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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 programme of the European Union. The plane has not been commercially launched yet, but Reaction Engines Limited, the Britishmarker design firm, says it could probably be developed into a working aircraft within 25 years, if there is market demand for it.


The LAPCAT A2 concept in the upper atmosphere
The vehicle is intended to have about 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 to fly from Brusselsmarker to Sydneymarker in about 4.6 hours; compared to around a complete day of travel with normal aircraft. The cost of a ticket is intended to be roughly business class level.



Alan Bond told The Guardian newspaper:

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 panel displays, showing images of the scene outside.


The Scimitar engines use related technology to the company's earlier SABRE an engine which is intended for space launch, but here 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 that 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 be made of lighter, but more heat susceptible materials such as light alloys.

The rest of the engine is described as having high-bypass (4:1) turbofan engine features to give it good efficiency and subsonic (quiet) exhaust velocity at low speeds. Unlike SABRE the A2's engine would not have rocket engine features.


  • Range:
  • Length:
  • 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), 0.375 lbf/lb·h @ Mach 0.9 (96,000 m/s - 9,600 seconds)
  • L/D: 11.0@5.9km Mach 0.9, 5.9@25km Mach 5
  • Noise: 101 dBa @ 450m lateral


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