Mach 4.5, in case you were wondering, is 4.5 x the speed of sound. For reference, the now defunct Concorde flew at up to Mach 2. BBC News reports on Airbus’s patent for a hyper sonic airplane: Airbus has won a patent for a hyper sonic passenger plane which could potentially fly from London to New York in an hour. Dubbed Concorde 2.0, the jet would be capable of flying more than four times the speed of sound.
According to the documents, the jet would reach speeds as high as Mach 4.5, or four-and-a-half times the speed of sound. That compares to Mach 2 for Concorde. The patent application says that the air plane would use a variety of engines that would serve different purposes and power would come from hydrogen stored on board. Two turbojets under the fuselage and a rocket motor in the rear would be used during take-off. It would lift off vertically like a Space Shuttle. Once launched, the turbojets would be shut down and retracted and the rocket motor would then kick in to climb to an altitude of more than 100,000 feet. Then ramjets, more usually used on missiles, would be ignited and the flight would reach a top speed of Mach 4.5