Race to be first with 'son of supersonic'

Paris (CNN) -- It turns out supersonic aircraft are just like buses: You wait years for one, and then two come along at once.

Almost eight years after Concorde touched down for the last time, plane manufacturers and designers at the Paris Air Show have unveiled rival "son of supersonic" concepts.

The first, aircraft manufacturer EADS's Zero Emission Hyper Sonic Transport (ZEHST), will be powered by biofuel made from seaweed, carrying passengers above the Earth's atmosphere and dramatically cutting flight times.

EADS says the plane's three engine types -- conventional jets, rockets and supersonic "ramjets" -- will allow it to speed at Mach 4, around 5,000 kmh.

That would cut the journey time from Paris to Tokyo from its current 11 hours to less than 2.5 hours.

There is a catch: The plane is not due to take-off until 2050.

The second, SonicStar, is billed by its creators Hyper Mach as "the future in flight." It will fly at twice the speed of Concorde, linking New York and Dubai in two hours, 20 minutes -- about the time it would take to watch just one in-flight movie -- and allow passengers to fly around the globe in under five hours.

Hyper Mach CEO Richard Lugg said the plane would make "the other side of the world feel like it's just down the road."

Lugg told reporters he had been inspired as a youngster watching the maiden voyage of Concorde, and had made it his "life's work" to come up with the next generation of hypersonic aircraft.