Mooney Aerodynamics

[Cargil48]

Guys, you are all experts, I'm not. But I've read a long time ago a very simple explanation. Air is a sum of very tiny particles, trillions of it in every square meter... Suddenly an airfoil shows up, travelling at a certain speed, and brings as lot of turmoil to this mass of air. Now let's think of two "twin particles", a and b, sitting just side by side up there. They are hit by the leading edge and get separated. a goes straight along the lower surface as the airfoil passes through the place, and b is separated from its "twin sister" and goes the upper path. Since this upper part is curved, b has to travel more than a to get united with it again at the trailing edge. This difference of speed creates a difference in pressure, "delta P", creating a low pressure area on the upper side, thus causing sort of a suction effect. We call that lift.

This we all know by heart since we were kids dreaming of becoming pilots one day... What we didn't know then and know now is that the problem starts at the wing's tip, where still air, not disturbed by any airfoil is met by airflows which have been disturbed by the difference in speeds along a path as shown in the pic I made. So, this makes the "still air" needing to "fill in" the low pressure area over the far end part of the wing. And this creates the famous vortices. To prevent this, we need a device to avoid this happening. That outer, still air layer, shall meet the other layer, which had been disturbed, more aft, when this latter one has been "pacified" after the airfoil has passed... Now, how we design that device we call "winglets" depends on some variables, most of all speed of the airfoil (wing), shape and area. Obviously a wing traveling at Mach .85 requires a different design than the one of a Mooney M20... 

Excuse my layman's way of putting it, but this is how I've gotten it explained long ago...

[ArtVandelay]

A and B are not twins, they don’t have to do anything, they each have their own forces acting on them.


Tom

[Austintatious]

28 minutes ago, Cargil48 said:

Guys, you are all experts, I'm not. But I've read a long time ago a very simple explanation. Air is a sum of very tiny particles, trillions of it in every square meter... Suddenly an airfoil shows up, travelling at a certain speed, and brings as lot of turmoil to this mass of air. Now let's think of two "twin particles", a and b, sitting just side by side up there. They are hit by the leading edge and get separated. a goes straight along the lower surface as the airfoil passes through the place, and b is separated from its "twin sister" and goes the upper path. Since this upper part is curved, b has to travel more than a to get united with it again at the trailing edge. This difference of speed creates a difference in pressure, "delta P", creating a low pressure area on the upper side, thus causing sort of a suction effect. We call that lift.

This we all know by heart since we were kids dreaming of becoming pilots one day... What we didn't know then and know now is that the problem starts at the wing's tip, where still air, not disturbed by any airfoil is met by airflows which have been disturbed by the difference in speeds along a path as shown in the pic I made. So, this makes the "still air" needing to "fill in" the low pressure area over the far end part of the wing. And this creates the famous vortices. To prevent this, we need a device to avoid this happening. That outer, still air layer, shall meet the other layer, which had been disturbed, more aft, when this latter one has been "pacified" after the airfoil has passed... Now, how we design that device we call "winglets" depends on some variables, most of all speed of the airfoil (wing), shape and area. Obviously a wing traveling at Mach .85 requires a different design than the one of a Mooney M20... 

Excuse my layman's way of putting it, but this is how I've gotten it explained long ago...

The part in bold has been proven false... The A and B air molecules do not meet back up at the trailing edge.  There is no law of physics that says they must.  The reality is that the B molecule gets there first.  this has been proven in wind and hyro tunnels.

[EricJ]

Another good, quick, short vid, with some nice visualizations:
 

 

[Austintatious]

27 minutes ago, EricJ said:

Another good, quick, short vid, with some nice visualizations:
 

 

I dont like that video...  it is more misinformation...  Deliberate downward displacement of air and Bournoullis principal are not just two different ways of looking at the same thing.  It is entirely different mechanisms.

Bournoullis principal is relevant to a venturi, not a wing.  

Also, There is nothing that necessitates downward movement of air molecules to create lift.  For aircraft, we usually have it, true.  But there are experiments that can simultainiously show that downward displacement is not required as well as prove that Bournoullis principal is not responsible for creating the low pressure. 

In a nutshell, it is the radial expansion of air.  Key word RADIAL.

I will keep tryign to find the website

[PT20J]

1 hour ago, Austintatious said:

The part in bold has been proven false... The A and B air molecules do not meet back up at the trailing edge.  There is no law of physics that says they must.  The reality is that the B molecule gets there first.  this has been proven in wind and hyro tunnels.

I'm glad @Cargil48 brought this up because this is an example of the simplifications that we've all been taught over the years that turn out not to be accurate. Here's a wind tunnel video using pulsed smoke that shows clearly what @Austintatious points out. 

 

It turns out that there are a couple of other problems with this explanation of lift. Even if you take a highly cambered airfoil (like the Clark-Y) the difference in path length isn't nearly enough to account for the difference in speed of the air over the top and bottom of the wing. Also, if you look at the Mooney root airfoil, it is curved on both top and bottom, so the path lengths are not that different at all.

http://airfoiltools.com/airfoil/details?airfoil=n63215-il

Skip

[Blue on Top]

Sorry, all.  I haven't listened to Rod's video yet, but I am an aerodynamicist.  I'll get to Rod's video later this evening.

In very simple terms everyone has made true statements (and the contrary is true, too).  Bernoulli cannot explain 100% of lift generation nor can Newton.  They are both utilized in the Navier-Stokes equations that used to be computed by hand, but are now imbedded in CFD programs.  For real CFD simulation, the boundary layer also has to be modeled.  There are also good CFD programs that model well enough to run loads programs and the like.  Some of the good programs will model the separation point, but programs are getting better (but not there yet) on modeling the flow (and boundary layer) after separation.  Now, for popular misconceptions.

#1 Air flow does not hit the physical "leading edge" of the airfoil.  Remembering that the wing is twisted (every span-wise local AOA is different), we'll simplify to 2D and look at a single span-wise location (say at the stall warning switch).  So, looking at a 2D airfoil, the air "hits" the airfoil below and aft of the leading edge at a point called the stagnation point.  The stagnation point is where the air hits the airfoil and stops (in a perfect computer world).  Air flow above the stagnation streamline (yes, there is upwash before the wing … and propeller) flows forward and around the top of the airfoil, and air flow below the stagnation streamline flows along the bottom of the airfoil.  The upper surface particles don't move faster because they know it's a longer distance.  They travel faster because they are pulled faster by a lower pressure.  The stall warning horn activates when the stagnation point is aft of the vane, and the forward moving air flow pushes the flipper up into the contacts inside the switch.  Brutally simple  

#2 (depending on AOA) Static air pressures on the bottom of the airfoil are not higher than ambient pressure.  At low AOAs the majority of the bottom of the airfoil is also below static ambient pressure.  They are higher than static pressures on the top of the airfoil, though.  It is this delta P that creates lift.

#3 Camber (curvature) is not required to create lift.  Note: the second video has a lot of errors in it.  The "curvature" (shape of the mean camber line) is a large factor in the efficiency of the airfoil.  The straight slope of Cl vs. AOA curves is the flat plate lift of the airfoil.  Note: airfoil design is complicated.

Time to take a breath.  Great thread.  -Ron

[PT20J]

1 hour ago, Austintatious said:

I dont like that video...  it is more misinformation...  Deliberate downward displacement of air and Bournoullis principal are not just two different ways of looking at the same thing.  It is entirely different mechanisms.

Bournoullis principal is relevant to a venturi, not a wing.  

Also, There is nothing that necessitates downward movement of air molecules to create lift.  For aircraft, we usually have it, true.  But there are experiments that can simultainiously show that downward displacement is not required as well as prove that Bournoullis principal is not responsible for creating the low pressure. 

In a nutshell, it is the radial expansion of air.  Key word RADIAL.

I will keep tryign to find the website

Try this one. A bit long and I had to watch parts of it several times to understand it (mostly ;-), but I found it pretty interesting.

Skip

[Blue on Top]

14 hours ago, carusoam said:

Let's talk stall strips for a moment, if we can...

1) Do they behave in a similar way, aerodynamically as speed brakes?

As in....

• 2) they disrupt the airflow about 3X the width of the strips themselves... including end effects (generally speaking)
• 3) briefly, a foot of mechanical disruption turns into a loss of lift for three feet of wing... (roughly speaking, end effects occur everywhere in flow challenges)
• 4) what defines there placement side to side?
• 5) At a high AOA where the stall strip is above the split line... it is like deploying a speed brake...
• Lack of lift, in that section of wing is going to make that wing get proportionally heavier...
• 6) So the buffet we are feeling... is lift from a section of wing that is getting turned off by airflow disruption locally near the stall strips...
• 7) and... the wing is still flying, in control near, the critical AOA...
• 8) As a pilot holding the plane’s attitude, so the stall strips are above the split line, the rest of the wing needs more AOA to maintain altitude...
• 9) what does the pilot see, perceive, feel, when this controlled loss of lift in those sections occurs?
• 9) Is it masked by the same feelings and observances as flying in turbulence...?

-a-

I've done a couple things with your post @carusoam to make it a little easier and shorter: I've removed text I don't reference and added numbers to your questions/my answers.

1) No; not at all.  The speed brake simply adds drag (the design intent is not to lose lift/separate air flow).

2)  The speed brake will cause drag.  Flow separation will happen behind the speed brake and a little to the sides, depending on the hole percentage and pattern.  The stall strip will separate flow at the leading edge with a triangle/wedge of separated flow behind.  As AOA increases, the pattern behind the stall strip will be a triangle with the base being the stall strip and the point pointing aft.  As AOA increases, the sides will spread out (get closer to being parallel to the ribs).  The sides will continue to spread with increasing, making a larger and larger wedge of separated flow (and lost lift).

3) Reference 2) above.

4) As far inboard as possible without a) the wake hitting the tail (or side of fuselage) and b) losing too much lift (that's not the intent).  Too far outboard and a non-symmetric deployment could get really ugly.

5) No.

6) The buffet you feel is either separated/turbulent flow hitting the wing and/or that flow hitting the horizontal stabilizer.

7) The majority of the wing is still fly through the stall (80%-ish).  If it goes into a spin, you are outside of the aft CG envelope or you have enough elevator to continue (it should fall in pitch first) … I won't go there at this time.

8) It is much, much easier to talk in terms of one AOA, aircraft AOA.  Pilots want to simplify the crap out of detailed engineering work, but in reality the have complicated it greatly.  From an aerodynamics point of view, the airplane has 1 AOA (yes, the local AOA is different at every point on the airplane).  The left and right wing have the same AOA  … until the airplane is in a spin.  Please simplify your life.  The way aero people think about a down aileron is NOT an increase in AOA because the chord line changes (that is incorrect). We think that that portion of the wing will stall at a lower AOA (we don't change the chord line).  If you want to change the chord line, also change the camber, the gaps, etc. … e.i. it's a completely different airfoil.

9) The pilot doesn't know and just continues to fly the airplane.  One will feel the drag of the speed brake … not the stall strip.

The second half gets letters … to be continued. 

 

 

 

[PT20J]

@Blue on Top makes excellent points ... again 

Years ago, Flying columnist Peter Garrison made the observation that even a child understands lift. It's angle of attack. They know this by "flying" their hand out the car window. My private pilot ground school instructor used to say that you could fly a sheet of plywood if you had the right angle of attack and enough power. I've come to the point where I think all the discussion of Newton and Bernoulli and camber and such is not very helpful to pilots. We cannot see the air and we cannot change the wing shape (excepting flaps). But angle of attack is something we can understand, visualize and control. The point of airfoil design is to use that angle of attack to generate lift efficiently my minimizing the associated drag.

Skip

[Blue on Top]

15 hours ago, carusoam said:

A) Briefly,

• how do those stall strips work?
• what do they do?
• C) how do we recognize it better?
• C) what do we look for the next time we are at a safe altitude practicing slow flight, to recognize the signs of stalls before they occur...

D) Is it possible that this is a very dynamic situation where the airflow is interrupted, restored, and interrupted again... in cycles...

• a loss of lift locally occurs,
• the AOA is improved by the loss of lift
• the airflow is re-established
• The full lift occurs again
• E) holding back on the yoke could potentially cause hundreds of pounds of lift to get interrupted, and then turned back, on as the AOA has the actual split line drift above and below the stall strips...

sorry for the long-winded questions... I got up early with ideas I needed to write down...   

Questions of a PP, not a test for the MS CFIs, engineers, or closet aerodynamicists... 

Best regards,

-a-

A)  Good one.  You're talking to an engineer  

b) Stall strips work by separating airflow behind them on the upper surface as AOA increases.  Airflow moving forward from the stagnation point (on the bottom of the airfoil) at some point can't make the corner around the stall strip and the flow separates.  That's why it is important that the leading edge of the stall strip be sharp.  We use stall strips to tailor the stall progression (inboard to outboard).

C) You can't … unless the wing is tufted.  It is all feel at this point.

D) Possible, but I have not seen that on a Mooney.  Citation X (with stall strips not in the certificated positions) and T-38, YES.  T-38 will do that all the way into the ground.

E) No. Reference "D)" above.  I'm kinda confused by the question.  

I love answering questions; we both become smarter.

Thanks, Ron

 

 

[EricJ]

2 hours ago, Austintatious said:

Bournoullis principal is relevant to a venturi, not a wing.  

Bernoulli's principal is actually independent of shape and just describes how energy is conserved across pressure (potential energy), kinetic energy and internal (thermal) energy.    If the kinetic energy increases (e.g., the speed increases), then generally the static pressure (potential energy) decreases to balance the total energy.

Even in a venturi, if you follow a particular molecule that rides along one side of a venturi and rides over the bump, it doesn't feel the influence of the opposite wall of the venturi as the diameter of the tube increases.   Eventually you just have a large, circular wing that you can unroll and still have the same effect happening on the top of the bump.    That's pretty much how Bernoulli's principal applies to wings.

 

Edited December 23, 2019 by EricJ

[Blue on Top]

18 minutes ago, PT20J said:

@Blue on Top makes excellent points ... again 

1) I've come to the point where I think all the discussion of Newton and Bernoulli and camber and such is not very helpful to pilots. We cannot see the air and we cannot change the wing shape (excepting flaps).

2) But angle of attack is something we can understand, visualize and control.

3) The point of airfoil design is to use that angle of attack to generate lift efficiently my minimizing the associated drag.

Skip

@PT20J  Aman, Brother!

1) Aerodynamicists don't think that way; they simplify.  We think in terms of (aircraft) AOA (1 value) that is required to stall that section of wing.  It's a simple curve of stall AOA vs wing span location.  Flaps (and ailerons) lower the aircraft angle of attack to stall that portion of the wing.

2) YES!  And they all say, "AMEN"    (note: sorry, I love my job).

3) And wing design is to tailor an elliptical lift distribution that stalls root to tip … and if you mess that up, there are stall strips and VGs to help  

Blue on Top, Ron

[Austintatious]

OK, I found a bit of info on the experiment I was talking about...

 

Basically a pipe with THICK walls has a hole in the center... air is blown strait down out of the hole.  A disk is placed flat below the hole.  One would assume that the disk would fall due to gravity AND the air pushing it downwards.  However that is not what happens... the Disk will stay close to the pipe, defying gravity.

Lift is being created by the radial expansion of the air.  This is proven by creating variety of fences that still allow the air to flow, but either allow it to expand radially or not.  In every case, if the fences prevent radial expansion, there is no lifting action.

Here is a drawing of what the basic experiment looks like.

I might 3d print a pip and several disk with fences to use as a demonstration.  would be easy and fun

https://physics.stackexchange.com/questions/329170/what-are-the-mathematics-behind-a-disc-being-elevated-by-air-flow

[Austintatious]

3 hours ago, EricJ said:

Bernoulli's principal is actually independent of shape and just describes how energy is conserved across pressure (potential energy), kinetic energy and internal (thermal) energy.    If the kinetic energy increases (e.g., the speed increases), then generally the static pressure (potential energy) decreases to balance the total energy.

Even in a venturi, if you follow a particular molecule that rides along one side of a venturi and rides over the bump, it doesn't feel the influence of the opposite wall of the venturi as the diameter of the tube increases.   Eventually you just have a large, circular wing that you can unroll and still have the same effect happening on the top of the bump.    That's pretty much how Bernoulli's principal applies to wings.

 

When you get down and dirty with Bernoulli, his original equation was regarding compressible fluids.  His equation is perfectly suited for closed loop systems.  It was adapted and altered for compressible fluids.

[Austintatious]

OK, I made a 3d printable experiment that strongly suggest that Bernoullis principal contributes little to lift, but also shows that downward movement of air molecules is not required.  In fact it shows that the lift generated by radial expansion of air can overcome the pressure exerted by a stream of air hitting a flat plate.

 

https://www.thingiverse.com/thing:4063238

[brndiar]

Excellente Lecture,

Despite Cameraman work worth to see. 

Graphics to the lecture is here:

https://docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit

 

Lg aus Austria.

M.

[ArtVandelay]

When you get down and dirty with Bernoulli, his original equation was regarding compressible fluids.  His equation is perfectly suited for closed loop systems.  It was adapted and altered for compressible fluids.

I think meant for the first sentence to say “Incompressible” fluids?

 

 

Tom

[Ibra]

Yes, density is constant in Bernoulli equations but you can re-write similar equations for compressible fluids on laminar airflow cross-sections (shockwaves surface are where density kinks), the maths are very easy to workout as you can still draw airflow cross-sections with similar physical properties, the only non-intuitive thing passing Mach >1 is that the section has to diverge for airflow to accelerate, so you have throw Mr Venturi to the bin and build parabolic nozzles 

The main issue is that to analytically calculate and understand the physical properties of the airflow you need to know the airflow lines, cross-sections, stagnation/separation points and boundary layers...that gets messy for turbulent airflows, although you can still apply Bernoulli style equations with dissipative terms but you will have a really hard time doing constant energy physics on fractals (turbulence from a 2D wing do lives in 2.89 dimensions )

For theory, you can just draw a wing and some airflow and walk-through some very simplified 2D equations or analogies, in practice, we only know the airflow speed/pressure at the start and end of that big wind tunnel 

 

Of course you can run Navier-Stokes equations on a super computer and check accuracy versus analytical solution on simple cases or empirical results on reduced models

When I used to work on these, I recall one did miserably failed while the other one seemed to work well, I let you guess which one?

Edited December 23, 2019 by Ibra

[Nippernaper]

9 hours ago, Blue on Top said:

A)  Good one.  You're talking to an engineer  

b) Stall strips work by separating airflow behind them on the upper surface as AOA increases.  Airflow moving forward from the stagnation point (on the bottom of the airfoil) at some point can't make the corner around the stall strip and the flow separates.  That's why it is important that the leading edge of the stall strip be sharp.  We use stall strips to tailor the stall progression (inboard to outboard).

C) You can't … unless the wing is tufted.  It is all feel at this point.

D) Possible, but I have not seen that on a Mooney.  Citation X (with stall strips not in the certificated positions) and T-38, YES.  T-38 will do that all the way into the ground.

E) No. Reference "D)" above.  I'm kinda confused by the question.  

I love answering questions; we both become smarter.

Thanks, Ron

 

 

So @Blue on Top, moving from the theoretical to the practical, if you happen to have one of those Mooneys that tends to drop a wing in the stall, even with the ball perfectly centered, so much so that a spin appears immanent (just had my flight review, and even with a CFI it was a hair-raising experience), is there anything that should be done about it?  Maybe have the stall strips adjusted to even out the lift on the two wings at the stall?  (Is this even possible?)  Consider adding VG's?  The point is of course to never inadvertently stall the wing in the first place, but given the dire consequences when the stall behavior is so bad, seems like it should at least be considered.

[Cargil48]

9 hours ago, PT20J said:

@Blue on Top makes excellent points ... again 

Years ago, Flying columnist Peter Garrison made the observation that even a child understands lift. It's angle of attack. They know this by "flying" their hand out the car window. My private pilot ground school instructor used to say that you could fly a sheet of plywood if you had the right angle of attack and enough power. I've come to the point where I think all the discussion of Newton and Bernoulli and camber and such is not very helpful to pilots. We cannot see the air and we cannot change the wing shape (excepting flaps). But angle of attack is something we can understand, visualize and control. The point of airfoil design is to use that angle of attack to generate lift efficiently my minimizing the associated drag.

Skip

How many articles of Flying I've read back some two decades ago... Peter Garrison, Richard Collins, McClellan and many others... But back to the point. I'm going maybe to abuse of your patience, but reading the above post something popped into my mind: Maybe there are two different effects which makes a wing go up, one called lift and second one simply deflection. Lift is created by the mentioned delta P, that example Peter Garrison mentioned in his article with the boy holding his flat hand out of the window of a moving car is  - may I say so? - not lift but the effect of deflection. Okay, both effects have the same outcome, they make the wing go up, but I think (maybe it's an evidence, but I'm no expert, as already said) we have to separate the two vectors. Many airplanes may need both factors, the heavier and the slower ones; others don't, the very fast ones and those having enough horsepower creating force through their propeller's blades. Let's see which kind of answers I may get now... 

[Blue on Top]

Generically, there are so many incorrect statements in the video.  At one point C1=C2 then later C1 does not equal C2.  C1=C2 is correct (nothing is adding or subtracting energy).  IOW (and this is how your altimeter and airspeed indicators work.  Ptotal = Pstatic + Pdynamic.  Pstatic is what your altimeter reads (and converts that pressure to altitude in feet).  Ptotal is the pressure that your pitot tube takes in.  rearranging the above equation Pdynamic = Ptotal - Pstatic.  So, using differential pressure in the airspeed indicator, we convert Pdynamic to airspeed.  Pdynamic, Qc, airspeed pressure or dynamic pressure (all of those are just different names for the same value) is 1/2 *rho*V^2.

Using the above equation, wing designers trade between Pstatic and Pdynamic to shape the airfoil.  In fact, some of the newer programs define a velocity gradient, and the program produces the airfoil shape.  

[Blue on Top]

44 minutes ago, Nippernaper said:

So @Blue on Top, moving from the theoretical to the practical, if you happen to have one of those Mooneys that tends to drop a wing in the stall, 1) even with the ball perfectly centered, so much so that a spin appears immanent (just had my flight review, and even with a CFI it was a hair-raising experience), is there anything that should be done about it?  2) Maybe have the stall strips adjusted to even out the lift on the two wings at the stall?  (Is this even possible?)  3) Consider adding VG's?  The point is of course to never inadvertently stall the wing in the first place, but given the dire consequences when the stall behavior is so bad, seems like it should at least be considered.

@Nippernaper  Yes, you can do something about it … especially if it goes the same direction every time.

1) Keep the ball centered.   No yaw --> No spin  

2) Stall strips get rid of lift, intentionally.  So … you have a little work to do.  a) How do your stall speeds compare to book?  b) Does the airplane roll the same direction all the time?  c) Does the airplane roll both with the flaps up and down?  d) Can you stop the roll with the rudder (or aileron … not recommended)?  d) Do the stall strips look like they are in the same position?  Span-wise is not as critical as up and down.

3) No VGs.  They add drag … and we don't know where to place them (they wouldn't help anyhow).  VGs may help if flow over the ailerons was separated (that should not be the case).

If you're keeping the wings level (within 15 degreed), you're meeting the certification requirements.  Keep the ball centered.  Something might be bent/twisted (aileron, flap, wing tip, etc.).  Your answers will lead us to a solution.

[Blue on Top]

58 minutes ago, Cargil48 said:

Maybe there are two different effects which makes a wing go up, one called lift and second one simply deflection. Lift is created by the mentioned delta P, that example Peter Garrison mentioned in his article with the boy holding his flat hand out of the window of a moving car is  - may I say so? - not lift but the effect of deflection. Okay, both effects have the same outcome, they make the wing go up, but I think (maybe it's an evidence, but I'm no expert, as already said) we have to separate the two vectors. Many airplanes may need both factors, the heavier and the slower ones; others don't, the very fast ones and those having enough horsepower creating force through their propeller's blades. Let's see which kind of answers I may get now... 

@Cargil48  It's not a one or the other.  It's 6 in one hand or 1/2 dozen in the other.  Bernoulli and Newton are just ways that we humans try to quantify/define Mother Nature (physics, aerodynamics, fluid dynamics, etc.).

An example that I use for myself is a seaplane.  What keeps a seaplane up?  Air and water are both fluids (both considered incompressible below M=0.3).  Initially, when the airplane is static, water buoyancy keeps it in place.  Displaced water weight = weight of the seaplane.  As the seaplane accelerates (gains velocity), less water buoyancy is required and "lift" is produced by hull planing (one could call this Newton if they wanted to … or the pressure is greater on the bottom than on the top, too).  When the seaplane gets on the step, there is now no water buoyancy, there is planing and the wing is producing some lift.  When airborne, all lift is produced by the wing.  So (and I apologize because I don't believe that there is a Mooney on floats) one can describe that whole sequence by physics … floatation, Newton or Bernoulli.

Whether the airplane is fast or slow doesn't matter.  All can be defined by pressures or Newton.  The F-18 creates vortex lift at high AOA (that's what the strakes are for).  Pressure above the wing is less than below the wing (or in this case, barn door (flat plate))

Blue on Top, Ron  

[Blue on Top]

4 hours ago, brndiar said:

https://docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit

Lg aus Austria.

M.

@brndiar  You can't believe everything that you find on the internet.  -Abraham Lincoln