I seem to be making these into a bit of a series: ‘when social media gets it wrong’ (see: Not A Baby Polar Bear and Not A Baby Giraffe). More often than not it’s one of those scraper accounts that post images for cheap engagements. I assume they do it to create ad revenue from sponsored posts. It can’t be worth that much, right?
Anyway, here’s the next in the series, a fighter jet visually “breaking the sound barrier”. Or is it?
You guessed it, it’s not. Although, there is some pretty cool science going on.
What is actually forming around the plane isn’t the visual representation of the sound barrier being broken, but is the formation of a condensation cloud around the aircraft referred to as a Prandtl–Glauert singularity – an annoyingly tricky-to-pronounce phenomenon that is more commonly known as either a vapour cone, shock collar, shock egg or donut.
These vapour cones are commonly associated with breaking the sound barrier, even though the effect usually occurs before the aircraft exceeds the sound barrier, although it isn’t just limited to aircraft: it can also be seen during rocket launches or even as what looks like a “shock wave” in explosions.
If you think images are cool, take a look at a vapour cone in action in this video. You can see condensation trailing from the less aerodynamic parts of the aircraft’s body with the white ring of the vapour cone blinking on-and-off about half way through.
How Are They Formed?
Vapour cones are created when pockets of air around a fast-moving aircraft drops in pressure. As humid air enters these areas of low pressure the temperature and density lowers allowing atmospheric water to condense into tiny droplets giving the opaque, white cloud.
One of the most important aspects in creating vapour cones is the humidity of the air, as without enough atmospheric water there will be no condensation droplets. You may notice that most images and videos of aircraft with these vapour cones tend to be flying just above bodies of water such as lakes or the sea.
Credit Where It’s Due
Most of the images that you see being passed around the internet are actually the work of a photographer named Darek Siusta, whose exceptional work you can find on his 500px page.