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Final Report Summary - HEXAFLY (High-Speed Experimental Fly Vehicles)

Civil High-speed transportation has always been hampered by the lack of range potential or a too high fuel consumption stemming from a too low cruise efficiency. Indeed, looking into the performance of classically designed high-speed vehicles, their performances drop nearly linearly with flight Mach number as indicated by the red line on Fig. 1. Over the last years, however, radical new vehicle concepts were proposed and conceived having a strong potential to alter this trend. This innovative approach is based upon a well elaborated integration of a highly efficient propulsion unit with a high-lifting vehicle concept. The realization of both a high propulsive and aerodynamic efficiency is based upon the minimization of kinetic jet losses while striving to the best uniformity but minimal induced velocity for lift creation. The dashed green line in Fig. 1 illustrates the potential of this innovative design methodology whereas the green line indicates what has been achieved as a revolutionary, high speed civil air transportation concepts worked-out along this new approach.

Performing a test flight will be the only and ultimate proof to demonstrate the technical feasibility of these new promising high-speed concepts versus their potential in range and cruise. This would result into a major breakthrough in high-speed flight and create a new era of conceptual vehicle designs.
At present, the promised performances can only be demonstrated by numerical simulations or partly experimentally. As high-speed tunnels are intrinsically limited in size or test duration, it is nearly impossible to fit even modest vehicle planform completely into a tunnel (Fig. 2). Therefore experiments are limited either to the internal propulsive flowpath with combustion but without the presence of high-lifting surfaces, or to complete small-scaled aero-models but without the presence of a combusting propulsion unit. Though numerical simulations are less restrictive in geometrical size, they struggle however with accumulated uncertainties in their modelling of turbulence, chemistry and combustion making complete Nose-to-Tail predictions doubtful without in-flight validation. As a consequence, the obtained technology developments are now limited to a technology readiness level of TRL=4 (components validated in laboratory).

The HEXAFLY project aims to achieve a first maturation and a proof of concept to experimentally flytest these radically new conceptual designs accompanied with several breakthrough technologies on board of a high-speed vehicle. This approach would increase drastically the Technology Readiness Level (TRL) up to 6 (System demonstrated in relevant environment). The emerging technologies and breakthrough methodologies strongly depending on experimental flight testing at high speed can be grouped around the 6 major axes of HEXAFLY:

1. High-Speed Vehicle Concepts to assess the overall vehicle performance in terms of cruiseefficiency, range potential, aero-propulsive balance, aero-thermal-structural integration, etc...
2. High-Speed Aerodynamics to assess e.g. compressibility effects on transition, aerodynamic vehicle shapes with high L/D, stability, etc…
3. High-Speed Propulsion to evaluate the performances of high-speed propulsive devices such as intakes, air-breathing engines (ABE), nozzles (SERN) including phenomena such as highspeed combustion, injection-mixing processes, etc…
4. High-Temperature Materials and Structures to flight test under realistic conditions high temperature lightweight materials, active/passive cooling concepts, reusability aspects in terms oxidation, fatigue, etc…
5. High-Speed Flight Control requiring real-time testing of GNC (Guidance Navigation Control) in combination with HMS/FDI technologies (Health Monitoring Systems/ Fault Detection and Isolation)
6. High-Speed Environmental Impact focusing on reduction techniques for sonic boom and sensitivities of high-altitude emissions of H20, CO2, NOx on the stratosphere.

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