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Stratospheric Flying Opportunities for High-Speed Propulsion Concepts

Periodic Reporting for period 2 - STRATOFLY (Stratospheric Flying Opportunities for High-Speed Propulsion Concepts)

Reporting period: 2019-12-01 to 2021-05-31

The H2020 STRATOFLY aimed at shortening of one order of magnitude the time needed to fly along long-haul routes, widening the area of operations of the aviation sector to the stratosphere and reducing, at the same time, the climate impact. The final goal consisted in assessing the potential of high-speed transport vehicle to reach TRL6 by 2035, with respect to key technological, societal, and economical aspects.
Benefitting from almost two decades of EU funded projects in the field of high-speed transportation, STRATOFLY started from the promising perspectives highlighted at the end of LAPCAT II project and moved forward studying the key technological and operational issues that must be solved to turn the concept into reality, focusing for the first time on the overall flight trajectory from the point of view of performance, operations and environmental compatibility.
From the technological point of view, STRATOFLY project has worked towards the achievement of the following main objectives:
1) Optimisation of innovative aircraft concepts: achieved through an improved aero-thermo-propulsive-structural characterization of the MR3 waverider concept throughout all mission phases.
2) Maximisation of the potential of embedded high-speed propulsion systems (six Air Turbo-Rocket (ATR) and a Dual-Mode Ramjet (DMR) achieved through (i) subsystem modelling, (ii) High fidelity numerical simulations and combustion experiments for pollutant and GHG emissions and (iii) Acoustic test campaigns coupled with high-fidelity simulations.
3) Integration of multi-functional systems achieved by designing the Thermal and Energy Management system, which integrates Propulsive, Propellant, Thermal Control, Thermal Protection, Electrical and Environmental Control Systems.
4) Minimisation of environmental impact, achieved thanks to (i) the exploitation of liquid hydrogen, (ii) the optimization of the propulsive system in cruise, (iii) the identification of noise reduction strategies (iv) the upgrade of atmospheric and climate impact models (v) and the trajectory optimization.
Besides these technical challenges, the H2020 STRATOFLY project addressed operational aspects, which are crucial for society:
5) Economic viability
6) Human factors, social acceptance, and safety
The overview of the result is here reported per each project objective:
1) Optimize innovative aircraft concepts. The multi-objective structural optimization of the adopted multi-bubble architecture revealed a reduction of about 40% in mass wrt the value estimated at the beginning of the design process. The aerodynamic characterization allowed for the generation of a comprehensive and reliable aerodynamic database, encompassing all flight regimes, which includes the contributions of the clean configuration, of the internal flow-path and of each flight control surface. The trajectory optimization, coupled with a dedicated market analysis has shown the possibility to attract 20% of the passengers on medium and long-haul routes (5000 to 20000 km).
2) Maximise of the potential of embedded high-speed propulsion systems. The complete integration of the propulsion subsystem led to the design of a fully shrouded nozzle configuration for the MR3. The analyses show the need to adopt noise abatement strategies, which may allow the MR3 to comply with current noise regulation and with the ACARE 2050 goals The exploitation of LH2 guarantees a fully decarbonized flight and the redesign of the DMR combustor guarantees a reduction close to 80% in NOx levels emissions in cruise condition, with respect to the initial baseline, while NOx emission during the LTO cycle seems to be very low (always less then 4 g of NOx per kg of LH2 in subsonic conditions).
3) Integration of multi-functional systems. The Thermal and Energy Management system revealed a high-power generation capability during the whole set of flight conditions (when engines are running), assuring more than 1MW of generated secondary power for on-board subsystems. This is sufficient to cover electrical loads requests, which are in the range of 200 – 800 kW depending on the flight phase.
4) Minimize environmental impact. Although water vapour is destroyed chemically at stratospheric altitudes, the methane oxidation and chemical recombination overcompensate the destruction and the ozone RF, which is positive for subsonic aviation is negative for supersonics and becomes positive for hypersonics, since the shortwave warming effects dominates. A clear indication could be given that a higher cruise altitude leads to a larger climate impact, because the water vapour accumulation in the atmosphere increases. This effect was shown to be stronger than fuel consumption changes due to different efficiencies at different altitudes.
5) Economic viability. Accurate analyses confirmed the economic feasibility of STRATOFLY MR3 which, expected with an enter into service in 2050 may be operated with ticket prices similar to those currently paid for business class on long-haul routes. The ticket price may be further reduced if the hydrogen sector will increase its productive rates.
6) Human Factors, social acceptance and safety. Dedicated mission analyses and casualty areas analysis demonstrated that the possibility to fully support the descent and landing phases with propulsive power, can improve safety levels and thus, the social acceptance. The compliance with human factors are carefully considered when designing the cabin internal layout, when planning the flight schedules, and when planning all mission phases.
STRATOFLY Project contributed to progress beyond state of the art, in several disciplines, from propulsion to aerothermodynamic, from hydrogen chemistry to climate impact. Simulation and test campaigns in the fields of jet-noise, high-speed combustion (liquid hydrogen) and climate impact science have contributed to increase the social acceptance of the high-speed aircraft concept, which has been proved to be environmentally compatible for noise levels (adopting adequate jet noise reduction techniques) and for NOx emission indexes during landing and take-off cycles. Furthermore, the decarbonization of the entire mission and the complete abatement of sonic boom annoyance over inhabited regions assures social acceptance. Beyond civil aviation, the results achieved in the field of the STRATOFLY project can contribute to a European paradigm shift in the Energy Sector, by demonstrating the advantages of exploiting liquid hydrogen instead of hydrocarbon as aircraft fuel, thus enhancing the innovation capacity and creating new market opportunities for greener liquid hydrogen production.
STRATOFLY Dissemination Event at Science is Wonderful Exhibition (Brussels, September 2019)
1:100 scale model of STRATOFLY MR3