One interesting panel at Oshkosh (EAA AirVenture) this year was regarding civilian supersonic aircraft (see the Supersonic Renaissance clip on YouTube).
As with most innovations in aviation, the big enabler is an innovation in engine technology. GE Aviation, currently celebrating its 100th anniversary, has a new engine that is mostly based on the latest subsonic civilian technology and three of these will drive a the Aerion AS2 plane forward at Mach 1.4 while burning roughly 2X the fuel per passenger-mile as a Gulfstream G650. The second enabler is cash and the Bass brothers are supposedly kicking in $4 billion.
So far so good if the goal is 4,200 nm over water (Gulfstream G650 range is closer to 7,000 nm).
What about going over land? After a five-year regulatory process, the U.S. effectively banned supersonic flight over land in 1973. The ban relates to speed, not to noise over the ground. An aircraft whose sonic boom was quieter than a Honda Accord driving by on the street would be banned, for example.
In a rare example of a NASA project that might have an effect on someone’s day-to-day life, NASA is currently hoping to test fly an X-59 “quiet supersonic” plane in 2021. This will supplement testing done in 2018 with a a modified F/A 18. The shape of the plane is designed to prevent shockwaves from different parts of the aircraft meeting and reinforcing each other. This may reduce the boom by 30 dBA and produce a sound like distant thunder.
NASA is currently planning do to 2-3 years of testing to gather civilian reaction and then turn numbers over to the FAA for the beginning of a regulatory process whose result will presumably be a decibel-time limit. If the regulatory process takes the same 5 years that it did from 1968-1973, that will be 7-8 years after 2021 before manufacturers such as Aerion can have any idea whether what they’re designing will be legal to operate from NY to LA (and thus ready for climate change activist Leonardo DiCaprio!). In other words, it will take longer than World War II and all of the innovation that happened in aviation during those 6 years!
(Two nights earlier, Burt Rutan had given a crusty old guy’s talk about how pathetic young Americans were with their anemic pace of innovation. The government, including today’s NASA was singled out as particularly sluggish and unambitious, thus leading to “some homebuilders in the Mojave Desert” running Americans’ only space flights with humans on board.)
One interesting thing is that an airplane can potentially fly at Mach 1.2 at 60,000′ without a sonic boom ever reaching the ground. The speed of sound is slower where the air is colder and apparently the wave will dissipate as it goes through warmer air (but what if Hillary Clinton and DiCaprio are at FL510 in a Gulfstream G650 just below? Will their Champagne glasses be rattled?)
Aerion is planning to be in service in 2026 and to meet all Stage 5 takeoff and landing noise restrictions. To keep the rabble from rioting, the company is claiming to be “carbon neutral”. Yes they will spend $4 billion (enough to plant 400 million trees?) and burn 2X the fuel of the biggest Gulfstream per seat-mile. But the fuel burned can be 100 percent biofuel (i.e., corn!).
More: watch the Supersonic Renaissance clip on YouTube.