Why is Bernouli's theory still used to explain flight in physics classes?

Question

This theory is based on the equal transit time assumption- that air above and below the wing must reach the trailing side of the wing at the same moment. This is simply not true, however, the theory is taught almost univerally in schools. Bernouli's theory is correct, but it does not come close to explaining heavier than air flight.

Wow, I guess I'll have to explain this further. As far as Bernouli's theory being tested and proven, that's complete baloney. Just think about it- it it were true- how would it explain a stunt plane? (flat wing) And yes, Bernouli's theory does only apply to laminar flow- but for the most part that simulates an airplane wing just fine. The real reason airplanes fly is the Coanda effect. It's not circulation, Bernouli, or any other theory. Now on with my question- why are these other theories still being taught as the answer?

Answer 1

Though both Bernoulli's principle and the Coanda effect are based on the same notion of a moving fluid, the latter has so far not yet proven to produce significant amouts of lift.

Answer 2

Bernouli's principle proves flight better than the coanda effect, by your own description. The bernouli perinciple does not require a "curved surface," as does the coanda effect. The coanda theory states that a fluid will tend to follow the curve of an object. This does not work for a wing with no camber. Bernoui's principle simply requires a stricture of some sort, and a variance in pressure.

Now, the coanda effect has been shown to result in heavier than air flight. The flying saucer test is an example of this.

I would imagine, though, that these two principles may be related. We may one day have an explaination of how both of these effects are produced from similar circumstances.

Answer 3

Better fire whatever physics teacher failed to convince you. Lift provided by a wing is extremely predictable and repeatable using the Bernoulli principle .

Re: Stunt planes - Their wings are symmetrical, not flat. But even a flat wing can generate lift with enough power. In either case, take a look at the flying principle of "Angle of Attack", which will describe an added element that contributes to the exposed wing surfaces that responded to the bernouli effect. Along with forward velocity, it determines whether the bernoulli effect is sufficient to maintain flight.

Answer 4

common wisdom now is that the primary source of lift is from the deflection of air molecules for any reason -- including just striking the bottom of the wing, and that a flat board can work for this purpose. the force that pushed those air molecules down, pushed the plane up.

smooth airfoils have the advantage of reducing drag and edge turbulence which prevents laminar flow. but a symmetrical foil achieves this goal.

a classic airfoil achieves a higher effective angle of attack for the same physical angle of attack, further reducing drag, thanks to the higher velocity air joining back up with the slower air at the back of the wing 'sheds vortices'

so, for an underpowered, barely able to fly, vehicle, an airfoil can make a big difference in whether it gets off the ground. But with today's rocket engines you pretty much don't even need wings, let alone the bernoulli effect.

Answer 5

I think you are missing an important part of the Bernoulli effect when it comes to planes flying upside down. Even a flat board put at the appropriate angle of attack creates a situation in which the air on top of the wing has to travel further than the air on the bottom of the wing. The greater the angle of attack, the greater the difference and the greater the lift (within limits of course).

Answer 6

Bernoulis principle doesn't state that the air must reach the the trailing side of the wing at the same time, just that faster moving air creates lower pressure.

Answer 7

You are WAY off the mark here, sport... The wings on a stunt plane are SYMETRICAL... the shape of the wing is the same on the top and the bottom. There are any number of NACA airfoils in the files for you to took at.

Bernouli's effect IS correct... you just haven't gotten the necessary academic background to understand it... yet... but keep in there... in another couple of years you will see how wrong your current hypotheses is.!

Answer 8

Bernoulli's principle is that in fluid flow an increase in velocity is associated with a simultaneous decrease in pressure. It stems from conservation of energy along a streamline, and so of course it fails for turbulent flow. It is backed by experiment and accounts for a large part of the lift on an aircraft wing.

The reason air flows faster over the top of a wing is conservation of mass. The path length is longer, and so if flow were not faster on the top then there would be a build up of air on top of the wing that would grow cumulatively with time. This clearly does not happen, so your assertion is clearly wrong.

It would be better if you based your arguments on observed phenomena rather than uniformed prejudices.

Answer 9

"Lift from an airfoil
Some people have attempted to explain how a wing generates lift, by invoking the Coandă effect. However, this theory does not produce quantifiable data, and so it is unable to predict such things as the thickness of the boundary layer. Professional aerodynamicists regard this theory as a fallacy."

Answer 10

all objects have same acceleration. But in practice we find air resistance and different objects take different time to reach earth.

Still we teach that all objects take the same time.

The same thing with Bernoulli's principle. The actual fact will be understood latter when they study about the flight of the plane