Thread by @bscholl

Boom! We cracked it! Today we are introducing Boomless Cruise—supersonic flights up to 50% faster with no audible sonic boom.

We quietly (har har) demo'd this on XB-1's first supersonic flight—three times actually. 🧵👇

How did that work? It's actually well-known physics called Mach cutoff.
When an aircraft breaks the sound barrier at a sufficiently high altitude, the boom refracts in the atmosphere and curls upward without reaching the
ground. It makes a U-turn before anyone can hear it.

Mach cutoff physics is a theoretical capability on some military supersonic aircraft; now XB-1 has proven it with airliner-ready technology.

Just as a light ray bends as it goes through a glass of water, sound rays bend as they go through media with varying speeds of sound. Speed of sound varies with temperature... and temperature varies with altitude. With colder temperatures aloft, sonic booms bend upward.

This means that sonic booms can make a U-turn in the atmosphere without ever touching the ground. The height of the U varies—with the aircraft speed, with atmospheric temperature gradient, and with winds. So
making this work requires tech not available in Concorde's era...

Boomless Cruise requires engines powerful enough to break the sound barrier at an altitude high enough that the boom has enough altitude to U- turn. And realtime weather and powerful algorithms to predict the
boom propagation precisely.

Boomless Cruise on Overture would not be possible without Symphony engines—which we're designing with enhanced transonic performance, allowing Overture to break the sound barrier at a high enough altitude for Boomless Cruise.

Overture's autopilot will have a "boomless" mode that automatically selects the fastest quiet speed while advising pilots on the fastest on most efficient altitude, based on predictions informed by realtime weather.

Top speed for Boomless Cruise varies with weather and can be as high as Mach 1.3—but will usually be between Mach 1.1 and Mach 1.2. At higher speeds, the geometry doesn't work and a boom will still reach the ground.

Boomless Cruise is not the same thing as "low boom" attempts to dampen sonic boom. Boomless Cruise results in no audible boom; at Mach 1.7, Overture will still make a boom.

So... in honor of Boomless Cruise, we are renaming the company 🤫Shhh Supersonic. OK, just kidding. But Boomless Cruise is no joke.

In addition to the 600+ routes that will benefit from Overture's existing Mach 0.94/Mach 1.7 hybrid speed, Boomless Cruise adds many other practical routes—including U.S. coast to coast flights up to 90 min faster.

Current regulations in the US prohibit supersonic flight over land, even if no audible sonic boom is produced. We look forward to working with regulators to update these regulations to unlock Boomless supersonic flight over land.