The plane is heavy and there’s gravity on earth. How does it just fly without falling down?
In: Physics
Step 1: It goes really fast.
Step 2: It has big flat wings that are tilted in such a way that the air hitting the wings gets directed downwards and the plane gets pushed up. You can feel this effect for yourself if you stick your hand out the window of a moving car. If you make your hand flat, how you tilt it changes whether your arm gets pushed up or down by the air.
Step 3: There’s some other stuff about how the “airfoil” shape of the wing effects things, but you don’t need to worry much about that at the ELI5 level. What I said above is the important bit.
Planes have 4 basic forces acting on them-
Gravity down to the center of the Earth
Drag – the backwards push due to the air
Thrust – the forewords push due to the engines,
Lift – the upwards push due to the wings
So they come in pairs, Lift/Gravity and Drag/Thrust.
I guarantee somebody will post a theory called the “Equal Transit Theory”, which (avoiding physics) says the wings create a zone of high pressure below them and a zone of low pressure above them due to air traveling at different speeds across the surfaces. **THIS IS INCORRECT (but still taught in wayyyy too many aerodynamics courses)**
Truth be told, lift is really confusing to explain without some high level physics and math, there really isn’t a good ELI5 of it, suffice to say it has to do with the way fluids work (in this case ‘air’ is considered a fluid in physics speak). It’s correct to say lift is caused by a pressure difference (high pressure below the wing pushes UP against low pressure above the wing) but the actual cause of the pressure differential is really complicated and difficult to explain without high level physics and maths. The best answer I can give you is that the wing’s *shape* introduces tiny little whirlpools and tornadoes in the air (invisible to the eye) that create the pressure differences, kind of like how when you comb your hand through the surface of water in a pool you see little whirlpools form in the wake? Kinda like that but powerful enough to lift an airplane.
The plane’s wings are shaped in a way that when they’re moving quickly, the air going over the wing goes faster than the air under the wing. This difference in air speeds causes a difference in air pressure – the air pressure above the wing is lower than the air pressure below the wing. The pressure difference results in an upward force that we refer to as “lift.”
If a plane generates a lift force that is greater than the force of gravity pulling down, it goes up. If the lift force isn’t quite as high as gravity, the plane goes down. When the lift force and gravity are balanced, the plane stays at the same altitude.
The pilot has various controls to adjust the amount of lift the plane is producing, and thus can control the plane’s altitude – to make it climb, to make it hold consistently at cruising altitude, and to lower it gradually when it’s time to land.
The wings are big and have different conditions on their top and bottom. The bottom, through design of wing shape, wing angle and plane speed, experiences more aerodynamic force upward than the top produces down (in both cases an aerodynamic force from air pressure is pushing against the surface). This means there is lift.
Specifically, the top surface has higher curvature when shape, angle and speed are combined. The curvature of air causes an increase in speed and a corresponding decrease in air pressure, to conserve momentum. The change in air pressure results in change in force experienced by the wing surface.
Bernoulli’s principal states that as the velocity of a fluid (air) increases, the internal pressure decreases. So, an “airfoil” is designed so that the air on top has to go farther, in the same amount of time as the air on bottom, therefore, it goes faster and has a lower pressure. The difference in pressure creates an upward force, or “lift” on the wing. There is also a component of force caused by the angle the flat bottom of the wing is directed into the air compared to the path of the plane. Neither of these forces would be enough to allow controlled flight alone. It takes both components, and selectively changing one or the other to produce what we know as controlled flight.
Latest Answers