European Hypersonic Cruise Passenger Study Set For New Tests

By Guy Norris

A team of European hypersonic researchers are preparing for wind tunnel tests of a Mach 8 concept that is designed to prove technologies for the development of future ultra-long-range, high-speed commercial vehicles and air-breathing space launch systems.

Funded under Europe's Horizon 2020 research and innovation program, Stratofly (Stratospheric Flying Opportunities for High-speed Propulsion Concepts) is targeted at fostering hypersonic capabilities for a 300-seat passenger vehicle cruising above 30 km (19 mi.) to TRL (technology readiness level) 6 by 2035. The project builds on the Lapcat waverider concept developed under earlier programs by the European Space Agency/European Space Research and Technology Center.

Using the 310-ft.-long Lapcat II MR2.4 version as a reference vehicle, the 30-month Stratofly effort is focused on classic hypersonic technology challenges such as propulsion integration, hot structures and thermal management. In addition, with environmental concerns at the forefront in Europe, the project also includes sustainability considerations such as fuel-burn efficiency, noise and emissions reductions, as well as operational issues such as life-cycle costs, safety and certification.

Coordinated by The Polytechnic University of Turin, Italy, the project team believes that sustainable hypersonic travel is feasible through the use of liquid hydrogen fuel and new trajectories that would enable flights from Europe to Australia in 3 hr. Specific targets include 75-100% CO2 reductions per passenger kilometer and 90% reductions in nitrous oxide (NOx) compared to current long-range transport aircraft. A version of the vehicle could also be adapted into the first stage of a two-stage-to-orbit space launch system, says the group.

Other members of the 10-strong consortium include the von Karman Institute for Fluid Dynamics in Belgium, which is focused on propulsion and noise; the Netherlands Aerospace Center, NLR, which is also part of the noise study; and CIRA, the Italian aerospace research center, which is conducting high-speed flow analysis. Propulsion systems and climate impact input is provided by Germany's DLR research organization, while ONERA, the French aerospace research center, is focused on emissions as well as plasma-assisted combustion in the vehicle's combined-cycle propulsion system. Sweden's FOI defense research agency is also part of the plasma combustion study.

The French National Center for Scientific Research is also evaluating the vehicle's potential climate impact, particularly in areas such as the effects of water droplets from the exhaust in the upper atmosphere. Studies of the overall business plan, human factors and hypersonic traffic management are being conducted by the Hamburg University of Technology, while the Spain-based Civil Engineering Foundation of Galicia is focused on structural analysis and optimization.

Like the original Lapcat design, the Stratofly MR3 waverider configuration is dominated by a large elliptical inlet and an integrated nozzle aft located between two canted tail fins. For takeoff and acceleration up to Mach 4.5, the vehicle is powered by six air turbo ramjets (ATR, also known as air turbo rockets) in two bays of three, each fed by secondary inlets in the primary intake. Above this speed, sliding ramps cover the ATR inlets as the vehicle accelerates and transitions to a dual-mode ramjet/scramjet (DMR) for the next phase of the flight.

The DMR is housed in the dorsal section, nested between the ATR ramjets, and is designed to operate in ramjet mode to above Mach 5 and scramjet mode up to Mach 8. The scramjet will incorporate a plasma-assisted combustion system to maintain the stability of the flame front and prevent the potential for flameouts. Tests of the plasma system in a combustor will take place later this year at ONERA, where supersonic combustion testing also took place for Lapcat. The tests will be conducted in November-December at ONERA's ATD5 facility and will focus on inlet conditions at Mach 3.7.

Also planned for later this year is a test of the full vehicle in the high-enthalpy wind tunnel at DLR's Gottingen research facility. Testing at DLR will run through September 2020 and is expected to target similar free-stream conditions as those tested on Lapcat II—around Mach 7.8. The work will assess aerothermodynamic characteristics and be used to validate the results of earlier computational fluid dynamics analysis of the MR3 design, which incorporates external and internal differences against the reference vehicle.

“We elevated the canard [a retractable feature for lower-speed flight] and redesigned the vertical tails,” says Davide Ferretto, a research assistant on the Stratofly team from The Polytechnic University of Turin. “We also redesigned the leading-edge radius of the inlet for increased efficiency as it feeds both propulsion systems.” As part of the redesign, the enclosed passenger compartment, which was divided into two sections running along each side of the vehicle, has been combined into a single cabin in the lower lobe of the fuselage.

https://aviationweek.com/propulsion/european-hypersonic-cruise-passenger-study-set-new-tests