Talk:Wing

I missed some brief introduction to the parts of bird and insect wings. --213.6.97.225 09:48, 11 Nov 2004 (UTC)

The disturbing thing about many of the so-called explanations of how aircraft wings generate lift rely on the SHAPE of the wing - specifically a curved upper surface and a more or less flat lower surface. However, many aerobatic and combat aircraft have fully symmetrical wing cross-sections (so they fly equally well when inverted) - and I have personally built and flown a powered radio controlled model aircraft with rectangular cross-section foam polystyrene wings specifically in order to show this theory of flight to be false.

Whatever explanation wins this debate, it cannot rely entirely on the shape of the wing. If a rectangular cross-section wing can generate lift - then downward deflection of the air due to the angle of attack of the wing into the airflow is surely the key factor. This business of air moving faster over the upper surface 'because it's a longer distance' - and hence taking advantage of the Bournoulli principle - can at best only be a small part of the explanation because the distances over and under a rectangular wing are exactly the same.

rectangular wings work due to their angle of attack - they deflect air downwards, the equal and opposite reaction is lift. However they also create a great deal of drag so are not very efficient. The shape of the wing only confers efficiency - it has no "magic properties" that creates lift by virtue of its shape. The rectangular wing argument is actually very useful in explaining lift. A simple chuck glider with a flat wing works, because it has an angle of attack. If you build it so that there is no angle of attack, it doesn't fly very well (though actually achieving a totally neutral angle of attack is quite hard in practice). If you build a model with a curved aerofoil section, it can still generate lift at zero or even small negative angles of attack, because a curved aerofoil is still able to have a positive lift coefficient at these angles. It is still deflecting air downward, because of the tendency of the air to stick to it and follow its curvature - only in this sense does the shape matter, and it only has an effect on the efficiency. The "longer path over the top" argument is totally bogus, and as you say, the rectangular wing proves it. The pressure distribution above and below the wing is an EFFECT of Newton's laws operating on the air, not a CAUSE of the lift produced. You will see a similar pressure difference even with a rectangular wing, though less pronounced and disturbed by turbulence. Graham 03:26, 23 Nov 2004 (UTC)

It is my understanding that scale phenomena and such things as birds' feathers are important for a good understanding of the subject. Can anybody begin to improve this article? I am not qualified in this field to provide either very good general remarks or settle notability concerns.Julzes (talk) 17:37, 26 May 2009 (UTC)Reply

`longer distance` - This isn't always the case. In the case of the M2-F2 (and later the rocket powered M2-F3), the 'longer distance' is on the bottom. There is a high amount of drag using this method, but that is the intent since it was a re-entry prototype. M2-F2 video Rcgldr (talk) 03:08, 26 January 2024 (UTC)Reply

• typical airfoil - link to photo of unusual lifting body air foil: m2f2.jpg

• Bernoulli and lift - To generate lift, a wing "violates" Bernoulli; the solid wing causes the air to flow downwards, even though there's lower pressure above (and in front) and higher pressure below (and behind). The wing forces the air to flow in the opposite direction that it would if the wing wasn't present but the pressure differentials were present.

Jeffareid (talk) 19:45, 4 October 2009 (UTC)Reply

No, a wing does not violate Bernoulli's principle.

Your comment about the wing causing the air to flow downwards suggests you are talking about a three-dimensional wing. The downwash due to trailing vortices does not contribute to lift, and it can be thought of as a secondary effect. To gain a clear picture of how a wing generates lift it is important to begin with the primary effect, and that is best done by considering a two-dimensional wing (ie a wing of infinite span, or a high aspect ratio wing operating at low lift coefficient.)

In the flow around a two-dimensional wing the bound vortex causes the air ahead of the wing to rise as it approaches the wing (called upwash) and the air behind the wing to fall (downwash). The result is that the upwash ahead of the wing is exactly equal to the downwash behind the wing. There is a change of momentum caused by the wing. This change of momentum is related to a downwards force on the air as it is influenced by the wing. There is an equal and opposite upwards force on the wing. Notice that the downwards force on the air is entirely downwards, no forward component. The upwards force on the wing is entirely upwards, no backward component and so no induced drag.

In the flow around a three-dimensional wing there is a pair of trailing vortices. These cause a downwash immediately behind the wing, and it persists for a very long time after the wing has passed. This persistent downwash is the result of the induced drag on the wing; it is not the result of the lift on the wing.

To better understand the generation of lift on a wing I suggest you focus on the bound vortex and its influence on the air approaching and leaving the wing. This is the primary effect of the wing. The trailing vortices and the persistent downwash are related to the induced drag and are merely secondary effects of the wing. The lift on a three-dimensional wing is much, much greater than the induced drag.

When people are talking or writing about the lift on airfoils, and they begin by talking about the downwash due to trailing vortices, and make no acknowledgement of the upwash due to the bound vortex, I know they are overlooking the primary effect that the wing and the airflow have on each other. Dolphin51 (talk) 22:27, 4 October 2009 (UTC)Reply

Most articles about 2d airflow state that downwash occurs. This was the first hit on a simple search: wing_airflow_2d Jeffareid (talk) 20:23, 5 October 2009 (UTC)Reply

 

There is no suggestion that downwash does not occur in 2D flow around an airfoil that is generating lift. What is stated about 2D flow is that there are no trailing vortices. (There is only the bound vortex.) The bound vortex causes upwash in the flow approaching the airfoil, and an equal downwash in the flow as it recedes from the airfoil. This is clearly visible in the attached diagram from Lift (force).

In 3D flow, the vortex system consists of the bound vortex plus a pair of trailing vortices. The trailing vortices cause weakened upwash ahead of the airfoil, and extra downwash behind the airfoil. This change causes the force vector to be tilted backwards slightly, and the backwards component is called induced drag. However, the lift on an airfoil is many times greater in magnitude than the induced drag so the total downwash on a wing is only slightly greater in magnitude than the total upwash.

The difference in magnitude between upwash and downwash is greatest for a low aspect ratio wing at high lift coefficient, and least for a high aspect ratio wing at low lift coefficient. Dolphin51 (talk) 21:57, 5 October 2009 (UTC)Reply

Ok, so now we get back to my original point. A wing creates a lower pressure zone above it and/or a higher pressure zone below it. Air accelerates in all directions towards the lower pressure zone, and away from the higher presure zone, except the presence of the wing itself prevents any upwards flow through the wing. The net result is a downwards flow of the surrouding air, in spite of the fact that the lower pressure zone is above and the higher pressure zone is below. If these pressure zones existed, but without the presence of the wing, the flow would be upwards, in a Bernoulli like fashion (acceleration from higher pressure to lower pressure zone). Instead the solid wing forces the flow to violate Bernoulli by flowing in the opposite direction.

A similar thing occurs with a propeller, the pressure is lower fore of the prop disk, and higher aft the prop disk. Even though the prop at any moment in time only occupies a small amount of the volume it sweeps out in the prop disk, it forces the air to flow from the low pressure zone in front of the prop to the high pressure zone behind it, again violating Bernoulli. In this case the speed across the prop disk remains about the same, while the pressure and acceleration are increased just aft of the prop disk. You end up with a Bernoulli violating increase in pressure with little change in speed. Jeffareid (talk) 00:40, 6 October 2009 (UTC)Reply

Acceleration of a fluid from a region of higher pressure to a region of lower pressure is an expression of Newton's second law of motion, not Bernoulli's principle.

Bernoulli's principle relates the speed and the pressure of a fluid at a point on a streamline. If the fluid speed at point A on a streamline is faster than at point B, Bernoulli's principle correctly predicts that the static pressure at A will be lower than at B. Bernoulli's equation doesn't talk about speed, but about dynamic pressure which is the kinetic energy of a unit volume of the fluid.

In the case of fluids, Newton's second law of motion relates static pressure and acceleration; and Bernoulli's principle relates static pressure and dynamic pressure. So perhaps your thesis should be that a wing violates Newton's second law of motion, not Bernoulli's principle.

The same paradox can be seen with a simple pendulum. The pendulum swings downwards, gathering speed. After passing its lowest point, the pendulum continues to swing upwards despite the fact that gravity is pulling in the opposite direction. The weight of the pendulum is acting downwards and yet the pendulum is moving upwards! Is this a demonstration of a simple pendulum violating Newton's second law of motion?

It is the same paradox with a wing generating lift. As air approaches the wing, it accelerates towards the low pressure region above the leading edge of the wing. As it passes the point of lowest pressure it has its maximum speed (in accordance with Bernoulli.) As it continues on its way it is constrained to follow the upper surface of the wing, which is angled downwards. The adverse pressure gradient causes it to slow, just like the pendulum slowing on its upward stroke. Eventually the air is so far from the wing it is no longer affected by the region of low pressure, and the air's velocity becomes constant, just as it was before it came under the influence of the wing.

The weight of a pendulum is constant, so when it reaches the top of its swing it begins to move downwards again. The pressure field around a wing is different. The pressure gradient is not constant everywhere around the wing, so as a parcel of air gets further away from the wing there is no tendency for it to stop and reverse direction, back towards the wing. Dolphin51 (talk) 02:11, 6 October 2009 (UTC)Reply

Switch to using the air as a frame of reference, which makes my point easier to understand. Before a wing interacts with the air, the air is still. After a wing interacts with the air, the air is moving, the "exit velocities" (velocity when and where pressure returns to ambient) of the components of the affected air will be non-zero. Somewhere during this process, a non-Bernoulli interaction involving some amount of work was peformed on the air, increasing it's total energy. Jeffareid (talk) 04:37, 6 October 2009 (UTC)Reply

You are correct in pointing out that in the wake left behind after the wing has passed, some of the air does not return to rest but has a residual velocity (or a non-zero exit velocity.) You are also correct in pointing out that this residual velocity is not consistent with Bernoulli's principle.

However, Bernoulli's principle is always stated to be applicable only to inviscid flows, or flows in regions of a flow field where viscous effects are non-existent or so insignificant they can be ignored. In Bernoulli's principle, first sentence, it states that the principle applies to inviscid flows. Viscous effects occur primarily in boundary layers and in the cores of vortices, so Bernoulli's principle does not hold true in these regions of the flow field. So Bernoulli's principle holds true everywhere in the atmosphere except in the boundary layer on the wing and in the wake behind the wing

It is the same with conservation of mechanical energy. Conservation of mechanical energy does not hold true where friction forces exist. (Bernoulli's principle is the application of mechanical energy conservation to fluid flows.) Where friction forces are at work, mechanical energy conservation does not hold true, but it isn't accurate to say that any object experiencing friction violates the Principle of Conservation of Energy. Dolphin51 (talk) 05:21, 6 October 2009 (UTC)Reply

• In the flow around a two-dimensional wing the bound vortex causes the air ahead of the wing to rise as it approaches the wing (called upwash) and the air behind the wing to fall (downwash). The result is that the upwash ahead of the wing is exactly equal to the downwash behind the wing. There is a change of momentum caused by the wing. - If the upwash and downwash are exactly equal, then where's the net change in momentum? Rcgldr (talk) 07:55, 21 October 2010 (UTC)Reply

  @Rcgldr: Consider the streamtube that encloses the airfoil. Every parcel of fluid moving in that streamtube approaches the airfoil with a slight upwards component of velocity (due to the upwash associated with the bound vortex.) As that parcel of fluid departs from the airfoil it has a slight downwards component of velocity (due to the downwash associated with the bound vortex.) The change in velocity of the parcel going from upwards to downwards indicates a downwards force on the fluid in the streamtube. The equal but opposite force is the upwards force on the airfoil. The upwards force is lift.

  Apologies for the delay of 13 years before you received a response! Dolphin (t) 09:26, 26 January 2024 (UTC)Reply

  @Dolphin51A glider with a very long wing span approximates a two-dimensional wing, and there is a net downwash. This is clear when a wing is close to the ground as the net downwash coexists with an increase in pressure between the wing and ground. That downwash also ends up being diverted by the ground both forwards and backwards, with the forwards component reducing drag. Rcgldr (talk) 15:30, 1 February 2024 (UTC)Reply

  @[[User:Dolphin51|Dolphin51] - simpler still, it's a Newton third law pair of forces, the wing pushes downwards on the air, coexistent with the air pushing upwards on the wing. The downwards force the wing exerts on to the air results in a net downwash (or if in ground effect, an increase in pressure of the air between wing and ground). Rcgldr (talk) 09:23, 2 February 2024 (UTC)Reply

  @Rcgldr: Thanks for your prompt reply. I’m always pleased to read comments about the aerodynamics of gliders because I used to do a lot of flying and instructing in gliders.

  You have written that “there is a net downwash”. If you mean what I think you mean I must say you are incorrect. In the atmosphere there can be regions of upwash and regions of downwash but the two are always equal in magnitude. If an aircraft were to cause downwash that was not exactly matched by upwash the mass of air below the altitude of the aircraft would increase! So wherever there is a region of upwash there must be a region of equivalent downwash at the same altitude. It is true that there is a region of downwash between the wingtip vortices trailing behind the wing and this downwash is directly associated with the lift-induced drag on the wing; but outside these wingtip vortices are two regions of upwash. This upwash has no effect on either the lift or drag on the wing but it is exploited by migratory birds that fly long distances in a V formation. It is believed that by flying in this way each bird obtains a small benefit by flying in the upwash of the bird in front and either to the left or right.

  The downwash between the wingtip vortices is the sole source of the lift-induced drag but this situation cannot be accurately described by saying "there is a net downwash". The mass flow in the downwash between the wingtip vortices is exactly matched by the mass flow in the upwash outside these vortices so there is no redistribution of mass in the atmosphere.

  You have also written that in ground effect there is an increase in pressure between the wing and the ground. That is also incorrect and I doubt you can find any reliable published source to support it. Aerodynamic lift is caused by a lowering of air pressure on the top surface of the wing. As the angle of attack on a wing increases, the air pressure on the top surface becomes progressively lower but the pressure on the bottom surface changes very little, if at all. This is true both in ground effect and out of it. It is easy to persuade yourself that the air pressure doesn’t increase between the wing and the ground. As you know, when air speeds up, its pressure decreases and streamlines get closer together; conversely when air pressure increases the air decelerates and streamlines get further apart. How could the streamlines between the wing and the ground get further apart? There is no room for them to get further apart because there is the wing above them and the ground below them, a defined distance apart.

  You have written that the forwards component of the downwash reduces drag. (You are referring to ground effect.) There is no forwards component of downwash, either in ground effect or out of it - I doubt you can find any reliable published source to support your idea. It is true that ground effect causes a reduction in lift-induced drag but that has nothing to do with a forwards component of downwash. As a wing moves closer to the ground or water the two wingtip vortices are impeded by the solid surface and the downwash becomes slightly weaker; so the lift-induced drag also becomes slightly weaker.

  Wikipedia's article on Downwash is inadequate and deals more with downwash caused by rotorcraft than by fixed-wing aircraft. For a year or more I have been working (slowly) on a substantially revised version in my Sandbox. You are welcome to peruse it, and particularly to read the quotations I have taken from various reliable published sources. You can read it at User:Dolphin51/Sandbox. Comments on the Talk page will always be welcome. Dolphin (t) 12:13, 2 February 2024 (UTC)Reply

@Dolphin51: - clearly there is net downwash from the rotor of a helicopter; why would a wing be any different? If you look at airfoils in wind tunnels that are sufficiently tall, or that are open at the top and bottom, there is a visible net downwash, most of it due to air being diverted downwards from above the wing [1]. Wing tip vortices can be fairly large, with significant downwash between them. Bird gliding through bubbles, momentary upwash followed by sustained downwash [2]. Planes flying through clouds [3] [4]. Another example, Formula 1 car in rain, before downforce no upwash [5], with downforce, upwash [6]. Rcgldr (talk) 07:11, 4 February 2024 (UTC)Reply

Actually, there is no net downwash from the rotor of a helicopter if it is simply hovering at a constant altitude. Conservation of momentum requires that the total momentum of the air + helicopter remain constant, and if the helicopter is not accelerating then it's momentum is not changing so the overall momentum of the air is also constant.

Now, the air in the vicinity of the copter is being accelerated downwards at a fairly high rate - enough that the mass x velocity of the air is equal to the weight of the helicopter. But the air forced downward eventually hits the ground and is accelerated upwards for no net momentum change an no net downwash.

The same analysis holds for a fixed wing aircraft in steady level flight. No change in momentum for the aircraft implies no net momentum change for the air. This perhaps paradoxical relationship between the aircraft's and the air's momentum is sometimes trotted out to discredit the Newtonian explanation of lift, but it's rather unconvincing since as you observe there is a significant downwash near the aircraft. Mr. Swordfish (talk) 19:54, 4 February 2024 (UTC)Reply

Mr swordfish: In the edit by Rcgldr dated 4 February he uses the expression “net downwash” twice, but he also uses “downwash” (without including “net”) twice; and “upwash” (without “net”) three times. He makes no distinction between the two versions of downwash and I now think he uses them synonymously. When he writes “net downwash” he means what all three of us mean when we simply write “downwash”. I am having more success in trying to understand Rcgldr’s position if I ignore the word “net” wherever he has written it.

It is likely his position is either a WP:Fringe theory or WP:Original research. Dolphin (t) 01:06, 8 February 2024 (UTC)Reply

@Mr swordfish: @Dolphin51: - Simplifying (no reference to net flow). I dispute "the upwash ahead of the wing is exactly equal to the downwash behind the wing", which conflicts with Lift_(force)#Explanation_based_on_flow_deflection_and_Newton's_laws, and where I used this video as an example [7]. I dispute "The mass flow in the downwash between the wingtip vortices is exactly matched by the mass flow in the upwash outside these vortices", where I used several videos showing downwash is greater than upwash with the wing tip vortices moving downwards. I agree that earth surface stops any downwash or mass flow. Rcgldr (talk) 03:41, 8 February 2024 (UTC)Reply

Rcgldr You quoted “the upwash ahead of the wing is exactly equal to the downwash behind the wing.” If you read the preceding sentence you will see it confines the context to two-dimensional flow or flow around a wing of infinite span. You also linked to “Lift (force)#Explanation based on flow deflection ...” which is not confined to two-dimensional flow so it is only to be expected that the two express slightly different sentiments. As you know, on a 3-dimensional airfoil or a wing of finite span, the downwash immediately downstream of the wing is greater than the upwash ahead of the wing; this causes the lift vector to be canted slightly backwards, and the backwards component is called lift-induced drag.

 

No fluid ever crosses a streamline. Here is a diagram of a vortex. The mass of fluid flowing between any pair of streamlines remains constant. Each element of fluid flowing between a pair of streamlines flows downwards some of the time, but then flows upwards some of the time. As a result, a vortex is incapable of a net redistribution of mass upwards, downwards, or sideways.

The vortex system in the flow around a wing can be represented by the horseshoe vortex. The velocity at a point in the flow around a horseshoe vortex is the vector sum of the freestream velocity plus the three vectors determined by the three legs of the horseshoe. Each of the legs of the horseshoe vortex is an irrotational vortex so the total downwash in the flow influenced by a wing is exactly matched by the total upwash. That is why aerodynamicists say total downwash is equal to total upwash, and an aircraft does not alter the density profile in the atmosphere. Dolphin (t) 07:23, 8 February 2024 (UTC)Reply

@Dolphin51:In "tall" wind tunnels with airfoils that span the wind tunnels, the downwash is greater than the upwash, but I don't know if this is considered to be a model of 2-d airflow. By "tall", I mean tall enough to allow for some visible vertical movement of air near the wing. Rcgldr (talk) 18:15, 8 February 2024 (UTC)Reply

If the airfoil spans the width of the tunnel, the flow is 2-D and there is no trailing vortices. The only vortex in the flow is the bound vortex which is still a vortex - the upwash hemisphere exactly matches the downwash hemisphere. What is your reasoning for saying “the downwash is greater than the upwash”? (Do you have a reliable published source or is it just something you observed in an online video?) Dolphin (t) 00:25, 9 February 2024 (UTC)Reply

@Dolphin51: - as seen in the videos, the vortices are moving downwards after an aircraft passes through a volume of air. Relative to the center of the downward moving vortices, upwash and downwash may be equal, but relative to the aircraft, the downwash is greater than the upwash (which is why the vortices move downwards). Rcgldr (talk) 18:15, 8 February 2024 (UTC)Reply

You appear to be describing the mutual interaction of a pair of counter-rotating vortices such as the pair of vortices trailing behind a fixed-wing aircraft. Each trailing vortex lies in the downwash region of the other trailing vortex so we must expect both vortices to drift downwards - exactly as happens in real life. Outside the downwash region between the two trailing vortices are two regions of upwash - one on the left and one on the right. Even though this vortex system drifts downwards due to mutual interaction, the mass flow in the downwash remains identical to the mass flow in the upwash. Dolphin (t) 00:34, 9 February 2024 (UTC)Reply

@Dolphin51: - Are you stating that a wing can produce lift without diverting the relative air flow downwards (assuming not in ground effect), whether in a 3D environment or a wing that spans a tall wind tunnel? Rcgldr (talk) 08:42, 9 February 2024 (UTC)Reply

No, I have never stated that.

The air flow close to the wing undergoes a change in direction, and this is responsible for the lift and the induced-drag on the wing. Elsewhere in the flow field the air has an upwards velocity component (upwash) so there is no accumulation of air below the altitude of the aircraft, but this upwash doesn’t add to, or subtract from, the lift experienced by the wing.

The air in the downwash is usually moving at faster speed than the air in the upwash, so even though the mass flow in the upwash and downwash are the same the momentum is very different. This is seen clearly in the flow around a helicopter - the air in the downwash through the rotor, and below it, is moving very fast in a column with a diameter about the same as the rotor diameter; but the air in the upwash outside the rotor drifts slowly upwards over a wide area. Momentum in the downwash is large but in the upwash it is small.

In my opinion, the best explanation of aerodynamic lift involves circulation around the wing, driven by the bound vortex. The circulation is used when applying the Kutta-Joukowski theorem to calculate the lift per unit of span. Dolphin (t) 10:23, 9 February 2024 (UTC)Reply

 

Dolphin (t) 01:45, 10 February 2024 (UTC)Reply

It might clarify my ideas if I adjust them to say “the rate of mass flow in the downwash is equal to the rate of mass flow in the upwash”. In the SI system of units the rate of mass flow would be measured in kilograms per second. Dolphin (t) 15:53, 9 February 2024 (UTC)Reply

@Dolphin51: - my issue was with the implication that upwash just in front of a wing equals the downwash just behind a wing, when much of that upwash occurs later on behind the wing. Rcgldr (talk) 20:56, 15 February 2024 (UTC)Reply

Rcgldr The fundamental principle to begin with is that a fixed-wing or rotary-Wing aircraft in flight does not alter the density profile in the atmosphere. Air moves downwards in places affected by the aircraft but it also moves upwards in other places at the same altitude. We can summarize this by saying “the total downwash (caused by an airfoil or aircraft) is equal to the total upwash”. We are referring to continuity of mass so by downwash we mean rate of mass flow in the downwash. Dolphin (t) 00:41, 16 February 2024 (UTC)Reply

The density profile of the air is slightly altered by an aircraft, due to increasing the pressure and density (by small amounts) below the aircraft resulting in the increase in the pressure | force exerted onto the earth surface equal to weight of air + aircraft. Rcgldr (talk) 02:57, 19 February 2024 (UTC)Reply

Rcgldr: If the true airspeed of the aircraft is no faster than about 0.4 Mach we will assume the flow is incompressible. In incompressible flows there is no change in the density of the air, is there?

If the flow is compressible but the aircraft is flying at sub-sonic speed there are momentary changes in the air density as the aircraft passes, but those momentary changes at any point in the atmosphere persist for a fraction of a second. In contrast, the trailing vortices and associated wake turbulence persist for a time measured in minutes.

Your information is not sufficient to negate the fact that the rate of mass flow in the upwash is equal to the rate of mass flow in the downwash. Dolphin (t) 06:01, 19 February 2024 (UTC)Reply

@Dolphin51: My prior statement is that density profile is altered (as soon as an aircraft becomes airborne), not that there is a continuous downwards flow of mass. Rcgldr (talk) 10:44, 19 February 2024 (UTC)Reply

Rcgldr: I’m very glad we agree that there is no net downwards flow of mass.

What leads you to think that the density profile in the atmosphere is altered by an aircraft becoming airborne? There are changes in the air pressure associated with the lifting action of the wing, but if we are assuming the flow is incompressible we must also assume the air density is unchanging. Dolphin (t) 12:37, 19 February 2024 (UTC)Reply

@Dolphin51: I'm assuming a real world case where air is compressible, even it it is just by a slight amount. Rcgldr (talk) 00:21, 20 February 2024 (UTC)Reply

Rcgldr: On 8 February you disputed my assertion that total upwash and total downwash are equal. We have been trying to settle that difference, or find common ground, ever since. Are you now saying that the reason the total mass flow in the upwash is not equal to the total mass flow in the downwash is due to the change in the density of the air at various locations around the aircraft while the aircraft is generating lift? Even when the change of density is just by a small amount? Dolphin (t) 00:58, 20 February 2024 (UTC)Reply

@Dolphin51:No. To clarify, I only disputed that the upwash immediately ahead of a wing is the same as the downwash immediately behind a wing. In the immediate vicinity of a wing, the downwash is greater, as seen in the videos of aircraft through clouds, birds gliding through walls of bubbles, and that airfoil spanning a tall wind tunnel. Some or most of the upwash occurs later, after a wing has passed through a volume of air, as well as the increased pressure zone below an aircraft returning to ambient, and there is no net vertical flow of mass of air for an aircraft in level flight. As for change of density, consider earth, air, and aircraft as a closed system, where the center of mass is constant. If the aircraft's center of mass has moved upwards, the air's center of mass has moved downwards. Rcgldr (talk) 05:39, 20 February 2024 (UTC)Reply

In this topic it is usually important to clarify whether we are talking about 2-dimensional flow, or flow around a wing or rotor of finite span. In 2-D flow the only vertical motions of the fluid are the upwash immediately upstream of the airfoil, and the downwash immediately downstream of the airfoil. These two elements must be equal if the density profile in the atmosphere is to be unaffected by passage of the aircraft.

If we are talking about the flow around a wing of finite span it is convenient to talk about the horseshoe vortex. Total upwash consists of the upwash ahead of the bound vortex plus upwash outside the two trailing vortices; and total downwash is confined to the region between the two trailing vortices and downstream of the bound vortex. In this flow the mass flow in the upwash upstream of the bound vortex is not exactly equal to the mass flow in the downwash downstream of the bound vortex. When we take account of the upwash outside the trailing vortices, total upwash is still equal to total downwash. Dolphin (t) 00:41, 16 February 2024 (UTC)Reply

@Dolphin51: Consider a large sealed box with 1 cubic meter of air weighing 1.222 kg. Say the box weighs 2 kg. The total weight of the box and the air inside is 3.222 kg. The air exerts its weight onto the box via a pressure differential that is lesser at the top and greater at the bottom resulting in a net 1.222 kg of downforce on the box. Open the box, put in a 1 kg model resting on the bottom of the box, and reseal the box. Total weight of the system is now 4.222 kg. The model then flies in horizontal circles within the box. It's a sealed box, so the total weight of box, air, and model remain at 4.222 kg, but the model does not touch the box. Instead the model has increased the vertical pressure differential within the box so that the air now exerts a net downwards force of 2.222 kg onto the box. The "mass of air below the altitude of the aircraft is increased", and above decreased. Similarly, the earth, atmosphere, and any aircraft in the atmosphere are parts of a closed system. Assuming no net vertical acceleration of the aircraft, then the total force of the atmosphere via pressure onto the earth's surface equals the sum of the weight of the atmosphere and the weight of any aircraft in the atmosphere. Rcgldr (talk) 17:00, 4 February 2024 (UTC)Reply

In this example of a model aircraft in a box, Rcgldr is making the point that the weight of the aircraft is ultimately borne by the Earth’s surface regardless of whether the model is sitting stationary on the ground or supporting itself in the atmosphere by generating lift. This point is already made clearly on Wikipedia - see Lift (force)#Lift reacted by overpressure on the ground under an airplane. Dolphin (t) 13:05, 5 February 2024 (UTC)Reply

Rcgldr and User:Dolphin51, the above discussion appears to be about aeronautical science, not about improving the article and therefore contrary to Wikipedia:Talk page guidelines. May I suggest that if you don't have a specific problem with the article and want to carry on this discourse that you move it one of your own talk pages. Cheers, HopsonRoad (talk) 01:09, 20 February 2024 (UTC)Reply

@HopsonRoad: - This started with a reply from Dolphin51 to a comment I posted 13 years ago. I don't know what the article looked like 13 years ago, but I'm happy with the article as it is currently written, specifically: "the wing deflects the airflow downwards as it passes the wing". I agree that this discussion should be moved elsewhere, but I don't know how this would be done. I posted my last comment, and waiting for a reply from Dolphin51, so he can post his last comment. I don't think the prior comments are needed anymore, but I don't know the accepted standard for removing all but a few comments from a discussion. Dolphin51 should be allowed to post a reply before the discussion is moved or removed. Rcgldr (talk) 05:58, 20 February 2024 (UTC)Reply

@Rcgldr, you can copy all or part of this to your talk page, if you wish, and notify your correspondents that you'd like to continue the discussion. This should remain in place and will ultimately be archived. Cheers, HopsonRoad (talk) 22:54, 21 February 2024 (UTC)Reply

@HopsonRoad, I already posted my last comment,no need to continue the discussion. I'm happy with the article as is.Rcgldr (talk) 06:03, 22 February 2024 (UTC)Reply

I think the opportunity for this discussion thread to achieve something beneficial has passed. I suggest we don’t pursue it any further. Rcgldr has disputed several of my comments. I am arguing that those comments are compatible with mainstream ideas within aerodynamics. On 2 February I gave Rcgldr access to my Sandbox containing a draft article on the subject of downwash. My draft contains multiple quotations from approximately ten well-known and reliable published sources. I invited Rcgldr to peruse my draft and make comments. He hasn’t done so. I don’t recall Rcgldr citing any reliable published source to support any of his ideas. On 4 February he nominated six on-line videos that he considers show phenomena that support his views on the matter. Wikipedia requires that its content can be independently verified using reliable published sources, and these sources must be identified in in-line citations. On-line videos are rarely regarded as reliable published sources. It is disappointing that Rcgldr did not attempt to identify any reliable published source to support his views. Wikipedia is not the place for views that cannot be verified using reliable published sources.

The discussion has been interesting and I thank Rcgldr for the respectful and conscientious way he participated but I don’t believe it has exposed any error or deficiency in any of Wikipedia’s articles on aerodynamics. I think it is unlikely that an error or deficiency will be exposed by continuing, therefore I suggest we close the discussion at this point. Dolphin (t) 12:50, 22 February 2024 (UTC)Reply

HopsonRoad and Dolphin51 - I've now posted references at User_talk:Dolphin51/Sandbox#Comments. Any further discussion can continue there.Rcgldr (talk) 23:39, 22 February 2024 (UTC)Reply

The first concept of a suitable wing was first described by George Cayley and Horatio Frederick Phillips. Although the method on which a wing works is the same with any type of wing, thicker or thinner wings are more suitable depending on the size of the airplane or animal using them. ^[1] (See also: the Reynoldsnumber)

In the beginning of aviation, wings were made using a much flatter profile than what's currently used. In the beginning, the thought was that the flatter the wings were, the better. Aldough this was correct to some degree (thinner wings have less weight and will thus demand less power from the engine), thinner wings can also generate less lift before stalling. This means that they are less suitable for use in aircraft.

The invention of the superiority of thicker wings was done by Ludwig Prandtl. Thicker wings were soon implemented into fighter airplanes of that period. ^[2]

In the 1930's, Eastman Jacobs of the U.S. National Advisory Committee for Aeronautics (NACA), developed and tested "families" of airfoils. The most successful of these were the NACA four-digit and five-digit series, and some of these are still in use today. These include the NACA's 23000 series which are probably the most widely used airfoil in history. Theodore Theodorsen then invented a mathematical method of calculating the pressure distribution on any airfoil, and this in turn then led Eastman Jacobs to creating a procedure to calculate profiles using digital computers. ^[3]— Preceding unsigned comment added by KVDP (talk • contribs) 13:45, 26 July 2010