Showing papers in "Aeronautical Journal in 2019"

Abstract: Airframe–propulsion integration concepts that use boundary-layer ingestion (BLI) have the potential to reduce aircraft fuel burn. One concept that has been recently explored is NASA’s STARC-ABL aircraft configuration, which offers the potential for fuel burn reduction by using a turboelectric propulsion system with an aft-mounted electrically driven BLI propulsor. So far, attempts to quantify this potential fuel burn reduction have not considered the full coupling between the aerodynamic and propulsive performance. To address the need for a more careful quantification of the aeropropulsive benefit of the STARC-ABL concept, we run a series of design optimisations based on a fully coupled aeropropulsive model. A 1D thermodynamic cycle analysis is coupled to a Reynolds-averaged Navier–Stokes simulation to model the aft propulsor at a cruise condition and the effects variation in propulsor design on overall performance. A series of design optimisation studies are performed to minimise the required cruise power, assuming different relative sizes of the BLI propulsor. The design variables consist of the fan pressure ratio, static pressure at the fan face, and 311 variables that control the shape of both the nacelle and the fuselage. The power required by the BLI propulsor is compared with a podded configuration. The results show that the BLI configuration offers 6–9% reduction in required power at cruise, depending on assumptions made about the efficiency of power transmission system between the under-wing engines and the aft propulsor. Additionally, the results indicate that the power transmission efficiency directly affects the relative size of the under-wing engines and the aft propulsor. This design optimisation, based on computational fluid dynamics, is shown to be essential to evaluate current BLI concepts and provides a powerful tool for the design of future concepts.

Abstract: The increasing environmental requirements in the air transport sector pose great challenges to the aviation industry and are key drivers for innovation. Besides various approaches for increasing the efficiency of conventional gas turbine engines, electric propulsion systems have moved into the focus of aviation research. The first electric concepts are already in service in general aviation. This study analyses the potentials of electric and turbo hybrid propulsion systems for commercial aviation. Its purpose is to compare various architectures of electrical powertrains with a conventional turboprop on a regional aircraft, similar to the ATR 72, on engine and flight mission levels. The considered architectures include a turbo-electric (power controlled and direct driven), hybrid-electric (serial and parallel) and a pure electric concept. Their system weights are determined using today’s technology assumptions. With the help of performance models and flight mission calculations the impact on fuel consumption, CO emissions and aircraft performance is evaluated.

Abstract: High-speed aircraft often develop separation-induced leading-edge vortices and vortex flow aerodynamics. In this paper, the discovery of separation-induced vortex flows and the development of methods to predict these flows for wing aerodynamics are reviewed. Much of the content for this article was presented at the 2017 Lanchester Lecture and the content was selected with a view towards Lanchester’s approach to research and development.

Abstract: There is a growing interest in the use of alternative fuels in gas turbine engines to reduce emissions. Testing of alternative fuels is expensive when done on a large-scale gas turbine engine. In this study, a re-commissioned small gas turbine auxiliary power unit (APU) has been used to test various blends of Jet A-1, synthetic paraffinic kerosene (SPK) and diesel with as well as eight other novel fuels. A detailed analysis of performance, gaseous emissions and particulate emissions has been presented in this study. It is observed that aromatic content in general as well as the particular chemical composition of the aromatic compound plays a vital role in particulate emissions generation. SPK fuel shows substantially lower particulate emissions with respect to Jet A. However, not all the species of aromatics negatively impact particulate emissions. Gaseous emissions measured are comparable for all the fuels tested in this study.

Abstract: An advanced geared turbofan with year 2035 technology level assumptions was established and used for the hybridisation study in this paper. By boosting the low-speed shaft of the turbofan with electrical power through the accessory gearbox, a parallel hybrid concept was set up. Focusing on the off-design performance of the hybridised gas turbine, electrical power input to the shaft, defined as positive hybridisation in this context, generally moves the compressor operation towards surge. On the other hand, the negative hybridisation, which is to reverse the power flow direction can improve the part-load operations of the turbofan and minimise the use of compressor handling bleeds. For the pre-defined mission given in the paper, negative hybridisation of descent, approach and landing, and taxi operations with 580 kW, 240 kW and 650 kW, respectively was found sufficient to keep a minimum compressor surge margin requirement without handling bleed.Looking at the hybridisation of key operating points, boosting the cruise operation of the baseline geared turbofan is, however, detrimental to the engine efficiency as it is pushing the cruise operation further away from the energy optimal design point. Without major modifications to the engine design, the benefit of the hybridisation appears primarily at the thermomechanical design point, the hot-day take-off. With the constraint of the turbine blade metal temperature in mind, a 500kW positive hybridisation at hot-day take-off gave cruise specific fuel consumption (SFC) reduction up to 0.5%, mainly because of reduced cooling flow requirement. Through the introduction of typical electrical power system performance characteristics and engine performance exchange rates, a first principles assessment is illustrated. By applying the strategies discussed in the paper, a 3% reduction in block fuel burn can be expected, if a higher power density electrical power system can be achieved.

Abstract: Product development, especially in aerospace, has become more and more interconnected with its operational environment. In a constant changing world, the operational environment will be subjected to changes during the life cycle of the product. The operational environment will be affected by not only technical and non-technical perturbations, but also economical, managerial and regulatory decisions, thus requiring a more global product development approach. One way to try tackling such complex and intertwined problem advocates studying the envisioned product or system in the context of system of systems (SoS) engineering. SoSs are all around us, probably in any field of engineering, ranging from integrated transport systems, public infrastructure systems to modern homes equipped with sensors and smart appliances; from cities filling with autonomous vehicle to defence systems.Since also aerospace systems are certainly affected, this work will present a holistic approach to aerospace product development that tries spanning from needs to technology assessment. The proposed approach will be presented and analysed and key enablers and future research directions will be highlighted from an interdisciplinary point of view. Consideration of the surrounding world will require to look beyond classical engineering disciplines.

Abstract: In order to ensure low-altitude safety, a tracking and recognition method of unmanned aerial vehicle (UAV) and bird targets based on traditional surveillance radar data is proposed. First, several motion models for UAV and flying bird targets are established. Second, the target trajectories are filtered and smoothed with multiple motion models. Third, by calculating the time-domain variance of the model occurrence probability, the model conversion probability of the target is estimated, and then the target type is identified and classified. The effectiveness and robustness of the algorithm is demonstrated by several groups of Monte Carlo simulation experiments, including setting different recognition steps, different model transformation probability, filtering and smoothing algorithm comparison. The algorithm is also successfully applied on the ground-truth radar data collected by the low-altitude surveillance radar at airport and coastal environments, where the targets of UAVs and flying birds could be tracked and recognised.

Abstract: One of the main challenges of future aircraft engines is to achieve low pollutant emissions while maintaining high combustion efficiencies and operability. The Flameless Combustion (FC) regime is pointed as one of the promising solutions due to its well-distributed reaction zones that yield low NOx emissions and oscillations. A dual-combustor configuration potentially facilitates the attainment of FC in the Inter-Turbine Burner (ITB). The development of such burner is dependent on knowledge regarding NOx formation and the parameters affecting it. It is known from the literature that the NOx formation mechanisms are different in FC. Therefore, in an attempt to clarify some of the mechanisms involved in NOx formation at relevant conditions, a chemical reactor network model developed to represent the ITB is explored. The role of prompt NOx was previously shown to be dominant at relatively low inlet temperatures and atmospheric pressure. In order to check these findings, five chemical reaction mechanisms were employed. All of them overpredicted NOx emissions and the overprediction is likely to be caused by the prompt NOx subset implemented in these mechanisms. Higher reactants temperatures and operational pressures were also investigated. Overall NOx emissions increased with temperature and the NOx peak moved to lower equivalence ratios. Operational pressure changed the emissions trend with global equivalence ratio. Leaner conditions had behaviour similar to that of conventional combustors (increase in NOx), while NOx dropped with further increase in equivalence ratio due to suppression of the prompt NOx production, as well as an increase in NO reburning. These trends highlight the differences between the emission behaviour of the ITB with those of a conventional combustion system.

Abstract: Multicriteria trajectory optimisation is expected to increase aviation safety, efficiency and environmental compatibility, although neither the theoretical calculation of such optimised trajectories nor their implementation into today’s already safe and efficient air traffic flow management reaches a satisfying level of fidelity. The calibration of the underlying objective functions leading to the virtually best available solution is complicated and hard to identify, since the participating stakeholders are very competitive. Furthermore, operational uncertainties hamper the robust identification of an optimised trajectory. These uncertainties may arise from severe weather conditions or operational changes in the airport management. In this study, the impact of multicriteria optimised free route trajectories on the air traffic flow management is analysed and compared with a validated reference scenario which consists of real flown trajectories during a peak hour of Europe’s complete air traffic in the upper airspace. Therefore, the TOolchain for Multicriteria Aircraft Trajectory Optimisation (TOMATO) is used for both the multicriteria optimisation of txrajectories and the calculation of the reference scenario. First, this paper gives evidence for the validity of the simulation environment TOMATO, by comparison of the integrated reference results with those of the commercial fast-time air traffic optimiser (AirTOp). Second, TOMATO is used for the multicriteria trajectory optimisation, the assessment of the trajectories and the calculation of their integrated impact on the air traffic flow management, which in turn is compared with the reference scenario. Thereby, significant differences between the reference scenario and the optimised scenario can be identified, especially considering the taskload due to frequent altitude changes and rescinded constraints given by waypoints in the reference scenario. The latter and the strong impact of wind direction and wind speed cause wide differences in the patterns of the lateral trajectories in the airspace with significant influence on the airspace capacity and controller’s taskload. With this study, the possibility of a successful 4D free route implementation into Europe’s upper airspace is proven even over central Europe during peak hours, when capacity constraints are already reaching their limits.

Abstract: The aviation industry relies on accurate models. These models are used to predict an aircraft system’s outputs, and thus allow an understanding of the parameters involved, which could lead to system improvements. This study focuses on the engine modelling of an aircraft, and on its experimental validation using the Cessna Citation X Research Aircraft Simulator designed by CAE Inc., equipped with a level D Flight Dynamics toolbox. Level D is the highest rank attributed by the Federal Aviation Administration FAA certification authorities for flight dynamics. The proposed model aims to predict the thrust and the fuel consumption for various altitudes, Mach numbers and throttle lever angles (TLA). Different generic static models, which correspond to their steady state, from the literature, were used in this study; however, most of them were validated under restricted hypotheses. An optimisation algorithm was used in order to tune the static model parameters with the set of identification flight test data. Another set of data was then used in order to validate the identified model. Furthermore, a dynamic model corresponding to the transient operations was identified. TLA steps, impulses and ramp perturbations were performed in order to identify the system response, and to validate system dynamic model with other flight tests than the identification tests.

Abstract: An important prerequisite for the design, assessment and certification of aircraft and their associated control systems is a quantitative specification of the environment in which the aircraft is intended to operate, for example, atmospheric gust. Gust loads on aircraft may induce detrimental influences such as increased aerodynamic and structural loads, structural deformation and decreased flight dynamic performance. This paper presents a systematic and comprehensive overview of important concepts and applications of gust loads on aircraft. This overview includes a brief research background, concepts, research techniques, influences and load alleviation measures of gust. Finally, we summarise some potential improvements in the future work. It is also recommended to learn from previous experiences to avoid aviation accidents due to flight through atmospheric gusts and turbulence.

Abstract: The special application environment puts forward the higher requirement of reliability of parts made from titanium alloy Ti–6Al–4V, which is closely related to the machining-induced residual stress. For the fact of the non-linear distribution of residual stress beneath the machined surface, distribution of peripheral milling-induced residual stress and its effect on fatigue performance of titanium alloy Ti–6Al–4V are still confusing. In the present study, residual stress profile induced by peripheral milling of Ti–6Al–4V is first studied. And then, energy criteria are proposed to characterise the whole state of the residual stress field. Finally, the effects of residual stress profile and surface energy on tensile–tensile fatigue performance of titanium alloy Ti–6Al–4V are discussed. The conclusions were drawn that the variation trend of surface residual stress (σr,Sur), maximum compressive residual stress (σC,ax), location (hr0) and response depth (hry) of residual stress profile with cutting parameters showed a similar pattern for both measure directions those parallel (σ1) and perpendicular (σ3) to the cutting direction. Cutting speed and feed rate have a main effect on surface residual stress, and the depth of cut has little effect on all the four key factors of residual stress profile. With the increase of cutting speed and feed rate, machining-induced surface energy tends to become larger. But increasing the depth of cut caused the strain energy stored in unit time to decrease. Furthermore, the effect of depth of cut on surface energy was weakened when the value of cutting depth becomes larger. Both the surface compressive residual stress and the maximum compressive residual stress are beneficial for prolonging the fatigue life, while large value of machining-induced surface energy leads to a decrease of fatigue life. Analysis of variance result shows that maximum residual compressive stress has a greater impact on fatigue life than other residual stress factors.

Abstract: With the aims of overcoming the limitations of the existing basic flow model derived from an axisymmetric generating body and extending the aerodynamic design method of the airframe/inlet integrated waverider vehicle, this study develops an upgraded basic flow model derived from an axisymmetric shock wave. It then upgrades the design method for airframe/inlet integration of an air-breathing hypersonic waverider vehicle, which is termed the ‘full-waverider vehicle’ in this study. In this paper, first, the design principle and method for the upgraded full-waverider vehicle derived from an axisymmetric basic shock wave are described in detail. Second, an upgraded basic flow model that accounts for both internal and external flows is derived from an axisymmetric basic shock wave by use of both the streamline tracing method and the method of characteristics (MOC). Third, the upgraded full-waverider vehicle is developed from the upgraded basic flow model by the streamline tracing method. Fourth, the design theories and methodologies of both the upgraded basic flow model and the upgraded full-waverider vehicle are validated by a numerical computation method. Finally, the aerodynamic performances and viscous effects of both the upgraded basic flow model and the upgraded full-waverider vehicle are analysed by numerical computation. The obtained results show that the upgraded basic flow model and aerodynamic design method are effective for the design of the airframe/inlet integration of an air-breathing hypersonic waverider vehicle.

Abstract: Scaled model test is an effective means to verify the design of a stiffened cylindrical shell. However, there is a problem of similarity distortion by use of the traditional dimensional analysis to design scaled models. In this present study, an equivalent similar method is proposed to solve the problem. The method is applied to an axial stiffened cylindrical shell, and the equivalent criteria and scaling laws satisfying the equivalent similarity of global bending mode are derived and verified by numerical examples. The results indicate that the similarity distortion caused by practical conditions for the stiffened cylindrical shell can be solved and the parameters of scaled model can be designed more freely with the proposed equivalent similar method.

Abstract: To solve the on-ground lateral direction control problem of the unswept flying-wing unmanned aerial vehicle (UAV) without rudder, steering system or breaking system, a control approach which uses differential propeller thrust to control the lateral direction is proposed. First, a mathematical model of the unswept flying-wing UAV on-ground moving is established. Second, based on the active disturbance rejection control (ADRC) theory, a yaw angle controller is designed by using the differential propeller thrust as the control output. Finally, a straight line trajectory tracking control law is designed by improving the vector field path following method. Experiment results show that the proposed control laws have a shorter response time, better robustness and better control precision compared with proportional integral derivative (PID) controller. The proposed controller has small computational complexity, simple parameter setting process, and uses practical measurable physical quantities, providing a reference solution for further engineering applications.

Abstract: The eddy dissipation model (EDM) is analysed with respect to the ability to address the turbulence-combustion interaction process inside hydrogen-fuelled scramjet engines designed to operate at high Mach numbers (≈7-12). The aim is to identify the most appropriate strategy for the use of the model and the calibration of the modelling constants for future design purposes. To this end, three hydrogen-fuelled experimental scramjet configurations with different fuel injection approaches are studied numerically. The first case consists of parallel fuel injection and it is shown that relying on estimates of ignition delay from a 1D kinetics program can greatly improve the effectiveness of the EDM. This was achieved through a proposed zonal approach. The second case considers fuel injection behind a strut. Here the EDM predicts two reacting layers along the domain which is in agreement with experimental temperature profiles close to the point of injection but not the case any more at the downstream end of the test section. The first two scramjet test cases demonstrated that the kinetic limit, which can be applied to the EDM, does not improve the predictions in comparison to experimental data. The last case considered a transverse injection of hydrogen and the EDM approach provided overall good agreement with experimental pressure traces except in the vicinity of the injection location. The EDM appears to be a suitable tool for scramjet combustor analysis incorporating different fuel injection mechanisms with hydrogen. More specifically, the considered test cases demonstrate that the model provides reasonable predictions of pressure, velocity, temperature and composition.

Abstract: This paper presents the results of a research performed at the Research Laboratory in Active Controls, Avionics and Aeroservoelasticty (LARCASE), at ETS, concerning optimisation strategies for cruise flight segments with imposed flight time (delimited by waypoints with required time of arrival constraints). Specifically, a new algorithm is presented that identifies the optimal vertical navigation profile (flight altitude and speed optimisation) for a cruise segment with imposed lateral navigation profile, bounded by two waypoints with required time of arrival constraints. The set of evaluated vertical navigation profiles are characterised by identical altitudes and speeds at their initial and final waypoints (at the beginning and the end of the cruise segment under optimisation), a maximum of one altitude step (relative to the initial altitude), and are flown at constant speed. This study investigates the flight performance increase (total cost reduction) for a flight along the optimal vertical navigation profile, relative to a flight at the optimal speed and initial cruise altitude. The evaluation was performed using a medium haul transport aircraft flight performance model, for three lateral navigation profiles and three wind profiles. The algorithm is targeted for Flight Management Systems platforms, to provide the optimal flight trajectory for the imposed lateral flight profile and time constraints.

Abstract: In order to prepare an advanced 4-stage high-pressure compressor rig test campaign, details regarding both accomplishment and analysis of preliminary experiments are provided in this paper. The superior objective of the research project is to contribute to a reliable but simultaneously less conservative design of future high pressure blade integrated disks (blisk). It is planned to achieve trend-setting advances based on a close combination of both numerical and experimental analyses. The analyses are focused on the second rotor of this research compressor, which is the only one being manufactured as blisk. The comprehensive test program is addressing both surge and forced response analyses e.g. caused by low engine order excitation. Among others the interaction of aeroelastics and blade mistuning is demanding attention in this regard. That is why structural models are needed, allowing for an accurate forced response prediction close to reality. Furthermore, these models are required to support the assessment of blade tip timing (BTT) data gathered in the rig tests and strain gauge (s/g) data as well. To gain the maximum information regarding the correlation between BTT data, s/g-data and pressure gauge data, every blade of the second stage rotor (28 blades) is applied with s/g. However, it is well known that s/g on blades can contribute additional mistuning that had to be considered upon updating structural models. Due to the relevance of mistuning, efforts are made for its accurate experimental determination. Blade-by-blade impact tests according to a patented approach are used for this purpose. From the research point of view, it is most interesting to determine both the effect s/g-instrumentation and assembling the compressor stages on blade frequency mistuning. That is why experimental mistuning tests carried out immediately after manufacturing the blisk are repeated twice, namely, after s/g instrumentation and after assembling. To complete the pre-test program, the pure mechanical damping and modal damping ratios dependent on the ambient pressure are experimentally determined inside a pressure vessel. Subsequently the mistuning data gained before is used for updating subset of nominal system mode (SNM) models. Aerodynamic influence coefficients (AICs) are implemented to take aeroelastic interaction into account for forced response analyses. Within a comparison of different models, it is shown for the fundamental flap mode (1F) that the s/g instrumentation significantly affects the forced response, whereas the impact of assembling the compressor plays a minor role.

Abstract: This paper describes the extensive numerical investigation carried out on a 203-mm spin-stabilised projectile to study the effects of Magnus force at high angles of attack on the stability and flight-trajectory parameters, for further validation and incorporation in a 6-DOF trajectory solver for flight-stability analysis. Magnus force typically influences the course of flight by causing the projectile to drift from its intended path in addition to generation of inbuilt dynamic instabilities in pitch and yaw orientation and is a function of AoA and spin rate. This study is a consolidation of the authors’ previous research on the same caliber projectile but with time-accurate analysis. It has been found that typically, the Magnus force and moment calculation requires time-accurate Navier Stokes equations to be solved numerically for accurate prediction(1,2). Hence, to complete the extraction of static and dynamic coefficients derivatives, unstructured time-accurate CFD analysis on multiple configurations, ranging from subsonic to supersonic Mach regimes, has been evaluated using Large Eddy Simulation (LES) and found to be suitable for capturing the desired effects. However, the LES simulation requires non-dimensional wall distance (y+) of the order of 0.5 – 1, with LES_IQ > 75% thus, is computationally-intensive. In addition, to cover the entire flight envelope from Charge 1 (249 m/s) to Charge 7 (595 m/s), at spin rate from 500 rad/s to 750 rad/s, 30 cases have been evaluated to generate the time-accurate coefficient library for integration with 6-DOF solver analysis. The results obtained have been compared with the available experimental data and found to be in reasonable agreement. The results of 6-DOF solver, incorporating the extracted coefficients, were compared with firing-table results, which further validated the computational methodology. This study provides an insight on how opposite flow interacts with the attached boundary layer due to spin rate and generates a turbulent interacting flow with variation in vortical structures for Q-Criterion vortex-flow visualization.

Abstract: The drive for increasing flight efficiency is resulting in wing designs that are of higher aspect ratios, lower in weight, increased wingspans and, consequently, require greater attention in the disciplines of aeroelastics and loads. This trend in aircraft design, along with past research experience with flexible aircraft, motivate a review of assumptions in gust models; especially, that of the gust maintaining a uniform spanwise profile. In this paper, the authors investigate the use of spanwise varying 1−cos gust models for loads prediction using a non-linear aeroelastic model of a conventional large transport aircraft. The comparison between a test case using conventional uni-dimensional approach and another, using multidimensional gusts, illustrates the impact of stepping away from traditional discrete tuned gust processes and adding a spanwise varying gust component. A methodology for processing and analysing the loads data arising due to the added dimension is also developed and both envelope and correlated loads are considered. Gust characteristics and resulting load factor are, respectively, considered for comparison between the two models, as both metrics define realistic gust encounters. In this case, it has been shown that spanwise variation of gust profiles leads to lower envelope loads if viewed in terms of conventional gust gradients. However, higher envelope loads are found if the maximum load factors are matched.

Abstract: Previous studies demonstrated that laminar separation bubbles (LSBs) in the absence of external disturbances or forcing are intrinsically unstable with respect to a three-dimensional instability of centrifugal nature. This instability produces topological modifications of the recirculation region with the introduction of streamwise vorticity in an otherwise purely two-dimensional time-averaged flows. Concurrently, the existence of spanwise inhomogeneities in LSBs have been reported in experiments in which the amplification of convective instability waves dominates the physics. The co-existence of the two instability mechanisms is investigated herein by means of three-dimensional parabolised stability equations. The spanwise waviness of the LSB on account of the primary instability is found to modify the amplification of incoming disturbance waves in the linear regime, resulting in a remarkable enhancement of the amplitude growth and a three-dimensional arrangement of the disturbance waves in the aft portion of the bubble. Present findings suggest that the oblique transition scenario should be expected in LSBs dominated by the convective instability, unless high-amplitude disturbances are imposed.

Abstract: The field data characterising aircraft accidental in-service damage was collected, sorted and processed. By means of probabilistic analysis, the wing damageability statistical parameters were determined. The scenarios of wing accidental impacts were described and the qualitative distribution of impact intensity over the wing surfaces was obtained. By means of original analytical method, the metal dent depth data were converted into impact energy data and energy probabilistic distributions were established. It was shown that the functional relationships generated on domestic data are generally consistent with similar foreign results obtained on other types of aircraft with serious differences in operating conditions. Along with realistic impact damage scenarios, the high energy impact events were considered. It was noted that in some cases severe damage events should not be addressed as extremely improbable and should be included into design and certification process.

Abstract: This paper aims at contributing to a better understanding of the effect of Tyler–Sofrin Modes (TSMs) on forced vibration responses by analysing a 4.5-stage research axial compressor rig. The first part starts with a brief review of the involved physical mechanisms and necessary prerequisites for the generation of TSMs in multistage engines. This review is supported by unsteady CFD simulations of a quasi 2D section of the studied engine. It is shown that the amplitude increasing effect due to mistuning can be further amplified by the presence of TSMs. Furthermore, the sensitivity with respect to the structural coupling of the blades and the damping as well as the shape of the expected envelope is analysed.The second part deals with the Rotor 2 blisk of the research compressor rig. The resonance of a higher blade mode with the engine order of the upstream stator is studied in two different flow conditions realised by different variable stator vane (VSV) schedules which allows to separate the influence of TSMs from the impact of mistuning. A subset of nominal system modes representation of the rotor is used to describe its mistuned vibration behaviour, and unsteady CFD simulations are used to characterise the present strength of the TSMs in the particular operating conditions. Measured maximum amplitude vs blade pattern and frequency response functions are compared against the predictions of the aeromechanical models in order to assess the strength of the TSMs as well as its influence on vibration levels.

Abstract: Experimental and numerical investigations into the linear and nonlinear aeroelastic behaviour of very flexible High Altitude Long Endurance (HALE) wings are conducted to assess the effect of geometrical nonlinearities on wings displaying moderate-to-large displacement. The study shows that the dynamic behaviour of wings under large deflection, and specifically the edgewise and torsion natural frequencies and modal characteristics, are largely affected by the presence of geometrical nonlinearities. A modular wing structure has been manufactured by rapid prototyping and it has been tested to characterise its dynamic and aeroelastic behaviour. At first, several simple isotropic cantilever beams with selected crosssections are numerically investigated to extract their modal characteristics. Experiments are subsequently conducted to validate the geometrically nonlinear dynamics behaviour due to high tip displacement and to understand the influence of the beam cross-section geometry. The structural dynamics and aeroelastic analysis of a very flexible modular selected wing is then investigated. Clean-wing wind-tunnel tests are carried out to assess flutter and dynamic response. The wind-tunnel model display interesting aeroelastic features including the substantial influence of the wing large deformation on its natural frequencies and modal characteristics.

Abstract: One of the challenges of modern engineering design is the amount of data that designers must keep track while performing system analysis and synthesis. This task is particularly important in the design process of complex systems such as novel aerospace systems where Modeling and Simulation play an essential role. The Agile philosophy stems from the field of Software Engineering and describes an approach to development in which requirements and solutions gradually develop through collaboration between self-organising cross-functional teams and end users. Agile Model-Based System Engineering (AMBSE) is the application of the Agile philosophy to Model-Based System Engineering. In this paper, AMBSE is accomplished through the application of the Object-Oriented System Engineering Method (OOSEM). OOSEM employs a top-down scenario-driven process that adopts System Modeling Language (SysML) and leverages the object-oriented paradigm to support the analysis, specification, design, and verification of systems. AMBSE assisted by mathematical modelling and safety assessment techniques is applied to the first design iterations of the main aircraft systems, allowing a comprehensive design exploration. The flight control system was chosen to illustrate the procedure in detail, emphasising the synthesis of a six-degrees-of-freedom model augmented by dynamic inversion control for a hypothetical supersonic transport aircraft satisfying class II MIL-F-8785C handling qualities. It is concluded that AMBSE presents promising properties to support future aircraft development within the current regulatory framework for aircraft design, while enabling a smooth transition from conceptual to preliminary design.

Abstract: System software subsystems in an unmanned aircraft system share hardware resources due to space, weight, and power constraints. Such subsystems have different criticality, requirements, and failure rates, and can cause undesired interference when sharing the same hardware. A component with high failure rate can reduce the reliability of the system unless a fault containment mechanism is adopted.This work proposes an asymmetric multiprocessor architecture to establish isolation at the hardware level for distributed implementation of safety-critical subsystems along with user defined payload subsystems on the same hardware with minimally reduced reliability of the system. To achieve that, subsystems are strategically segregated in separate processors, connected to an on-chip protective interconnect for inter-processor communications. A custom watchdog and reset mechanism are implemented to reset a specific processor without affecting the entire system if required. The architecture is demonstrated on a FPGA chip. In addition, an example of an optimised distribution is provided for a specific flight control system with five subsystems.

Abstract: The focus of this paper is on the modelling of miniature electromechanical actuators used in a morphing wing application, on the development of a control concept for these actuators, and on the experimental validation of the designed control system integrated in the morphing wing-tip model for a real aircraft. The assembled actuator includes as its main component a brushless direct current motor coupled to a trapezoidal screw by using a gearing system. A Linear Variable Differential Transformer (LVDT) is attached on each actuator giving back the actuator position in millimetres for the control system, while an encoder placed inside the motor provides the position of the motor shaft. Two actuation lines, each with two actuators, are integrated inside the wing model to change its shape. For the experimental model, a full-scaled portion of an aircraft wing tip is used with the chord length of 1.5 meters and equipped on the upper surface with a flexible skin made of composite fibre materials. A controllable voltage provided by a power amplifier is used to drive the actuator system. In this way, three control loops are designed and implemented, one to control the torque and the other two to control the position in a parallel architecture. The parallel position control loops use feedback signals from different sources. For the first position control loop, the feedback signal is provided by the integrated encoder, while for the second one, the feedback signal comes from the LVDT. For the experimental model, the parameters for the torque control, but also for the position control-based encoder signal, are implemented in the power amplifier energising the electrical motor. On the other hand, a National Instruments real-time system is used to implement and test the position control-based LVDT signal. The experimental validation of the developed control system is realised in two independent steps: bench testing with no airflow and wind-tunnel testing. The pressure data provided by a number of Kulite sensors equipping the flexible skin upper surface and the infrared thermography camera visualisations are used to estimate the laminar-to-turbulent transition point position.

Abstract: In this paper, a Gaussian process regression (GPR)-based novel method is proposed for non-linear aerodynamic modelling of the aircraft using flight data. This data-driven regression approach uses the kernel-based probabilistic model to predict the non-linearity. The efficacy of this method is examined and validated by estimating force and moment coefficients using research aircraft flight data. Estimated coefficients of aerodynamic force and moment using GPR method are compared with the estimated coefficients using maximum-likelihood estimation (MLE) method. Estimated coefficients from the GPR method are statistically analysed and found to be at par with estimated coefficients from MLE, which is popularly used as a conventional method. GPR approach does not require to solve the complex equations of motion. GPR further can be directed for the generalised applications in the area of aeroelasticity, load estimation, and optimisation.