MERGED: Engineer debunks theory of flight

[Sunfish]

Over to you.

I still think the Earth sucks....

Bernoulli eat your heart out..

Engineer debunks theory of flight
David Millward and Nick Collins London
January 27, 2012

AN ENGINEER has debunked one of the most common myths in science - why aircraft fly.

Aeroplanes fly because their wings cause the air pressure underneath to be greater than that above, lifting them into the air. For years engineers have been frustrated by a theory that wrongly explained the change in pressure.

The myth is common in textbooks, and even Einstein was rumoured to have subscribed to it.
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A Cambridge scientist was so fed up with it that he created a minute-long video to lay it to rest. The video, published on YouTube by Professor Holger Babinsky, seeks to explain in simple terms why the theory goes against the laws of physics.

According to the myth, the pressure change happens because the air on the curved upper surface of the wing has further to travel than that below the flat underneath surface, meaning it must travel faster to arrive at the other side of the wing at the same time.

The true explanation is nothing to do with the distance the air has to travel. The curvature of the wing causes the change in air pressure because it pulls some of the air upwards, which reduces pressure, and forces the rest beneath it, creating higher pressure.

Professor Babinsky explains that, although lift is caused by a pressure change between the top and bottom surfaces, it's due to the change in the shape of the air flow, rather than its speed. ''This is why a flat surface like a sail is able to cause lift,'' he says. ''In this case, the distance on each side is the same but it is slightly curved when it's rigged, acting like an aerofoil.''

Professor Babinsky filmed smoke passing across a wing. If traditional wisdom had been correct the smoke above and below should have reached the back at the same time. Actually, the plume above the wing reached the back much sooner.

Read more: Engineer debunks theory of flight (http://www.theage.com.au/travel/travel-news/engineer-debunks-theory-of-flight-20120126-1qjrc.html#ixzz1kexcWdhl)

[cficare]

if u push air down...the equal and opposite reaction is ....

[jas24zzk]

Cop this for a load!!!!

Not going to make my own comments at this point, but I thought more that a few of you might find it interesting.

Of interest, is how quick the paper closed comments to the article.

Engineer debunks theory of flight (http://www.theage.com.au/travel/travel-news/engineer-debunks-theory-of-flight-20120126-1qjrc.html)


Cheers
Jas.

PS...mods sorry if this was raised elswhere, but I only read godzone :D

[Jabawocky]

I never followed the Bernoulli version of events either.

Apparently wings fly regardless of what you believe :ok:

[stevep64]

I always had a problem with Bernoulli's principle as far as lift is concerned. I thought that was one of those things they didn't teach in BAK courses anymore, it was more about downdraft providing the lift. I stand to be corrected, because I'd really love to hear other's opinions, or theories.

This could turn into a downwind turn argument :\

[Chimbu chuckles]

Take a large spoon and dangle it, lightly held, between thumb and forefinger then slowly move it under a running tap...just let the water flow touch the curved surface and see what happens. You'll see a very strong demonstration of 'lift' but there is no movement of water down BOTH sides of the spoon...just the curved surface...but 'lift' is still produced.

Sails are NOT flat - they are 'cut' to have an aerofoil shape. As wind strength increases you manipulate various controls to flatten them and reduce lift to keep the boat upright - but they never end up 'flat' - even storm sails, designed for extreme wind strengths, are not flat.

Yes you can get a flat plate, give it an AoA, and get 'some lift' but efficient lift comes from accelerating air over a curved surface which produces reduced pressure - a static pressure delta - that sucks the wing up.

The spoon experiment above should prove to anyone which is the strongest force - suck or push.

[jas24zzk]

Well, maybe you should revisit Bernoulli's theory and re-read the article. Contemplate that for a while then watch the video. :E

and yer steve, I also hope this one can stay civil.

[cowl flaps]

This was one of the Henri Coandă theories many years ago.

[haughtney1]

Take a large spoon and dangle it, lightly held, between thumb and forefinger then slowly move it under a running tap...just let the water flow touch the curved surface and see what happens. You'll see a very strong demonstration of 'lift' but there is no movement of water down BOTH sides of the spoon...just the curved surface...but 'lift' is still produced.

Hmmmm, stby getting boring now eh Chuck? :}

[Ex FSO GRIFFO]

Like this example of the Coanda Effect
effect......


CoandaEffect - YouTube

Watch the flow after the spoon......

p.s. Thanks to You Tube etc.....

Cheers:ok:

p.p.s....All I know is that when the airspeed gets to be 'this', I pull back a little 'here' and the houses get smaller.....
I don't really care 'how'...I just am thankful that it 'does'.....:D:D;

[Chimbu chuckles]

Just got in from Shanghai actually:ok:

[flyingfox]

The curvature of the wing causes the change in air pressure because it pulls some of the air upwards, which reduces pressure, and forces the rest beneath it, creating higher pressure.
Pulls!? Please explain?

[muffman]

Some good explanations of this (and many other things) here:

See How It Flies (http://www.av8n.com/how/)

[Captain Sand Dune]

Yawn...............
Any reputable test book will tell you that there are several theories that have been developed to predict the performance of an aerofoil. The Equation of Continuity (that's the one that uses Bernoulli's Theorem) is but one (the most used, granted). There are also Momentum Theory (I personally prefer this one), Circulation Theory and Dimensinal Analysis that I am aware of.

The Equation of Continuity just happens to be the easiest to understand and is therefore the most widely used.

[Tiger35]

A lot of military jets only get airborne because of the curvature of the Earth and excess thrust, therefore a lot of military runways are "humped" in the middle to reduce take-off length. :cool:

[fujii]

Quote - "that sucks the wing up."


Reduced pressure does not suck. It is always the higher pressure which is pushing. To accept suction as a force, you would have to accept that the less fluid there is on one side, the more work it can do. Take it to the point that if, on one side of the aerofoil or whatever there was a vacuum, you would have to believe the absence of something can do work.

[Wally Mk2]

...........'griffo' thanks for yr post although I had to duck off to the loo only after a few short seconds of watching all that water flow:E.....wasteful it was too, some simply don't care about water conservation!:E
I recall doing such an experiment at school in a science class (yes that's about all I recall about school!).
A trick that dear old dad showed us as kids in the car was to stick ones hand out the window whilst moving along at speed & watch the change in lift as we either kept our hands flat against the wind on a shallow angle or curve/cup our hands, the latter produced far more a force upwards, dear old dad he was so clever & he was just a TV repair man!:ok:.

I'm with you 'griffo' ...............who cares???? I didn't invent the theory, I can't change it so I accept that when I haul back on the stick I go up along with the many tonnes of hardware strapped to my bum, I also get scared!:)

I subscribe to the theory that for every action there's an equal & opposite reaction, well so says Mr Newton & that's not the CH 9 guy either!:) So if it's good enuf for him it's good enuf for me:ok:
Now on with the theories!

Wmk2

[The Green Goblin]

I never accepted the scientific explanation as rational.

After playing aerofoils with my hand out of the car window all those years as a kid, you can feel lift. It's almost as if you a compressing the molecules and creating a solid which supports more weight the faster you go, or the more you collect.

[Ultralights]

so after watching the video, the curved upper surface, accelerates the air over the top... lowering pressure.... so whats new? the only difference i can see from conventional wisdom is the air passing above reaches the trailing edge before the air passing below... but the principle remains the same of the air flowing faster over the top... :confused:

[Avgas172]

excellent! ..... now what was I doing? oh yeh intopelating the discombobulator, :eek:
Firing The Discombobulator Steam punk Rifle - YouTube

[Pinky the pilot]

Firing The Discombobulator Steam punk Rifle

Hmmm.. think I'll stick with my Omark 44.:cool:

[rattly_spats]

Aeroplanes fly because their wings cause the air pressure underneath to be greater than that above, lifting them into the air. For years engineers have been frustrated by a theory that wrongly explained the change in pressure.It seems the good professor has simply managed to demonstrate that he agrees with NASA (http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html). This is hardly news.

Rattly.

[jas24zzk]

[/quote]After playing aerofoils with my hand out of the car window all those years as a kid, you can feel lift. It's almost as if you a compressing the molecules and creating a solid which supports more weight the faster you go, or the more you collect.[/quote]

I actually did this as an adult, and still enjoy it as a passenger. One thing I noted and played around with by changing my hand (airfoil shape) was how the hairs on the back of my hand reacted.

Whilst i can't agree with our learned 'professor', that bernoulli's theorem plays no part, I've always been one to believe several different elements of physics were at work.

We can't change the physics, (nature dictates them to us) merely continue our education as to what nature is doing.
--------------------------------------------------------------------

Watching the video demonstration, whilst I subscribe to the downwash theory (action/reaction theory) I was surprised at how little of the smoke actually struck the underside of the wing. If you watch it again, only one of the smoke runs strikes the wing, and there is little interference to the lower smoke streams as compared to the changes above the wing. I'd actually love to see the experiment redone with 2 changes, 1) more and much finer smoke jets. 2) a lower angle of attack.

Bernoulli's theory is only part of the equation. The belief that the air travelling over the top of the wing should arrive at the trailing edge at the same time as the air over the top, is fundamentally wrong in itself if you understand bernoullis theorem. In most discussions, people really only consider the air passing over the top, creating acceleration and lowering of pressure. If you open your mind, and consider what is happening below, and apply that to what you know about bernoulli's.........

over to you guys http://www.mustangtech.com.au/images/smiles/outtahere.gif

[Trent 972]

I actually did this as an adult, and still enjoy it as a passenger. One thing I noted and played around with by changing my hand (airfoil shape) was how the hairs on the back of my hand reacted.

Whilst i can't agree with our learned 'professor', that bernoulli's theorem plays no part, I've always been one to believe several different elements of physics were at work.

You can confirm/deny the theories by taking note of the behaviour of the hairs on the palm of your hand also. :E

[Ex FSO GRIFFO]

Whil(e)(st) you're drivin'....even......

:} :ooh:

[jas24zzk]

lol trent, you're right, its about as scientific as getting thumped on the 3kz by a falling apple

[SgtBundy]

Maybe I didn't understand it fully, but I always found the "air moves faster over the top because it has further to travel" explanation to be odd. Why would air move faster simply because it has "further to travel" (how does it know?). To my mind the curved surface deflects the air "up", the deflected air is pushed away from the wing surface and takes the path of least resistance, which is to continue with the airstream once it detaches from the wing. This reduces the pressure on top of it, causing the pressure differential that creates lift.

That was always my take on it, simple as it is, but I ain't no aerodynamicist.

[travelator]

I believe there are many different factors and theories at play with regards to how lift is created.
but I always found the "air moves faster over the top because it has further to travel" explanation to be odd. Why would air move faster simply because it has "further to travel" (how does it know?)
I have always rationalized this by thinking of how the airfoil moves through the air rather than how the air moves over the airfoil (as demonstrated in wind tunnels). Picture two air molecules stationary in the atmosphere, one sitting on top of the other. All of a sudden, along comes an airfoil and passes between them forcing them to part. The top one is displaced further than the bottom one as it travels up over the "hump" and then drawn back down. The bottom one is only moved downwards. When the airfoil departs the area, they meet up again and are both moving downwards (downwash). The extra VERTICAL distance covered by the upper portion results in greater velocity and therefore, according to Bernouli, reduced pressure.

[b_sta]

I have always rationalized this by thinking of how the airfoil moves through the air rather than how the air moves over the airfoil (as demonstrated in wind tunnels). Picture two air molecules stationary in the atmosphere, one sitting on top of the other. All of a sudden, along comes an airfoil and passes between them forcing them to part. The top one is displaced further than the bottom one as it travels up over the "hump" and then drawn back down. The bottom one is only moved downwards. When the airfoil departs the area, they meet up again and are both moving downwards (downwash). The extra VERTICAL distance covered by the upper portion results in greater velocity and therefore, according to Bernouli, reduced pressure.Totally false, there is absolutely no reason why a molecule on top of the aerofoil 'needs' to meet up with one on the bottom - the molecules on top of the wing don't know that there's any need to do so!

Personally I believe it's a combination of Bernoulli's theorem and downwash/action-reaction theory. The airflow over the top of the aerofoil increases its velocity due to camber and in doing so its static pressure falls, causing a pressure differential between the upper and lower surfaces. At the same time, as the lower pressure airflow deflects downwards past the separation point at the trailing edge of the wing (downwash), you get the equal and opposite reaction assisting in forcing the wing upwards. Everyone wins :ok:

[Pinky the pilot]

It bemuses me somewhat that even now, after over a century of powered flight, that whilst the general theory of how an aerofoil generates lift;

The airflow over the top of the aerofoil increases its velocity due to camber and in doing so its static pressure falls, causing a pressure differential between the upper and lower surfaces. (Thanks b_sta)

is known, it seemingly cannot be explained as to why is this so?:confused:

All I feel that I really need to know is that if I maintain sufficient airspeed the ground will not arise and smite me!:hmm:

[Dangnammit]

Symmetrical aerofoils.

Discuss :E

[Ex FSO GRIFFO]

"Angle of Attack",...Mr D ??

:)

[Charlie Foxtrot India]

The airfoil myth (http://warp.povusers.org/grrr/airfoilmyth.html)

http://www.df.uba.ar/users/sgil/physics_paper_doc/papers_phys/fluids/coanda_effect_94.pdf

I remember one of my instructors not understanding why I was laughing when he told me that aeroplanes flew "because of Bernouiili's effect" I really thought he was joking. I asked how you could force the mass flow of gasses through half a hole, the other half being infinity. And if this was the case then why did so many aircraft have symmetrical aerofoils and were able to fly upside down?
Beware the smart-arse students with a background in physics. :E Isaac Newton got it right.

[Old but not bold]

Wally, my old Dad did the same thing, stick yer hand out the window son..... it is amazing that the roads were not littered with kids hands as trucks went passed?
Whats even more scarey is my old man was a TV repairman too, geez you might be my half brother Wally.

Seriously though, when instructing, I had many students look at me with some doubt when trying to explain this doubtful principal.
One of my wise instructor collegues, John Hewit desribed his theory that it was a bit each way, you could put a piece of flat Masonite out the window of a moving vehicle and get signifcant lift but a curved would just make it more efficient. Low powered aircraft of the 20's and 30's needed lots of curve to produce lift whereas fast aircraft with large amounts of thrust could get away with thin symetrical wing sections?

"As long as they stay in the air" is the most imortant principal.:eek:

[Ultralights]

damn, i always thought it was money that made aircraft fly:}

[AeroAdz]

Even this "debunking" seems wrong...

Newtons 3rd law is what gives lift - high kinetic-energy air particles hitting the bottom of the wing, and pushing up. Simple as that. The pressure differential is a byproduct of this, but nowhere near strong enough to "suck" the aircraft up against gravity.

Check this out:
Kitfox Tuft Testing - YouTube

[Homesick-Angel]

It really seems as if a mix of the theories is probably closer to the reality than any one alone.. I love it how there is plenty of experience talking about this, even here on pprune and there is no definitive answer.

It seems that although they certainly fly, symmetric aerfoils are much more unstable, and therefore useful for aeros and high speed ac flown on AoA , but the fat old planks used for trainers and the like seem to give much more stability due to the more stubborn, yet benign movement of the centre of pressure.

I've always been troubled by bernoullis theorem on its own, but have no physics background to argue with myself properly about it!!

[Avgas172]

Happily I have been teaching my grandaughter the Avgas therom, ie: pull stick back plane goes up. Later (she is only 2 1/2) when I feel she is ready for it, I will add the rest ie: pull stick back further plane comes down again. :p

[Poeli]

"It seems the good professor has simply managed to demonstrate that he agrees with NASA. This is hardly news.
"

One of the things I have to do for my exam aerodynamics next friday is go to the NASA website and read the stuff about lift and drag and tell the professor why the way NASA explains it and writes it down is wrong.:rolleyes:

[travelator]

I recall a classic quote from one of the many previous occasions that this subject has come up. I wish I could claim credit for it.

Bernoulli "This apple is round"
Newton "No this apple is green"

[Wally Mk2]

I was in the Sim all day yesterday (felt like it anyway!) & I have come to the conclusion that the wings on a plane are there only for the carrying of fuel & somewhere to attach the engines as the Sim has no such devices (wings etc) & we still got off the ground & very scared I might add!!:)
So a new theory will have to be invented that covers Sim's as well please you genuineness/boffins out there:E


Wmk2

[Ex FSO GRIFFO]

'Bless me father, for I have Simmed.......

& now am 'current agin'....

:cool: