Coanda effect Vs Bernoulli
 

Which is the Correct explanation of Lift on an Aerofoil?? or do they both work together?:ugh:

Please don't rock the already teetering Newton vs Bernouilli boat by adding viscosity too!

They all work together.

If there's a guy who has a compressibility effect named after him then we'll be complete. I guess we can bring Maxwell into the mix there, or just resign ourselves to having to invite both Navier and Stokes to the party, and abandon all intuition.

Osborne Reynolds?

Osborne
 

Fair enough, Prof. Reynolds can be relied upon to select a highlight of all that messy stuff.

What's his number?

Surely everyone knows that only money can enable aircraft to fly.........and I mean lots of money!

Yes, but to offset the weight of the money, you have to pay engineers to make a curvature in a wing - twice, then stick one on each side of the fuselage, bye bye money hello lift.

NASA, them space people, dispels the idea of the Bernoulli theory and they say that lift is cause another way.

Thinking about it though, a pair of wooden planks could get you airborne if they had angle of incidence and were planed and sanded on the leading and trailing edges to enable air to flow smothly - plus a tailplane thus aligned with adept longitudinal dihedral and voila! You`ve got yourself an A350!

NASA denying Bernoulli, is what make me confused, So are the theory of Lift taught in flight schools all wrong then?? includes the Books Published by Mr Keith Williams, :).. Could someone be kind enough to explain the two theories " Sorry am a rookie :ugh:

As I understand it, all Newtonian physical theories are only methods to describe the outcome of a given phenomenon. So, by definition they cannot be regarded as 'correct' or 'incorrect'. There value lies purely in how well their results match observed/measured data. So, NASA cannot legitimately say that Bernoulli is wrong. All they can say is that other theories more closely correlate with the experimental data.

Reynolds is ex-directory.

Warning-this has been simplified for the Great British Public.
 

At about 35.30 mins in after Nigel has told you how it works, Kingston Uni and their take on Bernoulli.

But the Pressure difference does not hold true for Aircraft in Inverted flight or does it ??:ugh:

Newton vs Bernouilli vs Stokes
 

Maverick,

The simple arguments usually presented for lift are:

Newton: the wing deflects air down, leading to net descending air behind the wing, and so the air pushes the wing up. (Momentum is conserved by a net huge-scale rotation to keep the whole world static.) This is broadly conservation of momentum.

Bernouilli: Faster flow above the wing leads to a lower pressure above the wing, pushing the wing up. (Yet of course the air behind the wing is still directed downwards.) This is broadly conservation of energy. Compressibility makes it more complex when the speed rises towards that of sound, but that just means the internal energy of the air needs to be taken into account too.

Both descriptions are correct and required.

Viscosity sets how the flow changes as you move from infinity towards the wing, as neither the "Newton" not "Bernouilli" description provides a way to see where the flow streamlines go. To do that, the flow pattern has to solve the Navier-Stokes equation, which will give pressure and velocity fields that agree with, but encompass these other descriptions. "Coanda" describes the viscous connection that shapes the flow to dip behind the wing, so has more of a link to "Newton" in terms of the bulk flow, shaping the streamlines for "Bernouilli".

If you stick to considering the transfers of momentum and energy in the wing-airflow system, then you'll tell no lies. You might not be able to design a wing that way, but you can explain how one works when it's going fast enough or doesn't when it stalls.

Following on from awblain ..

As with all explanations, the desirable aim is to match (in a sensible way) the complexity of the explanation to the (educational or other) needs of the listener/user.

A lot depends on how close the listener needs to get to the heart and detail of the problem under consideration ie is a Dalton explanation adequate or does one need to get into Heisenberg, Schrodinger or Fermi ? As for bosons and fermions, spare me the details ...

Thus, there is no point in confusing a young child with an explanation of what might be going on in his digestive tract to cause the pain which is causing him grief and stopping his getting to sleep .. all he needs at the time is to know that it's OK and mummy will cuddle him until it's better.

Conversely, the RMO has no use for the child's explanation and seeks the detailed ins and outs of the relevant internal medicine considerations.

The pilot needs an idea of what is going on but, as he is not involved in estimations and the like, an overview is fine and Bernoulli fits the bill to an acceptable level .. warts and all. As to whether it is the best simple explanation is a moot point for which the answer is up for grabs. As for me, my preferred simple explanation is a Newtonian one which looks at the wing's magic bag of pixie dust which throws a bunch of air downwards .. giving the wing a lift (force) upwards ...

At the other end of the spectrum, the aerodynamicist generally gets revolved in detailed consideration of circulation theory from which he can estimate numbers (an outcome beloved of all engineers).

Point is it comes down to horses for courses .. pick the range of explanations which fit the bill and don't fuss too much about the others ...

As for Navier-Stokes, I could never figure out the answer ..

...and then Google the definition of "superstition"!

And if Coanda seems weird there's plenty witchcraft went on in old Eastern Europe. Check out Tesla and Schauberger.

....and if anyone mentions conveyor belts.

Shoot them. :ok:

Newton explains lift. :ok:

Bernoulli explains stall. :eek:

Coanda explains cavitation :hmm:

Reynolds doesnt have anything to do with flight :mad:

I'm probably less knowledgeable on this than others on this thread [1].

The best answer is that all of them are true. Newton & conservation of momentum is a basic law. The wing does push the air down, hence the air pushes the wing up. A planar wing would deflect air downward and provide lift.

The way I've always thought of Bernoulli is that it enhances / increases the "Newtonian" air deflecton. The curvature changes the pressure on the wing, gives an even lower pressure on the top and higher on the bottom than the planar wing would get. So the wing pushes the air down harder than a flat plane would, so gets a bigger Newtonian push up.

This gives a way to think about flying inverted... the same basic air deflection is happening, just less efficiently because the Bernoulli effect is worked against the lift rather than for it.

I think the confusion is that some textbooks describe some percent of lift as from Bernoulli and some from deflecting air. It is really all from deflecting air, just that some is deflected because of the basic planar shape, some increased amount because of the curve.

[1] But sadly, to everyone's disappointment, that won't keep me from posting. :)

I really don't care for the specifics of how wings work, just that they do if used correctly.:ok:

So, let me put down what I,understand reading the above comments Please correct me If I,am wrong.

Lift is a Combination of both Newtons Law and Bernoulli's Principle, Newtons law defines the reaction of an Aerofoil at an angle to a free stream flow of Air/fluid. An aerofoil pushes the air down which results in the air pushing the Aerofoil up, but an Asymmetrical Aerofoil would push the air downwards at greater velocity due Bernoulli's principle and thus create more Up force (lift)

Coanda effect describes the movement of this Air/fluid Particles around the airfoil and reason the air on upper surface dips below and Vice-Versa creating what we know as Wingtip Vortices.??

Inverted flight:-, a conventional Aerofoil can sustain such flight because of Newton's law but inefficient and would require higher AOA and for Symmetrical aerofoil like that of a fighter jet, it is easier to sustain such maneuvers because there is less pressure differential (Bernoulli) due to the aerofoil design.....:confused: