To become economically viable, supersonic cruise civil aircraft need to achieve unprecedented levels of cruise efficiency without excessive penalties to performance in other speed regimes. Cruise efficiency, comprising airframe and propulsion efficiency, needs to be increased by a combined total of approximately 30 percent in order to provide the required supersonic cruise range. In addition, significant reductions in the weight of high-temperature airframe and propulsion systems—on the order of 20 percent—is a key element of achieving practical supersonic flight. New materials and structural systems must achieve these weight targets without affecting life or damage tolerance.

Propulsion Efficiency
In order to achieve low-thrust-specific fuel consumption (TSFC) or high propulsion efficiency, the inlet, fan, core engine, bypass duct, and nozzle must be designed and optimized as an integrated system and installed in an optimal way on the airframe. To determine overall cruise efficiency, drag needs to be taken into account—including inlet-spillage drag, boundary-layer drag, inlet-bypass-bleed drag, and nozzle-aft-body drag. The inlet must achieve high-pressure recovery while maintaining good operability and stability. The engine cycle and the core engine must be designed to produce low-specific fuel consumption and high-specific thrust throughout the aircraft's operating envelope. Since a major portion of the flight of a supersonic aircraft occurs at higher altitudes than subsonic aircraft, a substantial gain may be realized by utilizing a variable cycle engine (VCE) system. A VCE system enables the core-engine-bypass ratio to change during flight from the higher bypass ratio flow required during takeoff to a lower bypass ratio needed for improved performance at supersonic cruise. The higher bypass ratio flow required during takeoff enables the meeting of future takeoff noise regulations with a lower jet noise nozzle that must achieve a high thrust coefficient and efficiency. The propulsion control system must maintain optimum performance and stable operation at all subsonic, transonic, and supersonic operation conditions, and during transients.

Airframe Aerodynamic Efficiency
Aerodynamic design for supersonic cruise aircraft requires efficient performance in concert with environmental and performance constraints.  A low-sonic-boom and low-drag design—including propulsion installation effects—must be approached by incorporating a broad range of technologies and techniques integrated into the overall airframe design.  Advances in an understanding of the complex surface and off-body flows for this vehicle type are required to achieve these unprecedented levels of multi-disciplinary design. Detailed experimental databases will be required to enable advances in computational fluid dynamics analysis and design methods. It is expected that novel and innovative approaches to concept design will be required. In addition, techniques such as advanced active flow control and aircraft morphing should be among the tools used to aid in optimal multi-point operations.

Lightweight, Durable Airframes and Engines
The airframe and propulsion system components for a supersonic aircraft must be lightweight while retaining appropriate durability and damage tolerance. The airframe life requirements for civil aircraft, combined with designs that incorporate slender fuselages and thin wings, indicate that airframe durability and damage tolerance must be studied in conjunction with lightweight material systems and structural configurations. Advanced airframe materials must be incorporated into innovative, light, adaptive structural concepts, optimized with the aid of advanced computational structural analysis tools.

Gas turbine engines will provide thrust during extended supersonic flight. Because of the extended supersonic cruise time with very high inlet air temperature, engine components will experience long-duration operation at high temperatures throughout the cruise portion of the mission. Innovative and advanced cooling approaches will be required in addition to improved materials and coatings to ensure the life and durability of hot-section engine components. Improved materials with thermal barrier coatings (TBC) and environmental coatings will be required for the combustor liners and turbine vanes and blades, and turbine and compressor disks will require improved materials. Creep and thermal mechanical fatigue properties of these hot section components must exceed those in subsonic engines. Combustor exit temperatures during cruise will result in turbine inlet temperatures about 300 degrees F higher than current subsonic engines. Significant weight reduction could be possible by introducing ultra-lightweight sandwich composite material/structural concepts for engine case and duct components. Making these case and duct components more multi-functional could enable other system-level benefits; for example, incorporating passive or active noise, thermal, or flow control features directly into case and duct structures could eliminate non-structural components that would otherwise be required, thereby enabling systems with reduced complexity and fewer parts.