Science with Dr Karl: How planes fly!

Dr Karl explore how planes fly

Planes! Have you ever watched a plane fly over and wondered how on earth it can soar through the clouds so effortlessly?

I always feel amazed when I see that giant double-decker plane, the incredible A-380. It weighs nearly 600 tonnes – as much as a small ship – and yet it can fly!

A plane’s wing is basically an ‘air deflector’: the wing pushes air down and, in return, the air pushes the wing up. So, the A-380 can stay 12,000m above the Earth because it is constantly pushing
air down. This is called ‘lift,’ one of the four things a plane needs to fly.

Think of a tiny plane, such as the single-engine, four-seater Cessna 172. It weighs just over a tonne (that’s one 600th the size of the A-380!). When it’s flying at 220km/h, its wings are pushing about five tonnes of air per second down towards the ground. The A-380 would need to push down a lot more air than that to stay in the sky!

But how does it work? Imagine you’re in a swimming pool, and you’re moving a table tennis paddle horizontally through the water. Now, if you tilt the paddle upwards a little at the front as you move it along, the paddle tries to rise towards the surface. This is the same effect that the air has on a plane’s wing.

On large passenger jets (like the ones you might have travelled in on a holiday), the wings are joined onto the plane’s long body at an angle of about 5-10 degrees, tilting upwards at the front. Just like the paddle, this causes the plane to rise up (and stay up) – high in the sky!

The three other elements needed for a plane to fly are weight, thrust and drag. The plane stays balanced in-flight because of how the weight is distributed – you don’t want the plane to be nose-heavy or tail-heavy!

Thrust is the force that moves the plane forward. Propellers or jet engines produce the thrust, just like a (smaller!) engine propels a car forward.

Drag slows the plane. You can feel drag when you walk against a strong wind. Planes are designed to let air pass around them with minimal drag, so that they can travel forwards with ease.

A plane flies when all four forces – lift, weight, thrust and drag – work together.

DID YOU KNOW? A plane’s ability to fly can be explained through a scientific theory called Newton’s Third Law of Motion. This law states that ‘for every action, there is an equal, but opposite, reaction’.

DID YOU KNOW? You can earn over $1 million for solving a maths problem! The Clay Mathematics Institute in the USA has seven problems up on their website. One of them deals with how air flows – yep, something that we still don’t completely understand!

DID YOU KNOW? In 1640, a physicist by the name of Evangelista Torricelli discovered that air has weight. At sea level, one cubic metre of air weighs about 1.25kg!