So there's the average jetliner that cruises at about 550 miles per hour, which is subsonic. There was, until 2003, the Concorde that used to cruise at about 1,334 mph, which was supersonic, but what about an airliner that is hypersonic? Well, that's what European aircraft manufacturer Airbus has just been awarded a patent for: an airliner that will cruise at about four and a half times the speed of sound. Pie in the sky, you might be thinking? How are they going to fly that fast? What about the sonic boom, the literal death knell of the supersonic airplane industry? Turns out, Airbus really kind of has thought of all of these problems, and it looks like they've solved them.
First of all, how do they plan to travel at mach 4.5? This is so cool: what Airbus is currently calling the "Ultra-rapid air vehicle" will have three kinds of engines. For takeoffs and landings it will have regular turbojet engines. These will get the plane off the ground and up to a certain altitude. Once there, the jet engines will be retracted into the fuselage, and the craft will ignite a pair of rocket engines! Sonic boom? not a problem. During its rocket burn, the Ultra-rapid air vehicle will be going almost vertical, so sonic booms will never hit the ground, meaning no one will ever hear them.
Once it has reached its maximum altitude, the craft will use its third engine type: ramjets, tucked under the craft's delta wings. These will allow it to cruise at Mach 4.5. At this speed, it will be able to carry 2 or 3 tons of cargo, or 20 passengers from London to New York in about an hour, a trip that takes about seven hours in a conventional jetliner today.
So, what amazing new technology will allow for this sort of unheard of performance? Well, almost all of the technology in this design is current: turbo jets, rockets, ramjets, a delta wing, these are all things we know how to build. The cleverness of this design lies mainly in the combining of all these technologies into one craft. There is one truly new idea which is crucial to the design, and will allow the plane to control itself during both subsonic and hypersonic flight: it's a pair of fins situated on the outer ends of the delta wings. At subsonic speeds, less than MACH 1, the fins will be oriented horizontally. Once the plane's speed exceeds MACH 1, however the fins will be oriented vertically. This will cause the center of pressure to be maintained at the same point, providing greater stability.