Community Research and Development Information Service - CORDIS

Periodic Report Summary 2 - HEXAFLY-INT (High-Speed Experimental Fly Vehicles - International)

Project Context and Objectives:
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. 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-INT project aims to test one of these radically new conceptual designs accompanied with several breakthrough technologies on board of the high-speed vehicle in free flight. This approach will drastically increase the Technology Readiness Level (TRL) up to 6 (System demonstrated in relevant environment).The emerging technologies and breakthrough methodologies strongly depending on flight tests at high speed can be grouped around the 6 major axes:

1. 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...
2. High-Speed Aerodynamics to assess aerodynamic vehicle shapes with high L/D, aerodynamic manoeuvrability, 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 high-speed 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.
To mature this flight testing, a scientific mission profile has been worked within a precursor Level 0 project called HEXAFLY followed by a proof-of-concept based upon:
- a preliminary design of a high-speed flight test vehicle covering the 6 major axes
- selection and integration of the ground-tested technologies developed within LAPCAT I & II, ATLLAS I & II and other national programs
- identification of the most promising flight platform(s)
which allowed addressing following items:
- identification of potential technological barriers to be covered in the HEXAFLY-INT project
- assessment of the overall ROM-costs to work the project out in the HEXAFLY-INT project
- the progress and potential of technology development at a higher TRL
The vehicle design, manufacturing, assembly and verification will be the main driver and challenge in this project in combination with a mission tuned sounding rocket. The prime objectives of this free-flying high-speed cruise vehicle shall aim for
- a conceptual design demonstrating a high aerodynamic efficiency in combination with a high internal volume
- a positive aerodynamic balance 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 impact by deploying dedicated ground measurement equipment
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 in the US and Russia. However, the trade-off study within HEXAFLY took into account the following issues:
• minimum needed internal volume to contain all necessary subsystems for a free-flying vehicle
• a modest financial envelope for hypersonic flight testing (~25M€ compared to the >250M€ cost for X-51 in the USA),
• the know-how and expertise acquired recently through the German SHEFEX-I/II projects and the Italian USV project
• the affordable launchers presently available,
• the existing databases generated within ATLLAS I/II and LAPCAT I/II
• the high altitude expertise and related flight control acquired in flight during the SHEFEXII flight and theoretically and in ground experiments during FAST20XX
• the availability of large test facilities in Russia and Australia for risk-reduction
resulted finally into a most promising choice of a ~3m long flight vehicle.
Besides the vehicle and platform definition, the suitability of the launch site and test range was assessed in terms of potential limitations on the mission and scientific objectives, i.e. flight corridors, TTC (telemetry, tracking and command), safety aspects (termination) and recovery.
Besides the high-speed flight experiment, an additional flight experiments will be performed to cross-check the viability of the vehicle concept for later deployment as passengers’ aircraft i.e.:
- low-speed flight experiments in the Danger Area 451 (Univ. of Sydney) to verify the take-off and landing potential of the waverider based vehicle

Project Results:
1.2.2 Launcher Preparation and Launch Campaign
In order to maximize chances for telemetry data reception during the experimental flight, the vehicle shall be launched at the highest possible eastward azimuth from CLA, taking into account flight safety restrictions. The heading of the range border towards east is 80 deg and shall not be exceeded during the flight, which requires keeping some margins to this border for potential deviations from the nominal trajectory and reaction time for the ground controlled flight termination system. The assessment of maximum launch azimuth has started and will continue during the third period. A redundant telemetry coverage during most parts of the experimental flight is possible with TM stations at CLA, Natal and a mobile TM station close to Fortaleza providing a range capability of at least 280 km for TV and TM signal reception, however the range requirement is increasing for launch azimuths less than 80 deg. LII investigations on utilizing a 2 m dish mobile TM station has shown that TM data link at 3.3 Mbit/s is possible for the 80 deg azimuth trajectory, but TV link is limited to 150 km. The Nov. 2015 failure of a S40 motor in the SARA mission at CLA has caused grounding of the similar S43 motor and requires a requalification program including x-ray surveys and static firing. As no potential alternative booster could be identified, it was agreed by the IAB, RAB of Europe, Russia and Australia to pursue discussions with DCTA and AEB. The lack of vibration data from the S43 motor has blocked the structural analysis and layout of the payload. At the end of the second period DLR received high frequency acceleration sensor data from the 6th S43 static firing measured on the front dome, enabling the determination of the vibration spec. On the re-entry trajectory for the propelled concept, LII optimized the trajectory of the EFTV insertion into the engine research window to attain the highest possible values of Mach number and flight altitude at the entry to the engine research window.

1.2.3 Experimental Flight Vehicle and In-Flight Measurement
Considerable progress towards the critical design review was made regarding the experimental flight vehicle and the inflight measurements. In particular, the following progress and achievements were made:
• Characterization of the load cases on the ESM and EFTV structure and equipment during the flight trajectory including FE Model verification, stiffness requirement verification and structural re-design, frequency response analysis at spacecraft level (EFTV+ESM) and frequency response analysis on the equipment.
• Evaluation of the current vehicle configuration in terms of: materials, equipment and sensors installation, interface control document definition, CoG and Moments of Inertia determination, preliminary IMU performance specification.
• Refinement of Guidance and Control algorithms (GNC) based upon the available aerothermal-structural loads, interface and mission requirements, actuators and inertial platform characteristics.
• A conceptual design of the ESM cold gas system was conducted and the electrical and mechanical interfaces between the EFTV and ESM were defined.
• Hot structure parts were optimized including an increase of the aileron thickness at critical positions, a redesign of the torsion bar and its interface as well as the leading edge segments.
• The technical specifications of the servo actuator were frozen and the procurement process could be started.
• Radiation pattern simulations of the TM and TC antennas were performed based on verified antenna characteristics to allow for antenna position optimization with respect to the various flight trajectories.
• The concept of the instrumentation and data acquisition has been further improved and a detailed map of sensor position and cabling was designed.
• The data acquisition unit was further optimized to meet the requirements regarding mass and volume, sampling rate, number of channels and system architecture. Bandwidth requirement estimations were conducted.
• The Flush Air Data System (FADS) reached CDR level with further investigations, including wind tunnel tests, starting after freezing of the internal configuration.

1.2.4 Full-Scale Experimental Models for Ground Tests
Two models were produced in CIAM for power concept research in reported period. The first one is thick-walled combustion chamber from copper alloy for long-time connected-pipe tests in T-131 in TsAGI. The second one is high thermal resource facility module for free-stream tests in C-16VK in CIAM.
Based on data obtained in EFTV aerodynamic experiments in T-116 the elements of intake transition grits were manufactured in TsaGI. For measuring the temperatures on the model surface, thermocouples were installed on the upper (leeside) and the lower (wind-side) surfaces of the model.

1.2.5 Ground-Based Experimental Support and Verifications
Several aerodynamic and aero-propulsive tests of the models had been performed by the Russian partners. The full-scale aero-propulsive wind-tunnel model has been tested for a short duration in the C-16VK facility at CIAM. A positive effective thrust of the engine has been repeatedly measured at several regimes of engine operation. The combustion chamber model (internal flow-path with injectors) has been tested in the T-131 facility at TsAGI. Self-ignition of hydrogen was achieved at all investigated conditions corresponding to free-steam Mach number M=7.4. Only at low values of the ER burning wasn’t stabilized.
Three aerodynamic test campaigns of the EFTV Powered Concept aero-model were performed in the T-116 wind tunnel. The 1st campaign showed that the intake of the model with smooth internal surface started just in a very limited range of T-116 test regimes due to low free-stream perturbation in T-116 and laminar boundary layer condition on the intake surface. Several variants of boundary layer tripping during a second test campaign enlarged the operational domain of the intake, and the results became closer to that obtained in other wind tunnels. The 3rd test campaign showed that, in order to be effective, transition grit should consist of the roughness elements dispersed on the intake surface in lateral direction.
Two aerodynamic test campaigns were performed for the EFTV Glider Concept. During the 1st campaign, aerodynamic characteristics and controls effectiveness were determined. The 2nd test campaign of the model was dedicated to study of different transition grits influence on boundary layer transition on the Glider surface.

1.2.6 Simulation Support and Verifications
The “Simulation Support and Verifications” groups all numerical analyses needed as support to the overall mission scenario with respect to ‘Aero-Thermal Simulations’, ‘Thermal and Structural Analysis’ and ‘Trajectory, Flight Mechanics and Control’.
Regarding aero-thermal simulations, the following main activities were achieved:
• simulating by CFD the separation of the EFTV glider from the support module ESM, with the aim to evaluate the aerodynamic effect of the asymmetric payload with respect to separating the EFTV from this support module
• analysis of aerodynamic behaviour of EFTV and assessment of its performance, in terms of efficiency, stability and manoeuvrability, in view of the needs of Flight Mechanics and GN&C
• definition of a CFD test matrix and execution of accurate viscous (fully turbulent and three-dimensional) CFD simulations
• definition of TsAGI T-116 wind tunnel test matrix and follow-up of the test campaign
• rebuilding some of the transition experiments of TsAGI T-116 at TsAGI by CFD to discriminate transition phenomena from strong secondary flows induced at the nose and leeward fuselage.
• setup of an aerodynamic model (AM) for the train EFTV+ESM and the glider EFTV, with related model of uncertainties (MU), based upon a more populated aerodynamic database with viscous effects and results of wind tunnel campaign at TsAGI T-116 facility
• provision of this model with related uncertainties and MCI data to Flight Mechanics for the calculation of the re-entry nominal trajectory of the train from apogee up to ESM separation with related dispersion (and with the application of the attitude control by Cold Gas System), followed by the EFTV glider nominal trajectory with related dispersion and for the design of Flight Control System
• extraction of hinge-line moments for the glider aileron by CFD simulations in flight conditions to design the actuation lane and to select the actuator device
• The radiative equilibrium wall temperature decreased more than 100 K if the emissivity of the aeroshell was increased from 0.4 to 0.9. So, the utilization of high emissivity thermal paints is thus a potential route to reduce the aeroshell thermal loads.
• A dedicated CFD evaluation of the EFTV including the telemetry antenna on the fuselage windward side was performed which ultimately confirmed that the antenna withstands the thermal loads.
With respect to thermal and structural analysis, the following progress was made
• Thermal analysis leading to a proper material selection for EFTV and ESM taking into account the effects of different aerothermal environment considered (effect of margin uncertainty and laminar-to-turbulent transition evaluated);
• Thermal Protection System definition for EFTV and ESM
• Internal equipment heating, due to conduction from the hot structure via the fixations, radiation from the hot structure, own dissipative power, and proposed different solutions for the thermal internal insulation
Progress on trajectory, flight mechanics and control entailed
• Re-entry trajectory for the full train on the basis of a Cold Gas System mounted onto the ESM for exo-atmospheric attitude alignment
• Alternative trajectory analyses for the EFTV with banking along with preliminary Monte-Carlo simulations to anticipate the overall effects of dispersions
• mission feasibility analysis with respect to the Mission Requirements, with latest configuration;
• contribution to the definition of the requirements for the GNC subsystem, in terms of preliminary actuator and inertial platform specifications.

Potential Impact:
- define the requirements and operational conditions for the scientific mission;
- perform a detailed layout of a flight vehicle able to test technologies along the 6 major axes;
- define the required flying platform with the needed adaptations;
- carrying out extensive on-ground tests and numerical simulations to reduce uncertainties and risks; preferably on full-scale flight representative models;
- manufacturing the experimental flight test vehicle along with the needed adaptations to the launcher;
- assembling, integrating, verifying and testing the experimental payload and the related launcher;
- carry out the flight experiment and collect the data;
- perform a post-flight analysis;
- disseminate the results.
List of Websites:
www.esa.int/techresources/hexafly_int

Related information

Reported by

EUROPEAN SPACE AGENCY
France

Subjects

Transport
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