The Supersonic Airliner- Will It Be Economically Viable?
This article originally premiered on The Washington Post.
Can you imagine making a day trip from New York to London? That’s exactly what the futuristic aircraft company Boom hopes to enable with their new supersonic airliner. Boom is promising a trans-Atlantic flight time of a mere 3 hours at flight speeds of Mach 2.2 (2.6 times faster than the typical commercial airliner).
But, you might ask, what’s so special about this? The Anglo-French Concorde flew supersonic routes from 1976 to 2003. If the Concorde could do it with 1960’s technology, what makes Boom’s approach unique?
Well, the Concorde no longer flies. The end of the Concorde was presaged by the fiery crash of Air France flight 4590 near Paris – Charles de Gaulle on July 25, 2000, but economic pressures were the predominant reason. Simply put, the airlines were hemorrhaging money by flying the Concorde.
The challenges to supersonic commercial flight were, and continue to be, enormous: The Concorde’s fuel burn was excessively high, in order to produce enough thrust to overcome aerodynamic drag at those high flight speeds. The temperature of the aircraft’s skin in supersonic flight gets hot (over 300°F at Mach 2.2) as the high-energy supersonic airflow collides with the surface. And, supersonic flight is prohibited over land due to the destructive nature of the aircraft’s sonic boom, which is created when sound waves and pressure disturbances coalesce into a very strong pressure jump called an N-wave.
So, how does Boom propose to overcome these challenges? Well, jet engine technology has improved dramatically over the past 50 years since the Concorde was designed, making the fuel burn much more manageable. Higher bypass ratio engines (with a larger fan at the front) burn less fuel and produce less noise. Also, modern computational fluid dynamics tools are being used to design the aerodynamic characteristics of the aircraft, to minimize drag in the supersonic regime where shock waves contribute significantly to the overall drag. Modern carbon-fiber composite structures are being used for much of the aircraft structure, allowing the designers more freedom to optimize the aerodynamic shape and minimize aerodynamic heating effects at these high flight speeds. And, Boom’s designers are leveraging the latest understanding developed by NASA and others to reduce the strength of the sonic boom, possibly paving the way to a relaxation of the regulatory standards to allow supersonic flight over the US.
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