Did you know that while engineers know how to create airplanes that can remain airborne, science has yet to fully solve the mystery behind their ability to stay in the sky? Today, let’s explore what we know about how planes fly and what we still have to unravel. Fasten your seatbelts and get ready to soar through the wonders of flight.
Flight is governed by four fundamental aerodynamic forces: thrust, drag, lift, and weight (gravity).
Thrust is the force that propels an aircraft forward, generated by its engines, propellers, or jet turbines. It is the dynamic power that overcomes drag, the resistance encountered by the aircraft as it displaces the air. To minimize drag, airplanes are intentionally designed with a sleek and elongated shape, featuring a pointed nose. This streamlined design reduces the surface area and allows the airplane to glide through the air with minimal resistance.
You can observe the concept of drag by sticking your hand out of a moving car window. The amount of drag depends on factors like the size of your hand, the car’s speed, and the air density. Slowing down the car will decrease the drag acting on your hand.
Gravity pulls the plane vertically downward, but it is the force of lift that defies gravity and keeps the plane in the air. For an airplane to maintain flight, the force of lift must be equal to or greater than the weight of the aircraft. And the heavier an object, the stronger the force of gravity, so lighter airplanes require less lift (and thrust) to ascend and remain airborne.
Theories about how lift is generated still spark debates. Scientists often divide into two camps. The first camp believes that lift is generated by the pressure difference created by the airflow over the wings. This is where Bernoulli’s theorem comes into play. The theorem states that as the speed of a fluid, such as air, increases, its pressure decreases, and vice versa.
In the context of flight, the shape of an airplane’s wings, with their curved upper surface and flatter lower surface, creates a pressure difference. When air encounters an obstruction on the top of the wings, its path narrows, causing accelerated flow and reduced pressure. Meanwhile, the airflow beneath the wings moves more slowly, creating higher pressure. This pressure difference generates lift, keeping the airplane in the air.
Another theory explaining lift is based on Newton’s third law of motion, which states that for every action, there is an equal and opposite reaction. According to this theory, an airplane stays in the air because the wings push the air downward. Since air has mass, this downward push by the wings generates an upward force: lift.
Newton’s third law provides a more universal and comprehensive understanding of lift compared to Bernoulli’s theorem. Its explanation, unlike Bernoulli’s approach, applies to wings of any shape, whether curved or flat, symmetrical or asymmetrical, and it remains valid even when the aircraft is flying upside down. And while both Bernoulli’s theorem and Newton’s laws are correct, none of them fully explain how objects generate aerodynamic lift or the reason for the lower pressure atop the wing.
That being said, there is an opportunity to win over $1 million by solving a math problem. The Clay Mathematics Institute in the USA has posted seven challenging problems on their website, one of which focuses on the perplexing nature of airflow. It’s incredible to think that something as fundamental as air remains a puzzle we have yet to fully comprehend!
Quotes
“The moment you doubt whether you can fly, you cease for ever to be able to do it.” ―J. M. Barrie, Peter Pan
“You wanna fly, you got to give up the shit that weighs you down.” ―Toni Morrison, Song of Solomon
“If you were born without wings, do nothing to prevent them from growing.” ―Coco Chanel
“There is one spectacle grander than the sea, that is the sky; there is one spectacle grander than the sky, that is the interior of the soul.” ―Victor Hugo, Les Misérables
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References
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