EADS has used the opening day of the 2011 Paris Airshow to showcase an aircraft of the future concept which contemplates speeds beyond Mach 4, meaning it could make the run from Tokyo to London in under 2.5 hours. The ZEHST (Zero Emission Hypersonic Transport) study incorporates three different propulsion systems and could carry passengers to heights of 100,000 feet (32 km) while still meeting the projected European Commission targets for reduced noise, CO2 and NOX emissions by 2050. Blue sky indeed!

The study by EADS INNOVATION WORKS and ASTRIUM (the space technology arm of EADS) builds upon the Spaceplane project which began in 2006 and was presented in Paris as a full-scale mock-up in 2007. Similar in its vision to Virgin Galactic, the Spaceplane is designed to carry four passengers and a pilot to an altitude of over 100 km for the view of a lifetime. ZEHST in contrast, is designed as a commercial transport system for long haul flights - though "long haul" becomes a little redundant if you can reduce what is now a 10-12 hour flight to around two hours.

The ZEHST project is centered around evaluating the design and technological challenges of achieving these ambitious goals. These include the investigation of smart materials that could deal with the incredibly high temperatures the plane would be subject to (we're talking 1000 degrees Celsius) and examining ways to reduce sonic booms as well as minimizing the impact of emissions on the ozone layer.

The viability of hydrogen as the main fuel is also being evaluated, which brings us to what is perhaps the most interesting aspect of the concept - the three tier propulsion system. Stage one would see turbojet engines running on biofuel used for a conventional runway take-off and climb to 5 km at speeds of Mach 0.8. Hydrogen/liquid oxygen-powered rocket engines would then kick-in for a steep climb to around 23 km and a speed of Mach 2.5. In the final phase two air breathing, hydrogen fueled ramjets would take over to take the aircraft to "an optimum Mach number in terms of fuel consumption beyond Mach 4" and an altitude of around 32 km. On the way down the turbojets would be re-engaged at a height of 10 km to facilitate a conventional landing. Managing the transition between these phases is another of the big challenges faced by the project.

In all of this, EADS says the aim is to give passengers a "normal" flight experience where they would be subject to no more than 1.2g.

So when can we expect to see some of these ideas get off the ground? 2050 is the ballpark time-frame, but a small scale demonstrator could be a reality by 2020.

The ZEHST study has been undertaken in partnership with ONERA and is sponsored by the French Agency Direction Generale de l'Aviation Civile (DGAC).

Source: EADS