Reusable thermal protection systems are one of the key technologies that have to be improved to enable long-duration hypersonic flights. Transpiration cooling has been demonstrated to be one of the most promising active cooling techniques in terms of coolant mass requirements and disturbance of the external flow. Previous numerical studies, conducted by the authors on the conjugate boundary-layer/material-response analysis, along with the current manufacturing capability of manipulating the natural properties of porous materials (e.g., porosity, permeability, and thermal conductivity) have demonstrated the cooling potential when variable transpiration is considered. In this work, a methodology for the nonintrusive characterization of the local effective permeability of a complex carbon–carbon porous structure is proposed. The concept of effective permeability, conceived as the local blowing capability of a porous structure with respect to a selected coolant fluid, is also discussed. Specifically, the coolant (air) mass flux blown from a conical porous surface has been measured by a hot-film probe at a distance specified by an appropriate reference elementary area and the Reynolds number based on the channels’ diameter. These measurements have then been related to the pressure gradient across the local material’s thickness by using Darcy’s law. Measurements have revealed a higher effective permeability near the nose of the cone where two longitudinal delaminations have been identified. The asymmetric blowing capability of the cone highlights the importance of characterizing the entire thermal protection system instead of defining the overall properties of the material, which can be drastically different at the full-scale level due to the geometry, the system integration (i.e. structural constraints), and the intrinsic defectology coming from the manufacturing process. Additionally, the mass fluxes measured on the external porous surface will support the numerical aerothermal rebuilding of the wind-tunnel experiment on the transpiration cooling.

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The purpose of this paper is to identify, for given technology levels (TRL) and mission requirements, those parameters that are critical for preliminary sizing of a hypersonic airbreathing airliner. Mission requirements will dictate a solution space of possible vehicle architecture capable of meeting cruise conditions as well as of taking-off (TO) and landing. In practice, once defined a range of cruise vehicle architectures, constraints are imposed (as to all passenger airliners), such as: 1. take off (=TO) and landing distance (so-called field length, FL): FL no longer than for the B-747-400, or 10000 ft; 2. completing TO with one engine off; 3. max acceleration at TO and climb-out (CO) = 0.4 g; 4. Hydrogen fuel (Meeting NOx emission limits (EINOx) is a further constraint not discussed in this paper).These constraints enable focusing on a realistic design out of the broad range of vehicles capable of performing the given mission. Thus a realistic vehicle must not only integrate aerodynamics and propulsion system; in fact, it is the result of many iterations in the design space, until performance and constraints are successfully achieved and met.The Gross Weight at Take Off (TOGW) was deliberately discarded as a constraint, based on Previous studies by Czysz. Typically, limiting from the beginning the TOGW leads to a vicious spiral where weight and propulsion system requirements keep growing, eventually denying convergence. In designing passenger airliners, in fact, it is the payload that is assumed fixed from the start, not the total weight.A parametric analysis of the hypersonic vehicle architecture is presented: in particular, optimal size, weight and geometrical shape are defined for different mission requirements. This analysis has shown that, it is possible to define a range of possible successful solutions for the European LAPCAT II project.

The current European project LAPCAT II has the ambitious goal to de¦ne a conceptual vehicle capable of achieving the antipodal range Brussels Sydney (∼ 18,000 km) in about 2 h at Mach number Ma = 8. At this high speed, the requirement of high lift to drag (L/D) ratio is critical to high performance, because of high skin friction and wave drag: in fact, as the Mach number increases, the L/D ratio decreases. The design of the vehicle architecture (shape and propulsion system) is, as a consequence, crucial to achieve a reasonably high L/D. In this work, critical parameters for the preliminary sizing of a hypersonic airbreathing airliner have been identi¦ed. In particular, for a given Technology Readiness Level (TRL) and mission requirements, a solution space of possible vehicle architectures at cruise have been obtained. In this work, the Gross Weight at Take-O¨(TOGW) was deliberately discarded as a constraint, based on previous studies by Czysz and Vanderkerkhove [1]. Typically, limiting from the beginning, the TOGW leads to a vicious spiral where weight and propulsion system requirements keep growing, eventually denying convergence. In designing passenger airliners, in fact, it is the payload that is assumed ¦xed from the start, not the total weight. In order to screen the solutions found, requirements for taking-o¨(TO) and landing as well as the trajectory have been accounted for. A consistent solution has ¦nally been obtained by imposing typical airliner constraints: emergency take-o¨and landing. These constraints enable singling out a realistic design from the broad family of vehicles capable of performing the given mission. This vehicle has been obtained by integrating not only aerodynamics, trajectory, and airliner constraints, but also by integrating the propulsion system, the trimming devices and by doing some adjustments to the conceptual vehicle shape (i. e., spatular nose). Thus, the ¦nal vehicle is the result of many iterations in the design space, until performance, trajectory, propulsion systems, and airport constraints are successfully met.

A study was conducted to demonstrate an approach to sizing of a fully integrated hypersonic commercial airliner, which was based on the parametric sizing methodology. It consisted of defining a set of equations that relates mission requirements to geometry, aerodynamic, and propulsion efficiencies, which were solved simultaneously. The next step involved identifying the final configuration of a wholly integrated hypersonic vehicle with trimming, control surfaces, and an integrated propulsion system. Vehicle weights, along with volumes and aerodynamic efficiencies were iterated until all weights converge and the thrust required to climb and cruise was met by engines specification