Science with Dr Karl: How aeroplanes fly!

Explore the astonishing forces that keep aeroplanes in the sky…

“Planes! Have you ever watched an aeroplane fly over and wondered how 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!

So, how does it manage it? Well, a plane’s wing is basically an ‘air deflector’ – which means that the wing pushes air down and, in return, the air pushes the wing up. So, the A-380 can stay 12,000m above Earth because it is constantly pushing air down. This is called ‘lift,’ one of 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 220kmph, its wings are pushing about five tonnes of air per second down towards the ground. The A-380 needs to push down a lot more air than that to stay in the sky, because it’s heavier!

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 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) 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.”