Aerodynamics And Why Paper Planes Flies!

One of the many hobbies I enjoyed while growing up (and still some times now) is making paper planes. Friends would come to school with new designs that they had found in books and occasionally, if they were super rich, from online. There were classic designs like the Zebra and Clipper to more complicated designs like the Hurricane and Albatross; though we didn’t know the actual names for them at the time. Nor, did we know how these gravity defying pieces of paper did it. Let’s look into it with some history on flight!

Some History

Some of the first solid designs for flying machines came from Leonardo Da Vinci (1452 – 1519) in the early 1500’s. There are documented cases of people before him creating machines to fly but most of them more closely resemble gliders. People like Armen Firman (810 – 887) who built a glider-esk machine in 875 AD and Eilmer of Malmesbury aka The Flying Monk ( 980 – unknown) who glided 2 football fields when jumping off a tower in 1010 using similar designs of Firman. Da Vinci designed a range of machine using inspiration from birds, bats, kites, dragon flies and the falling of leaves.

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The most prominent machine (the ornithopter above) would fly thanks to the pilot pedaling a crank that would make the wings flap; closely resembling a bat. One of the issues with these machines was that the energy requirements to get his machines to fly exceeded the energy that could be made by a human pilot. Despite scenes from the video game Assassins Creed: Brotherhood, there is no real evidence to suggest that the machines were ever built let alone flew. This is a point of debate however as some of his notes could be interpreted to suggest otherwise. Designs for traveling balloons occurred later in 1670 with the first manned balloon flight occurring in 1783. It wasn’t until the end of 1903 that the first heavier than air, powered flight took place.

Flying Wright

The Wright brothers, Wilbur and Orville, are credited with the world’s first airplane (the Wright Flyer I) though they had successfully constructed gliders a couple of years prior. The catalyst for their success was the three-axis control that allowed for them to steer and balance the machine at the same time; considered the main problem of flight. Though successful, there was a lot of skepticism that followed the brothers. This resulted in European newspapers calling them liars in 1906 as there were issues around the legitimacy of their claims. Regardless, this was a stepping stone that has lead to the amazing craft that we have today that allows us to transverse the globe. How do craft, heavier than air, stay in the sky though?

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How Flight Works

It was in 1799 that English engineer, Sir George Caylay ( 1773 – 1857), first highlighted the four forces which act upon a heavier than air craft; which later resulted in him being called “the father of aviation.” Though he first connected all four forces, work previously done by people such as Aristotle, Isaac Newton and Danial Bernoulli led him to the conclusion. These forces are thrust, lift, drag and weight. All these forces work in opposite direction to the rest with some needing to be greater than the others for flight to be achieved.

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Weight:

Weight is the downward force that an object has due to gravity. Mass and weight are very different with your mass being constant but your weight changing due to gravity (hence “weightlessness” when in space). Myself, an approximately 90 kg man, would have a weight of approximately 34 kg on Mercury, 15 kg on the moon and 228 kg on Jupiter; all because of the differences in gravity.

Thrust:

Thrust is the reactive force that is in the opposite direction to the air being pushed backwards. This is done usually by the propeller at the front of small aircraft, or by the jet engines on larger planes. As the propeller spins faster, more air is forced back over the plane and wings increasing thrust; the forward force.

Lift:

Lift is a force usually attributed to the fixed wing of a plane and is generated as the air moves over the wings, shaped as an airfoil. An airfoil is a streamline shape that creates less drag than lift as air moves over it; resulting in a total positive lift. Newton’s Third Law of Motion states that “for every action, there is an equal and opposite reaction.” Put into practice, as the airfoil (wing) pushes air downwards, the air pushes back on the airfoil generating lift and making it go up.

Drag:

Drag, sometimes called air resistance, is the force that opposes the movement of the plane through the air. When in the car next, stick your hand out the window and change the shape or curve of your hand; the more your feel the wind, the more drag your hand is generating. You can even curve your hand to be similar to that of an airfoil. Doing so forces the air down but your hand to go up when slightly relaxed (give it a try!). Cars are now designed to generate as less drag as possible hence their smooth, curved bodies.

Paper Planes

These four forces also need to be considered we designing and throwing your own paper planes. Though only temporary, your hand acts like the jet engine or propeller moving air over the wings and body of the plane; this force is thrust. When you throw your paper plane at a slightly upwards angle, the wings force the air downwards similar to an airfoil generating lift. The thing that makes the plane eventually stop and fall to the ground though; drag. Drag is the force applied to the plane by the air passing over it. If you want your plane to fly further, you need to make sure there is as less drag as possible. So give it at shot! Experiment with different designs at home and see what you can change to make your plane go the distance.

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