Ignore this chapter
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction of and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.
We take for it granted that we can fly from one side of the world to the other in a matter of hours, but a century ago this amazing ability to race through the air had only just been discovered. What would the Wright brothers—the pioneers of powered flight—make of an age in which something like 100,000 planes take to the sky each day in the United States alone? They'd be amazed, of course, and delighted too. Thanks to their successful experiments with powered flight, the airplane is rightfully recognized as one of the greatest inventions of all time. Let's take a closer look at how it works!
How do planes fly?
If you've ever watched a jet plane taking off or coming in to land, the first thing you'll have noticed is the noise of the engines. Jet engines, which are long metal tubes burning a continuous rush of fuel and air, are far noisier (and far more powerful) than traditional propeller engines. You might think engines are the key to making a plane fly, but you'd be wrong. Things can fly quite happily without engines, as gliders (planes with no engines), paper planes, and indeed gliding birds readily show us.
If you're trying to understand how planes fly, you need to be clear about the difference between the engines and the wings and the different jobs they do. A plane's engines are designed to move it forward at high speed. That makes air flow rapidly over the wings, which throw the air down toward the ground, generating an upward force called lift that overcomes the plane's weight and holds it in the sky. So it's the engines that move a plane forward, while the wings move it upward.
How do wings make lift?
In one sentence, wings make lift by changing the direction and pressure of the air that crashes into them as the engines shoot them through the sky.
Pressure differences
Okay, so the wings are the key to making something fly—but how do they work? Most airplane wings have a curved upper surface and a flatter lower surface, making a cross-sectional shape called an airfoil (or aerofoil, if you're British):
In a lot of science books and web pages, you'll read an incorrect explanation of how an airfoil like this generates lift. It goes like this: When air rushes over the curved upper wing surface, it has to travel further than the air that passes underneath, so it has to go faster (to cover more distance in the same time).
According to a principle of aerodynamics called Bernoulli's law, fast-moving air is at lower pressure than slow-moving air, so the pressure above the wing is lower than the pressure below, and this creates the lift that powers the plane upward.
Although this explanation of how wings work is widely repeated, it's wrong: it gives the right answer, but for completely the wrong reasons! Think about it for a moment and you'll see that if it were true, acrobatic planes couldn't fly upside down. Flipping a plane over would produce "downlift" and send it crashing to the ground.
Not only that, but it's perfectly possible to design planes with airfoils that are symmetrical (looking straight down the wing) and they still produce lift. For example, paper airplanes (and ones made from thin balsa wood) generate lift even though they have flat wings.
"The popular explanation of lift is common, quick, sounds logical and gives the correct answer, yet also introduces misconceptions, uses a nonsensical physical argument and misleadingly invokes Bernoulli's equation."
Professor Holger Babinsky, Cambridge University
But the standard explanation of lift is problematic for another important reason as well: the air shooting over the wing doesn't have to stay in step with the air going underneath it, and nothing says it has to travel a bigger distance in the same time. Imagine two air molecules arriving at the front of the wing and separating, so one shoots up over the top and the other whistles straight under the bottom.
There's no reason why those two molecules have to arrive at exactly the same time at the back end of the wing: they could meet up with other air molecules instead. This flaw in the standard explanation of an airfoil goes by the technical name of the "equal transit theory." That's just a fancy name for the (incorrect) idea that the air stream splits apart at the front of the airfoil and meets up neatly again at the back.
So what's the real explanation? As a curved airfoil wing flies through the sky, it deflects air and alters the air pressure above and below it.
That's intuitively obvious. Think how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: your body is diverting the flow of water as it pushes through it, and an airfoil wing does the same thing (much more dramatically—because that's what it's designed to do). As a plane flies forward, the curved upper part of the wing lowers the air pressure directly above it, so it moves upward.