If there's one area where the 21st century has gone backwards technologically, it's in supersonic passenger flight. With the grounding of the Concorde fleets in 2003, flying faster than the speed of sound reverted to a military monopoly, but that hasn't kept engineers from trying for a revival. Now Airbus' Marco Prampolini and Yohann Coraboeuf have been granted a US patent for an "ultra-rapid air vehicle" designed to fly at 20 km (12.4 mi) higher than conventional aircraft and over four times the speed of sound – twice the speed of Concorde.

Even in its heyday, civilian supersonic flight held on by the skin of its teeth. Concorde may have carried the wealthy and glamorous across the Atlantic in under three hours, but only 20 were ever built after an Anglo-French development program in the 1960s that was compared to the Apollo Moon landings in cost and complexity.

A combination of sonic booms, restrictive US FAA regulations, and the Arab oil embargo of the 1970s made the Concorde economically unviable and it ended up as a tiny fleet, only flying with British Airways and Air France because of French and British government pressure. Meanwhile, the Soviet Union's Tupolev TU-144 "Concordski" had an extremely short career after a fatal crash at the Paris Air Show in 1973.

The Airbus patent takes the idea of the Concorde, boosts the performance and reduces the impact of the infamous sonic boom. According to Airbus, the craft is essentially a flying tanker with most of the fuselage made up of liquid oxygen and ecofriendly liquid hydrogen. Forward of this is a passenger cabin for 24 people, with the cockpit in the bow.

It's also a very odd looking airplane with a gothic delta wing that gives it a strangely truncated look, as if it had been whittled down to fit into an unusually narrow hangar. The gothic delta is similar to a conventional delta wing with a 70 to 75-degree sweep, except that the leading edges of the wings are curved into the shape of a gothic window frame. Behind these, set on cylinders, are trapezoidal fins on the trailing edge of each wing. These not only take on the tasks of a conventional tail's rudder and elevators, but also alter the center of pressure as the fuel and oxygen are burned to keep the aircraft properly trimmed.

But what really sets the Airbus dsign apart is its suite of propulsion systems used to keep it aloft. On a typical flight, it would take off like a conventional plane using ordinary turbojet engines, but once in the air, an open door in the stern of the plane reveals a rocket motor. When this fires, it sends the aircraft into a near vertical trajectory, accelerating it to supersonic speeds.

As the airplane approaches Mach one, the turbojets shut down and retract into the fuselage. On completion of the acceleration phase the plane is now flying at anywhere from Mach 4 to Mach 4.5 at an altitude of 30,000 to 35,000 m (100,000 to 150,000 ft). The rocket motor shuts down and is again concealed as the aft door slides shut to reduce drag. A ramjet now kicks in and the aircraft cruises along its flight path and can cover a range of 9,000 km (5,600 mi) in three hours – the equivalent of Tokyo to Los Angeles or Paris to San Francisco. Meanwhile, the wing fuselage design dissipates the sonic shock wave over 110 to 175 km (68 to 109 mi) and angles it at 11 to 15 degrees so it doesn't reach the ground. At the end of the journey, split flaps reduce speed and the turbojets take over for approach and landing.

Airbus says that the supersonic passenger craft can operate from conventional airports so long as they can supply the cryogenic propellants. It wouldn't interfere with existing air corridors, would operate in all weather, and only the rocket motor requires special maintenance. According to its specifications, it could carry two or three tons of cargo, which is equivalent to 24 passengers and luggage.

It's highly unlikely that the Airbus supersonic will ever be built, but if it is, a ticket won't be cheap. The company sees it as catering to VIP passengers who need to make round-trip transcontinental trips in a single day. Alternatively, the craft could also have military applications as a fast strike craft invulnerable to conventional anti-aircraft weapons and interceptors, yet capable of operating over long distances to employ EMP weapons against high-value targets.

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