Reaction Engines A2

The Reaction Engines Limited A2 (called the A2) is a design study for a hypersonic airliner. The airliner is intended to provide environmentally-friendly, long range and high capacity commercial transportation. It is being examined as part of the LAPCAT(Long-Term Advanced Propulsion Concepts and Technologies) program of the European Union. The plane is not commercially launched, but Reaction Engines Limited, the British design firm, says it could probably be developed into a working aircraft within 25 years, if there is market demand for it.

Development

The vehicle is intended to have about 20,000 km range and good subsonic and supersonic fuel efficiency, thus avoiding the problems inherent in earlier supersonic aircraft. The top speed is projected to be Mach 5+. It calls for the use of liquid hydrogen as a fuel, which has twice the specific energy of kerosene, and can be used to cool the vehicle and the air entering the engines via a precooler.

The developers say it would be able fly from Brussels to Sydney in about 4.6 hours. The cost of a ticket is intended to be roughly business class level.

"Our work shows that it is possible technically; now it’s up to the world to decide if it wants it."- Alan Bond, managing director of Reaction Engines Limited

Design
Capabilities
Alan Bond told The Guardian newspaper:

The A2 is designed to leave Brussels International Airport, fly quietly and subsonically out into the north Atlantic at Mach 0.9 before reaching Mach 5 across the North Pole and heading over the Pacific to Australia.

Another advantage of the design is that, while the 143 metre-long A2 is much bigger than conventional jets, it would be lighter than a Boeing 747 and could take off and land on current airport runways.

However, the A2 design does not have windows. The heat generated by traveling so quickly makes it difficult to install windows that are not too heavy. One solution Reaction Engines has proposed is to install flat screen panels, showing images of the scene outside.

Engines
The Scimitar engines use related technology to the company’s earlier SABRE engine which is intended for space launch, adapted for very long distance, very high speed travel.

Normally, as air enters a jet engine, it is compressed by the inlet, and thus heats up. This means that high speed engines need to be made of technologies and materials that can survive extremely high temperatures. In practice, this inevitably makes the engines heavier and also reduces the amount of fuel that can be burnt to avoid melting the gas turbine section of the engine, which in turn reduces thrust at high speed.

The key design feature for the Scimitar engines is the precooler, which is a heat exchanger which transfers the heat from the incoming air into the hydrogen fuel. This greatly cools the air, which allows the engines to burn more fuel even at very high speed, and allows the engines to made of lighter, more heat susceptible materials such as light alloys.

The rest of the engine is described as having high-bypass turbofan engine features to give it good efficiency at low speeds.

Specifications
- Range: 20,000 km 
- Length: 143 m 
- Fuel: Liquid hydrogen 
- Passengers: 300 (Single Class) 
- Cruising speed: Mach 5 
- SFC: 0.86 lbf/lb?h @ Mach 5 (40,900 m/s - 4,170 seconds)

FACTS

Design mission

Brussels to Sydney
(via North Pole and Bering straits to avoid supersonic overflight of Eurasian land mass) 
Distance: 18700 km

Flight time: 4.6 hours (under realistic air traffic control conditions)

Reserve range: 5000 km @ Mach 0.9 
Payload 300 passengers (plus baggage)

Vehicle parameters

Gross takeoff mass: 400 tonnes

Fuel mass: 198 tonnes (liquid hydrogen)

Fuselage length: 139 m

Fuselage diameter: 7.5 m

Wingspan: 41 m

Wing area: 900 m2

Performance 
Mach 0.9 cruise Lift/Drag 11.0 (5.9 km altitude) SFC 96.0 kN/kg/s
Mach 5.0 cruise Lift/Drag 5.9 (25-28 km altitude) SFC 40.9 kN/kg/s
Takeoff sideline noise @450m 101.9 dBA

Costs 
Estimated 13 year Development program @ ?22,600 M (2006 prices)
Vehicle sale price ?639 M (assuming production run of 100 vehicles)
One way ticket price (Brussels ? Sydney) ?3940

The above table is from the Reaction Engines website and is subject to different copyrights.

All text is available under the terms of the GNU Free Documentation License.
(See Copyrights for details.) 
If you have more information do contact me!