Why can airplanes keep flying? The secret of lift created by wings and air
Hello, I am Risa Muraoka, representative of Ichi Logi.
Have you ever wondered about something when boarding an airplane?
Why can such a heavy mass of iron keep flying in the sky for hours?
It does not flap its wings like a bird, but simply floats in the sky with its wings spread. What supports that massive airframe is the laws of physics occurring between the wings and the air.
This time, I will carefully explain the mechanism of how airplanes fly, focusing on the keyword 'lift'.
The 'four forces' that support an airplane
For an airplane to continue flying stably, four forces must be in balance.
Upward force: Lift This is the force that pushes the airplane upward, created by the special shape of the wings and the flow of air. It is the core force of flight; without it, an airplane cannot float in the sky.
Downward force: Gravity This is the force that constantly pulls the airplane toward the ground due to its weight. By lift overcoming this gravity, the airplane can stay afloat in the sky.
Forward force: Thrust This is the force that moves the airplane forward, created by the engine burning jet fuel. It is precisely because of this thrust that air flows over the wings and lift is generated.
Backward force: Drag This is the resistance force created when the airplane hits a wall of air while moving forward. By balancing thrust and drag, the airplane can maintain a constant speed.
A state where an airplane is flying stably is a state where these four forces are perfectly balanced. During takeoff, lift exceeds gravity, and during landing, that balance is intentionally disrupted.
The 'special shape' of the wings creates lift
When you look at an airplane wing from the side, the upper side is curved and the lower side is relatively flat. This cross-sectional shape is called an 'airfoil'.
This shape is the key to generating lift.
When an airplane moves forward, air splits and flows above and below the leading edge of the wing. At this time, because the upper side has a larger curve, the air flowing over the top must travel a longer distance than the air flowing underneath. To pass through a longer distance in the same amount of time, the air on the top side must flow faster than the air on the bottom side.
This state of 'faster air on top and slower air on the bottom' is the direct cause of generating lift.
Bernoulli's principle—the mysterious relationship between speed and pressure
This is where the law discovered by the 18th-century Swiss scientist Daniel Bernoulli comes in.
'The faster a fluid (air or water) flows, the lower its pressure becomes.'
You can experience this phenomenon in everyday life. Have you ever felt like your body was being pulled in when standing on the edge of a platform as a train enters at high speed? That is because the pressure of the fast-flowing air decreases, pulling your body toward it.
Applying this to an airplane wing, it works like this.
Upper side of the wing: Air flows faster → pressure is lower
Lower side of the wing: Air flows slower → pressure is higher
Pressure has a property of pushing from higher to lower. In other words, the higher pressure on the underside of the wing pushes the wing upward. This is the true nature of "lift."
The larger the wing area, the greater the force generated by this pressure difference. The reason jumbo jet wings are so massive is to secure the lift necessary to support the weight of the aircraft.
What happens at the moment of takeoff
As an airplane begins to run down the runway, its speed increases due to engine thrust. As the speed increases, the amount of air flowing into the wings increases, and the lift also grows.
Eventually, the moment lift exceeds gravity, the airplane gently leaves the ground. That moment of takeoff is a dramatically physical moment where the balance of the four forces changes all at once.
Once cruising altitude is reached, the pilot adjusts the engine output to balance the four forces again. This state is the "stable flight" we experience while on board.
Everyday "whys" broaden the world
Knowing how an airplane flies changes the view when you board one next time. You will be able to see that the wings visible outside the window are maintaining a precise balance using air and the laws of physics.
Knowledge increases the resolution of our daily lives.
When something you were "just riding on" changes into "something whose mechanism you understand," the world becomes a little richer. I believe that this "change in perspective" is exactly what liberal arts aims for.
Next time, I will also deliver an article that deciphers the world from familiar questions.
Risa Muraoka, Representative of Ichi Logi
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