High-speed air-breathing propulsion pushes the limits of Mach numbers
By Bayindir H. Saracoglu, Khaled Sallam and Friedolin Strauss|December 2024
The High-Speed Air-Breathing Propulsion Technical Committee works to advance the science and technology of systems that enable supersonic and hypersonic air vehicle propulsion.
High-speed propulsion technologies made strides this year.
In March, Boom Supersonic of Colorado completed the first subsonic flight of its XB-1, the world’s first independently developed supersonic jet, at the Mojave Air & Space Port in California. The XB-1 demonstrator features technologies including carbon-fiber composites, digitally optimized aerodynamics and an innovative propulsion system for efficient supersonic flight. XB-1 completed its fifth subsonic test flight in October, and Boom founder Blake Scholl said the company remains on track to roll out the first of its Mach 1.7 airliners, Overture, in 2028 with commercial flights beginning in 2029.
In March, GE Aerospace began initial tests of a hypersonic dual-mode ramjet, 11 months after the design phase started. The ramjet showed “a threefold increase in airflow compared to previously flight-tested” demonstrators, GE said in a press release. Meanwhile, in Canada, Space Engine Systems of Edmonton tested near-full-scale versions of its complete DASS GNX turbo-ramjet engine at various air-fuel equivalence ratios in July and August, in order to validate higher-fidelity computational fluid dynamics analyses. Researchers also performed early destruction testing, guiding the incorporation of various cooling methods for improved stability. As of October, integration of the engine into the full-scale Hello-1 X demonstrator vehicle was underway. Hello-1 X is designed to operate at 32 kilometers altitude and reach Mach 5.
In Australia, Hypersonix Launch Systems and Rocket Lab progressed toward the planned flight test of the Disruptive Autonomous Rapid Transit hypersonic aircraft. DART is to be powered by Hypersonix’s SPARTAN hydrogen-fueled scramjet engine, with aerodynamic surfaces for flight control. Plans call for Rocket Lab to launch DART at Mach 7 over the Atlantic Ocean in 2025 as part of the U.S. Defense Innovation Unit’s Hypersonic and High-Cadence Airborne Testing Capabilities Program.
Since January, the University of Queensland in Australia has pioneered inductive and resistive heating of shock tunnel models, including hydrocarbon fueled scramjet combustors, in order to fill in a missing piece of the puzzle of fully replicating flight conditions in short-duration test facilities. Such ground tests allow researchers to more accurately model the effects of flight-realistic wall temperatures on system performance and fundamental flow phenomena before they commence with high-cost flight testing.
In April, the Japan Aerospace Exploration Agency, JAXA, tested scramjet engines at Mach 6 at the ramjet engine test facility at the Kakuda Space Center in Japan. JAXA also conducted scramjet tests adapted for speeds over Mach 8 at Kakuda’s High Enthalpy Shock Tunnel and component tests for the Ramjet Engine for High-Mach Integrated Control experiment.
In Europe, the Netherlands Organisation for Applied Scientific Research, TNO, refined its ultrasound burn rate measurement system for solid -fuel ramjets. The improved design relies on an innovative post-processing method to convert raw test data into burn rates, enhancing researchers’ ability to assess combustor performance during solid-fuel ramjet ground tests. In July, a ground test program in TNO’s aeropropulsion test facility was performed to verify the functionality and performance of the improved system.
The Institute of Space Propulsion at the German Aerospace Center, DLR, continued its classic hydrogen fuel test campaigns within the European Multidisciplinary Design Optimization and Regulations for Low-Boom and Environmentally Sustainable Supersonic Aviation, or MORE&LESS, project for emissions testing. The upcoming sustainable aviation fuel ramjet emission measurements for this project were prepared in the middle of the year. DLR internal campaigns with a different scope, such as high-temperature material testing for scramjet combustion chamber components and development campaigns for a new and improved injector, completed the year’s test schedule.
Contributors: Jesse Kadosh, Joel Malo de Molina, Hideyuki Tanno, Vincent Wheatly and Wolter P.W. Wieling
