Coanda and Bernoulli principles in inverted flight. 1

[DeanBrooksAllen]

I have a simple question.
I watched this video explaining how the airplane wing works with the Coanda and Bernoulli principles.

https://youtu.be/OCh4svEfDmE

I know that the airfoil is made so that the airflow lifts the plane. But in an inverted flight situation should the plane drop? Now the wing pushes towards the ground. How then does inverted flight exist?
Perhaps by activating ground spoilers you could have a lift in inverted flight?

 

[3DDave]

I had to stop when they misspelled Bernoulli.

In any case it's a matter of what the angle of attack is and the results of that angle and the specific airfoil.

If one changes the angle of attack from above the horizon to below the horizon the wing will produce lift in a negative direction.

If one inverts a wing and then gives it a negative angle of attack, the angle of attack is above the horizon, so it is likely to produce lift. It may also produce a great deal of drag because airfoils aren't typically designed to be efficient with large negative angle of attack operating conditions.

 

[rb1957]

an upside down (inverted) wing can produce lift by pitching the airplane to give the inverted wing section a positive angle of attack.

the aerodynamics are clearly not optimum since the wing is designed to fly right way up. This means that by design there are aerodynamic tweeks in the wing to create the most productive wing lift. A wing creates lift (simply) by two things …
1) angle of attack
2) camber

Right way up the camber of the wing adds to the angle of attack, for inverted flight the angle of attack needs to overcome the camber component (ie you'll have a higher AoA inverted)

another day in paradise, or is paradise one day closer ?

 

[VEBill]

Basic Newtonian physics states that a mass of air must be accelerated downward in order to provide a lifting force upward. F=mA. That much has to be true.

Other explanations can also be true, but objections (in the details) and counter-examples (e.g. your inverted flight case) are often raised.

How wings actually work is still an active topic (for some).

e.g.

https://www.grc.nasa.gov/

http://www/k-12/airplane/wrong1.html

Book: "The Enigma of the Aerofoil: Rival Theories in Aerodynamics, 1909-1930"

 

[btrueblood]

Planes that routinely fly upside down (stunt biplanes f'rinstance) usually are built with symmetric airfoils (NACA 00xx profiles or similar). While this makes them less efficient in normal cruise than a similar aircraft with more modern wings, it means they can transition from normal to inverted flight with less difficulty, less drag, and typically a more well-defined stall angle of attack.

 

[Compositepro]

A sheet of plywood can fly. It is a shame that so many explanations about how planes can fly, exclusively discuss the airfoil shape of a wing. To anyone of intelligence, the obvious question is then, how can planes fly upside down? The airfoil shape is not required for flight It is simply the most efficient shape because it reduces turbulence due to separation of the airflow from the top surface of the wing. An airfoil is shaped like the airflow would be without turbulence at an optimal angle of attack.

 

[IRstuff]

The cheap balsa airplanes are excellent examples of how well flat wings can fly, and paper airplanes are also a good example of not needing an airfoil, per se, since many get lift boost from flaps. Below is a world-record flying time paper airplane

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[berkshire]

If you get a chance to be out in the real world around an airport, seen if you can see a Citabria and Decathlon fly. They are essentially the same aircraft however the Decathlon has a symmetrical wing. The Citabria does not. When you see the Decathlon fly inverted the deck angle is much lower because of that wing, an advantage. Also when the Decathlon takes off, its flight performance is worse than the Citabria, because that wing is generating less lift, a dis-advantage.
B.E.

You are judged not by what you know, but by what you can do.

 

[rb1957]

I think you can see the effect just by googling pictures of inverted airplanes … you'll see they fly (quite well) with a more pronounced tail down attitude (increasing the wing AoA) than when flying normally.

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

CAUTION... in addition to comments by others...

Learning to fly continuously inverted is a 'piloting art' that is fraught with possible danger... not the least of which is loss of orientation and uncoordinated control movements resulting in los of control.

As I recall continuous [as-opposed-to transient] inverted flight has many 'odd' aspects... such as the added negative [stick-push] angle of attack [-AOA] relative to upside-down pilot... which is needed to provide positive lift to maintain level flight.

This is particularly acute, when turning in inverted flight: the -AOA has to be 'further increased' [negative sense] to maintain straight-and-level; and 'reversed adverse yaw' has to be over-come by the rudder to make a 'coordinated turn', which can be a real piloting challenge. Also, a typical cambered wing airfoil [as opposed to a symmetrical airfoil] has a very different [shallower] 'lift curve' while inverted, so there is a possibility of 'premature stalling inverted' with too-aggressive control movements and/or unintentional uncoordinated control [pitch/yaw/roll] movements. I suspect that this scenario + pilot disorientation is a likely contributing cause for low altitude inverted flight accidents [for instance] during airshows, such as this...

https://www.youtube.com/watch?v=n3Vp9DRHpYU

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[LiftDivergence]

Found this to be a quite interesting lecture:

Doug McLean | Common Misconceptions in Aerodynamics
Michigan Engineering
Doug McLean, retired Boeing Technical Fellow, discusses several examples of erroneous ways of looking at phenomena in aerodynamics, that have either taken hold in parts of the aerodynamics community or have been expressed in books or papers by other authors. These examples are mostly about interpreting the basic physics of the phenomenon in question.

https://youtu.be/QKCK4lJLQHU

Keep em' Flying
//Fight Corrosion!

 

[verymadmac]

Coanda and Bernoulli are just tools that have largely been superseded by navier-stokes, but I am struck by the related question with an aerofoil at negative AOA, is the airflow path over the top of the aerofoil actually shorter once one accounts for movement of the stagnation point?

 

[Sparweb]

A wing creates lift (simply) by two things …
1) angle of attack
2) camber

Camber being entirely optional.

I've had to sit through several lectures from people with no idea how a wing generates lift, yet couldn't put a stop to the whole disaster because the speaker was a pilot; and the worst case was when that pilot was MY flight instructor soon to be charged with examining my flying performance. Knowing how to fly an aircraft does not exactly mean one knows how an aircraft flies!

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[IRstuff]

Sure, lots of people who drive couldn't even begin to explain how a car works, either.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[moon161]

... is the airflow path over the top of the aerofoil actually shorter once one accounts for movement of the stagnation point?

This is one concept one of my professors would actively say was not valid- twins separated at the stagnation point do not necesarily meet again at the trailing edge.

Edit, on a reread, maybe that's not what you were saying either.