Other than the CFD question, how do you suppose that bouyancy has a role in lifting an airplane? Have you tried to compare the Reynolds and Grashof numbers for this problem?

Archimedes principle of buoyancy explains the physics of how balloons float. There are simple experiments which show that it's possible to apply buoyancy to helicopters. Specifically: A helicopter in a hover displaces a mass (or weight) or air down each second that is equal to its own mass (or weight).

I'm now trying to do the same for airplanes. I was hoping to use CFD to estimate the volume of air displaced displaced downwards by the wings. Then use this to estimate the mass of air displaced.

If this thesis was correct, then it would be a significant insight into the physics of flight.

Unfortunately Reynolds and Grashof numbers don't say much about the volume of air?

The physics at the basis of the lift of a helicopter is totally different from that of the lift of an airplane. For the airplane you have to focus on the basis of Bernoulli principle and the specific design of the airfoil.

I'm only attempting to verify if airplanes achieve buoyancy.

Bernoulli is irrelevant to the project. In any case, NASA disproved Bernoulli as an explanation for the physics of flight back in the 1970's.

Bernoulli is debated in a more complex framework where vorticity is present in inducing relevant effect. Displacement of air mass due to the airfoil can be simply evaluated, to show that cannot balance the weigh. Not like a helicopter. Generation of aerodinamics force is still studied in its fundamental physics

Have a look here to have the idea of hystorical Bernoulli principle vs. the vorticity-based idea. The later is a natural correction of theory that does not contradict the explanation provided by Bernoulli

https://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html

https://www.grc.nasa.gov/WWW/K-12/airplane/right2.html

In your intention, the theory of the rotation should produce a displacement of mass to subtain the flight. Just compute a simple 2D potential flow, then design a volume over the airfoil and compute the total mass displacement in this volume.

Sure. But for this project it doesn't matter whether Bernoulli can or cannot be applied to explain flight.

I'm looking at HOW MUCH air is displaced down by the wings; not HOW the air is displaced. A subtle but important difference.

There is not difference in substance, the airfoil moving in air induces a mass displacement you can compute starting from a simple 2D incompressible, steady, potential flow model. You can solve this problem also in the PDEtoolbox of Matlab, the potential flow problem is Div Grad phi = 0, prescribing the velocity normal component (Neumann BCs) on the airfoil. Note that a constraint (Kutta condition) fixes the unicity of the problem. Then, you can compute the flow velocity field and define a proper volume to evaluate the mass displacement through the surfaces.

great. Thanks

Nicholas Landell-Mills and Filippo Maria Denaro :

We need to clear our understanding about the important issue of lift generation for heavier than air machines. By definition L/W is significantly more than one and that tells you about the lift generated is significantly more than buoyancy. I suppose that is first issue addressed by early pioneers of aircraft flight like Wright brothers. Buoyancy is important for dirigibles. Please consult a good book on aerodynamics. If you are interested in finding out the small contribution due to buoyancy, then also it is very easy to estimate.

Thanks for the msg. To be clear, I understand that you mean that: Lift = Weight of Airplane = Mass of airplane x Gravity. (Newtons 2nd law of motion.) Therefore: Lift cannot equal Mass of Airplane. The logic here is correct, there is no evidence that this is true in reality.

I am investigating whether Lift = Mass of Airplane (not Weight of Airplane). Let me explain below. See images attached.

This textbook approach above is actually wrong, as evidenced by commercial airliners that fly with a Thrust-to-Weight ratios as low as 0.3. Note that this is a Thrust-Mass ratio of about 3.0 (assuming gravity is 9.8 kgm/s2).

Engine thrust is used to push the airplane forward and for lift. (Thrust = Forward motion + Lift). Given that: Lift < Thrust < Weight of Airplane. Then logically, lift must be a lot less than the weight of the airplane.

In turn, I wonder if it is feasible for: Lift = Mass of airplane (ie. buoyancy). An airplane in flight pushes air down, this then pushes air elsewhere up. This air resists the airplane's action of pushing air down. The airplane is just circulating the air like a helicopter and balloon. So the airplane lift only needs to match its own mass, not its weight.

Nicholas Landell-Mills

I don't understand you ...lift is a force, when you suppose Lift = Mass that implies Mass*gravity ...

Tapan K. Sengupta also stated what I wrote above, the "buoyancy" is not so relevant

Textbook physics says that to fly, lift must equal the weight of the airplane.

Lift = Weight of Airplane = Mass of Airplane x Gravity

Does this answer your question?

Then, what you would demonstrate is that the flux of air through a surface S below the airfoil, that is Int[S] rho*v.n dS (flow rate = mass/time), is equal to the mass of the airplaine/time. You can use CFD to show if that is true.

Nicholas Landell-Mills : If lift is equal to weight in cruise, then the million dollar question is how do you get up to the cruise altitude? By climbing - right? And during climb your lift will be more than weight. This question is too hypothetical! What are we discussing anyway? In any 101 course, students are taught that L/W has to be more than one, as you not only climb in pitch plane, you will due to manuevers. Please google (v,n)-diagram. Seriously!

Sure, this is what I was also taught at school. But is there any scientific evidence that it is correct?

As I say above, there is well established evidence that many airplanes fly with Thrust-to-Weight ratios < 1; In these cases lift < thrust < weight.

For a more detailed explanation for this: Deleted research item The research item mentioned here has been deleted