Triple-engine trick, fuels return to supersonic travel

Eight years after shelving Concorde, European firm EADS now thinks supersonic passenger aircraft could make a comeback - but not until 2050.

The Airbus owner believes that a novel combination of propulsion technologies might make supersonic travel both cost-effective and environmentally acceptable. The firm estimates speeds of Mach 4 are attainable - that's nearly 5000 kilometres per hour.

"Concorde was 1950s and 1960s technology. We think the three different propulsion types we're considering - one of which we have perfected for the Ariane rocket - could make this achievable by 2050," says EADS spokesman Gregor von Kursell.

(Image: EADS)

The firm revealed its hypersonic plane design at this week's Paris Air Show. Called the Zero Emission Hypersonic Transport (ZEHST) it would take off conventionally - using two-rear-mounted jet engines burning an algae-derived biofuel - but at an altitude of 6 kilometres would then turn to an Ariane-style liquid oxygen and liquid hydrogen-fuelled rocket engine.

The rocket engine lofts the delta-wing plane - which looks like a scaled-up Lockheed SR71 Blackbird spyplane - to the stratosphere at an altitude of 32 kilometres. Once in that ultra thin air, a "ramjet" slung beneath each of the delta wings handles the flight's Mach 4 cruise phase.

Unlike a regular jet engine, a ramjet has no compressor turbine and uses its sheer speed (they work up to Mach 5) to scoop enough high-pressure air in for efficient combustion. What's critical is that air does not enter a ramjet too fast: front-mounted "shock-cones" slow the airflow to subsonic levels.

If this three-way (jet/rocket/ramjet) propulsion choreography can be made to work, EADS expects Tokyo to London flights to take just 2 hours and 20 minutes.