Hypersonic green machine EADS’ Mach 4 airliner

HYPERSONIC GREEN MACHINE

EADS’ revolutionary proposal for a Mach 4 airliner uses spaceplane technology to achieve minimum emissions and noise.

AT this year’s Paris Air Show EADS presented a concept study for a highspeed transport system. This Mach 4 aircraft is intended to fly long-haul routes – for example Tokyo-Paris or Tokyo-Los Angeles – in less than 2 hrs 30 min, while having a very limited impact on the environment and being operated as a standard aircraft.

EADS Innovation Works and Astrium – in partnership with the French national aerospace research laboratory ONERA – have launched a feasibility and systems study sponsored by France’s Directorate General for Aviation (Direction Générale de l’Aviation Civile – DGAC). Called ZEHST (Zero Emission High Supersonic Transport). This high-speed transport concept definition draws on know-how from Astrium’s suborbital spaceplane project and is one of the projects incorporated in EADS Innovation Works’ eCO2avia activities, which also include such efforts as demonstrating the feasibility of using biofuels and electric power for aviation.

Reducing travel times for passengers is a key driver in the development of the world’s air transportation system. Not only will longhaul airliners of the future have to be fast, they will need to meet the air transport industry’s ambitious environmental protection goals, including those spelled out in the European Commission’s roadmap ‘Flightpath 2050’. This European Commission report sets the targets of reducing aircraft CO2 emissions by 75 per cent, along with reductions of NOx by 90 per cent and noise levels by 65 per cent, compared to levels of the year 2000.

ZEHST demonstrators are planned for the end of the decade, to be followed by development towards an operational vehicle. Numerous technological challenges need to be mastered so that future high-speed commercial transport systems can achieve the required performance while also meeting tomorrow’s environmental constraints. Studies have to identify how requirements and objectives can be aligned with technical aspects.

Three steps

An initial ZEHST propulsion system concept based on liquid hydrogen as the main fuel has been conceived as the first step towards a basic reference solution. The next steps in this long-term project will then be to validate the environmental signature of this concept and specifically its propulsion system architecture. The type of fuel to be used will eventually be selected in the light of its environmental performance but also its production and distribution, while also addressing energy management and the concept’s acceptance by future passengers, crew and the public. Tests and demonstrators will be critical milestones towards the completion of this second phase of the roadmap. The third step of the project will then deal with product requirements of a high-speed aircraft capable of flying a hypersonic intercontinental mission while still being ‘green’, quiet and operated as a year 2050-standard aircraft.

“The initial concept represents a propulsion system architecture which is driven by flight safety considerations and by the requirements to minimise exhaust gas and noise emissions, in particular to mitigate the sonic boom,” said Jean Botti, chief technical officer of EADS. “We are on a very early stage with this research programme. First series planes flying with technology resulting from this concept will not fly before 2040.”

Three engine types

Three types of engines are operated in sequence for the various flight phases of a long-range flight at hypersonic cruise speed. Mastering the ascent and descent phases of the flight profile will be eased by

the know-how derived from research carried out on the Astrium spaceplane over the past five years.

The thrust required for the ZEHST’s initial flight phase – beginning with the normal takeoff from a standard runway through to the initial cruise, the climb to 5km altitude and acceleration to Mach 0.8 – will be provided by two high-power, low-bypass turbojet engines without afterburners (reheat), that operate on biofuel.

Ignition and operation of two small liquid hydrogen / liquid oxygen-powered booster rocket engines followed by the ignition of a larger one (derived from the types used in the Ariane commercial launch vehicle) enable the aircraft’s continued steep climb towards the cruising altitude and the acceleration through the transonic speed regime up to a speed of Mach 2.5.

Once sufficient speed has been reached and an altitude of 23km attained, two air-breathing hydrogen-fuelled ramjets are employed for the aircraft’s cruise flight at beyond Mach 4, the optimum Mach number in terms of fuel consumption, and at an altitude of up to about 32km. Ramjets have no rotating parts – air is rammed into the combustion chamber using the forward speed of the aircraft and slowed to subsonic speeds by an inlet cone before combustion. Ramjets can produce sufficient thrust only when an aircraft is already moving faster than Mach 2.

When approaching the destination, a gliding descent and deceleration to subsonic speed will be performed, followed by the re-ignition of the aircraft’s turbojets at an altitude of 10km for the approach to a normal landing – with sufficient thrust output to allow for the possibility of a runway go-around or diversion to another airport should it be necessary.

An overarching design criterion of the ZEHST concept is that passengers should have a ‘normal’, comfortable in-flight experience without requiring any special equipment or training. For a short period of time during the steep rocket engine-powered climb and acceleration, ZEHST passengers would feel mild acceleration forces not exceeding 1.2g.

The ZEHST programme is in part a product of a French-Japanese cooperation, as the Groupement des Industries Françaises Aéronautiques et Spatiales (GIFAS) and the Society of Japanese Aerospace Companies (SJAC) signed a Supersonic Technologies Cooperation Agreement during the 2005 Paris Air Show. n Visit: www.eads.com