Enabling Technologies for Future Tactical High-Speed Combined Cycle Vehicles

Reusable hypersonic aircraft platforms offer the possibility to provide valuable ISR and global strike capabilities to the DoD to bolster national security. Future aircraft powered by Turbine Based Combined Cycle (TBCC) architectures will have the ability to take off from a runway using a traditional turbine propulsion mode and accelerate to hypersonic speed, transitioning from turbine to ramjet and potentially scramjet propulsion modes along the way. There are significant technical challenges for this propulsion architecture since a single propulsion system must operate over a large range of Mach number and dynamic pressure. Most TBCC investigations have focused on “over-under” configurations as studied in DARPA’s Falcon program or side-by-side configurations, requiring two separate engines and engine flowpaths – a turbine and a dual mode ramjet (DMRJ), for example – but these arrangements are not the only possible solutions. Whether the propulsion architecture is an over/under turbine+DMRJ solution or a turboramjet solution, there are several major challenges facing the design of combined-cycle hypersonic systems. These challenges have been explored in several DARPA and USAF programs.  A key fundamental challenge impacting both turboramjet and TBCC architectures is maintaining robust operability over the range of the flight envelope especially at low speeds and high altitudes where pressures in the engine are low. The proposed work will evaluate the possible system level benefits of using selective energy deposition to enhance operability and potentially enable significant system level benefits. These benefits will be studied through engine ground testing and analyzed through trade studies for relevant combined cycle vehicle concepts.