[imagesource: Lockheed Martin]

Sonic booms caused by supersonic aircrafts have been banned because the sound is so loud it is considered a serious form of noise pollution.

A traditional supersonic aircraft can release a sonic boom that is more than 100 decibels when in flight, which is far louder than the average fireworks display.

You can imagine the complaints that this kind of noise will bring in, so the Federal Aviation Administration (FAA) in the US cut to the chase and banned commercial supersonic flight over land in 1973.

But NASA and Lockheed Martin are concocting something that might make the FAA reconsider, reports CNET.

They’re busy building a needle-like aeroplane, the X-59 QueSST (short for Quiet Supersonic Technology), which is designed to be so quiet that it could reshape aviation.

At the Armstrong Flight Research Center, just outside of Lancaster, California, the aircraft will soon be put to the test, and attempt to fy quicker than the speed of sound without generating an explosive sonic boom.

This will work by “minimising the shock waves that cause a sonic boom midflight, reducing its sound at ground level to 75 decibels”.

According to NASA, that’s about as loud as a car door slamming down the street – not a worthy complaint from any neighbour.

Luckily, the principles of physics and aerodynamics needed to pull this off are well established, according to Lockheed Martin’s X-59 program director, David Richardson:

When the X-59 takes to the skies, the goal is to generate a “sonic thump” and by doing so, convince regulators like the FAA that a ban on supersonic passenger travel over land can be overturned.

The plane basically has to be designed to avoid as much of the compressed air that comes out in all directions causing a sonic boom when it flies at supersonic speeds, or  faster than the speed of sound.

Hence, the sweeping lines, unbroken curves, and a narrow cockpit concealed in the centre for just one passenger.

This is according to NASA’s acoustic testing technical lead for the X-59, Larry Cliatt:

“We want to keep [the shock waves] parallel and separated from each other so they don’t combine into a loud sonic boom,” says Cliatt.

“So we’re dragging out those volume changes, making them very gradual across the entire body of the aeroplane.”

The testing will include a number of phases.

First, Lockheed will conduct initial flight tests to make sure everything is working as expected.

Then, in 2023, NASA will begin “acoustic validation” testing to ensure the sonic boom has been satisfactorily scaled back to a sonic thump.

Once that is all good, an F-15 fighter jet will chase the X-59 and measure the shockwaves being produced by the aircraft mid-flight.

This will include some very cool schlieren photography, which is photographing a plane moving faster than the speed of sound using the sun as a backdrop – a feat in timing more precise than threading a needle.

We shared some images of how that looks here.

Then, the acoustic testing phase will happen:

NASA will set up an array of microphones across a 30-mile-long stretch of the Mojave Desert in California to measure the sonic thump and make sure it’s as quiet as intended.

The final round of testing will be flying the X-59 over a handful of cities and towns across the United States to gauge the community response.

It’s all in those 200 milliseconds of sound from the sonic boom – over in the blink of an eye.

Here’s a video with more information if you’re keen:

[source:cnet]