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Almost two decades after Concorde's last flight, supersonic commercial aircraft could soon take to the air again. Several manufacturers have announced their intention to launch commercial supersonic aircraft in the next few years. This is why the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), together with its international partners, is investigating the environmental impact of a future fleet of supersonic aircraft. The goal is to assess both noise emissions and climate impact. The results of this research should help to reduce the environmentally harmful effects of such a fleet.

"Concorde was subject to air transport regulations that allowed higher emissions compared to aircraft flying in subsonic conditions. The new generation of supersonic jets will have to comply with the rules that apply to conventional aircraft," explains Lars Enghardt, Head of the Engine Acoustics Department at the DLR Institute of Propulsion Technology. To set new certification rules, the authorities will need to rely on extensive data. The EU project SENECA (noiSe and EmissioNs of supErsoniC Aircraft) is making an important contribution to collecting this data.

Two new supersonic aircraft classes are planned – business jets and airliners

The scientists will first perform computer-based design and analysis of two different supersonic aircraft classes – business jets carrying approximately 10 passengers and airliners with up to 100 passengers, having a similar capacity to that of the Concorde. The business jets will be able to reach Mach numbers of between 1.4 and 1.6 in cruise flight. The supersonic flight regime begins at Mach numbers above one. At cruising altitude, an aircraft must travel at around 1000 kilometres per hour to achieve this. The fastest business jets currently in service have a Mach number of 0.9. The planned supersonic airliners might even reach Mach numbers between 1.8 and 2.2 at cruising altitude. This would make them more than twice as fast as current airliners.

"Reconciling the efficiency of aircraft in cruise flight and noise emissions near airports is difficult," says Robert Jaron from the Institute of Propulsion Technology, explaining the challenges in designing the aircraft. "Because of the need for better airflow behaviour, supersonic aircraft are particularly long and narrow, and have small engines. However, for noise reduction during take-off and landing, engines with larger diameters would be preferable." According to the DLR team, which also includes the Institute of Atmospheric Physics, there is still room for improvement, especially in the take-off procedure. The poor glide performance of supersonic aircraft in subsonic flight is compensated for by the use of particularly powerful engines. A higher take-off speed with an early reduction of the engine thrust could reduce noise pollution near airports. This possibility is also being investigated in the project. SENECA is also investigating pollutant emissions and their influence on the climate. Supersonic air traffic will fly much higher than current commercial airliners and will therefore likely have a different impact on the atmosphere.

The project partners currently assume that the first new supersonic aircraft will only fly over water, not over land, at supersonic speeds due to the problems caused by sonic booms. Sonic booms are being analysed in detail as part of the EU project MORE&LESS, in which DLR is also involved. Here, the researchers will determine how different aircraft shapes affect the intensity of the sonic boom.