When a plane goes fast enough, it compresses the air it is flying through so much that it can change its density.
NASA and the US Air Force have been trying to visualise this effect for years so they can build better supersonic aircraft and enable them to go faster than the speed of sound.
Until recently, these kinds of tests were contained to wind tunnels on the ground.
There, researchers used the schlieren technique, invented by German physicist August Toepler in 1864, to understand more about how air was travelling around supersonic aircraft.
Schlieren imaging is a way to see the differences in air density, using a particular setup of lenses and cameras.
Now, NASA researchers have adapted this method to visualise supersonic aircraft in flight. Bringing the Schlieren method into the air has been challenging because the aircraft carrying the imaging equipment has to fly right above the plane it’s recording, and travel just as fast — which, during supersonic imaging, is faster than the speed of sound.
The T-38C, a supersonic US Air Force training jet that NASA imaged, travelled at a top speed of Mach 1.09 during the tests. (Mach 1 is the speed of sound, which is about 768 mph at sea level.)
But the tricky manoeuvring was worth it for these gorgeous images, showing the shock wave of the T-38 flying over the Mojave Desert:
As the plane moves through the air at supersonic speeds, it disrupts the air’s density, resulting in the different colour lines here — the shock waves that are a result of the plane’s motion.
These shock waves act just like the wake behind a boat, which happens because it disrupts the water by moving faster than the water waves were moving.
Air pressure right at the tip of the cone is normal, while the pressure inside the cone is high because of the plane passing so quickly through it and pushing the atoms of air together.
Here’s another schlieren image visualising the supersonic flow of the T-38 jet in flight:
Understanding more about how supersonic aircraft affect the air around them could help develop ways to make planes quiet enough for commercial travel, opening the door to make the trip from LA to NYC a whole lot faster.
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