right or wrong????

[SkyWestCRJPilot]

If it were all Newton then what's the point of flaps, slats, and vortex generators? What's the point of slotted flaps that allow high energy air below the wing to energize the air above the wing maintaining the boundary the layer and lift. According to Newton's 3rd law all that air below the wing coming above the wing in those sloted flaps is wasted lift. What's the point of spoilers which "spoil" the airflow above the wing thus reducing lift. If Newton's 3rd law were the only factor invovled all airplanes would have symetrical airfoils but that's not the case. Thousands of aeronatical engineers over the years must all be mistaken about their aeronautics then. Better let the engineers at Boeing know before they put a cambered supercritical airfoil on the 7E7. Like others have said, it's not so simple as just Newton or just Bernoulli.

 

[HerrJeremy]

Have you ever studied photos of an air foil in a wind tunnel with pulsed smoke streams? It's very interesting, because it allows you to compare air flow velocities. What it shows clearly is that the air over the top of the airfoil flows faster than the air below the wing. and it's not just because of the longer path (another false premise) If we take 2 adjacent air molecules that part company at the stagnation point, one going over the wing and one going under the wing, it's true, they do *not* meet at the training edge, far from it, the one over the top actually *beats* the one going under the wing.

So, if your "debunking" of Bernoulli hinges on the equal transit fallacy, then think again. Bernoulli's principle isn't based on the idea of equal transit times.

Doesn't the existence of wingtip vorticies disprove the "equal transit times" theory anyway?

 

[BeechSlapped]

Very good post by A Squared.

To add a bit more: I think we all agree that it is an undisputed fact that there is a difference in pressure between the upper and lower surfaces of an airfoil. This is the ACTUAL mechanical cause of lift because there are only TWO ways that a fluid can exert a force on a body: through pressure and shear stress. On smaller aircraft shear stress is low enough that it can be neglected. So it is that pressure difference, and that alone, which causes lift.


The next question is why is there a pressure difference? Well, this is due to the variances in flow velocities along each and every part of the airfoil surface. Here is where it becomes complicated and here lies the souce of the confusion. The problem is that everyone has been trying to give a simple explaination as to why the flow speeds up and slows down along the airfoil. This requires use of formulas known as the Navier-Stokes equations which are far beyond the scope of this board. These equations use conservation of energy to solve for the pressure, velocity, and density of the flow at a given point. They are nearly impossible to solve unless one uses a Computational Fluid Dynamics computer program. This is how it is done today. How did they do it long ago? They basically stuck an airfoil section in a wind tunnel and measured the lift and drag empirically.

Anyway, in conclusion, all you Newton desciples out there need to realize that the downwash produced by a wing is simply a BYPRODUCT of lift, it is not the reason FOR it. However, using this downwash will give a fairly accurate result if you want to calculate lift, just remember that the physical mechanism is pressure differential.

Finally, let me throw this out for thought and discussion. The physical reason for thrust from a jet engine is the sum of the internal pressures and NOT the high-velocity exhaust from the nozzle. This is merely a byproduct of thrust.

BeechSlapped

 

[mar]

The Curve Ball

For MSW--

Believe it or not I'm still living out of boxes from my last move, thus all of my aerodynamic texts are unavailable.

But there is a theory of lift based on circulation and explains why the curve ball curves and the tennis/golf ball slices.

Basically the threads/fuzz/dimples all energize the boundary layer and create (redistribute) the low pressure areas.

There were experimental applications to aircraft (rollers in the wings) to help energize the boundary layer but I think they found vortex generators to be cheaper, lighter, more reliable and easier to work on.

As for Bernoulli vs. Newton....well, it's like my pitch vs. power answer: It Depends.

Or maybe it's just all PFM.

 

[VivaZapata]

So let me get this straight.

Contrails are actually plumes of experimental gasses.

And "Bernoullian lift" doesn't exist.

And blacks in America were better off in the Fifties.

Yes Typhoon1244, Welcome to the "*Bizarro World".


*Seinfeld

 

[A Squared]

frog,

Yes, that's an excellent analysis. I've used the same argument in previous discussions. The trouble is the "bernoulii is a fraud" folks generally lack the bacic high school math skills to even grasp what you are saying, let alone understand that it neatly trumps their position.

Herr Jeremy

>>>>Doesn't the existence of wingtip vorticies disprove the "equal transit times" theory anyway?

Yeah, sure, if it needs disproving. That's one of many things that disproves it. No-one actually beleives in it. For some bizzare reason though, many of the arguments presented by the "bernoulii is a fraud" crowd center are based somehow on the equal transit time concept, as if it was relevant.
The only place you will find the "equal transit time" concept is in children's science book written by someone who doesn't understand lift themselves, and in the FAA Flight training Handbook (sad commentatry on the FAA) A few years back, there was a guy who was making a lot of "bernoulii is a fraud" noises, he even managed to get his pap published in an aviation magazine or two. His argument was this: The air going over the top has to have the same transit time as the air under the bottom, so if we measure the length of the top surface and the bottom surface, we can calculate the difference in velocity between top and bottom. Then if we plug those numbers into Bernoulii's equations, we can show that it can't possibly generate enough lift to keep the airplane up. He was right, the numbers didn't work out. They wouldn't, couldn't, his basic premise for his entire argument was dependent on the "equal transit time" fallacy. That has been known not to be true for at least as long as folks have been putting pulsed smoke streams in wind tunnels (1920's maybe?) If you didn't catch that his numbers were based on the "equal transit time" fallacy, they sounded good. If you did notice this, it was clear that his numbers were completely meaningless, just a bunch of computational diarrhea.

 

[Typhoon1244]

...a bunch of computational diarrhea.

I'm going to incorporate that into my everyday vocabulary!

 

[HerrJeremy]

on the topic of wing aerodynamics.....I was noticing a RJ on the ramp a few weeks ago(later found out it was a Canadair). On the bottom of each wing there were 5 fin-like protrusions. Are they there to help the wings' efficiency, or are they just housing for some mechanism of the wing?

 

[Typhoon1244]

on the topic of wing aerodynamics.....I was noticing a RJ on the ramp a few weeks ago(later found out it was a Canadair). On the bottom of each wing there were 5 fin-like protrusions.

Those are aerodynamic fairings for the flap hinges and actuators. They smooth the airflow over what would otherwise be a chunky, irregular object sticking out of the bottom of the wing.

You see the same thing on most modern jetliners. (The fairings on the 747 would make decent boats...they're huge!)

 

[GeorgeTG]

from the "horse's" mouth

What is Lift

cheers
George