The Supersonic Question · August 2019Part 2 of 3
Silent Supersonic Jets? Hold My Beer…
The second article in the August 2019 supersonics sequence examined one of the defining obstacles to renewed commercial supersonic flight: sonic boom—and the technologies being explored to reduce or avoid it.
Originally published on 23 August 2019. Reproduced as originally written.
As a new crop of aerospace entrepreneurs is propelling us into the next phase of commercial supersonic flight, there has been no shortage of scary headlines to accompany their efforts. CNBC, The Guardian and other news and opinion outlets all uncritically amplified acoustic doomsday predictions earlier this year based on a single environmental think tank report.
Back in the 70s, the U.S., European countries and others outlawed civil SST flights over land for fear that sonic booms posed too great of a danger to public health. Many of today’s alarmists, so it seems, are looking to resuscitate those same public fears of 45 years ago in the hope that the next wave of supersonic aircraft will be dead on arrival.
But the gloomsters have clearly not reckoned with the sheer ingenuity and passion of our global corps of aeronautical engineers who always relish a good challenge. If you want to get something done, just tell them “it can’t be done”.
And so, in recent years, engineers have set out to eliminate the much-maligned 110 decibel sonic boom of the old Concorde that rattled windows and startled people (although apparently not chickens). Taking advantage of new cloud computing and CFD simulation capabilities to test wing and fuselage shapes, modern SST prototypes can now be designed to separate shockwaves as they travel away from the aircraft, effectively avoiding sonic boom. Combined with the use of carbon fiber and flying at higher altitudes, it is foreseen that supersonic cruise noise levels could be limited to about 80 decibels, roughly 100 times quieter than the Concorde.
Alternatively, sonic boom could be avoided using supersonic laminar flow control technology and advanced avionics. Laminar flow wings featuring a modified bi-convex airfoil can prevent the plane from entering turbulent flow. Specialized instrumentation can be used to inform pilots if they are flying over a portion of the atmosphere whose properties (mainly temperature and wind) will prevent sonic boom from reaching the ground by refracting the boom shockwaves, a phenomenon known as “Mach cut-off”.
Beyond this, more revolutionary R&D is underway seeking to combine a jetfuel-powered turbine, superconducting electric power and propulsion generation, and a magnetic-power flux field system with an ion plasma annular injection combustor. Designed to travel at Mach 3.0 (that is about 3,675 km/h, or a kilometre per second), the Supersonic Magnetic Advanced Generation Jet Electric Turbine (S-MAGJET), relies on ion plasma injected ahead of the plane’s shock wave to significantly reduce drag and the sonic boom.
If that sounds like science fiction, remember that the same was said about sonic boom suppression only two decades ago.