ORAC
7th Sep 2020, 17:23
From AW&ST. Most of the rest of the article is a long list off previous TBCC and RBCC designs and possible options. None seem to be pinpointed as probable choices and, presumably, that might be up to the bidders.....
https://aviationweek.com/defense-space/aircraft-propulsion/us-air-force-studies-rocket-based-hypersonic-flying-testbed-plan
U.S. Air Force Studies Rocket-Based Hypersonic Flying Testbed Plan
To fully exploit the military utility of hypersonic speed in roles beyond high-speed weapons, the U.S. Air Force is stepping up its decades-long quest to develop a combined-cycle air-breathing propulsion system as an enabler for reusable vehicles.
The plan promises to unlock the wider tactical potential of Mach 5-plus capability and fulfill the long-held ambitions of hypersonic proponents, who since the 1960s have envisioned high-speed vehicles for roles ranging from intelligence, surveillance and reconnaissance to multi-stage-to-orbit launch systems. However, despite numerous studies and ground tests of scaled multicycle propulsion systems, two major questions still face developers: Which is the best propulsion system combination for the reusable hypersonic cruiser role? And how should the chosen concept and its mode transitions be flight-tested at a usefully representative scale?
Now, as the U.S. Air Force enters a fast-paced four-year flight-test program of rocket-boosted hypersonic weapons—both gliders and scramjet-powered—the service is quietly preparing to answer these questions by planning development of an air-breathing demonstrator vehicle. Dubbed Mayhem, the flying testbed plan came to light in August in Air Force Research Laboratory (AFRL) budget planning documents that describe a proposal to develop “multicycle engines.”
First disclosed in a request for information published on Aug. 12 for an “Expendable Hypersonic Multi-Mission Air-Breathing Demonstrator,” Mayhem is expected to be capable of hosting at least three different payloads on each flight. The vehicle was also known early in its inception phase as “a ‘Multi-Mission Cruiser’ due to the focus on sustained hypersonic flight capabilities independent of potential payloads,” says the AFRL.
Although the choice of propulsion system has not yet officially been determined, the AFRL is believed to be leaning in favor of a rocket-based combined cycle (RBCC) over the alternative turbine-based combined cycle (TBCC). For hypersonic applications, rocket-based multicycle concepts have been studied principally for operation at speeds up to Mach 6-plus and altitudes of 100,000-200,000 ft.
The RBCC differs from the better-known TBCC configuration in that the initial acceleration to ramjet/scramjet takeover speed is provided by air-augmented or ducted rocket power rather than an air-breathing turbojet. At higher Mach numbers for vehicles designed for space access, the system would also transition to pure rocket propulsion for the final ascent.......
The AFRL says TBCC options will also be considered for Mayhem. Led by the Air Force, DARPA and NASA, TBCC technology development over the past two decades has focused largely on testing high-speed turbines to close the gap between jet and ramjet/scramjet takeover transition, as well as the control and mechanics of mode transition.
Testing of high-Mach engines, conducted over the past decade under the Air Force/DARPA High-Speed Turbine Engine Demonstration program and follow-on AFRL Supersonic Turbine Engine for Long-Range program, paved the way for the ongoing Advanced Full-Range Engine (AFRE) initiative. Led by DARPA, together with the Air Force, AFRE is testing elements of a TBCC system designed for future runway-based reusable hypersonic vehicles operating up to Mach 5. AFRE builds on previous Mode Transition and Falcon Combined-cycle Engine Technology efforts, the latter completed in 2009.
Combining an off-the-shelf turbine and dual-mode ramjet/scramjet (DMRJ), the AFRE engine uses mass-injection precompressor cooling to boost the maximum speed of the turbine. The water injection system, together with the common turbine/DMRJ inlet, combustor and nozzle, are due to be integrated later this year into the complete TBCC assembly. Freejet testing of the engine is set to occur in 2021......
https://aviationweek.com/defense-space/aircraft-propulsion/us-air-force-studies-rocket-based-hypersonic-flying-testbed-plan
U.S. Air Force Studies Rocket-Based Hypersonic Flying Testbed Plan
To fully exploit the military utility of hypersonic speed in roles beyond high-speed weapons, the U.S. Air Force is stepping up its decades-long quest to develop a combined-cycle air-breathing propulsion system as an enabler for reusable vehicles.
The plan promises to unlock the wider tactical potential of Mach 5-plus capability and fulfill the long-held ambitions of hypersonic proponents, who since the 1960s have envisioned high-speed vehicles for roles ranging from intelligence, surveillance and reconnaissance to multi-stage-to-orbit launch systems. However, despite numerous studies and ground tests of scaled multicycle propulsion systems, two major questions still face developers: Which is the best propulsion system combination for the reusable hypersonic cruiser role? And how should the chosen concept and its mode transitions be flight-tested at a usefully representative scale?
Now, as the U.S. Air Force enters a fast-paced four-year flight-test program of rocket-boosted hypersonic weapons—both gliders and scramjet-powered—the service is quietly preparing to answer these questions by planning development of an air-breathing demonstrator vehicle. Dubbed Mayhem, the flying testbed plan came to light in August in Air Force Research Laboratory (AFRL) budget planning documents that describe a proposal to develop “multicycle engines.”
First disclosed in a request for information published on Aug. 12 for an “Expendable Hypersonic Multi-Mission Air-Breathing Demonstrator,” Mayhem is expected to be capable of hosting at least three different payloads on each flight. The vehicle was also known early in its inception phase as “a ‘Multi-Mission Cruiser’ due to the focus on sustained hypersonic flight capabilities independent of potential payloads,” says the AFRL.
Although the choice of propulsion system has not yet officially been determined, the AFRL is believed to be leaning in favor of a rocket-based combined cycle (RBCC) over the alternative turbine-based combined cycle (TBCC). For hypersonic applications, rocket-based multicycle concepts have been studied principally for operation at speeds up to Mach 6-plus and altitudes of 100,000-200,000 ft.
The RBCC differs from the better-known TBCC configuration in that the initial acceleration to ramjet/scramjet takeover speed is provided by air-augmented or ducted rocket power rather than an air-breathing turbojet. At higher Mach numbers for vehicles designed for space access, the system would also transition to pure rocket propulsion for the final ascent.......
The AFRL says TBCC options will also be considered for Mayhem. Led by the Air Force, DARPA and NASA, TBCC technology development over the past two decades has focused largely on testing high-speed turbines to close the gap between jet and ramjet/scramjet takeover transition, as well as the control and mechanics of mode transition.
Testing of high-Mach engines, conducted over the past decade under the Air Force/DARPA High-Speed Turbine Engine Demonstration program and follow-on AFRL Supersonic Turbine Engine for Long-Range program, paved the way for the ongoing Advanced Full-Range Engine (AFRE) initiative. Led by DARPA, together with the Air Force, AFRE is testing elements of a TBCC system designed for future runway-based reusable hypersonic vehicles operating up to Mach 5. AFRE builds on previous Mode Transition and Falcon Combined-cycle Engine Technology efforts, the latter completed in 2009.
Combining an off-the-shelf turbine and dual-mode ramjet/scramjet (DMRJ), the AFRE engine uses mass-injection precompressor cooling to boost the maximum speed of the turbine. The water injection system, together with the common turbine/DMRJ inlet, combustor and nozzle, are due to be integrated later this year into the complete TBCC assembly. Freejet testing of the engine is set to occur in 2021......