Over the past several years, the British company Reaction Engines Limited (REL), in cooperation with other organizations, has been developing the SABER (Synergetic Air Breathing Rocket Engine) project. The goal of this project is to create a fundamentally new hybrid engine capable of using atmospheric air and a liquid oxidizer. To date, the project has shown some success.
Project development
The concept of the REL SABER engine is based on ideas laid down and partially tested back in the eighties. At that time, British specialists were developing the HOTOL spaceplane, for which a hybrid engine of the LACE type was proposed. That project could not be implemented, but his proposals found application in new developments.
The design of the SABER in its current form began at the turn of the last decades. Some studies have been carried out to shape the overall look of the hybrid engine and determine the path of its development. In the future, REL was able to interest potential customers and get support, which accelerated the work.
By now, REL has completed the bulk of the design documentation and has begun testing individual engine components. Two in-house test facilities in the UK and the USA are used to test products.
Some of the components and concepts have been tested in practice and have proven their potential. In the near future, there should be a full hybrid prototype with all tested components. Its testing under the conditions of the stand will begin in 2020-21. The timing of the appearance of an engine suitable for installation on real aircraft remains unknown. This will probably not happen until the second half of the twenties.
Hybrid design
The SABER product must operate in the atmosphere and beyond, developing the required thrust and providing acceleration to high speeds. Such requirements have led to the need for a special design with specific features. It contains elements characteristic of turbojet, ramjet and liquid-propellant rocket engines. Their use in different combinations makes it possible to have several modes of operation for different stages of flight.
The SABER engine contains several main components housed in a single housing. The head part of the product is given under the frontal air intake with a central body. The latter is made in the form of a conical fairing and can be moved along the axis of the engine to change the air supply to the system. In some modes, the air supply is completely shut off.
A cooling system for the incoming air is placed directly behind the intake. It is calculated that when flying at high speeds, the air inlet should warm up to a temperature of 1000 ° C or higher. A special pre-cooler with several thousand thin tubes filled with liquid helium should reduce the air temperature to negative values in a fraction of a second. An anti-icing system is provided.
The central part of the engine is occupied by the so-called. the core is a special compressor designed to compress the incoming air before it is sent to the combustion chamber. In this respect, SABER is similar to traditional turbojet engines, but it lacks the turbine behind the combustion chamber and some other elements. The compressor is driven by a turbine that takes energy from the air cooling system.
The combustion chamber from the SABER composition is similar to the assemblies of liquid propellant rocket engines. With the help of a turbo pump, it is proposed to supply fuel and an oxidizer - gaseous air or liquid oxygen, depending on the operating mode. In both modes, liquefied hydrogen is used as fuel.
Around the main combustion chamber is a second chamber similar to a ramjet engine. It is designed to work in certain modes and increase the total engine thrust. Like the main combustion chamber, the auxiliary once-through combustion chamber runs on hydrogen.
Now the goal of the SABER project is to develop a hybrid engine with sufficiently high performance and limited dimensions. The finished product should not be larger than the serial Pratt & Whitney F135 - no more than 5, 6 m in length and less than 1, 2 m in diameter. At the same time, versatility and high performance should be ensured.
Depending on the operating mode, such a SABER variant will be able to provide flight at speeds up to M = 25. The maximum thrust in the "air" mode will reach 350 kN, in the rocket mode - 500 kN. The main positive feature will be the ability to solve all problems using a single engine.
Modes of operation
The SABER engine can be used on vehicles of various classes, primarily on aerospace vehicles. The presence of several modes of operation will provide the possibility of horizontal take-off and landing, flight in the atmosphere and entry into orbit.
Takeoff and flight in the atmosphere should be performed using the first mode of engine operation. In this case, the air intake is open, and the "core" supplies compressed air to the combustion chamber. After acceleration to high supersonic speeds, the direct-flow combustion chamber is switched on. The use of two circuits, according to calculations, provides a flight speed of up to M = 5, 4.
For further acceleration, the third mode is used. On it, the air intake is closed, and liquid oxygen is supplied to the main combustion chamber. In fact, in this configuration, the SABER becomes a semblance of a traditional rocket engine. This mode provides maximum flight performance.
Applications
So far, the hybrid engine from REL exists only in the form of documentation and individual units, but its areas of application have already been determined. Such power plants should be of interest in the context of the further development of aviation and astronautics, incl. at the junction of these two directions.
SABER or a similar product will be useful in the creation of promising hypersonic atmospheric aircraft for various purposes. With the use of such technologies, it is possible to create transport, passenger or military aircraft.
The full potential of a hybrid engine can be unleashed with an aerospace plane. In this case, SABER will provide horizontal take-off and landing, as well as an exit to the required altitudes, followed by acceleration and flight into orbit. A spaceplane with hybrid engines should have important advantages that make it easier to operate.
SABER developments can be implemented as separate components. So, REL believes that the developed cooling system of the incoming air can be used for the modernization of existing or for the development of promising turbojet engines. The most interesting results from this can be obtained in the field of high-speed aviation.
At its core, the SABER Project offers a set of key technologies for building a hybrid multi-mode engine. On their basis, you can create a real product of the required dimensions with the specified characteristics. For the first tests, a medium-sized, high-performance SABER is created. If there is interest from customers, new modifications may appear that meet specific requirements.
Practical practice
The first studies and tests within the SABER project took place in the early tenths and were intended to find optimal design solutions. To date, REL has completed the design and has begun the process of testing individual components of the hybrid engine.
A few weeks ago, the development company announced that it was conducting bench tests of the air cooling system. During the test, the air velocity at the inlet to the device reached M = 5, the temperature - 1000 ° C. It is reported that the prototype successfully coped with its tasks and provided a sharp and rapid decrease in flow temperature. However, no specific numbers were named.
Previously reported checks on other engine components. The completion of all these activities allows REL to move on to the assembly of a full-fledged prototype engine. Its appearance is expected in 2020-21. At the same time, bench tests will be held, according to the results of which it will be possible to determine the real development prospects.
Reaction Engines Limited highly appreciates its new project and believes that it has a great future. How objective such assessments are and whether they correspond to reality is not completely clear. The answer to such questions can only be given in a few years, after the completion of all the necessary measures and the creation of a real aircraft with SABER engines.
