Making viable hypersonic commercial airplane designs including a Mach 8 cruise passenger vehicle

HEXAFLY aims to create a multi-disciplinary platform where several breakthrough technologies can be mounted on board for testing in free flight at high speed. This approach will create the basis to increase gradually the Technology Readiness Level (TRL).

The emerging technologies and breakthrough methodologies strongly depending on envisaged flight tests at high speed can be grouped around the 6 major axes:

* High-Speed Vehicle Concepts to assess the overall vehicle performance in terms of cruise-efficiency, range potential, aero-propulsive balance, aero-thermal-structural integration, etc…

* High-Speed Aerodynamicsto assess aerodynamic vehicle shapes with high L/D (lift to drag ratio), aerodynamic manoeuvrability, stability, etc…

* High-Speed Propulsion to evaluate the performance of high-speed propulsive devices such as intakes, air-breathing engines (ABE), nozzles (SERN) including phenomena such as high-speed combustion, injection-mixing processes, etc…

* 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…

* 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)

* High-Speed Environmental Impact focusing on reduction techniques for sonic boom and sensitivities of high-altitude emissions of H20, CO2, NOx on the stratosphere.

Current Mach 8 designs would use about 600 liters of fuel per passenger for a 12000 mile trip. At $1 per liter this would be about $600 per passenger for the fuel. The ticket for the flight would still need to cover the cost of the vehicle, insurance, salaries for all the support and flight staff and profit.

Long-range potential of high-speed vehicles in function of flight Mach number: Red: achievable with classical designs with minimal integration; Green: present designs based upon strongly integrated propulsion-vehicle designs with a potential limit (dashed line)

A paper describes the MR2, a Mach 8 cruise passenger vehicle, conceptually designed for antipodal flight from Brussels to Sydney in less than 4 hours. This is one of the different concepts studied within the LAPCAT II project. It is an evolution of a previous vehicle, the MR1 based upon a dorsal mounted engine, as a result of multiple optimization iterations leading to the MR2.4 concepts. The main driver was the optimal integration of a high performance propulsion unit within an aerodynamically efficient wave rider design, whilst guaranteeing sufficient volume for tankage, payload and other subsystems.

It is conceptually feasible provided liquid hydrogen is used as a fuel. With a GTOW of 400tons and a fuel burn of 180tons, the antipodal range from Brussels to Sydney is achievable within 3 hours.

The prime objectives of the Hexafly free-flying high-speed cruise vehicle shall aim for:

* a conceptual design demonstrating a high aerodynamic efficiency in combination with high internal volume
* a gliding flight at a cruise Mach number of 7 to 8 in a controlled way making optimal use of advanced high-temperature materials and/or structures an evaluation of the sonic boom
* Once conceived, the aerodynamic performance from Mach 8 down to Mach 3 to 5 can be determined as a secondary objective.

The level of complexity and the number of technologies to be potentially integrated largely depends on the affordable size of the flight vehicle. The presently available ground facilities within Europe limit the size to ~1.5m length whereas ~4.5m seems to be an upper limit stemming from presently on-going flight experiments.

Mach 5 Lapcat A2 reaction engines design

SOURCES – ESA Hexafly project, Reaction Engines UK, Hikari Project, Wikipedia