Thirty Years of donning it wrong.

[Cats]

Bernoulli was wrong!
Daily Telegraph page three, 3/05/2001, any comments, he worked for me for 20,000 hours.

[DeltaTango]

What's that all about?

DT

[doggonetired]

Any chance of a transcript or précis for those of us without access to the paper version?

[Basil]

Encarta 98 says that lift is caused by deflection of air downwards due (for the top surface) to Coanda effect, and:
"One of the fundamental forces studied in aerodynamics is lift, or the force that keeps an airplane in the air. Airplanes fly because they push air down. The leading edge of an airplane wing is higher than the trailing edge. As the wing moves through the air, it pushes down the air that flows underneath it. The third law of motion formulated by English physicist Sir Isaac Newton states that every action causes an equal and opposite reaction (see Mechanics: The Third Law). As the wing pushes the air down, the air pushes the wing up. Lift is often explained using Bernoulli’s principle, which relates an increase in the velocity of a flow of fluid (such as air) to a decrease in pressure and vice versa. The pressure on the upper side of an airplane wing is lower than that on the lower side, but this is an effect of lift, not its cause."

I queried this with the Faculty of Aerodynamics at Imperial College a few years ago and they adhered (pun intended) to the view that Bernoulli Effect is a cause, and not an effect, of lift.

I'd have thought that both the Newtonian and Bernoulli theories are valid and inter-related; neither likes alpha>stalling AoA http://www.pprune.org/ubb/NonCGI/eek.gif well, unless you're up for a spot of fun :)

It's at:
http://www.telegraph.co.uk/et?ac=002101993503854&rtmo=3SBrYBqM&atmo=rrrrrrrq&pg=/et/01/5/3/wfly03.html

[Quidnunc]

Most problems in physics can be solved using a number of different techniques. Depends on which angle you came at it from.
e.g the path of a ball through the air can be predicted using either laws of gravity, or laws of conservation of energy. Both are different methods, but both give the same result..
I think it's good to know that Bernoulli and Newton agree!

[Diesel8]

Back in the days I could read, I saw in a text book, that downward deflection of air is 30 or so percent of lift and the rest is due to Mr. Bernoulli.

[FE Hoppy]

Yes when I was a boy I read about "direct action"lift and pressure differential lift.
I like to believe its all due to the will of the 300 pax on board now.

[RVR800]

See

http://www.monmouth.com/~jsd/how/htm/airfoils.html#toc52

[overdoverover]

Maybe it's due to the fact that hot air rises, most aeroplanes have at least one pilot on board! :)



[This message has been edited by overdoverover (edited 03 May 2001).]

[OzDude]

Hang on a minute! Isn't this about a month overdue? I thought April fools was only done on the 1st of that month.

For those of you who want to see Bernoullis principle in action just go to your kitchen and find a spoon, hold it with the tips of your thumb and forefinger at the tip of the handle so the spoon is dangling downward and able to sway. Go to the sink and turn on a tap so the water is running smoothly but not too forcefully and gently move the back of the spoon into the flow of water.

Now those of you who have not studied aerodynamics might expect the spoon to be deflected away from the flowing water and if that is what you expected you will be suprised to find that the opposite happens. All you have to do now is turn everything 90 deg so that you imagine the water is flowing horizontally and the curved back of the spoon is the curved upper surface of a wing. Whether the water is moving and the spoon is stationary or vice verca doesn't matter as the principle is the same and you can apply fluid dynamics to air or water, the only difference really being the density.

I see nowhere in the article mentioned anything about the dynamics of drag and that would play a HUGE part of any theory to do with air 'sticking' to a surface! As for throwing Bernoullis theory out of the window... well it was some American who wrote the original article and just like the film U571 where history is re-written... well you know. (No offence intended to my American cousins who may think that this is a yank bashing exercise).

[spannerhead]

Whilst your sat at your computer, reach over and get a sheet of A4 from your printer.
Now then. Hold the shorter edge of the A4 under your bottom lip leaving the sheet to hang down. Blow...This proves Bernoulli.
I suppose sticking your hand out of the car window proves Newton

[Huck]

It has become quite fashionable among aviation management majors to poo-poo Bernoulli and insist we're all out there riding surfboards in the sky.

They never can quite explain, however, the effect spoilers have on lift - without changing the "downward deflection" of air at all!

Truth is - they're getting hung up on frame of reference. We all studied aero by sitting on the wingtip, as it were, and observing. Change your reference point to the ground, watching a plane fly by, and you have to use a whole different method to explain lift. Same song, just second verse.

[Hugh Jorgen]

As long as I don't have to sit any resit exams!!!! - Is it still pull to go up and push to go down?

[The Unteleported Man]

Bernoulli explains the pressure distribution around a wing well. However classic Bernoulli doesn't suggest that air is accelerated - a requirement if you want to achieve lift.

The 'how it really flies' link above is a good treatment of the subject. If you want to get into circulation, rotation, the theory of Kutta etc buy 'Theory of flight' by von Mises.

Back to that teaspoon: have a look how the water deflects the opposite way to the teaspoon...

No flight training program I've seen adequately explains lift.

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Reality is that which, when you stop believing in it, doesn't go away.

[BOAC]

Well there! I always thought it was done by those little yellow eyes fixed to the top of the wing on a 737.
Must buy a better quality paper.
Yep, Ozdude, I checked the date too!

[Herod]

Doesn't suggest air is accelerated? Then how the hell does it get around the greater camber of the top surface to meet its mate who has only come around the shorter, bottom way? If it doesn't than I've been aviating a myth for thirty years. Ouch!!

[Pointer]

This sounds like the chicken&eggs thing, well here's my eurocent's worth ( and it ain't much either!)

Your mate is not excelerated he took the long way around with less traffic( like when you do trying to beet traffic on your way to...)

O what i'mproving every day that either one of the things is right even with a 4,5deg glide!

HOW many points was that..?

[Bash]

Scientific theories are constantly tested and conventional wisdom challenged. It's healthy that way. Einstein did not prove Newton wrong. He just went further towards explaining. Some of Einstein's theories are incomplete. Where quantum mechanics meets special relativity for example. That's why the worlds greatest brains are looking for a 'Grand Unifying Theory'. I'm a flat earth man myself and I'd like to know why we don't ever fly over the edge?

[This message has been edited by Bash (edited 04 May 2001).]

[Bash]

I always thought I had a handle on this but now I'm not so sure. The aerofoil is moving not the fluid. Therefore perfectly static air has a velocity relative to the wing surface. The stuff in contact with the top has to get round a longer way so it's velocity relative to the surface of the wing is higher than the velocity, relative to the wing surface, of the stuff underneath. The velocities of the two air streams relative to each other remain the same. If this produces the pressure differential which constitutes the force we call lift then there must be an equal and opposite force. Presumably that's why the the air is deflected downwards. I also thought that the angle of the wing relative to the airflow has a bearing and is why an aerofoil can actually produce lift the wrong way up. The torygraph was talking about a perfectly flat surface at an angle to an airflow deflecting air down and producing a reaction force upwards. Surely all the forces interact to produce lift and have at the same time effect each other. I haven't got a bloody clue!

[hairy_kiwi]

Answering, ‘How does an aircraft fly?’ must surely be rated as being as awkward a subject to broach as ‘Where do I come from?’ Only that when you’ve finished the latter question it’s not followed by any more. ;) :) ;)

Our technology correspondent’s article in the Telegraph reads just like most of the rest of the articles about aircraft, (aircraft accidents especially) published in newspapers; apparently definitive yet lacking substance.

I like Gail M. Craig's explanation in his book ‘Stop Abusing Bernoulli! How Airplanes Really Fly.’, Regenerative Press, Anderson, Indiana, 1997),
Here's a précis at:

http://www.geocities.com/galemcraig/

Another really nice explanation with good diagrams along the same lines as G. Craig by some well qualified physicist working at some windy tunnel in Batavia IL and his mate, an associate Prof. at the University of Washington at:

http://www.aa.washington.edu/courses/aa101/paper.pdf

[The Unteleported Man]

And another point: it's no necessery for the air going over the top to "meet its mate" going around the bottom. This becomes quite obvious if you study circulation. But the really neat thing is that aeroplanes do fly! :)

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Reality is that which, when you stop believing in it, doesn't go away.

[Steepclimb]

What! after nearly a hundred years of flying, we're still arguing over how it happens!

Many is the time I've been flying and looked out at the wings and thought, 'I know what the books say, but it still looks impossible.'

I've been involved in this argument before, it can get quite heated at times. The fact is that Bernoulli is quite intuitive where as the the other stuff....well it requires some thinking. Imagine trying to explain it to a student PPL.

To be perfectly honest, it should be straightforward to find out precisely what are the forces involved in this day and age. It seems obvious that they're interrelated. After all it's not magic or religion, just physics.

It wouldn't be the first time, basic principles were found to be in error though, I seem to remember being told that the direction of current flow in electricity was found to be different to what was postulated for years?