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Airplane Pilot's As Physicists
Hi All,
There is a long discussion ongoing in rec.aviation.piloting about what causes lift on a plane. You can read from the link below. Please note that about 80% of the post are mostly ad hominem attacks and should be ignored. There are some small bits of real discussion. http://groups.google.com/group/rec.a...11fa289cd7864a I am an electrical engineer with experience in analag design and software, with math and physics background that you would expect of an electrical engineer. There are many points made in the discussion, but I would like to focus on one in particular for the sake of progress. There are people in the pilot's group, who think that lift on a wing is analyzed as such: 1. There is air on outside of top of wing that is pushing down, but reduced because of aerodynamics. 2. The *inside* of the wing contains air pushing up against the underside of top of wing . 3. Let us ignore that the same air inside the wing pushes down on the overside of bottom part of wing. 3. The difference in pressure against the underside of the top wing on the inside of wing and top of wing on outside, is what gives plane lift. Note that they ignore the pressure inside the wing that pushes downward on the wing. I am trying to convince them that, if there is air on the inside of the wing, it pushes against all sides of the inside of the wing, including both top underside and bottom overside, and thereby nullifying any effect it would have on the wing. Lift is caused by a difference in pressure between the underside of the bottom of the wing, and the overside of the top of the wing. I count 8-9 people in the group who are utterly convinced that I am inept at physics, mathematics, etc. Note that some of these people have been flying aircraft for years, even decades, while I am still a student pilot. Comments from anyone who knows physics welcome. -Le Chaud Lapin- |
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Airplane Pilot's As Physicists
Le Chaud Lapin wrote in
ps.com: Hi All, There is a long discussion ongoing in rec.aviation.piloting about what causes lift on a plane. No, there isn't. There are people who know perfectly well how it works trying to tell a ccouple of k00ks who think they know Bertie |
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Airplane Pilot's As Physicists
On Oct 9, 4:08 pm, Le Chaud Lapin wrote:
Hi All, There is a long discussion ongoing in rec.aviation.piloting about what causes lift on a plane. Heh. I know the argument. I think it's broken out here (sci.physics) many times. (a) It's the Bernoulli effect due to the shape of the wing cross-section, the way we were all taught as kids. (b) No, it's just the angle of attack. I'm no expert, but I heard enough in similar arguments here to convince me that the angle-of-attack people are right and the shape of the wing has more to do with controlling turbulence. There are people in the pilot's group, who think that lift on a wing is analyzed as such: 1. There is air on outside of top of wing that is pushing down, but reduced because of aerodynamics. 2. The *inside* of the wing contains air pushing up against the underside of top of wing . Er... that's a new one. OK, I haven't heard this argument then. 3. Let us ignore that the same air inside the wing pushes down on the overside of bottom part of wing. 4. The difference in pressure against the underside of the top wing on the inside of wing and top of wing on outside, is what gives plane lift. You can consider that last just a definition of lift. You won't get lift unless the upward forces are stronger than then downward forces. Note that they ignore the pressure inside the wing that pushes downward on the wing. A wing doesn't need to be hollow to fly. I am trying to convince them that, if there is air on the inside of the wing, it pushes against all sides of the inside of the wing, including both top underside and bottom overside, and thereby nullifying any effect it would have on the wing. Lift is caused by a difference in pressure between the underside of the bottom of the wing, and the overside of the top of the wing. I count 8-9 people in the group who are utterly convinced that I am inept at physics, mathematics, etc. Note that some of these people have been flying aircraft for years, even decades, while I am still a student pilot. Comments from anyone who knows physics welcome. As I said, I lean toward the angle-of-attack arguments now. Take a flat rectangle, tilt it into the wind. The wind blows against the front which is also the bottom, not the back/top. So the forces are on the bottom. Why does that translate into lift? I forget the exact arguments but from first principles if the effect is to change the direction of the incoming air molecules, then by conservation of momentum that translates into equal and opposite change of momentum of the surface, i.e. pressure with an upward component. - Randy |
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Airplane Pilot's As Physicists
Randy Poe wrote in
oups.com: On Oct 9, 4:08 pm, Le Chaud Lapin wrote: Hi All, There is a long discussion ongoing in rec.aviation.piloting about what causes lift on a plane. Heh. I know the argument. I think it's broken out here (sci.physics) many times. (a) It's the Bernoulli effect due to the shape of the wing cross-section, the way we were all taught as kids. (b) No, it's just the angle of attack. I'm no expert, but I heard enough in similar arguments here to convince me that the angle-of-attack people are right and the shape of the wing has more to do with controlling turbulence. There are people in the pilot's group, who think that lift on a wing is analyzed as such: 1. There is air on outside of top of wing that is pushing down, but reduced because of aerodynamics. 2. The *inside* of the wing contains air pushing up against the underside of top of wing . Er... that's a new one. OK, I haven't heard this argument then. 3. Let us ignore that the same air inside the wing pushes down on the overside of bottom part of wing. 4. The difference in pressure against the underside of the top wing on the inside of wing and top of wing on outside, is what gives plane lift. You can consider that last just a definition of lift. You won't get lift unless the upward forces are stronger than then downward forces. Note that they ignore the pressure inside the wing that pushes downward on the wing. A wing doesn't need to be hollow to fly. I am trying to convince them that, if there is air on the inside of the wing, it pushes against all sides of the inside of the wing, including both top underside and bottom overside, and thereby nullifying any effect it would have on the wing. Lift is caused by a difference in pressure between the underside of the bottom of the wing, and the overside of the top of the wing. I count 8-9 people in the group who are utterly convinced that I am inept at physics, mathematics, etc. Note that some of these people have been flying aircraft for years, even decades, while I am still a student pilot. Comments from anyone who knows physics welcome. As I said, I lean toward the angle-of-attack arguments now. Take a flat rectangle, tilt it into the wind. The wind blows against the front which is also the bottom, not the back/top. So the forces are on the bottom. Why does that translate into lift? I forget the exact arguments but from first principles if the effect is to change the direction of the incoming air molecules, then by conservation of momentum that translates into equal and opposite change of momentum of the surface, i.e. pressure with an upward component. - Randy Well, thanks be to god that that';s been authoritatively setttled. Bertie |
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Airplane Pilot's As Physicists
On Oct 9, 3:22 pm, Randy Poe wrote:
On Oct 9, 4:08 pm, Le Chaud Lapin wrote: Hi All, There is a long discussion ongoing in rec.aviation.piloting about what causes lift on a plane. Heh. I know the argument. I think it's broken out here (sci.physics) many times. (a) It's the Bernoulli effect due to the shape of the wing cross-section, the way we were all taught as kids. (b) No, it's just the angle of attack. I'm no expert, but I heard enough in similar arguments here to convince me that the angle-of-attack people are right and the shape of the wing has more to do with controlling turbulence. There are people in the pilot's group, who think that lift on a wing is analyzed as such: 1. There is air on outside of top of wing that is pushing down, but reduced because of aerodynamics. 2. The *inside* of the wing contains air pushing up against the underside of top of wing . Er... that's a new one. OK, I haven't heard this argument then. 3. Let us ignore that the same air inside the wing pushes down on the overside of bottom part of wing. 4. The difference in pressure against the underside of the top wing on the inside of wing and top of wing on outside, is what gives plane lift. You can consider that last just a definition of lift. You won't get lift unless the upward forces are stronger than then downward forces. Note that they ignore the pressure inside the wing that pushes downward on the wing. A wing doesn't need to be hollow to fly. I am trying to convince them that, if there is air on the inside of the wing, it pushes against all sides of the inside of the wing, including both top underside and bottom overside, and thereby nullifying any effect it would have on the wing. Lift is caused by a difference in pressure between the underside of the bottom of the wing, and the overside of the top of the wing. Thanks Randy, But before we talk about what causes lift on the plane, we should clear up the basic physics 1st. Note that what I have described above has nothing to do with airplanes really. If you read carefully, the premise of what they are saying is that, if you have, for example, a sealed jar with air in it, you are permitted to consider the air on the _inside_ of the jar, pushing up on the lid as contributing to a force to lift the jar off the ground, but you are not allowed to consider the air on the _inside_ of the jar, pushing down on the jar un the upper surface of the bottom of the jar. -Le Chaud Lapin- |
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Airplane Pilot's As Physicists
Le Chaud Lapin wrote in
ups.com: On Oct 9, 3:22 pm, Randy Poe wrote: On Oct 9, 4:08 pm, Le Chaud Lapin wrote: Hi All, There is a long discussion ongoing in rec.aviation.piloting about what causes lift on a plane. Heh. I know the argument. I think it's broken out here (sci.physics) many times. (a) It's the Bernoulli effect due to the shape of the wing cross-section, the way we were all taught as kids. (b) No, it's just the angle of attack. I'm no expert, but I heard enough in similar arguments here to convince me that the angle-of-attack people are right and the shape of the wing has more to do with controlling turbulence. There are people in the pilot's group, who think that lift on a wing is analyzed as such: 1. There is air on outside of top of wing that is pushing down, but reduced because of aerodynamics. 2. The *inside* of the wing contains air pushing up against the underside of top of wing . Er... that's a new one. OK, I haven't heard this argument then. 3. Let us ignore that the same air inside the wing pushes down on the overside of bottom part of wing. 4. The difference in pressure against the underside of the top wing on the inside of wing and top of wing on outside, is what gives plane lift. You can consider that last just a definition of lift. You won't get lift unless the upward forces are stronger than then downward forces. Note that they ignore the pressure inside the wing that pushes downward on the wing. A wing doesn't need to be hollow to fly. I am trying to convince them that, if there is air on the inside of the wing, it pushes against all sides of the inside of the wing, including both top underside and bottom overside, and thereby nullifying any effect it would have on the wing. Lift is caused by a difference in pressure between the underside of the bottom of the wing, and the overside of the top of the wing. Thanks Randy, But before we talk about what causes lift on the plane, we should clear up the basic physics 1st. Note that what I have described above has nothing to do with airplanes really. If you read carefully, the premise of what they are saying is that, if you have, for example, a sealed jar with air in it, you are permitted to consider the air on the _inside_ of the jar, pushing up on the lid as contributing to a force to lift the jar off the ground, but you are not allowed to consider the air on the _inside_ of the jar, pushing down on the jar un the upper surface of the bottom of the jar. Oh for ****'s sake. You push on something it moves, right? Everone already knows that, Stephen hawkings. While you're trying to agitate in a physics froup why don;'t you ask them how it's physically possible to get your head that far up your own ass. Bertie |
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Airplane Pilot's As Physicists
On Oct 9, 3:31 pm, Sam Wormley wrote:
Ref:http://www.physlink.com/Education/AskExperts/ae627.cfm Question: If an airplane wing provides lift (an airfoil), how does a plane fly upside down? Asked by: Lee Hathcox Answer: The same way that your hand gets pulled upwards if you stick it out the car window and tilt it. The lift of an airfoil is determined by two things - the shape of the wing, and it's angle of attack. Angle of attack is the angle between the flat surface of the wing, and the oncoming air stream. So when I roll the airplane upside down... if I push the stick forward, that pushes the nose of the plane towards the sky, and increases my angle of attack, even though I'm upside down. So, the shape of the wing doesn't change, and it pulls me down, but the angle of attack I control, and I can make it push me up. So when the lift from angle of attack in the up direction, exceeds the lift from the shape of the wing, in the down direction, you can balance the force of gravity acting on the plane. You can see the influence of angle of attack, because even if your hand isn't shaped like a wing, you can see how the angle and the force of the air push it in whichever direction you choose. Even though this (new) thread is not about what causes a wing to lift, I just wanted to say for the record that I agree with this answer, that it is both AoA and curvature of the wing. -Le Chaud Lapin- |
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Airplane Pilot's As Physicists
Le Chaud Lapin wrote in
oups.com: On Oct 9, 3:31 pm, Sam Wormley wrote: Ref:http://www.physlink.com/Education/AskExperts/ae627.cfm Question: If an airplane wing provides lift (an airfoil), how does a plane fly upside down? Asked by: Lee Hathcox Answer: The same way that your hand gets pulled upwards if you stick it out the car window and tilt it. The lift of an airfoil is determined by two things - the shape of the wing, and it's angle of attack. Angle of attack is the angle between the flat surface of the wing, and the oncoming air stream. So when I roll the airplane upside down... if I push the stick forward, that pushes the nose of the plane towards the sky, and increases my angle of attack, even though I'm upside down. So, the shape of the wing doesn't change, and it pulls me down, but the angle of attack I control, and I can make it push me up. So when the lift from angle of attack in the up direction, exceeds the lift from the shape of the wing, in the down direction, you can balance the force of gravity acting on the plane. You can see the influence of angle of attack, because even if your hand isn't shaped like a wing, you can see how the angle and the force of the air push it in whichever direction you choose. Even though this (new) thread is not about what causes a wing to lift, I just wanted to say for the record that I agree with this answer, that it is both AoA and curvature of the wing. Quick, call NASA. Bertie |
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Airplane Pilot's As Physicists
Le Chaud Lapin wrote:
I am trying to convince them that, if there is air on the inside of the wing, it pushes against all sides of the inside of the wing, including both top underside and bottom overside, and thereby nullifying any effect it would have on the wing. You are trying to convince one person - there is no plural. Just for the record, I pointed the OP at the following NASA web pages and after first thanking me, has decided NASA's explanation is somehow suspect: http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html Note follow-ups set to sci.physics only. |
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Airplane Pilot's As Physicists
Randy Poe writes:
As I said, I lean toward the angle-of-attack arguments now. Take a flat rectangle, tilt it into the wind. The wind blows against the front which is also the bottom, not the back/top. So the forces are on the bottom. The essential feature of an airfoil is that it twists the flow of air as it passes (or as the airfoil passes through still air, which is equivalent, and that's how it works in airplanes). The air is accelerated downward, and this engenders an equal and opposite force that is lift. So how does a wing produce lift? By twisting air downwards, creating a downwash. Accelerating a mass of air downwards tends to accelerate the wing upwards, and there's your lift. The theory gets more complicated when you try to explain exactly how and why airfoils twist an airflow. Just looking at a flat board with a positive angle of attack, you'd think that it would twist the air, and that's exactly what it does. But the devil is in the details. Fortunately, aviators don't have to know or care about the details. All they need to know is that a wing with a positive angle of attack (and below the stall angle) will generate lift. Lift, like so many other phenomena in physics, can be analyzed and explained in a number of different, equally valid ways, depending on one's point of view. All analyses and explanations converge on the same reality. Of course, some explanations of lift are just plain incorrect, and unfortunately a few of them are quite widespread. |
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