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This paper will provide a comprehensive and detailed description of the multidisciplinary activities performed by the Italian Aerospace Research Center (CIRA) and Tecnosistem-Engineering and Technology (TET) to design the hypersonic non-propelled glider Experimental Flight Test Vehicle (EFTV) and its experimental flight trajectory. A synthesis of the relevant aspects, means and methodologies used for assessing EFTV’s aerodynamic behaviour and aerothermodynamic features, materials and thermal protection system, structural loads and stress analysis, and trajectory is reported. All these aspects depend on each other and together they lead to the definition of the vehicle and the mission matching the initial requirements. Different approaches for the different phases of the flight are also defined. The final aim of the activity is to define methods and standards for different critical aspects of high-speed flying systems and then to collect valuable flight data to validate methods and technologies in a dedicated experimental flight campaign.

This paper discloses the architecture and related performance of an environment control system designed to be integrated within a complex multi-functional thermal and energy management system that manages the heat loads and generation of electric power in a hypersonic vehicle by benefitting from the presence of cryogenic liquid hydrogen onboard. A bleed-less architecture implementing an open-loop cycle with a boot-strap sub-freezing air cycle machine is suggested. Hydrogen boil-off reveals to be a viable cold source for the heat exchangers of the system as well as for the convective insulation layer designed around the cabin walls. Including a 2 mm boil-off convective layer into the cabin cross-section proves to be far more effective than a more traditional air convective layer of approximately 60 mm. The application to STRATOFLY MR3, a Mach 8 waverider cruiser using liquid hydrogen as propellant, confirmed that presence of cryogenic tanks provides up to a 70% reduction in heat fluxes entering the cabin generated outside of it but inside the vehicle, by the propulsive system and other onboard systems. The effectiveness of the architecture was confirmed for all Mach numbers (from 0.3 to 8) and all flight altitudes (from sea level to 35 km).

Airbreathing hypersonic flight is an ongoing challenge with the potential to cut air travel time and provide cheaper access to space. Waveriders are potential candidates for achieving hypersonic cruise speed or proper acceleration within the atmosphere. Current research tends to focus on key issues like flight mechanics, thermal loading, aero-elasticity, aerodynamic and aerothermodynamics at hypersonic speeds. Design problems in each of these areas must be solved if the design of a hypersonic waverider-like vehicle is to be viable. In this framework, the HEXAFLY-INT project aims at testing in free-flight conditions an innovative gliding vehicle with several breakthrough on-board technologies to be launched along a suborbital trajectory. Its preliminary conceptual design has been carried out by means of tools suitable to design vehicles to fly in hypersonic conditions. Aerodynamic and trajectory analyses have been carried out to assess mission capability as well. Once the aeroshape and the reference mission have been identified, system and sub-system analysis have been performed to close the system loop. The main results of the design analysis carried out during the preliminary phase of the study (such as vehicle aerodynamics and aerothermodynamics, re-entry trajectories, structures and mechanisms, and on the overall system, as well), are presented in this work.

The purpose of this paper is to describe the procedures used to evaluate structural and thermal loads experimented by the HEXAFLY-INT Experimental Flight Test Vehicle (EFTV) and Experimental Service Module (ESM) during the ascent phase of the flight trajectory. The HEXAFLY-INT payload will be launched by a rocket in a suborbital trajectory having an apogee at around 90 km and Mach 8. During this phase the structure is subjected to the launcher environment that includes several events which generates static, random and sinusoidal acceleration and by a fixed thermal distribution. The load conditions due to mechanical loads have been defined by dynamic analyses by means of MSC Nastran software. Thermal loads have been identified by using Ansys Workbench software. The thermo-structural load conditions due to launcher environment have been defined by means of an interpolation procedure for transferring thermal distribution from Ansys to the Nastran FE Model.

The design of the wing leading edge of re-entry vehicles is a very challenging task since severe aerothermal loads are encountered during the re-entry trajectory. Hence, advanced materials and structural concepts need to be adopted to withstand the elevated thermal gradients and stresses. Furthermore, particular attention must be paid to the design of hot areas and connections between hot and cold areas of the structure, where the presence of major thermal gradients associated to significant thermal expansion coefficients variations, can lead to damage onset and failure. In order to face this issues, Ceramic Matrix Composites are generally employed as passive hot structures due of their capability to operate at elevated temperatures retaining acceptable mechanical properties. In the present work a novel thermo-structural concept of an hypersonic wing leading edge is introduced and verified by means of an advanced finite element thermo-structural model.

Re-entry winged body vehicles have several advantages w.r.t capsules, such as maneuverability and controlled landing opportunity. On the other hand, they show an increment in design level complexity, especially from an aerodynamic, aero-thermodynamic, and structural point of view, and in the difficulties of housing in operative existing launchers. In this framework, the idea of designing unmanned vehicles equipped with deployable wings for suborbital flight was born. This work details a preliminary study for identifying the best configuration for the hinge system aimed at the in-orbit deployment of an unmanned re-entry vehicle’s wings. In particular, the adopted optimization methodology is described. The adopted approach uses a genetic algorithm available in commercial software in conjunction with fully parametric models created in FEM environments and, in particular, it can optimize the hinge position considering both the deployed and folded configuration. The results identify the best hinge configuration that minimizes interface loads, thus, realizing a lighter and more efficient deployment system. Indeed, for such a category of vehicle, it is mandatory to reduce the structural mass, as much as possible in order to increase the payload and reduce service costs.

CIRA has recently set up a research and development project with Italian industrial partners, with the aim of develop hot structures based on ceramic matrix composites technology (C-C/SiC), code named SHS-CMC project. The project focuses on the application of the technology on the control surface of a re-entry vehicle, with the final objective of reaching TRL 5/6, to be spent in more challenging projects such as ESA SPACE RIDER. Thanks to CIRA heritage on ESA EXPERT flap plasma wind tunnel testing, the demonstrator of SHS-CMC project technology will be based on the EXPERT flap geometry, to be tested for final TRL assessment, in more demanding environment such as those of ESA-SPACE RIDER atmospheric re-entry phase. Besides the manufacturing process development it is of paramount importance to have robust and reliable thermal-mechanical models for design, in which both the material anisotropy and the most representative heat transfer phenomena are modelled and validated through test. In the present work the thermal model of the technological demonstrator has been set up. The validation of the model has been obtained trough numerical experimental correlation of PWT test on a similar test article developed in the frame of ESA EXPERT project. The virtual test shows good agreement with experiments in terms of temperature maps. This is the first step to be accomplished before the final qualification test and numerical-experimental validation of the SHS-CMC technology demonstrator, and subsequent TRL assessment.

Copyright © 2017 ASME. Over the last years, innovative concepts of civil high-speed transportation vehicles were proposed. In this framework, the Hexafly-INT project intends to test in free-flight conditions an innovative gliding vehicle with several breakthrough technologies on-board. This approach will help to gradually increase the readiness level of a consistent number of technologies suitable for hypervelocity flying systems. The vehicle design, manufacturing, assembly and verification is the main driver and challenge in this project. The prime objectives of this free-flying high-speed cruise vehicle shall aim at a conceptual design demonstrating a high aerodynamic efficiency in combination with high internal volume; controlled level flight at a cruise Mach number of 7 to 8;an optimal use of advanced high-temperature materials and structures. Present research describes the aero-thermal design process of the Experimental Flight Test Vehicle, namely EFTV. The glider aeroshape design makes maximum use of databases, expertise, technologies and materials elaborated in previously European community co-funded projects LAPCAT I & II [1][2], ATLLAS I & II [3][4] and HEXAFLY [5]. The paper presents results for both CFD and Finite Element aero-thermal analysis, performed in the most critical phase of the experimental flight leading to the selection of materials for the different components and to a suitable Thermal Protection System. ispartof: PROCEEDINGS OF THE ASME INTERNATIONAL MECHANICAL ENGINEERING CONGRESS AND EXPOSITION, 2017, VOL 1 vol:1 ispartof: ASME International Mechanical Engineering Congress and Exposition location:Tampa, FL date:3 Nov - 9 Nov 2017 status: published

The purpose of this article is to investigate the so-called verification and validation methodology for the vibration study of automotive structures, in particular natural frequencies and frequency response functions. In computational mechanics, the main objective of verification and validation leading to numerical and experimental works is to assess and improve the predictive capability of finite element models. Three main applications are presented throughout the article. The first application deals with spot weld modelling techniques. Four spot weld models are critically investigated for this study, namely two point-to-point and two surface-to-surface approaches. Two examples are treated: an assembly of two plates with three spot welds and a cradle. The second application deals with modelling galvanized structures. The study is focussed on automotive engine cradles. Experimental comparison between welded and galvanized assemblies highlights the mechanical effects due to galvanization. Finite element models, specifically developed for galvanized assemblies, are presented. The third application deals with a vehicle windscreen that is a sandwich structure made of glass and polymers. The dynamic behaviour of the windscreen under free–free conditions, in the presence of intra variability due to temperature variation, is discussed. Solid finite element models and multilayer shell models are assessed and compared.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Over the last years, innovative concepts of civil high-speed transportation vehicles were proposed. These vehicles have a strong potential to increase the cruise range efficiency at high Mach numbers, thanks to efficient propulsion units combined with high-lifting vehicle concepts. In this framework the Hexafly-INT project has the scope to test in free-flight conditions an innovative gliding vehicle with several breakthrough technologies on-board. This work describes the aero-thermal design processes of the Hexafly-INT Experimental Flight Test Vehicle, namely EFTV. ispartof: Proceedings of SPACE 2016 ispartof: SPACE 2016 Conferences and Exposition location:Long Beach, California date:13 Sep - 16 Sep 2016 status: published

Over the last years, innovative concepts of civil high-speed transportation vehicles were proposed. These vehicles have a strong potential to increase the cruise range efficiency at high Mach numbers, thanks to efficient propulsion units combined with high-lifting vehicle concepts. Nonetheless, performing a flight test will be the only and ultimate proof to demonstrate the technical feasibility of these new promising concepts and would result into a major breakthrough in high-speed flight. In this framework the Hexafly-INT project has the scope to test in free-flight conditions an innovative gliding vehicle with several breakthrough technologies on-board. This work describes both the thermo-structural design process of the Hexafly-INT Experimental Flight Test Vehicle, namely EFTV, and of the Experimental Service Module, namely ESM. The paper will present results of a Finite Element thermal analysis, performed in the most critical phases along the flight trajectory in order to drive a preliminary material selection.

The main purpose of this paper is to investigate verification, validation and variability issues applied to an industrial component: a car windscreen. The windscreen is a sandwich structure whose stacking sequence contains five layers. The two external thick layers are made of glass, while the three thin intermediate layers are made of appropriate polymers. In this framework, two main objectives are identified for this paper. The paper focuses the attention on the study of the dynamics of an acoustic windscreen under free-free and real boundary conditions. An application of the verification and validation methodology is presented to assess the capability of finite element models to predict the natural frequencies of the acoustic windscreen, in presence of intra variability due to temperature variation. Indeed, intra variability of glue and polymers' elastic properties leads to intra variability of the dynamic behaviour of the windscreen. Experimental campaigns, in free-free and real boundary conditions, have been performed in a climatic chamber. The effect of the temperature changes on the windscreen vibration behaviour has been evaluated and the component experimental intra variability estimated. A numerical study has been performed as well. Three different numerical models have been considered: a simplified model in free or clamped conditions, a trimmed body model. The verification stage, including convergence studies, concludes that the multilayer shell model approach is valid at low temperature, when polymers are relatively stiff. On the contrary, at higher temperature, polymers are very flexible and shell models lead to significant errors due to considerable transverse shear effects. Finally, the main result is that a solid model must be used for the windscreen to correctly reproduce the physics at different temperatures. A validation stage, involving numerical and experimental results, has been performed to evaluate the predictive capability of the developed numerical models. Validation metrics, which assess the mean value and the variability level of the frequencies, are proposed. The finite element models lead to very satisfactory results for the mean values of the frequencies. The general trends of the experimentally observed intra variability are also well reproduced. Nevertheless, further investigations are necessary to improve the predictive capability of the numerical model that currently underestimates the experimental intra variability. This discrepancy is essentially due to the complex non-linear behaviour of polymers.

Copyright © 2015 by ASME. The Hexafly-INT project intends to test in free-flight conditions an innovative gliding vehicle with several breakthrough technologies on-board. This approach will create the basis to gradually increase the readiness level of a consistent number of technologies suitable for high-speed flying systems. This paper presents a Finite Element thermal analysis of the Experimental Flight Test Vehicle, combining information coming from the flight trajectory, the structural layout, the vehicle aerothermodynamics and the thermal behavior of the preliminarily selected materials in high temperature conditions. Numerical results show the thermal performances of the selected high temperature resistant materials in moderate enthalpy flow conditions and provide fundamental information on the thermal loads to be considered for structural analyses. ispartof: Proceedings of the ASME 2015 International Mechanical Engineering Congress & Exposition vol:1-2015 ispartof: International Mechanical Engineering Congress & Exposition (IMECE2015) location:Houston, Texas, US date:13 Nov - 19 Nov 2015 status: published

Achieving airbreathing hypersonic flight is an ongoing challenge with the potential to cut air travel time and provide cheaper access to space. Waveriders are potential candidates for achieving hypersonic cruise or acceleration flight within the atmosphere. Current research tends to focus on key issues like thermal loading, aero-elasticity and aerothermodynamics at hypersonic speeds. Design problems in each of these areas must be solved if a hypersonic waverider design is to be viable. In this frame the HEXAFLY-INT project aims at the test in free-flight conditions of an innovative gliding vehicle with several breakthrough technologies on-board to be launched along a suborbital trajectory. Its preliminary conceptual design has been carried out by means of a number of numerical tools suitable to design vehicles flying in hypersonic conditions. The main results of the design analysis carried out during the preliminary phase of the study, such as vehicle aerodynamics and aerothermodynamics, re-entry trajectories, structures and mechanisms, and on the overall system, as well, are presented in this work.

This paper describes the activities carried out by CIRA in the frame of the SCRAMSPACE flight activities. CIRA is investigating applications of Ultra High Temperature Ceramics (UHTC) for space applications. In order to test new UHTC based technologies, in real flight conditions, CIRA and University of Queensland carried out cooperation for the SCRAMSPACE project. CIRA contributed to the flight experiment realizing two ceramic fins, embedding different newly developed technologies. The paper describes shortly the development of the materials used for the test articles, the thermostructural analyses carried out for the design of the payloads. The payload integration is then described along with the launch activity in Andoya, Norway. Unluckily the first stage of the rocket suffered a failure at the beginning of the flight and, even if the payload operated as expected, it was never injected in the correct trajectory and the flight failed in providing the expected scientific results. The final part of the paper describes the activities carried out in CIRA for the design of a model holder that shall permit to test the Qualification Models of the fins in CIRA Plasma Wind Tunnel SCIROCCO.

The purpose of this paper is to present a general overview of a re-entry space vehicle study and a synthesis of the methodologies developed as well as the main results obtained. The final objective is to give a contribution to implement and evaluate the thermo-structural performance of a pair of Ultra High Temperature Ceramic (UHTC) winglets developed by CIRA. Therefore, the test-case consists of two winglets made of fibber reinforced massive UHTC coupled with a metallic interface. A plasma sprayed UHTC coating has also been applied on refractory metal. The winglets are mounted on a carrier vehicle which will fly at Mach numbers approximately equal to 8 over the altitude range 27-32 Km. A massive numerical study has been performed. In order to assess the capability of finite element models to predict the winglet thermo-structural behavior, several models have been developed. Finally, a solid finite element model is necessary. Solid meshes are first developed in order to identify the highly accurate numerical solution and to study the influence of mesh refinement. The performed convergence analysis shows the “just necessary model” is a solid FEM model whose mean element size for the winglet is 0.9 mm. A thermal as well as a structural analysis have been performed. The main thermal results show that the launch phase is not critical while the re-entry is more demanding. Indeed, the UHTC tip gets close to about 1500°C in a short time and the aluminum is heated up to 362°C at the end of the flight. The heating on the aluminum surface of the vehicle is mostly caused by conduction from the winglet to the vehicle, and not by the wake of the winglet. The hot spot downstream the winglet is always cooler than the area just beneath the winglet. A zirconium coating will be applied to the aluminum to let these temperatures to be sustained by the material without any relevant degradation. The combination of thermal and mechanical load have also been analyzed. Heat fluxes applied are timechanging depending by the wall temperature. Numerical predictions show how the structure is not affected by the inducted stress. The two winglets as well as the whole vehicle are actually being manufactured and the numerical prediction will be shortly validated by several experimental tests in CIRA’s GHIBLI and SCIROCCO plasma wind tunnels facilities.