How do planes fly? Planes are able to fly because of the physics involved. Air moves more quickly over an airplane’s wing’s top than its underside when it is in flight. As a result, lift occurs (much like when you blow on a piece of paper). This means that air is drawn up and over.
Every day, airplanes take to the air and transport people who require their services across the entire country or around the globe. How do they fly, and what powers them? Let’s examine how and what propels airplanes into the air!
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How Do Planes Fly?
The noise of the engines will be the first thing you hear if you’ve ever watched a jet plane take off or land. Traditional propeller engines are far quieter than jet engines, which are long metal tubes burning a continuous rush of fuel and air. It’s a common misconception that an airplane’s ability to fly depends on its engines. Gliders, paper airplanes, and even gliding birds are examples of objects that can fly quite happily without engines.
It’s important to understand the distinctions between the engines and the wings as well as the various tasks each performs if you want to comprehend how airplanes fly. The engines on a plane are made to propel it forward quickly. This causes the air to flow quickly over the wings, which causes the air to fall toward the ground. This causes an upward force known as lift, which overcomes the plane’s weight and holds it in the air. So it’s the engines that move a plane forward, while the wings move it upward.
How Do Wings Generate Lift?
In a nutshell, wings create lift by modifying the pressure and direction of the air that strikes them as the engines propel them through the air.
Now that we know that the wings are essential for making something fly, how do they function? 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):
You can read an incorrect explanation of how an airfoil like this produces lift in many science books and online articles. 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). The pressure above the wing is lower than the pressure below due to Bernoulli’s law, which states that fast-moving air has a lower pressure than slow-moving air. This creates the lift that propels the plane upward.
Although this explanation of how wings function is frequently given, it is incorrect: it provides the correct answer, but for the exact opposite reasons! If you give it some thought, you’ll realize that acrobatic aircraft could not fly upside down if it were true. Flipping a plane over would produce “downlift” and send it crashing to the ground. Furthermore, it is entirely feasible to create planes with symmetrical airfoils (looking straight down the wing) and still have them produce lift. For instance, even though they have flat wings, paper airplanes and those constructed from thin balsa wood can produce lift.
But the conventional theory of lift is flawed for another crucial reason as well: nothing mandates that the air passing over the wing must move a greater distance faster than the air moving underneath it. Think of two air molecules entering the wing’s front and separating so that one of them soars upward over the top and the other whistles downward straight. There is no reason for those two molecules to arrive at the back of the wing at the exact same time; they could instead connect with other air molecules. This flaw in the standard explanation of an airfoil goes by the technical name of the “equal transit theory.” This is merely a fancy name for the fallacious notion that the air stream divides at the front of the airfoil and neatly reassembles at the back.
So what’s the actual justification? The air pressure above and below a curved airfoil wing changes as it travels through the sky by deflecting air. Intuitively, that is obvious. Think about how it feels when you slowly walk through a swimming pool and feel the force of the water pushing against your body: an airfoil wing does the same thing (much more dramatically because that’s what it’s designed to do), diverting the flow of water. The air pressure directly above a moving plane is reduced as it moves forward due to the wing’s curved upper portion, which causes the air to rise.
Why does this happen? As air passes over the curved upper surface, its natural tendency is to move in a straight line, but the curve of the wing pulls it around and back down. The same number of air molecules are compelled to occupy more space as a result, which lowers the pressure of the air by effectively stretching it out into a larger volume. The air pressure beneath the wing rises for precisely the opposite reason: as it moves forward, the wing compresses the molecules of air in front of it into a smaller volume. The difference in air pressure between the upper and lower surfaces causes a big difference in air speed (not the other way around, as in the traditional theory of a wing). The speed difference (observed in actual wind tunnel experiments) is much greater than what the straightforward (equal transit) theory would suggest. As a result, if our two air molecules separate at the front, the one traveling over the top will reach the back of the wing much sooner than the one traveling under the bottom. No matter when they arrive, both of those molecules will be speeding downward—and this helps to produce lift in a second important way.
If you’ve ever stood near a helicopter, you’ll know exactly how it stays in the sky: it creates a huge “downwash” (downward moving draft) of air that balances its weight. Helicopter rotors are very similar to airplane airfoils, but they rotate in a circle as opposed to flying forward in a straight line. However, just as with helicopters, airplanes also produce downwash; we just aren’t aware of it. Though less obvious, downwash is just as crucial as it is with a chopper.
This second aspect of creating lift is much simpler to comprehend than pressure differences, at least for a physicist: in accordance with Isaac Newton’s third law of motion, if air pushes an object upward, that object must push back downward (in an equal and opposite manner). Therefore, a plane also produces lift by using its wings to force air behind it downward. That happens because the wings aren’t perfectly horizontal, as you might suppose, but tilted back very slightly so they hit the air at an angle of attack. Lift is created by the angled wings’ ability to push down airflow coming from both above and below, whether it’s faster or slower moving. The airfoil’s curved top produces significantly more lift because it significantly alters the path of the incoming air by pushing down more air than the straighter bottom does.
You may be wondering why the air even descends behind a wing. Why, for instance, doesn’t it strike the leading edge of the wing, curve upward, and then continue horizontally? Why is there a downwash rather than simply a horizontal “backwash”? Remember from our earlier discussion of pressure that a wing lowers the air pressure directly above it. The air is still at its normal pressure, which is higher than the air directly above the wing, higher still, well above the plane. So the normal-pressure air well above the wing pushes down on the lower-pressure air immediately above it, effectively “squirting” air down and behind the wing in a backwash. In other words, an angled airfoil wing creates a pressure difference that causes a downwash, which creates lift. The pressure difference and downwash are not two separate phenomena, but rather integral parts of the same effect.
Now that we understand that wings are tools used to propel air downward, it is simple to comprehend how planes with flat or symmetrical wings (or upside-down stunt planes) can still safely fly. The plane will experience an equal and opposite force, called lift, that will keep it in the air as long as the wings are generating a downward flow of air. In other words, the pilot flying upside-down develops a specific angle of attack that produces just the right amount of low pressure above the wing to keep the aircraft in the air.
Can You Lift How Much Weight?
In general, the air flowing over the top and bottom of a wing follows the curve of the wing surfaces very closely—exactly as you might if you were tracing its outline with a pen. However, as the angle of attack rises, the smooth airflow behind the wing begins to break down and become more turbulent, which lessens the lift. The air no longer flows smoothly around the wing at a specific angle (generally around 15°, though it varies). There’s a big increase in drag, a big reduction in lift, and the plane is said to have stalled. The term “stall” is a little confusing because the plane’s engines continue to run and it continues to fly; it simply refers to a loss of lift.
If you’ve ever made a paper airplane, you’ll know that planes can fly without wings that resemble airfoils. The Wright brothers demonstrated this on December 17, 1903, and it has been proven ever since. In their original “Flying Machine” patent (US patent #821393), it’s clear that slightly tilted wings (which they referred to as “aeroplanes”) are the key parts of their invention. Their “aeroplanes” were simply pieces of cloth stretched over a wooden framework; they didn’t have an airfoil (aerofoil) profile. The Wrights realized that the angle of attack is crucial: “In flying machines of the character to which this invention relates the apparatus is supported in the air by reason of the contact between the air and the under surface of one or more aeroplanes, the contact-surface being presented at a small angle of incidence to the air.” [Although the Wrights were outstanding experimental scientists, it’s important to keep in mind that they lacked our current understanding of aerodynamics and a complete understanding of exactly how wings function.
Unsurprisingly, the larger the wings, the more lift they produce: Doubling the area of a wing (that’s the flat area you see looking down from above), doubles both the lift and drag it produces. Large aircraft have enormous wings because of this, such as the C-17 Globemaster in our top photo. But if they move quickly enough, small wings can also generate a lot of lift. In order to generate more lift during takeoff, airplanes have wing flaps that can be extended to force more air downward. Lift and drag vary with the square of your speed, so if a plane goes twice as fast, relative to the oncoming air, its wings produce four times as much lift (and drag). By rapidly spinning their rotor blades, which are essentially thin wings that spin in a circle, helicopters generate a significant amount of lift.
Air is no longer discharged behind an airplane in a clean manner. (For instance, you could picture someone pushing a large air crate straight down out of the back door of a military transport vehicle. But things don’t really work that way!) Each wing actually sends air down by making a spinning vortex (a kind of mini tornado) immediately behind it. It’s similar to when a fast train rushes by you while you’re standing on a platform at a train station and doesn’t stop, leaving what seems like a huge sucking vacuum in its wake. A plane’s vortex has a rather complicated shape and is moving mostly downward, but not entirely. However, some air actually swirls upward either side of the wingtips, reducing lift, despite the massive draft of air moving down in the center.
Exactly How Do Airplanes Take Off?
The Bernoulli principle** helps keep the balance of forces during takeoff and landing of aircraft. To accomplish this, angles are used. This concept underlies the ability to fly for all aircraft, including paper airplanes, model aircraft, and air-powered aircraft. The speed of a fluid as it passes over a curved surface increases on one side and decreases on the other.
The “angle of attack” refers to the angle at which an airplane begins its takeoff. A 3 degree angle of attack is the ideal for a successful takeoff. As long as other forces, such as atmospheric resistance and engine thrust, are augmenting the force generated by the wings’ downward pressure, the pressure will also serve as lift.
What Forces Maintain An Aircraft In The Sky?
Aircraft move because of Newton’s first law, just like all other objects on earth. Four different forces work together to keep an airplane in the air. Let’s go over these forces once more and how they contribute to keeping aircraft in the air.
- Lift: Lift is the primary force that keeps airplanes in the air. Air passing over an aerofoil generates lift, making it function much like a wing. More lift will be produced the greater the difference between the horizontal and vertical velocities. There are two distinct types of lift: induced and angle of attack, which further complicates matters. The wing’s tilt with respect to the incoming air stream is referred to as the angle of attack. The air passes through a spinning propeller to produce induced lift, which is produced by powerful engines.
- Drag: The force that prevents an object from moving through the air is called drag. Lift and weight both contribute to drag in an aircraft. Larger wings produce greater amounts of drag while more weight makes it harder to keep the plane in the air
- Weight: The force that prevents an object from moving through air is called weight. There are two ways to find it: either as weight from lift or weight from gravity. Gravitational weight exerts a downward force on an aircraft, making it more difficult for it to maintain flight. An aircraft will experience an upward force as a result of weight due to lift, which makes it simpler for an aircraft to maintain flight.
- Thrust: The force that pushes and pulls an airplane in the opposite direction from the direction of gravity is called thrust. A jet engine, a propeller, or any other type of propulsion system can produce it. The forward thrust, which moves the airplane upward and forward, is one component of this force. Back thrust is the opposite, and it keeps an aircraft in the air by counteracting the effects of gravity.
See more about How Is Butter Made?
How Does An Airplane Turn?
Learning to change directions is the first step in learning to fly. An aircraft must move in the direction that is opposite to the turn itself in order to exit or enter it.
Another crucial factor is the speed at which an airplane turns. Slow turns will make the flight more difficult to control while fast turns will make it difficult for other aircraft to track them.
- Rate of Turn: This kind of flight maintenance requires skill to be able to keep three planes in each other’s airspace without colliding. An aircraft must keep turning quickly to accomplish this.
- Angle of Attack: Learning to change directions is the first step toward flying. An aircraft must fly in the opposite direction from the turn itself in order to exit or enter it. Another crucial factor is how quickly an aircraft turns. Slow turns will be more difficult to control than fast turns, and other aircraft will find it difficult to track them.
Landing The Plane
Not just getting an airplane in the air is crucial for a flight; the pilot also needs to safely land the aircraft’s passengers! Pilots lower the plane gradually to allow passengers to comfortably adjust to changing pressure levels, unless there is an emergency. Pilots generally operate by the “rule of three,” meaning the plane descends 300 meters (1,000 feet) every three miles. This is equivalent to a descent angle of roughly three degrees.
A pilot must slightly reduce a plane’s lift during a careful descent so that its weight can bring it back to the ground. In doing so, they reduce lift by reducing thrust and raising drag. (If you find this confusing, keep in mind that a plane without thrust, i.e., standing still – does not lift into the air.)
Pilots may pitch the plane’s nose upward to accomplish this, which will increase air friction and generate drag. A pilot may employ flaps and slats to increase drag as the plane continues to descend. When the aircraft begins its final descent, the landing gear is extended, the vehicle lands on its back wheels, and brakes are applied to slow the vehicle.
Keeping It Airborne
When discussing how an airplane flies, there are numerous variables at play. In order for an airplane to stay in the air, pilots must learn how to control these four factors: lift, drag, weight, and thrust.
Brief History Of Flying
Although the Wright brothers are now credited with creating the airplane, they were far from the first to take to the skies. Many cultures have creation myths that describe flight occurring without the aid of technology.
The Wright brothers were well aware of Sir George’s work and realized they would need to develop an aircraft using this technology if they wanted to actually fly.
In 1903, at Kitty Hawk, North Carolina, they made their first successful attempts at flight.
The propeller on their 40-foot-long aircraft was turned by their internal combustion engine, which also served as the vehicle’s power source. They would continue to test and redesign the aircraft over the ensuing years, and today we know it as the Wright Flyer.
Many people started experimenting with various aircraft shapes and sizes after the Wright brothers demonstrated that they could fly. The “Flying Pig,” a biplane built by the Germans, made its first flight in 1910.
The Wright brothers went on to develop a variety of models, as well as flight training and aerial demonstrations, but it didn’t take long for those who had been motivated by their success to take these concepts and give them a shot for themselves. The first licensed pilot in the United States made his first flight in 1914.
How Quickly Does A Flight Depart?
The length of the runway affects how quickly an airplane takes off. A plane needs to be moving faster when it is lifted into the air the farther the distance is between the runway’s end and the destination of the flight.
How Far Do Airplanes Travel?
The lifting power of an aircraft determines its height in the air. Commercial aircraft can fly between 500 and 3500 meters in the air. Greater lifting power of larger aircraft makes them more suitable for flying higher than smaller aircraft.
How Far Can A Plane Travel?
The amount of fuel determines how long the flight will be. Because they are constantly burning fuel as they soar through the air, airplanes require constant refueling. Smaller aircraft can travel up to 100 miles, while larger aircraft can travel up to 2,400 miles before their fuel tanks need to be refilled.