If you’ve ever folded a piece of paper, chances are you were making a paper airplane. It’s possible to make paper planes look similar to their giant counterparts, but most of the time we just like to make simple ones that we can construct quickly and toss into the air! Have you ever noticed that some designs fly faster or farther than others? Well, there’s a few scientific explanations for this that we’ll discuss in today’s blog.
Number One: Newton’s Law of Motion
Number One: Newton’s Law of Motion
The first theory we’ll look at is this: airplanes can fly because their wings make the air deflect downward, which lifts the plane as it is forced upward. Sir Isaac Newton (1643-1727) is well known for his discovery of the law of gravity, but he also discovered the Laws of Motion, one of which states that for every action, there is an equal and opposite reaction. As this law suggests, the wings of an airplane must do something to the air to make it react and push the plane up - we call this lift.
We can see another good example of this law in kites, where the forces acting on them include their own weight, the lift and drag (a force that works opposite of a moving object’s lift), and the tension in the line connecting the kite to you. When all of these forces balance out, the kite flies at a stable altitude, or height in the air. If the wind outside picks up, the kite’s altitude will increase (if you let out a bit more of its controlling line), causing the lift and drag forces to increase as well. When this happens, the forces are no longer balanced and there is a net - or total - vertical force applied on the kite, and in return, it moves vertically instead of staying in one place. If we take out the tension force of the line, we can apply this concept to an airplane!
Number Two: Bernoulli’s Principle
Another theory of interest involves motion in a fluid. David Bernoulli (1700-1782) discovered that as the velocity in a fluid increases, its pressure decreases in return. His principle applies to any fluid, and since air is a fluid, this applies to air as well. This means that airplanes can fly because the pressure above its wing is less than the pressure below its wing.
We can see another good example of this law in kites, where the forces acting on them include their own weight, the lift and drag (a force that works opposite of a moving object’s lift), and the tension in the line connecting the kite to you. When all of these forces balance out, the kite flies at a stable altitude, or height in the air. If the wind outside picks up, the kite’s altitude will increase (if you let out a bit more of its controlling line), causing the lift and drag forces to increase as well. When this happens, the forces are no longer balanced and there is a net - or total - vertical force applied on the kite, and in return, it moves vertically instead of staying in one place. If we take out the tension force of the line, we can apply this concept to an airplane!
Number Two: Bernoulli’s Principle
Another theory of interest involves motion in a fluid. David Bernoulli (1700-1782) discovered that as the velocity in a fluid increases, its pressure decreases in return. His principle applies to any fluid, and since air is a fluid, this applies to air as well. This means that airplanes can fly because the pressure above its wing is less than the pressure below its wing.
Let’s take a look at this principle in a different setting. Imagine a room full of people running around in different directions. With so many people going different ways, they’re bound to collide with each other - and the walls - multiple times. Now if we have the same amount of people running in one direction down a hall, there will be fewer and less intense collisions. When we apply concepts from physics to these groups of people, we can see that in the closed room, the overall (net) speed was zero, and the pressure (shown by the rate of collisions) was quite high. In the hallway, the net speed of the group was greater than zero and the pressure was much lower than in the room.
In that example, we see that there are two types of pressure: static pressure and total (or ram) pressure. When applied to a flying airplane, the static pressure would be what we’d have when the plane is flying with the wind, instead of against it. Air presses against the plane equally in all directions, with this pressure decreasing as the plane’s speed increases - which is defined as the Bernoulli principle!
Number Three: The Coanda Effect
In that example, we see that there are two types of pressure: static pressure and total (or ram) pressure. When applied to a flying airplane, the static pressure would be what we’d have when the plane is flying with the wind, instead of against it. Air presses against the plane equally in all directions, with this pressure decreasing as the plane’s speed increases - which is defined as the Bernoulli principle!
Number Three: The Coanda Effect
You might also notice that some airplanes have curved wings. A common question regarding the Bernoulli principle is this: why are curved wings important? Well, according to Henri Coanda (1886-1972). “a fluid stream which comes in contact with a gently curved solid surface will tend to follow that surface.” By curving the top of an airplane's wing, air above it has to travel farther (as the distance is greater) than the air below, forcing the air to move faster. The result is lower pressure on top and more pressure on the bottom. This effect amplifies the Bernoulli principle, but as most paper airplanes (and birds!) have “flat” wings so it’s not as important as the other two laws of flight.
Try it Out!
To demonstrate the Bernoulli principle, this simple experiment requires only two pieces of paper! Hold one piece of paper horizontally in each hand, close to your face. Now blow between them and you’ll see that the pieces of paper will get closer to each other, instead of farther away.
Make your own paper airplane! In the file attached to this post, we’ve created a document to help you fold your paper plane. Print it out and follow the instructions in the video to create your own paper airplane. The first step is to fold the paper in half, lengthwise along dotted line number 1. Then fold the edges of the paper down to where it’s folded in half, starting with dotted line number two, on both sides. Do the same for line number 3 and number 4. Keep the flaps on the outside so that the paper can catch some air!
Try it Out!
To demonstrate the Bernoulli principle, this simple experiment requires only two pieces of paper! Hold one piece of paper horizontally in each hand, close to your face. Now blow between them and you’ll see that the pieces of paper will get closer to each other, instead of farther away.
Make your own paper airplane! In the file attached to this post, we’ve created a document to help you fold your paper plane. Print it out and follow the instructions in the video to create your own paper airplane. The first step is to fold the paper in half, lengthwise along dotted line number 1. Then fold the edges of the paper down to where it’s folded in half, starting with dotted line number two, on both sides. Do the same for line number 3 and number 4. Keep the flaps on the outside so that the paper can catch some air!
| paper_airplane_template.pdf |
References:
https://www.grc.nasa.gov/www/k-12/airplane/newton1k.html
http://www.aviation-for-kids.com/experiments.html
http://www.thermofluids.co.uk/effect.php
Image Credits:
“Paper Plane Vector Illustration”. Released into the public domain. Uploaded on 4/1/2017 from publicdomainvectors.org.
Kratochvil, Petr. “Flying Plane”. Released into the public domain. Uploaded on 4/2/2017 from publicdomainpictures.net
Siedlecki, Piotr. “Razorback Plane”. Released into the public domain. Uploaded on 4/1/2017 from publicdomainpictures.net
https://www.grc.nasa.gov/www/k-12/airplane/newton1k.html
http://www.aviation-for-kids.com/experiments.html
http://www.thermofluids.co.uk/effect.php
Image Credits:
“Paper Plane Vector Illustration”. Released into the public domain. Uploaded on 4/1/2017 from publicdomainvectors.org.
Kratochvil, Petr. “Flying Plane”. Released into the public domain. Uploaded on 4/2/2017 from publicdomainpictures.net
Siedlecki, Piotr. “Razorback Plane”. Released into the public domain. Uploaded on 4/1/2017 from publicdomainpictures.net
