On January 28, the experimental XB-1 aircraft achieved a remarkable milestone by breaking the sound barrier three times during its inaugural supersonic flight, and notably, it did so without producing an audible sonic boom detectable from the ground.
This breakthrough supports the vision of making supersonic travel accessible, environmentally sustainable, and considerate of communities on the ground, as stated by industry leaders.
When an aircraft travels through the atmosphere at supersonic speeds, it alters the surrounding air pressure, generating sound waves. Upon surpassing Mach 1, or approximately 1224 kilometers per hour, these sound waves merge to create a shock wave that radiates from the flight path. Usually, this sonic boom can be heard miles away, causing disturbances like rattling buildings and shattering glass.
The disruptive nature of sonic booms has led to the retirement of the iconic Concorde commercial airliner in 2003, triggering bans on commercial supersonic flights in various countries. Since then, aerospace engineers have been focused on designs that allow for supersonic travel while mitigating the boom’s effects.
In a significant development, the XB-1 leveraged a phenomenon known as the Mach cutoff. By flying at higher altitudes where sound travels slower, the aircraft can exceed the speed of sound without generating a boom that reaches the ground; rather, the shockwaves deflect upward due to the increasing sound speed as they descend.
However, achieving optimal flight conditions requires precise atmospheric forecasting of temperature and wind, as these factors influence the ideal altitude and speed for supersonic aircraft operations.
During its latest test flight on February 10, the XB-1 maintained supersonic speeds while avoiding boom production. Insights gained from these test flights are being applied to the upcoming commercial airliner, Overture, which aims to provide supersonic travel over land that could be up to 50% faster than current commercial options, drastically reducing travel time from New York to Los Angeles by 90 minutes.
Additionally, operating at supersonic speeds on shorter routes may result in lower fuel consumption compared to cruising just below the sound barrier. However, experts note that utilizing Mach cutoff predominantly benefits supersonic business jets, as it may yield limited economic advantages for commercial airlines.
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