Lift as a theory?

Question

Why are people trying to disprove the way an airplane flies? They say that an airfoil is a myth and that Bernoulli's Principle is just a theory. Ok how do thousands of aircraft takeoff everyday?????

Answer 1

Scientists and engineers use the word "theory" in a little bit different way from the way it is used in ordinary conversation.  People use "theory" to mean "guesswork" or "speculation."  (As in "I have a theory as to why Ellen left her husband...")

But that is not what "theory" means in science and technology.  Theory means a body of related information, axioms, corollaries, and conclusions that together provide the best support for an explanation of an observed phenomenon.

Now that you understand the meaning of the word "theory," you will no longer be drawn into the discussions of confused people who think that "theory" means "unproven."

In aeronautical science, the phenomenon of aerodynamic lift is very well understood, and there is no question as to how it works and what is taking place.  The entire previous discussion unde this question is incorrect.

Please visit your library, or do an internet search on "Bernoulli's principle," and "aerodynamic lift" for detailed information.

Good luck!

Answer 2

i dont get the story from your small passage here but what the F***, people are absolutely insane if they still believe this c**p today.

Also, if this is something to do with religionon could you fill me in and tell me what religion particly. (excuse the spelling)

+ there proably to dumb to understand it and the world around us.

Answer 3

Its referred to as a theory because the actual vehicle that causes lift to happen is still not exactly understood.  The coefficient of lift is a variable that is thrown into the equation in order to make the equation equal observed data.  Without it, the math won't work.

The exact effects of AoA, air density, and velocity and their relationship to one another is not defined very well.  The Cl variable allows rough predictions to be made, but even the best computers at Boeing cannot really design a perfect airfoil.  All the simulations are based off observed numbers that really cannot be accurately defined.

To sum up my rambling statement:  Lift is still kind of a mystery, even to aerospace engineers.

Edit:  I was not trying to imply that engineers simply guess at anything or that airplanes are mystery machines that nobody understands.  I am merely trying (unsuccessfully) to point out that all of our knowledge about lift is based simply on a trial and error type of engineering.  Like "if I do (a) the results are ____ and if I do (b) the results are _____. "

Engineers can predict very well what will happen when a wing is designed and built.  The good folks at Boeing and Airbus do a fantastic job.  However, there is not real mathematicla equation with defined variables that can predict lift.  The "Lift Equation" is mostly just a training tool used to demonstrate to young aviators which factors they are dealing with and how they relate to each other.

The "Theory" of lift is called a theory only in the scientific sense.  It is nearly impossible to PROVE anything.  It is not as simple as proving that an airplane flies.  One would have to PROVE that the lift produced is always exactly equal to what is predicted.  And that still (and probably never will be) has not been done simply because of the Coefficient of Lift.  Its just a fudge factor thrown into the equation to make it work.  It is an undefined variable that has no real finite value, its a training aid.

A non-aviation related analogue I can draw you is the "Theory of Gravity."  Everyone knows that gravity does exist.  Everyone knows that scientists can measure and predict what will happen when a body is acted on by gravity.  thanks to Newton and Einstein, the results of gravity are VERY well understood and extremely accurate measurements can be done to predict the resulting actions of any gravitational force.  However, the actual vehicle by which gravity affects anything is still speculative.  The graviton has not been demonstrably proven to exist, even though it can be inferred.  Simply because we do not yet know HOW gravity affects us does not mean we do not understand its effects.

Lift is much the same way.  We can measure and predict it.  We understand lift far better than gravity as a matter of fact.  However, the idea that we can predict to 100% accuracy what will happen over a wing is just silly.  If one air molecule was moved slightly it would render all computations moot.  We can do a good enough job at it to predict how fast an airplane will fly, or how high it will go but to suggest that we can to it perfectly is simply not true.

Answer 4

Mass hysteria!

Answer 5

Bernoulli's Priciple is right they cant. im a pilot i should know.

Answer 6

Jason is right on. Basically, fluid dynamics are so complex that we can't EXACTLY measure how lift works. There is a Newtonian element at work because as air flows over the wing, it drops down behind it. This applies to Newton because that air mass driving down exerts a force upwards (every action has an equal but opposite reaction). This force is acting separately from Bernoulli's principle. The debate is over which one is more important. If you're seeing people saying it's all rubbish, then they're just crazy. We've done a great job of figuring the whole thing out but even if we can't exactly define everything, the results still speak for themselves. Airplanes fly whether you believe it or not.

Answer 7

Jesus? Anyways, some people are just crazy. There are people who still think the world is flat.