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Airplanes at work


goodyhi11
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Aeroplanes work (if you are talking about wings) on the principle that The curved surface on the top of the wing has air moving slowly over it therefore less air molecules and therefore low pressure, the opposite underneath.

 

However this is only Theory a fairly good one, but a theory non the less.

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Aeroplanes work (if you are talking about wings) on the principle that The curved surface on the top of the wing has air moving slowly over it therefore less air molecules and therefore low pressure' date=' the opposite underneath.

 

However this is only [b'] Theory [/b] a fairly good one, but a theory non the less.

The curved upper surface of an aerofoil accelerates the air passing over it, compared to the air passing underneath it. This results in relatively lower pressure above the foil than below it (lift).

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However this is only Theory [/b'] a fairly good one, but a theory non the less.

 

"only a theory" ? A theory...as opposed to what?

 

Anyway, look up Bernoulli's principle. When a fluid moves faster the pressure decreases. So the pressure is lower above the wing, giving lift.

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I read (on HowStuffWorks.com, I believe) that Bernoulli's principle works, but that there's no exact reason as to why the air above the wing has to get behind the wing at the same time as the air below the wing (as in, why two air particles going above and below the wing at the same time have to make it to the end of the wing at the same time). Still, it works.

 

Oh, and if you go to howstuffworks, the article they have on how planes work is pretty informative.

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I read (on HowStuffWorks.com, I believe) that Bernoulli's principle works, but that there's no exact reason as to why the air above the wing has to get behind the wing at the same time as the air below the wing (as in, why two air particles going above and below the wing at the same time have to make it to the end of the wing at the same time). Still,

 

Continuity. It's very easy to see if the fluid is incompressible. But I think the argument for a gas is that if it didn't happen, you'd get a higher pressure as the gas built up, which would then exert a larger force and accelerate the gas. So the steady state condition is that the continuity equation holds.

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The curved upper surface of an aerofoil accelerates[/i'] the air passing over it, compared to the air passing underneath it. This results in relatively lower pressure above the foil than below it (lift).

 

AKA Bernoulli's Principle

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Ummm......

 

I read where Bernoulli's principle wasn't the primary reason responsible for lift. If a wing is stationary within a wind tunnel, very little lift is created as air is forced over its surfaces...curved or not. How would you explain the Bernoulli principle for a "fully symetrical" wing which has an identical curvature on both sides.

 

The primary cause of lift is the angle of attack. The relationship of where the wing is pointed and the speed of the air flowing over it.

 

I think this is correct.

 

Bettina

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Um, kinda.

 

If you have a symetrical airfoil (teardrop shape), and the long axis is parallel to the airflow, then no lift. But bernouli's principle still applies; the air displaced by moving over or under the airfoil has reduced pressure. It just cancels out with a symetrical airfoil at 0 degree: the air has to move the same distance over the top and bottom, so the pressure decreases but isn't unequal, hence no lift.

 

However, if you tilt that airfoil, the has lift now because of bernouli's principle: now that it's tilted, the air flowing over the top is more decelerated than the air flowing under it, which results in a difference in pressure, hence lift.

 

Also, some airfoils, such as asymetrical and cambered airfoils, can indeed produce lift at 0 degree, or lower (in some very specialized cases).

 

Mokele

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Um' date=' kinda.

 

If you have a symetrical airfoil (teardrop shape), and the long axis is parallel to the airflow, then no lift. But bernouli's principle still applies; the air displaced by moving over or under the airfoil has reduced pressure. It just cancels out with a symetrical airfoil at 0 degree: the air has to move the same distance over the top and bottom, so the pressure decreases but isn't unequal, hence no lift.

 

However, if you tilt that airfoil, the has lift now because of bernouli's principle: now that it's tilted, the air flowing over the top is more decelerated than the air flowing under it, which results in a difference in pressure, hence lift.

 

Also, some airfoils, such as asymetrical and cambered airfoils, can indeed produce lift at 0 degree, or lower (in some very specialized cases).

 

Mokele[/quote']

 

Ummm.... :)

 

This is a great article on what I meant and why cambered airfoils can still fly upside down, or a flat plate can still be a wing. My dad has a pilot friend that comes over a lot so I picked up a lot from him. He likes to talk.

 

Bettina

 

http://www.allstar.fiu.edu/aerojava/airflylvl3.htm

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  • 2 months later...

Oo. Very old thread. Just picked it up. Anyways, there is the "downwash" principle, which is an alternative to Bernoulli's. Asymetrical wings may generate lift "according" to Bernoulli's principle, but symetrical wings generate lift too. So that suggests the downwash principle. It says that the lift is generated by air flowing onto the wing and being DEFLECTED by the curvature downwards, thus creating an upwards lift. Many pilots refer to this principle for its simplicity. Ive heard people calling it the "Newtonian" principle, but I dunno if it is really called that.

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  • 4 months later...
It is called the newtonian principal or something like that because it goes back to Newtons 3rd law about action and reaction being equal.

 

As Mokele pointed out in post 13, it still ends up being Bernoulli's principle.

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What hasn't been mentioned is what makes a aeroplane bank.

Well, luckily science isnt the only area that I have good knowledge about.

On both wings their are two control surfaces called ailerons. For the aeroplane to roll and yaw left the left aileron (which is basically a large slat) moves upwards creating drag while the ailerone on the right moves in the opposite direction (downwards) creating more lift. The effect: the drag causes one wing to slow and drop and the left wing to lift without slowing causing roll then yaw in the intended direction.

You should also be understand now why aircraft lose airspeed during tight turns.

A critical control surface sitiuated horizontally on the tail allows an aircraft to change its pitch attitude and is comprehensively named: elevator. During the takeoff roll the aircraft will gather enough airspeed so that the elevator (including ailerons, rudder etc) will become affective. The elevator will deflect or move upwards causing the out of balance from the CG of the aircraft which allows the wings to become airborne in the pitch attitide intended. In other words the nose will rise and the wings will travel in the pitch angle and climb (depending on its angle of attack).

For a aeroplane to pitch downwards, the elevator will deflect in the opposite direction (downwards) causing the wings to change its angle and thus attitide, ie the aircraft will descend.

I would be happy enough to carry on and talk about elevator trim, rudder and rudder trim, flaps, spoilers or speedbrakes and basically everything aeroplane. But because this is a science forum, it should therefore intended to be just a science forum.

 

First Officer: Gisburnuk Kiddin.....

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Just to make it clear, I mentioned: "The elevator will deflect or move upwards causing the out of balance from the CG of the aircraft " in my response.

To clear this confusion, the airoplanes CG (centre of gravity) remains the same in relation to the aircraft during the climb. The lift changes but the CG does remains near its centre. If the CG was to change then the aircraft would be out of balance and thus erratic and dangerous to fly.

In relation to a balance ie a seesaw then it would be clear to assume one end is up and the other end is down in relation to its centre spot CG.

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I don't think that the airfoil shape so much creates a partial vacuum above the wing as it smooths the flow of air over the wing. If the top were flat, there would be a partial vacuum and it would be turbulent. The bottom can get away with being flatter because it hits the air head-on but it also benefits from a curve to make airflow smoother. My opinion is that the wing lifts from the bottom like a kite. They actually are saying that anyway, because vacuum doesn't suck or pull. The other side of the wing is pushed.

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The wing creates a partial vacuum behind it as it pushes air aside. "Behind" is also "above" if the wing is tipped so that the leading edge is higher than the trailing edge. It doesn't take a curved surface to create the vacuum, and it doesn't take accelerating the air over the curved surface. The curved surface is required to allow the displaced air to flow over it smoothly. A flat wing isn't going to lack lift. It is going to start bucking at a much lower airspeed.

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Only if there is something in place to keep the plane from climbing. Too high an angle of attack will cause the plane to try to spin on its left-right axis. This is pitch. Turbulence over the wing will cause a tendency to buck up and down, changing the angle of attack randomly and abruptly. That laminar flow that keeps a vortex from forming just above the wing is more important than any lift from the Bernoulli principle, which as I said requires a push from the underside anyway.

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