Well, the first one steers around the fact that wings push air downwards. Wings are identical in function to helicopter rotors, ship propellors, and jet engine turbine blades which all operate by throwing mass one way and moving the other way. Also, the first explanation usually (but not always) includes an incorrect description involving the necessity of particles A and B splitting and rejoining after the wing has past. And the first one implies that symmetrical wings won't work (they do,) and implies that a plane cannot fly upside down (it can.)

So, now you know which one I prefer! ... > Reaction to deflecting > (accelerating) the air is the PRIMARY cause and the changes in pressure > is the SECONDARY EFFECT that transfers the reaction to the body. ... [GIF Collection, Airfoil Misconception: ]

"...Pulsed smoke streams illustrate that the parcels of air which are divided by the leading edge DO NOT recombine at the trailing edge. Therefor the "wing shape" explanation of lifting force falls apart..." ] ... [Main address to above address: ] "...He mentions that this "phase shift" effect is proportional to lift. If any airfoil attack angle is adjusted in order to eliminate this phase shift, lift is eliminated as well..." ] ... So, since the parcels of air do not rejoin, and in fact it seems that this "phase shift" is a necessary component of the lift-generating mechanism, it becomes very wrong to base the "Bernoulli" airfoil explanation on a requirement that the parcels rejoin at the trailing edge. I doubt that this fact will do much to counter the spread of this misconception. After all, it's in all the textbooks, and how can that many textbooks be wrong? ;) ..."

regards,

Glenn

Glenn,

Thanks for providing such a great reference! Anyone who doesn't think the airmass isn't deflected down only has to look at the exhaust stains on the side of old Mustangs!

Hey Glenn Excellent post and links.

As a side note and out of curiosity: The dual inward-rolling vortices are trailed behind planes with standard or sweptback wings. With swept-forward wings (e.g. the Grumman X-29 jet), how would those vortices appear? Would they roll in the same (inward), or opposite (outward) direction? I have an RC model with forward swept wings, and have often wondered how the trailing vortices would appear.

Bill(oc)

The vortex is formed because of the difference in pressure above and below the wing. At the wing tip, the pressure differential will force air from below the wing, around the tip to the low pressure region above the wing. This is what causes the air to start swirling in the vortex.

So the sweep of the wing has no effect on the direction of rotation of the vortex. It will always wrap around the tip from the bottom to the top. Look here

for information on wing tip vortex formation. Take a look at the pictures on the left side of the page.

Dave

You are trolling I suppose? You do know of the various ways to simulate a wing of infinite aspect ratio? No downwash does not need to violate any known physical laws, Newton's or otherwise. Or do I misunderstand your request? If I understand your request then I am happy you feel I have such a bright future. But I would point out others knew this close to

100 years ago so I doubt if I am in postition to collect much reward.

No one is going to calculate lift from this model as it is a misrepresentation of air flow and what pressures exist at various points on the surface of a wing. In fact if 1. were even close to physical reality the center of lift would be behind 50% of the chord rather then the actual place you find it.

Unfortunately 2. is no better. The top front of the wing forces air up so there is net down force on the top front of the wing. Then the bottom back of the wing forces air down thus pushing it up while the top back of the wing is sucked up by the air it is sucking down. Just like in case 1 above the center of lift would be behind 50% of the chord. No one knows how to do the calculation for either case 1 or case 2 and if you did the results would not conform to physical reality.

Both are flawed thinking from the very start and thus doomed to fail.

Neither is correct.

I think you are saying that text books state that there is no phase shift? Or rather the site you are quoting says there is no phase shift in text books? I can not imagine where anyone who has looked at any text books could possibly come to such a conclusion. I can only surmise that whoever makes such a statement has never read any college level text used in teaching the science of lift by an airfoil at subsonic speeds.

| Doug McLaren wrote: | | > To be more precise, I don't belive that aerodynamic lift can exist | > without downwash. ... | You are trolling I suppose?

Not at all.

| You do know of the various ways to simulate a wing of infinite | aspect ratio?

I guess I can think of a few ways to approximate it. Probably the simplest would simply be a wing with a very ver large aspect ratio, though I am aware that there are other ways.

But even after ignoring any effects of the ends of the wings, if a wing is creating lift, it's also creating a downwash.

| No downwash does not need to violate any known physical laws, | Newton's or otherwise. Or do I misunderstand your request?

I think you're misunderstanding Newton's third law, but I'm also aware that 1) this has been discussed here before, and 2) I think you've seen it, and 3) if you weren't convinced then, I'm probably not going to convince you now.

And besides, I wouldn't want byrocat to get this thread closed. That was his last warning, after all.

| If I understand your request then I am happy you feel I have such a | bright future. But I would point out others knew this close to 100 | years ago so I doubt if I am in postition to collect much reward.

I'm not so sure about what they `knew' 100 years ago, but I see little point in debating it here. We could move it over to a more appropriate newsgroup if you wished -- sci.physics or rec.aviation.misc would probably work, with the former being a bit more appropriate.

Ultimately, with a model airplane that's grossly overpowerd, you can do lots of things regarding the airfoil and wings and such and it'll still fly. An extreme example is the `Hydroboat' that we've seen lots of movies of -- I don't think anybody will claim that it's an efficient flier, but it's pretty obvious that it does fly.

Hey Doug-

Ain't it amazing how many folks slept through Physics 101, ya' know Newton, F=MA, and such?

People that don't understand the part of downwash in producing lift should stand in the sand under a hovering UH-60 Black Hawk until they gain enlightenment. A basic education in aerodynamics is only seconds away.

Abel

=2E..

I think you know that center of lift (CL)/aerodynamic center (AC) is=20 normally about 1/4 of the way from the leading edge to the trailing edge.=

"... "Is lift created by downwash?" =2E.. lift is the re-action to the turning of the flow. No turning, no lift [Half of the turning must be between the leading edge and the CL/AC] =2E.. Center of Lift =2E.. For most thin airfoils, this is near the quarter chord =2E.."

Some of them - Yes. Will follow as "Incorrect Theory #1".

-

"... =2E.. So what do we now teach? I believe we must teach the facts. If there is=20 an inconsistency with the FAA's books and written test because of=20 oversimplification or dated material, we must be well prepared to avoid=20 confusion in our teachings. =2E..

*The Three Incorrect Theories of Lift* *NASA offers three incorrect theories of lift that are commonplace in=20 our teachings* : =2E..":

Incorrect Theory #1: "Longer Path" og "Equal transit" Theory:

Incorrect Theory #2: "Skipping stone" theory: Incorrect Theory #3: "Venturi" Theory:

- *Coanda Effect: Understanding Why Wings Work: "... But, even as a child, I found that it presented me with a puzzle: how=20 can a plane fly inverted (upside down). When I pressed my 6th grade=20 science teacher on this question, he just got mad, denied that planes=20 could fly inverted and tried to continue his lecture =2E.. the Coanda effect: the downward-curved wing entrained the airflow to=20 move downward, and a force upward is developed in reaction =2E.." -

AC/CL is normally about 1/4 of the way from the leading edge to the=20 trailing edge. - But where is it with full *flaps* ? :

"...*Flaps increase lift dramatically* without that much change=20 in the angle of attack of the wing. It may not seem that way because=20 when flaps are extended, a noticeable change in pitch attitude usually=20 will follow. But that=92s what it really is=97a change in pitch attitude =

resulting from the *greater downwash* produced by the reconfigured wing..= =2E"

regards,

Glenn

It's the downwash that produces much of the lifting forces. Even at zero AOA, an assymmetrical airfoil such as the Clark Y will generate lift, as the air over the top surface is accelerated and as it leaves the trailing edge its path is downward. That downflowing air still has higher velocity, and the net effect is downward flow. The reaction to that is lift. Such a wing will fly inverted, but not efficiently at all and will require considerable AOA to do it. A barn door will fly inverted, too. The difference in pressure between the top and bottom of the wing is only a few percent, not nearly enough to lift the airplane. The centre of pressure changes with AOA because the laminar flow over the top of the wing breaks up as AOA increases and the stall angle is approached. The low pressure is destroyed by the turbulence, so that as the airflow breaks up over the aft areas of the wing, the remaining low pressure's centre is more forward. Even in cruise the centre of pressure is forward of the 50% point, since there is no perfect airfoil. As the wing stalls and all of the flow is turbulent, the centre of pressure moves back again, helping to lower the nose and regain a lower AOA. A really good website showing the airflow patterns is here:

You can see the the air molecules don't "meet up again" at the trailing edge. There's also a good explanation of circulation theory that shows the pressures that want to pitch the wing downward. The vortex isn't just a result of the wingtip. The lower pressure on top of the wing causes spanwise flow inward, so that the air doesn't flow straight back from leading edge to trailing edge. Near the fuselage it's relatively perpendicular to the span, but farther out it is flowing inward, pulled by the lower pressure. Underneath, the higher pressure causes outward flow. The result at the tips, where the two flows can interact, is a vortex, but also along the training edge there are smaller vortices formed in the downwash. Minimizing vortices is difficult, but narrow, pointed wingtips help. That spanwise flow causes drag where it has to flow over such things as the ribs on a fabric or mylar-covered airplane.

Dan

CL isn't 1/4 of the way from the leading edge. That's about where the forward CG limits is, and the aft limit is around 33%. CL will be a little behind the aft CG to maintain pitch stability.

Lowering flaps increases AOA and angle of incidence over the flapped span. The chord line is drawn through the leading and trailing edges, and lowering the trailing edge changes that line. Lowering flaps also increases camber. Camber is the difference in distance from the chord line to the upper and lower surfaces of the airfoil. A symmetrical airfoil has no camber. Fowler flaps, which run in tracks, also increase wing area. An inherent pitch-up with flap application is due to the increased downwash over the horizontal stab. Some airplanes have the stab in a place where it's affected that way, and others don't. The Cessna 172 has a relatively strong pitch-up on flap application, while the Glastar will shove its nose down rather sharply. Both have Fowler flaps. My old Auster had two elevator trim tabs, one run manually as normal, and the other coupled to the flap mechanism to counter the pitch change forces. Applying flaps moves the centre of pressure aft, so the normal reaction is nose-down.

Dan

Perhaps our problem in getting to a common ground is we simply are not talking about the same physical phenomena? I am going to try to state in fairly rigourous terms what I think you mean by downwash. If I am incorrect in any way in trying to state what you think please correct me as needed.

You have clearly stated that you believe there are two fluid flows, one is tip vortex and the other is down wash. So let me set up a frame of reference to talk about so we are all on exactly the same page.

Consider an airfoil passing thru still air at exactly 5000 feet elevation above mean surface level. Now inscribe a sphere such that the sphere is exactly 5000 feet above mean surface level. This sphere will just touch the trailing edge of the wing as it passes through the air. The sphere will cover the whole earth at 5000 feet altitude. Locally I think you can consider this sphere to be a flat plate. I am going to ignore the occasional mountain that sticks through the sphere as you do not want to fly into the side of a mountain in general.

Now tip vortex induces an outboard circulation of air in the vertical direction and an equal downward circulation behind the end portion of the wing. This vortex is moving real fast. So fast that it is not uncommon for the rate of spin to cause adiabatic cooling in the center of the vortex sufficient to condense water vapor into water droplets. This is the condensation trail you can often see behind the wing tip. With respect to the surface of the sphere I described above there is an exactly equal mass of air moving vertical and outboard across the sphere to the mass of air moving downward across the sphere behind the wing. This vortex does not produce any lift at all as you are moving exactly equal masses up and down across the surface of the sphere. Yet it took a bunch of energy to produce the vortex. The energy the wing gave up to the air to produce the vortex appears as drag on the wing. As no lift was produced and work was done drag is the only available option.

Behind the wing there is also downwash of some magnitude. All of the mass of air in this downwash is permanently injected BELOW the surface of the reference sphere. You are saying that this permanent injection of a significant mass of air below the reference sphere causes lift based on Newton's action/reaction law. It would seem that the air must be permanently injected below the surface of the sphere, otherwise it would simply be part of the inner portion of the tip vortex.

Things to consider. If I shrink the sphere enough there will come a time when the air is no longer injected below its surface. For instance at one inch above mean ground level I think it is safe to say that none of this downwash is felt. So I presume at some altitude of the sphere between one inch and 5000 feet there exists a sphere surface that the air no longer penetrates. As an experiment that any of us could do we could stand off the end of a runway as planes approach to land. It is pretty easy to get to points where the plane passes overhead at an altitude of no more then 500 feet. I have done this on numerous occasions myself. I notice that even under large commercial planes which weigh half a million pounds I can not detect the slightest downward air flow when I am standing on the ground. I recently did exactly this at an airport in KY and watched the leaves of trees right next to me. I suppose these trees were 50 feet tall. The wind was dead calm. I not only could not feel any downwash from the wings I could not see the tree leaves stir in the slightest either before or at any time after the plane passed directly overhead. So it starts to sound a lot like the downwash induced by the wing does not travel very far below the surface of the sphere that just touches the trailing edge of the wing.

Please correct the above to your understanding if I am not correct in stating what you believe is physical reality.

A Clark Y has zero lift at a negative 5 deg angle of attack (or a zero deg angle of incidence). When you fly it inverted you must fly it at a postive angle of attack of greater then 5 degrees (zero angle of incidence) to reach positive lift. At one degree postive angle of incidence either inverted or upright exactly the same amount of lift is generated as Mises shows over and over in his book. But inverted the drag goes up like crazy. So it all depends on how you define efficient. My definition, and that used in general in aircraft design, is how good the wing is at producing lift at any given angle of incidence. But simply because it is a good lift producer does not mean it will fly worth a hoot. It may lift just fine but drag so overpowers the propulsion system that the plane flys like a dog. In models my instuctor felt you should not leave trainers until you could fly an inverted figure 8. My first model was an eagle with a 40 FP on it. Inverted the drag was so high you could hardly get the airspeed to do any better then fly in level flight in a straight line with this thrust. Put a 46 on it and it was easy to fly inverted figure 8s.

This is an interesting statement. I took the wing shape off a Tiger model (symmetrical much like an Eppler 168) and built pressure taps into it at various points on the surface both top and bottom. I then put this wing in a wind tunnel and measured the actual pressures at the taps at a variety of angles of incidence and at air speeds of 40 mph. By integrating the pressures measured on the top and bottom I was easily able to come up with well more lifting force then needed to fly the plane. Or well less if the angle of incidence were too low. As I recall the data only a 2 degree angle of incidence (or angle of attack. They are equalivalent for a symetrical foil.) generated more then enough pressure difference at 40 mph airspeed to fly an eight pound plane. By the way, this was a large wind tunnel with regard to the wing span. So I did nothing to destroy the loss of lift caused by the tip vortex. Can you please explain to me what I did wrong?

I agree this is a really good website.

It sure does. But unless you are racing drag is of little consequence the vast majority of the time in a model. Models fly at such miserably low reynolds numbers that drag simply does not amount to much that a slightly larger powerplant can not overcome with ease. Besides, most models have far larger drag contributors then caused by the airfoil being less then perfect.

| > | Doug McLaren wrote: | > | | > | > To be more precise, I don't belive that aerodynamic lift can exist | > | > without downwash. | > ... | > | You are trolling I suppose? | >

| > Not at all. ...

| Perhaps our problem in getting to a common ground is we simply are not | talking about the same physical phenomena? I am going to try to state | in fairly rigourous terms what I think you mean by downwash. If I am | incorrect in any way in trying to state what you think please correct | me as needed. | | You have clearly stated that you believe there are two fluid flows, one | is tip vortex and the other is down wash.

No, I haven't. What I have clearly stated is right up there, and I didn't trim it out so you can refer to it if desired.

What I mean by downwash is that if a wing is creating lift in a given direction that air must be deflected in an opposite direction. If the wing is flying level, creating a lift vector that points up, the air being deflected downwards is often called downwash.

| Behind the wing there is also downwash of some magnitude. All of the | mass of air in this downwash is permanently injected BELOW the surface

Permanently? Air moves. It's a fluid.

| of the reference sphere. You are saying that this permanent injection | of a significant mass of air below the reference sphere causes lift | based on Newton's action/reaction law.

No, I'm saying that if there's a force pushing the wing up (often called lift) then there's a equal and opposite force pushing something down, and when that force is applied to the air around a wing, the end result is often called downwash. I don't care if the air movement takes the form of vortexes or whatever, but ultimately air is pushed/accelerated downwards.

Though the air doesn't go down far, as the air molecules bounce into other air molecules and eventually come to rest again. But ultimately aerodynamics, fluid dynamics and indeed thermodynamics in general aren't about tracking individual molecules -- they're about looking at the average behaviors of lots of molecules.

This page has a nice picture of a jet coming out of some clouds, about half-way down --

(Even if you feel that the page is full of nonsense, you can look at the pretty pictures without being corrupted, right?)

and you can definately see the effects of the downwash. You can also see that it doesn't punch a hole in the cloud all the way down, as the airflow gets too spread out, and the plane has already left.

Note that a helicopter in the same place could eventually `cut' a hole in the cloud, as it would not be moving on as it creates lift. (You do agree that propellers are just wings that are spun around, producing lift, right?)

| I notice that even under large commercial planes which weigh half a | million pounds I can not detect the slightest downward air flow when | I am standing on the ground.

If the 747 flew 15 feet over your head, you'd feel it -- though it certainly wouldn't crush you, and more of what you'd feel would be the turbulence and such caused by it.

If it's 5000 feet up, the weight of the plane is spread out over many millions of square feet, and so only a very tiny part of that would be pushing on you -- and the atmosphere is pushing up on you too, so you won't feel it.

Really, what would happen is that the atmospheric pressure would increase very slightly under (well, under and behind) the plane. The increase and then decrease would be rather gradual (because it would be so spread out), and so I doubt the human body could detect it unless the plane was right overhead, and a leaves on a tree won't move either (as the pressure on both sides of the leaf will still be the same.) But I'll bet it could be measured with sufficiently sensitive detectors.

A somewhat similar situation happens when swimming. If you dive 30 feet down, there's now tons of water above you, but you're not pushed down further because there's water below you pushing up. (The pressure will nearly double at that depth, however, and so that could eventually crush you if your body couldn't adjust it's internal pressure (fortunately, it can.) But this pressure change (1 atm to 2 atm) is still millions of times higher than what would be caused by a

747 flying thousands of feet above you.

| next to me. I suppose these trees were 50 feet tall. The wind was | dead calm. I not only could not feel any downwash from the wings I | could not see the tree leaves stir in the slightest either before or at | any time after the plane passed directly overhead. So it starts to | sound a lot like the downwash induced by the wing does not travel very | far below the surface of the sphere that just touches the trailing edge | of the wing.

Either way, the Earth is ultimately supporting (on the average) the entire weight of the plane, both when it's landing and when it's flying.

If you want an analogy, take a 1 lb bird in a 10 lb bird cage. If the bird is perched, a scale will read 11 lbs for both. If the bird is hovering in the cage, what will the scale read? 10 lbs? 11 lbs? Something in between?

(Of course, the answer is it depends. If the cage is solid like if it were made of glass, the weight will average out to 11 lbs. If it's an open air cage like most captive birds live in, one that's made of wire, then the average measured weight will be slightly more than 10 lbs. And if the cage is merely a theoretical construct with no bars at all (but it still weighs 10 lbs), then the weight would be 10 lbs.

The Earth and it's atmosphere would generally correspond to the totally enclosed glass cage.

| Please correct the above to your understanding if I am not correct in | stating what you believe is physical reality.

This stuff really isn't on-topic at all. Would you like to move it to sci.physics? (I suspect that the regulars there would rip you to pieces, but you might enjoy that.)

To make this somewhat on-topic, do you not feel the downwash of a R/C helicopter or 3D plane when it's hovering just above you? In that case, the propeller is just another wing -- the only difference is that it's going around in circles rather than standing still, which also makes it easier to detect as the effect isn't moving.

And to talk about flat wings and propellers, often ceiling fans and the like have flat blades (wings) -- since the air velocities involved aren't very fast, any lack of efficiency isn't very signifigant, and so it's just cheaper to do it that way. But in a R/C model prop, you'll find that the propeller does have an airfoil shape -- this is because it's more efficient than a flat blade, though a flat blade would work too -- just not as well.

People on the ground don't feel airliner downwash because it's spread out and because they are too close to the gound themselves. The air movement near the ground from an aircraft at altitude is minimal on nothing. The folks who run orchards often have to deal with the risk of frost early and late in the season. As night falls and the sun stops heating the earth's surface, the temperature of the air near the ground will fall and if it's cool enough frost will form on whatever it can, including fruit. Not far above the surface, however, the air temperature has remained essentially what it was during the day, and we have what's called the nocturnal inversion. Orchardists sometimes contract air operators to fly their small aircraft over the orchard on frosty nights, at around 50 or 75 feet, to drive the warmer air down into the trees. If there was no downwash created, there would be a lot of wasted time and money in such pursuits, and a lot of dead fruit. Peter Garrison, a writer with FLYING magazine, once wrote of a trip he made to a Mexican airport. Security being what it often is in such places, the folks he met at the airport took him out to the edge of the runway when they saw a 747 approaching to land. Laying down in the grass, they waited as the jet passed over just before it was to touch down, and the downwash and vortices (which are a result of the lift/downwash pehnomenon) picked up Garrison and his friends and threw them some distance through the grass. Great sport. Can't tell them that there's no downwash below an airplane. I also have a friend who lost an airplane to helicopter downwash when the machine hovered too close and blew the airplane against the hangar. Downwash and vortices are most apparent (and most destructive) when the airplane is heavy and at low airspeed. Aircraft spacing along airways and on approach has to take into account the disturbed air, lest the following pilot loses control.

Nothing. Some of the pressure you measured on the bottom was reaction pressure caused by deflecting air downward and creating downwash. Any pressure above ambient would be from reaction.

Dan

At Sky Harbor airport in Phoenix years ago, you could park at the E end of the main runway, next to the glidepath, to watch the jets land. You could definitely _hear_ the 'birdies'- the swirling eddies made by the tip vortices. Even after the jet was on the ground and taxiing you could sometimes still hear the birdies it left in the air. Kinda cool, and spooky.

Bill(oc)

Well I have refered to it and do not have a real clue as to what you think other then downwash behind the wing causes lift. So I am going to try finding out what you think by simply asking yes/no questions.

1.Do you believe tip vortexes are created somehow by wings? Please answer yes or no.

1. If tip vortexes are created by wings do you think they cause lift? Yes means they cause lift. No means they do not cause lift. Please answer yes or no.
2. Does a model airplane wing compress the air somehow someplace? Please answer yes or no.
3. Is the Conanda effect a direct and demanded result of Newton's laws? Please answer yes or no.
4. If I define efficiency of lift production as follows:

Efficiency = Lift produced by experimental airfoil/Lift produced by the best airfoil

And if both experimental airfoil and best airfoil are identical in aspect ratio and planform, the airspeed past the two foils is identical and the angle of incidence is lets just say 4 degrees for both, then:

*Is a flat airfoil going to have an efficiency of much less then 1? Please answer yes or no. *Is a Clark Y airfoil flown inverted going to have an efficiency of much less then 1? Please answer yes or no. *If the answer to either of the above two questions about efficiency is no is the efficiency of either much greater then 1? Please answer yes or no.

1. Do you think that the incidence meter you buy at the hobby shop measures the correct angle of incidence for all airfoils? Please answer yes or no.
2. If the answer to question 6 is no do you think the meter measures angle of attack for all airfoils? Please answer yes or no.

I think I said I was standing 500 - thats hundred - not 5000 feet below the plane. If I mistyped I am sorry. I intended to say 500. No downwash. No movement of leaves.

Yes, I understand the conservation of mass.

You know how to copy the thread to a new news group just as well as I do. But thinking that physicists are the sole authoritys on fluid mechanics is a bit of a push. For instance my undergrad physics book had a section on what caused a thrown baseball to curve. The only problem was the book used Bernoulli to explain why a thrown ball can curve. And it just happens to make it curve in exactly the wrong direction! Not a single professor bothered to ever tell us what the book predicted in terms of direction of curve was exactly wrong. I can only surmise that baseball pitchers know more about curve balls the physics professors.

1. On the other hand a physics professor at U of Indiana wrote an article for MA maybe two years ago and he clearly stated that in his view almost all the lift we see in a wing is due to Bernoulli. I am sure you saw his article. Perhaps you feel he was wrong? If you feel he was wrong to say Bernoulli causes almost all the lift we observe please answer yes or if he was correct please answer no.
2. In a link provided very kindly by another poster:

Please refer to figure 3.2. Do you believe this diagram reasonably accurately displays the actual air flow patterns around an airfoil. I will specify that this diagram is for an airfoil which has an infinite aspect ratio (which is a detail the author of the web site probably felt was unneeded detail which would confuse the casual reader). I will also specify that this diagram is for one specific reynolds number and is not intended to be accurate in every detail for every single reynolds number(which is also detail the author did not feel was needed). Further I will specify that the airflow past the foil is well under the speed of sound which I honestly do not recall if the author addressed in any way.

Would this airfoil be producing lift with the airflows as shown? Please answer yes or no.

By the way, I have seen the pic of the plane coming out of the clouds before as I am sure most people on this group have also. All I see is a very striking picture of tip vortexes. Sorry but I see no evidence of downwash in this picture at all. But it still is a really neat picture. The pic I am referring to is Figure 5 at the web site:

It is going to take me a while to learn what you actually think by asking yes no questions. But it seems the only way forward.