Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Somerled on November 17, 2010, 03:26:01 PM
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I can't count the number of times it has been explained to me that lift is generated by air going furtherover the top of the wing than the bottom, thus forcing the air moving above the wing to move faster to catch up with the air below the wing, causing lower pressure and thus lift.
God, that explanation bugs me.
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Lift comes when the air below the airplane wing is pushing up harder than the air above it is pushing down. It is this difference in pressure that enables the plane to fly. Pressure can be reduced on a wing's surface by making the air move over it more quickly. The wings of a plane are curved so that the air moves more quickly over the top of the wing, resulting in an upward push, or lift, on the wing. at least that's how it's always been explained to me
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Lift comes when the air below the airplane wing is pushing up harder than the air above it is pushing down. It is this difference in pressure that enables the plane to fly. Pressure can be reduced on a wing's surface by making the air move over it more quickly. The wings of a plane are curved so that the air moves more quickly over the top of the wing, resulting in an upward push, or lift, on the wing. at least that's how it's always been explained to me
Then why don't airplanes fall to the ground when they are upside down?
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Then why don't airplanes fall to the ground when they are upside down?
They do, without sufficient thrust
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Then why don't airplanes fall to the ground when they are upside down?
Ever see an inverted Cesna cruising around?...
Many non-performance aircraft are very much aerobaticly incapable.
Also to add, even in the game, almost all aricraft need a good bit of down elevator (while inverted) to keep the nose up and maintain level inverted flight. This bleeds your E and speed because because the angle of your wings needs to be agressivley angled against your angle of flight, causing the wings to act more like a kite while inverted to generate the necessary lift, and less like a desired aerodynamic lift-inducing wing (can an aero engineer verify my understanding of that, or am I a mile off?).
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Ever see an inverted Cesna cruising around?...
Many non-performance aircraft are very much aerobaticly incapable.
Then how does any aircraft fly upside down?
One better, i offer you a 707 flying upside down
(http://www.aviationpics.de/airshow/707buzz3.jpg)
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Then how does any aircraft fly upside down?
One better, i offer you a 707 flying upside down
(http://www.aviationpics.de/airshow/707buzz3.jpg)
Massive amounts of thrust.
As for the 707, it still generates quite alot of thrust but look at the angle of attack he's holding to keep it in the air. It wouldn't be able to hold that attitude for a very long time.
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Then why don't airplanes fall to the ground when they are upside down?
turn the engine off see what happens, thrust my friend :aok
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The tail is an upside down wing. :D
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A must read for anyone interested in piloting an aircraft is "Stick and Rudder" by Wolfgang Langewiesche. Written in the 1940's, it's still available in print and adequately explains the 'theory of lift'. The same theory works for sailing vessels as well.
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Then why don't airplanes fall to the ground when they are upside down?
because you counter that lift with the elevator.
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Thrust, Weight and Pressure.
Bernoulli.
That'll get you started.
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magic :noid
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what kind of magic?
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gremlins :noid
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what kind of magic?
The magic of whodo
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I was going to type out a long response, but I cba right now. I wrote a report on what causes lift for a school report (high-school equivalent, so nothing too strenuous :P) a year or so ago, if you want a copy send me a PM. basically, many of the theories floating around are wrong, such as the Bernoulli one, the 'skipping stone' one and the 'Venturi nozzle' as well. However, a large amount of lift is made by 'flow turning' (i.e. the air which is moving horizontally relative to the wing is deflected by the wing, and given a downward component of velocity. The downward acceleration of the air is what produces the force) and also by the circulation of air around the wing (I kinda suck at putting this into words, but for reasons I've forgotten, when a wing (or just flat piece of material) moves through the air, a circulation pattern is set up (but due to the high speed of the wing relative to the air mass, the resultant effect is that the velocity is lower on the bottom of the wing, and higher on the top, and therefore the pressure is higher on bottom & lower on top) and because of this there's a net upwards force).
if you want a superb website to begin understanding aerodynamics, here's where you should start, IMO: http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html (http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html)
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what kind of magic?
magic dust, man!
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I was going to type out a long response, but I cba right now. I wrote a report on what causes lift for a school report (high-school equivalent, so nothing too strenuous :P) a year or so ago, if you want a copy send me a PM. basically, many of the theories floating around are wrong, such as the Bernoulli one, the 'skipping stone' one and the 'Venturi nozzle' as well. However, a large amount of lift is made by 'flow turning' (i.e. the air which is moving horizontally relative to the wing is deflected by the wing, and given a downward component of velocity. The downward acceleration of the air is what produces the force) and also by the circulation of air around the wing (I kinda suck at putting this into words, but for reasons I've forgotten, when a wing (or just flat piece of material) moves through the air, a circulation pattern is set up (but due to the high speed of the wing relative to the air mass, the resultant effect is that the velocity is lower on the bottom of the wing, and higher on the top, and therefore the pressure is higher on bottom & lower on top) and because of this there's a net upwards force).
if you want a superb website to begin understanding aerodynamics, here's where you should start, IMO: http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html (http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html)
So Bernoulli is wrong but your theory, which is actually a fairly good explaination of a practical application of Bernoulli's principal related to aerodynamics is right?
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So Bernoulli is wrong but your theory, which is actually a fairly good explaination of a practical application of Bernoulli's principal related to aerodynamics is right?
I'm not quite sure what you mean, but I don't have any special theory of lift...I was essentially rephrasing (possibly incorrectly) what I remember from a year or 2 ago. That said, the commonly-used 'explanation' involving equal transit times for particles above and below the wing is wrong (if that's what you were referring to by Bernoulli).
Also, here's what I was on about:https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B6lxyC60vLUdYWJkNjllMzQtNzA1Ni00MjE0LWFkNDYtNDM2ZDg4ZDM4YjA1&hl=en&authkey=COXu8cEM (https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B6lxyC60vLUdYWJkNjllMzQtNzA1Ni00MjE0LWFkNDYtNDM2ZDg4ZDM4YjA1&hl=en&authkey=COXu8cEM)
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I just eat a lot of beans and my body takes care of the rest.
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I was going to type out a long response, but I cba right now. I wrote a report on what causes lift for a school report (high-school equivalent, so nothing too strenuous :P) a year or so ago, if you want a copy send me a PM. basically, many of the theories floating around are wrong, such as the Bernoulli one, the 'skipping stone' one and the 'Venturi nozzle' as well. However, a large amount of lift is made by 'flow turning' (i.e. the air which is moving horizontally relative to the wing is deflected by the wing, and given a downward component of velocity. The downward acceleration of the air is what produces the force) and also by the circulation of air around the wing (I kinda suck at putting this into words, but for reasons I've forgotten, when a wing (or just flat piece of material) moves through the air, a circulation pattern is set up (but due to the high speed of the wing relative to the air mass, the resultant effect is that the velocity is lower on the bottom of the wing, and higher on the top, and therefore the pressure is higher on bottom & lower on top) and because of this there's a net upwards force).
if you want a superb website to begin understanding aerodynamics, here's where you should start, IMO: http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html (http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html)
You sir are correct.
The whole concept of 'air moves faster to catch up with the slower air' crap is wrong. THIS is why airplanes can fly upside down without falling out of the sky. Otherwise, the vector of lift would be pointing downwards along with gravity.
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Some planes are so ugly that the Earth repels them, the Stuka is a fine example :D
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Couple NASA articles on the production of lift
'Flow turning'- what, according to NASA, produces lift
http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html
What somerled is talking about, the most popular myth about the production of lift
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
Venturi Theory
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong3.html
'Skipping'
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong2.html
Mis-application of Bernoulli's principles...
http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html
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Some planes are so ugly that the Earth repels them, the Stuka is a fine example :D
nonononono silly sapp person dood. you're thinking of helicopters, and me-109's. :devil
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An even better question...
How can a man pour a glass of ice tea, without spilling a drop, while piloting an aircraft through a barrel roll. :O
Check it out, and don't miss the passage beginning at about 2:30
http://www.youtube.com/watch?v=9ZBcapxGHjE&feature=player_embedded#! (http://www.youtube.com/watch?v=9ZBcapxGHjE&feature=player_embedded#!)
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Its alright, all 800,000 certificated pilots in the US were taught false information about the Bernoulli Principle. It makes so much sense, it has to be incorrect!
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get a low speed fan, a smoke machine, and an r/c model. you don't need to run the model. just run the smoke across the wing. you'll see how it works.
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Its alright, all 800,000 certificated pilots in the US were taught false information about the Bernoulli Principle. It makes so much sense, it has to be incorrect!
If they are being taught that lift is generated by having to go faster to catch up with slower air under the wing, then yeah, they are being taught incorrectly.
Ask yourself this: Why does air going over the top of a wing care what speed air going under the wing is going? Why does it want to catch up?
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Ask yourself this: Why does air going over the top of a wing care what speed air going under the wing is going? Why does it want to catch up?
You have to look at air as a fluid, and also as being in a static state. Before the air moves over the wing it is basically stationary in relation to the airplane. If you were to move a wing through water the displaced molecules would try to rejoin at their original spot after the wing passes. It's the same for air.
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You have to look at air as a fluid, and also as being in a static state. Before the air moves over the wing it is basically stationary in relation to the airplane. If you were to move a wing through water the displaced molecules would try to rejoin at their original spot after the wing passes. It's the same for air.
What you said about viewing air as a static fluid is completely correct, however that theory of lift is wrong.
If you move a wing (or indeed any object) through water, the area around and behind that object will be disturbed. If that theory were true, I can't imagine any reason why 'wake turbulence' would exist (since that the molecules most affected by the passing of the wing would be the ones that hit the wing - but if those molecules return to their original position after the wing has passed, why would any other particles further away be affected more than those two?).
You can see this by these two things (which both demonstrate that the particles don't return to their original position). On a small scale, try this: move your finger (or a streamlined object) through a tub of water. You'll notice that there will be a lot of ripples throughout the tub (and if you can be bothered to put in some ink or food colouring, than you'll see that the water gets disturbed quite a lot). On a larger scale, watch this video: http://www.youtube.com/watch?v=uy0hgG2pkUs (http://www.youtube.com/watch?v=uy0hgG2pkUs). As far as I can tell, that video effectively kills the equal transit time theory - since those air molecules are most definitely not returning to their original positions!
Also, this webpage has a fairly basic wing simulator, and gives a more in-depth explanation of why that theory doesn't hold up. http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html (http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html)
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People may also want to read http://en.wikipedia.org/wiki/Coand%C4%83_effect
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What you said about viewing air as a static fluid is completely correct, however that theory of lift is wrong.
If you move a wing (or indeed any object) through water, the area around and behind that object will be disturbed. If that theory were true, I can't imagine any reason why 'wake turbulence' would exist (since that the molecules most affected by the passing of the wing would be the ones that hit the wing - but if those molecules return to their original position after the wing has passed, why would any other particles further away be affected more than those two?).
I'm well aware of wake turbulence and wingtip vortices. When you fly patterns in a DA-20 alongside C-130's you get all kinds of opportunities to test them out. That's why I threw that word "try" in there.
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Its alright, all 800,000 certificated pilots in the US were taught false information about the Bernoulli Principle. It makes so much sense, it has to be incorrect!
Yeah, I'm sure NASA has no clue what they're talking about... I mean, those guys are smart, but they're no rocket scientists... :rolleyes:
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with enough power you can make a brick fly
(http://t0.gstatic.com/images?q=tbn:ANd9GcTNM4BPA-sFylnHtt5Opg0R-TwF7fs7a1GevoSdobh4zY0QlSiFjg)
(http://media.ebaumsworld.com/picture/frankiebaby/massivefart.jpg)
a actual flying brick
http://www.youtube.com/watch?v=B6QEECgdW6E (http://www.youtube.com/watch?v=B6QEECgdW6E)
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Actually this is pretty simple, it's more of a vacuum over top of the wing. The shape of the wing enhances the lift by forcing the air over the top of the wing faster. If the air is going faster that means less dense air is at the top surface of the wing, thereby, creating more lift/vacuum.
lol, upon reading the first comment of this thread I finally figured out how the faster air could affect the amount of lift. This would be in the theory of fluid dynamics of gas flowing through a nozzle.
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Then how does any aircraft fly upside down?
One better, i offer you a 707 flying upside down
(http://www.aviationpics.de/airshow/707buzz3.jpg)
this was when the 707 was shown to the public. he thought it up on the spot and had no idea what was going to happen to the aircraft. best, most dangerous stunt done to show off a new aircraft to the public in my opinion. kudos to the pilot :aok
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My understanding was that it was mostly the angle of attack that produces lift. Aircraft can fly level while upside down by pitching enough to make the angle of attack of the wing positive, even in the case where the wing is normally rigged such that it would be negative without pitching. Airfoils can and usually are shaped to enhance lift of course but a flat wing will produce lift if given the right angle of attack. I would hazard a guess that just about any shape produces lift given the right orientation (or even spin, such as to throw a fastball or curveball in the game of baseball).
Now if you want to ask exactly how angle of attack produces lift, I'll leave that to NASA or the Aero Engineering department here at Purdue. Personally I'm sufficiently convinced that it happens by sticking my hand out the window of a moving car.
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Flying inverted will only be possiblewith enough power, and will neverdeliver you with the same speed....