# planes shouldn't fly then!!

Discussion in 'Physics & Math' started by scifes, May 19, 2009.

1. ### scifesIn withdrawal.Valued Senior Member

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is it true that planes generate life because their wings' top side is curved..and that makes the air "passing" the top side of the wing generate acceleration (or is faster) than it's counterpart in the lower side..thus generating lift??
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COW MANURE....!

why can planes fly upside down then??

3. ### cosmictravelerBe kind to yourself always.Valued Senior Member

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Nope, wings cannot create life that I know of as yet!

Because there is enough air going over the wings whether or not it is flying in either condition to create LIFT! Air doesn't change just because you ae upside down. The air still passes over the wing either way.

5. ### OliHeute der Enteteich...Registered Senior Member

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Some are some aren't - some aerofoils are perfectly symmetrical - it's the angle they present to the airflow that determines path length and thus lift.

Because they fly slightly nose up, rather than horizontally, so that the aerofoil presents a longer path over the (new) top than it does on the (new) underside.

CT
That would provide "lift" in a downward direction - not conducive to long flights

The air doesn't change but the path presented does: unless the angle of attack is adjusted.

Last edited: May 19, 2009

7. ### geistkieselValued Senior Member

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The leading edge of the wimng splits the air in two parts. The air going over the upper curve has a lomgeer path to the trailing edge, hence the air is spread out more and hence the air proessure is greater on the underside al levelof the wing.

When flying a normal level pushing the stick forard lifts the tail up by the angle of the horizontal stabalizer. Flip over (uipside down) and push the stick forward which will aim the nose the same way reacting to 'stick down' in normal flight. In inverted flight the nose will follow the syick fporward command which prevents the plane from falling through the air. At this point the plane is supported by the combination of horizontal stabalizer and wing that is trying to overcome the force of the horizontal stabaLizer putting a torque around the axis of the wings..

8. ### PeteIt's not rocket surgeryRegistered Senior Member

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Here's something I posted on this topic [post=1426940]two years ago[/post], in response to a post by DH in a thread about control surfaces. I never got an answer to my question:

A vigorous debate!
Bernoulli or Newton's Laws for Lift?
Bernoulli vs Newton (F1-Country.com)
Bernoulli vs Newton (Webwings.com)
An aerodynamicist's view of Lift (The Physics Teacher, abstract only. Full text available for purchase or subscription).

Would an airfoil with this profile produce lift at zero angle of attack? It seems to me that the simple Newton's Laws model says no, while the simple Bernoulli equation model says yes.

9. ### PeteIt's not rocket surgeryRegistered Senior Member

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If you’ve been standing on a soapbox supporting one theory over another, there’s no need to hide your face the next time you pass the flight-school water cooler. The truth is that, among the Newton-Bernoulli disputers, neither party is wrong. According to Dr. Jean-Jacques Chattot, professor of Mechanical and Aeronautical Engineering and director of the Center for Computational Fluid Dynamics at the University of California-Davis, the descriptions of lift advocated by Newton and Bernoulli “are actually the same thing, just from two different perspectives.” How is this possible? Take another look at the dates when Newton and Bernoulli lived...

10. ### OliHeute der Enteteich...Registered Senior Member

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Meh, I didn't want to get into all that Pete, I thought the simpler explanation (angle of attack) would suffice for scifes given his, er, limited understanding of the principles.

11. ### NasorValued Senior Member

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While both are basically descriptions of the same thing, I like the 'angle of attack' way of explaining it a lot better. Simple physics tells us that in order to stay flying, the plane must continuously defect air downward - otherwise you break Newton's laws of motion. The Bernoulli version of the explanation usually gives people the erroneous idea that a plane could fly without deflecting air downward.

12. ### PeteIt's not rocket surgeryRegistered Senior Member

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Angle of attack is important, of course. But, Bernoulli also explains how air can be deflected downward even when the angle of attack is zero (or even less) for asymmetrical airfoils.

13. ### PeteIt's not rocket surgeryRegistered Senior Member

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Yeah. I was just a little annoyed at an old argument being thrown up as if it was a brand-new-idea thunk up by scifes.

14. ### granpaRegistered Senior Member

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you are confusing force with motion. holding the plane in the air requires a force. not motion. the air is indeed being deflected around the wing but this sets up a vortex around the wing that is self sustaining. when the plane changes speed or direction or pretty much anything it leaves behind a vortex of air. this is due to the downward motion of air that everyone expects. but when the plane isnt changing speed then it doesnt leave any disturbance behind (neglecting turbulence).

it is a principle of aerodynamics that vortexes are conserved.

15. ### nietzschefanThread KillerValued Senior Member

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Fuck not this again.

16. ### nietzschefanThread KillerValued Senior Member

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Pretty much what I concluded when I read those links. They are arguing semantics.

The other thread linked here (in which I was a belligerent) was an argument on how control surfaces work(they work on the same principals of lift). Some people actually believe they work like tires on a car or something.

17. ### Blender3d777Registered Member

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...you do need both, actually, I think. Think of a fan, how far does that go when turned on? Not very far, but this would be like a wing that only uses newtons method. But if you take that design, and somehow create a low pressure above it, by lengthening one of the sides you get a low pressure upwards force, plus that air moving downwards, creating a downwards force...

just my thoughts.

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19. ### OliHeute der Enteteich...Registered Senior Member

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That would be because it isn't going fast enough to generate any lift.
If you could up the rpm then it would move.

20. ### NasorValued Senior Member

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The problem is, in the normal "The air traveling over the wing goes faster than the air traveling under the wing" version of the Bernoulli explanation, people usually get the idea that the Bernoulli principle allows the air to magically exert a net upward force on the wing without the air being deflected downward. Looking at the diagrams of airflow over the wing that you usually see in low-level textbooks and random internet pages, it's common to see the airflow depicted as having the air from to top and bottom of the wing simply recombine and move directly backwards relative to the wing, rather than downward.

Example: https://home.comcast.net/~leighanne.kraemer/Lesson Plans/Science/bernoullisprinciple.htm

Of course you are correct that the downward deflection of air will result in vortices that might result in no net downward motion of air overall, but the point is that the air that's actually coming off the wing has to move downward in order for there to be any sort of lift. With the simplified Bernoulli explanation that many people use, there would be no reason for vorticies to form because there wouldn't be any reason for air to be deflected downward.

21. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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Mod Warning to ili:

Please don't troll this sub forum. Go to free thoughts.

22. ### leopoldValued Senior Member

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1. magic.
2. wires.
3. god.
4. you are the one upside down.
5. hallucination.
6. conspiracy.

edit:
after seeing bens warning to ili i've decided to include the following minor detail.
7. a combination of wing geometry and speed creates a condition known as lift.

Last edited: May 21, 2009
23. ### OliHeute der Enteteich...Registered Senior Member

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It was Ili, not me (no relation) that got the warning.