Mach Cutoff

Two weeks ago, I watched live via Starlink as the Boom Supersonic XB-1 test aircraft broke the sound barrier in level flight, the first all-civilian aircraft to do so. This success promises the return of commercial supersonic flight, at least over ocean. This week, during the final test flight, I learned that no sonic boom had reached the ground in any of the XB-1’s supersonic passes. This suggests the possibility – for the first time – of commercial supersonic flight over land.

Normally, a transonic aircraft near Mach 1 sheds pressure discontinuities called shock waves, which can disturb people on the ground. Such sonic booms have curtailed the development of supersonic commercial flight. However, atmospheric refraction, due to temperature and wind-speed gradients, can bend the shock wave rays, as in a mirage, so they never reach the ground.

The XB-1 is a technology demonstrator for Boom’s planned Overture airliner, which Boom hopes will restore supersonic commercial flight for the first time since the retirement of the Concorde over 20 years ago. Boom has already built an Overture assembly plant in North Carolina, where I currently live.

Despite widespread video conferencing, many people need to fly long distances. Hopefully, by the 2030s, Overture will shrink the globe by flying Mach 1.7 over ocean and Mach 1.0 to 1.3 over land using detailed altitude, temperature, and weather information to ensure that no boom reaches Earth. (Concurrently, NASA is developing the X-59 Quesst quiet-supersonic-technology low-boom demonstrator, which involves carefully shaping the aircraft to minimize the ground level boom.)