By Thomas Hillebrandt and Lilly Zerbst, SWR
The myth of the impenetrable sound barrier
75 years ago, pilots feared that flying at supersonic speeds would actually break the "sound barrier" and their planes would be smashed – until test pilot Chuck Yeager was the first to "break through" and escape unharmed.
The "sound barrier" phenomenon is pure physics: air is a gas with a certain density – the faster an airplane moves through the air, the more it compresses the gas molecules in front of it and generates pressure waves. At the speed of sound, the plane catches up with its own pressure waves. If it flies even faster, it breaks through this "wave wall" – the "sound barrier". The strong air pressure fluctuations of the wave wall spread to the ground and are perceived as a loud bang below the flight path.
The first supersonic flight
On October 14, 1947, everything is ready at Muroc Air Base in California: the Bell X-1 rocket plane is refueled and then coupled to a Boeing B-29, which carries the jet, which is only ten meters long, to an altitude of 2,000 meters . There, the then 24-year-old Chuck Yeager climbed into the narrow cockpit of the X-1 and waited for the command to release the connection to the carrier aircraft.
After detaching, Yeager accelerates the X-1 and becomes the first human to fly faster than sound. A sonic boom is heard for the first time in aviation history.
Use of supersonic aircraft in the transport sector
A few decades after Yeager's pioneering work, it became possible to transport passengers at supersonic speeds. With more than 30 years in service, the Anglo-French Concorde was retired in 2003 as the last supersonic passenger aircraft. Now companies like the US company Boom Supersonic are again working on using supersonic aircraft in the transport sector.
Legal requirements for supersonic flight
The legal basis for this still has to be created in Europe: limit values for noise, emissions and climate impact do not yet exist. Among others, Robert Jaron from the German Aerospace Center (DLR) in Berlin wants to provide the necessary data. Together with his team, he creates a basis at the Institute for Propulsion Technology that allows new supersonic commercial aircraft to take off and land in Europe at all. Because for this they need an approval, which must be linked to limit values.
Need for research in the civil use of supersonic aircraft
The EU research project MOREandLESS is to analyze the supersonic boom in detail. To do this, Robert Jaron and his team simulate the take-off and approach of the new supersonic jets. They calculate everything that affects noise and pollutant emissions. In two years the necessary data should be delivered to the certification authorities.
Noise pollution: Supersonic speed only permitted over water
According to Jaron, the technological challenge also lies in minimizing the sonic boom so that the aircraft can also fly over land at supersonic speeds. At the time, the Concorde passenger aircraft was only allowed to fly at supersonic speed over water. The project partners are currently assuming that this restriction will also apply to the first new supersonic aircraft.
Potential of supersonic mobility
The planned supersonic jets and airliners could be more than twice as fast as the currently fastest business jets. They would then transport up to a hundred passengers at over 2,000 kilometers per hour. The CEO of Boom Supersonic wants to go even further: He dreams of being able to fly anywhere in the world in four hours or less. A flight from London to New York with the Concorde took just over three hours.
Supersonic aircraft are not (yet) profitable
The Concorde was not able to prove the economic benefits of supersonic mobility: Despite the high ticket prices, it never flew into the black. High development costs and enormous fuel consumption were to blame. Even modern supersonic aircraft consume about five to seven times as much fuel as a subsonic aircraft.
Today, nations are no longer behind the development of supersonic mobility, but rather private companies that have to open up new markets with their products. However, DLR scientist Robert Jaron suspects that this will take at least another decade.
Editor's note: An earlier version of the article stated that the Concorde was the first supersonic airliner. However, the Soviet Tupolev Tu-144 flew supersonic for civilian purposes as early as 1968.