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How do Airplanes Fly?

Soren Sugalski, 27


For nearly all of history, mankind was confined to the ground, and dreams of flying seemed as reachable as the clouds. While progress toward flight was slow, the 19th century brought about a wave of technological advancements, such as the telephone, the car, and the locomotive. As technology evolved on the ground, engineers turned their attention to a different frontier and began exploring the possibility of flight. One of the first breakthroughs occurred in 1852, when Henri Giffard became the first man to pilot an aircraft lighter than air. Then, in 1903, the Wright brothers pioneered a new realm of flight, becoming the first men to ever pilot a heavier-than-craft. Albert Santos-Dumont and Gustave Whitehead also made claims to have been the first, on the basis that the Wright brothers’ aircraft was launched off a rail, and its flight was not verified by experts. However, historians today generally recognize the brothers as the first to achieve modern, man-piloted flight.


Since 1903, flight technology has evolved tremendously, allowing people to fly faster, longer, and further than ever before. Today, roughly three million people fly on commercial airplanes within the United States daily, and more than 10-20 million fly around the world. Other aircraft are used for transportation of goods, military purposes, or even outer space exploration. Despite the shocking importance of airborne travel, few people know what actually makes these heavy aircraft fly. Airplanes are extremely large, and there is no intuitive explanation as to how they can remain airborne for so long. So how can this be done? Unsurprisingly, getting to giant vehicles like the 90,000 pound Boeing 737 into the air requires careful engineering and knowledge of the fundamental forces that act on objects in flight.


The four main forces that act on an aircraft are drag, lift, weight and thrust, which accelerate the plane backwards, upwards, downwards, and forwards, respectively. Obviously, lift is the one of the most important of these forces, as it is what makes takeoff possible. Airplane wings are specifically designed to redirect airflow and generate lift, based on the angle and curvature of their surface. There are two main ways in which lift can be envisioned. The first is through the Coanda effect, which states that a flowing fluid will tend to stay attached to a surface, creating a “clinging” sensation. When airflow reaches the front of a wing, the air is dispersed equally over the top and bottom and rejoins itself at the back. However, the air on the top “clings” to the curved surface of the wing, so that the top airstream gets angled downward. When it reaches the back of the wing, this upper airstream pushes the lower airstream down in turn, causing the entire flow to be directed downward. The lifting effect that results from this redirection of air can be explained by Newton’s Third Law, which explains that when an object exerts a force on another object, the second object exerts an equal and opposite force on the first. Therefore, when air exerts a downward force, an equal and opposite lifting force is experienced by the plane. The other explanation for the force of lift can be derived from Bernoulli’s Principle, which states that an increase in the speed of a fluid results in a decrease of pressure. When the air is split into two streams by a wing, the top stream has to travel further and faster in order to meet up with the bottom stream at the back of the wing. This results in the speed of the air over the wing being much faster, causing the difference in air pressure explained by Bernoulli’s Principle. The resulting difference in pressure forces the bottom air to move from high to low concentration, creating the same lifting sensation.


There are many other ways that engineers manipulate lift and other forces acting on an aircraft. One way is by changing the angle of the wing relative to incoming wind, otherwise known as the “Angle of Attack.” Increasing the angle of attack forces the air downward at a steeper angle, creating more lift at the expense of greater drag. Similarly, the surface area of the wing, thickness of the wing, or speed can all be manipulated to generate lift. Sometimes, pilots want to exploit these forces during a specific stage of flight, which can be done via extendable flaps at the back of the wing and leading edge slats at the front. These devices temporarily increase the surface area of the wing and allow planes to fly at lower speeds during takeoff and landing. Spoilers serve the opposite purpose of slats and flaps, which extend upward to decrease lift and slow the plane down. These are often used during landing to keep the aircraft grounded as it slows down to a stop. While all of these devices can be effectively used to regulate commercial flight, they are only truly effective in the realm of general aviation (~100-350 MPH). In order to achieve high speeds and maximize aerodynamics, faster jets require different technology. These extremely fast flying speeds are often referred to in terms of a “mach” or a rough multiple of the speed of sound. Sound waves travel through the air at roughly 767 MPH (aka Mach 1), meaning that the subsonic realm of flight is located between 350 and 760 MPH. Even faster military aircraft can fly at supersonic speeds between Mach 1 and 5 (760-3500 MPH), while the fastest planes fly hypersonic (3500-7000 MPH).


Here are some fun facts about airplanes that you probably did not know. While the engines of an airplane are essential to maintain its speed and lift, some aircraft can fly even after losing one of their engines. This was proven in 2014, when the Boeing 787 Dreamliner flew 5 hours and 30 minutes with only one engine active. Another interesting fact about airplanes is their immense fuel consumption, burning gallons in mere seconds. While this value may seem ridiculous, it is important to take into account the amount of passengers they carry, which can be as much as 400-500 people. Without factoring in passenger count, the fuel consumption of the large Boeing 747 is about 0.2 MPG. However, the same aircraft achieves 100 MPG per person, a figure that is impressive even when compared to modern day cars, which often only achieve 30MPG. Have you ever wondered why you always get thirsty on an airplane? Humidity levels at high altitudes are always much lower than on the ground, causing our bodies to lose moisture much more rapidly. The average humidity levels at altitude reside around 20%, while typical humidity levels on an average day in Tennessee vary between 53% and 84%. This causes moisture to be removed from our bodies at a much faster rate, due to the extreme dryness of the air. Most strangely of all, some engineers use “dead chicken guns” to test the reliability of their airplanes. This test is done by firing dead chickens into the windshield and engines to ensure that they would not break down in the event of a real bird collision. Surprisingly, this is actually a very common situation, and these tests could be the difference between an engine failure and a successful flight.


While airplanes may seem to defy the laws of nature, their ability to fly is actually based on simple and logical principles of motion. Due to this misconception, many view flying as dangerous and unpleasant, or are scared to travel long distances in the air. In fact, airplanes are much safer than most forms of transportation, with far lower accident and fatality rates than cars or motorcycles. The chances of dying in flight are about one in eleven million, while the lifetime odds of dying in a car crash can be as much as 1/100. This is due in part to their strict safety protocols, and the rigorous checks which are performed before every single flight. Furthermore, they carry backup systems for nearly every single component that could fail during the flight, such as a small extra engine and replacements for most devices in the cabin. Regardless of whether you think flying is a safe way to travel, all can agree that it is one of the most fascinating developments of the twentieth and twenty-first centuries. I have no doubt that flying will continue to change the world, and as technology advances there is no telling how far it will take us next.

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