Well , the theory that the air on top was trying to keep up with the air underneath never made sense to me. What law of physics did that idea come from? But, as someone already said, that's the only change in the idea, correct? The air does flow more quickly over the top, it's just that the reason is no longer because they need to keep up with their buddies.

I have a feeling that it came from a conservation law which was used in the derivation of Bernoulli's principle. Someone more current on it can feel free to nitpick me, but IIRC, if you evaluate it at two points, i.e. all of the top surface and all of the bottom surface, you are implying that the mass flow through the top surface and the bottom surface is equal. You can't "just ignore this", because it's implicit in the derivation of the equation.

One major issue with Bernoulli, apart from the qualitative arguments discussed previously, is that it has no accommodation for acceleration. This means that fluid velocity is the only factor in the determination of inertial forces when using it, which is incorrect.

The plane/treadmill thread was literally hundreds of pages long at RCGroups.com...

I guess it depends which theory you subscribe to. I had believed the low pressure over, high pressure under, was the cause of lift. It's the theory that more or less states aeroplanes are sucked into the air. There seems to be a lot of problems with that theory when you consider aerofoil types, AoA and of inverted flight.

The key concept (that's news to me) is that lift is generated by turning air down and away from the aeroplane (every action has an equal opposite reaction). Hence you can hang all kinds of gubbins (engines/landing gear/stores) under a wing and aslong as you can turn the air downwards as it passes the trailing edge you're good to go.

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

Cheers

Not to screw with your mind any more, but the thing is that a pressure differential is basically the end result of turning the air. When using applying Bernoulli's principle, it would seem that this is due to a velocity difference. When applying Newton 2nd/N-S eqns, it's due to differences in velocity, acceleration other pressure fields and anything else*. Just because in Newton's 2nd you have a force F term doesn't mean that you go from having an incorrect pressure to a mystically correct force, per sé - this force manifests itself in a pressure as well, so in both cases, as in reality, lift is generated by a difference in pressure. The key is in what generates it, which is where it gets pedantic.

The error isn't that "one uses pressure differences and one turns the air" - it's more like "one only uses velocity differences, whereas the correct one accounts for turning/accelerating the air.". The end result in *both* cases is that you get a pressure differential - lift. Note also that pressure is force divided by surface area, so you can relate Newton's 2nd to surface pressure changes.


*(the N-S equations are quite general enough for additional things, like Coriolis, magnetic field coupling, and stuff like that to be "bolted on")

"This nacent revisionism will void all previous theories of flight (however anal it may be), whilst Bournelli turns over his grave etc'

While I realize that you were joking, I also realize that it is easy to forget that his theories had nothing to do with flight, although they will be forever connected with it. He was working with water pressure.

OK, that's all ... well, confusing.

But will my plane be able to fly tomorrow ? I plan on flying into the Sun n" Fun fly-in.

That depends in which theory you believe:\

- if you think Bernouilli was right, it will fly
- if you think NASA is right, well... check your insurance papers.

Update, not sure why, but the plane still flew. So did a lot of others. Landing pattern a bit crowded.

So I guess most airplanes are still flying even if they don't know why.

It may have some relationship to magic. I've noticed that none of the aircraft can takeoff and fly until some guy in the tower performs some ritual and says the magic words. Then you can fly.

'tis indeed the truth. You must never, ever cast aspersions upon that person in the tower, as they hold much power, over life and death, and can really ruin your day.
You might also want to say a few words to ensure that the rain gods don't... rain on your parade...

I'll get my coat.