The last passenger jet capable of breaking the sound barrier landed after its last flight in 2003. The European Concorde jets had been flying across the Atlantic since 1976, but not without problems.
In addition to consuming massive amounts of fuel, these jets were prohibited from flying at full speed except over seas. When the engines broke the sound barrier, the noise became so exasperating that it could both break glass and cause hearing damage.
In fact, high-speed flights have been banned overland in the United States since 1973 due to a number of complaints. But NASA is now planning to remedy this, according to a press release.
NASA and Lockheed Martin have jointly developed the jet X-59 QueSST, whose special design is supposed to dampen the sound barrier down to a single impact sound.
The noise breaks glass
When an aircraft exceeds the speed of sound and thereby breaks the sound barrier, the incident creates a tremendous noise, up to 110 decibels, called a sound barrier breach or “sonic boom”.
Temperature, air pressure and aircraft construction materials all play a role in when the sound barrier is broken, but at an altitude of 10 km, where it can be 60 degrees below zero, the sound barrier can be broken at a speed of 1,062 km.
When an aircraft approaches the speed of sound, sound waves are compressed in front of the plane and form a “wall of sound”. Pressure waves in front and behind the engine form a collective shock wave that can be heard from the ground as an extremely loud crash.
Now planes cannot break the sound barrier unless they are over the sea or at an altitude of 9,145 meters above land. Most passenger jets only reach a speed of 926 km/h.
Because the sound barrier failure is so powerful that it can break glass and cause great discomfort to people, engineers have long sought ways to reduce the noise.
The design disperses shock waves
At NASA, people now think they have found such a design with the X-59 QueSST (Quiet SuperSonic Technology).
This is still an experimental machine, 29.5 meters long and 9 meters wide, and it is intended to study how to reduce the sound barrier failure as much as possible. The results could then be used for other models, eg passenger jets.
Using a design model called Computational Fluid Dynamics, the engineers were able to predict how air molecules would have to behave in order not to cause unpleasant noise.
The narrow and flat contours of the jet were then designed based on these tests.
The design should disperse the sound waves in such a way that no sound barrier failure is created. Instead, only a quiet thump should be heard – if anything is heard on the other side.
This experimental machine can reach a speed of Mach 1.42, which corresponds to a speed of more than 1,510 km.
In comparison, the Concorde engines reached just over Mach 2. The Mach number is a unit of measurement in which the speed of an object is measured as a percentage of the speed of sound.
The cockpit of the X-59 is undeniably special as the nose is so long and pointed. The pilots won’t be able to see much out the windshield.
Instead, they have a small HD screen that uses a special technology that NASA calls the eXternal Vision System and is supposed to provide safe control of the machine. Small sensors on the plane provide images for the pilots.
Sound from passenger aircraft for 2030
A small model of the machine has already been successfully tested in wind tunnels, after which a full-scale prototype has gone through ground tests.
At NASA, it is expected that the X-59 will be able to make its first test flight in 2023. Then experiments will be made to break the sound barrier over built-up areas.
