September 29, 2022

Have you ever heard of vapour trails?!

In this episode of Let’s Dive In, RTÉjr Radio’s science show, your hosts Julie and Phil join Red Arrows pilot Nick Critchell to find out that jet planes have magical powers like Elsa from Frozen!

Tune in at 7pm this evening or press play above now!

One of the things Phil and I love about this podcast is that we get to speak to some really cool people about the questions that you ask us. And, this time, it’s no different! I think Phil had an absolute blast, and here’s why!

Our question for this show is about how airplanes make those trails of clouds in the sky. Now, they might look like all the other clouds you see in the sky, but they’re not the same. These trails made by planes are called contrails, or condensation trails.

A cloud is a bunch of water droplets that are floating in the sky. The water droplets form when water vapour, which is an invisible gas, turns into liquid water droplets, or condenses, around a tiny particle of dust in the sky.

The water vapour is formed when actual water evaporates. For example, you leave a towel to dry out in the sun… and it dries. Or you leave a cup of water outside on a sunny day, and you come back after a while and some of it’s missing.

It wasn’t your sibling that drank it! What happened was the water in the towel or the cup evaporated. It changed into that invisible gas and floated away into the air.

This happens with oceans, rivers and lakes all the time. And all this water vapour drifts up into the air and when the conditions are right, they turn back into droplets of water and form clouds. Right, so, if that’s how our regular rain clouds form, how do the trails of clouds behind airplanes form.

The airplanes you see high up have jet engines. “A jet engine works by burning fuel. And a product of burning fuel is that you get water. At the back of these airplanes you’re getting lots of water,” says Nick Critchell, Squadron Leader and Red 3 with the aerobatics team the Red Arrows.

Nick is part of the Red Arrows!

If you go high enough, the air gets cold enough to immediately freeze any water that’s out there. The science behind the freezing process is that water cannot freeze on its own – it has to hold onto something.

And another product of what’s coming out of the back of an engine is tiny tiny particles of soot, because there’s a little fire going on inside the engine.

So if it’s cold enough, the water will freeze to these particles. And if the plane is going fast enough, you get a trail of these tiny little ice crystals coming out of the airplane, which look like clouds! “So we call it a cloud, but it isn’t”

So, what is really happening is that all pilots are singing Let It Go from Frozen as they fly across the sky!

Tune in to find out how some jet planes make these Elsa Trails, or contrails, and why some jet planes don’t. And also how the Red Arrows work with a team to make their famous coloured trails in the sky.

Make sure to subscribe HERE or wherever you get your podcasts!

AND read all the Let’s Dive In articles with experiments to try at home HERE!