Staff publications (AA)

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Open Access
Advanced diagnostics of aircraft structures using automated non-invasive imaging techniques: a comprehensive review
(MDPI, 2025-04-01) Bardis, Kostas; Avdelidis, Nicolas P.; Ibarra-Castanedo, Clemente; Maldague, Xavier P. V.; Fernandes, Henrique
The aviation industry currently faces several challenges in inspecting and diagnosing aircraft structures. Current aircraft inspection methods still need to be fully automated, making early detection and precise sizing of defects difficult. Researchers have expressed concerns about current aircraft inspections, citing safety, maintenance costs, and reliability issues. The next generation of aircraft inspection leverages semi-autonomous and fully autonomous systems integrating robotic technologies with advanced Non-Destructive Testing (NDT) methods. Active Thermography (AT) is an example of an NDT method widely used for non-invasive aircraft inspection to detect surface and near-surface defects, such as delamination, debonding, corrosion, impact damage, and cracks. It is suitable for both metallic and non-metallic materials and does not require a coupling agent or direct contact with the test piece, minimising contamination. Visual inspection using an RGB camera is another well-known non-contact NDT method capable of detecting surface defects. A newer option for NDT in aircraft maintenance is 3D scanning, which uses laser or LiDAR (Light Detection and Ranging) technologies. This method offers several advantages, including non-contact operation, high accuracy, and rapid data collection. It is effective across various materials and shapes, enabling the creation of detailed 3D models. An alternative approach to laser and LiDAR technologies is photogrammetry. Photogrammetry is cost-effective in comparison with laser and LiDAR technologies. It can acquire high-resolution texture and colour information, which is especially important in the field of maintenance inspection. In this proposed approach, an automated vision-based damage evaluation system will be developed capable of detecting and characterising defects in metallic and composite aircraft specimens by analysing 3D data acquired using an RGB camera and a IRT camera through photogrammetry. Such a combined approach is expected to improve defect detection accuracy, reduce aircraft downtime and operational costs, improve reliability and safety and minimise human error.
Open Access
Adaptive UAV control with sensor and actuator faults recovery
(MDPI, 2025-03-01) Bekhiti, Abdellah; Souanef, Toufik; Toubakh, Houari; Horri, Nadjim; Kafi, Mohamed Redouane; Bouzid, Zakaria
This paper presents an adaptive fault-tolerant control strategy tailored for fixed-wing unmanned aerial vehicles (UAV) operating under adverse conditions such as icing. Using radial basis function neural networks and nonlinear dynamic inversion, the proposed framework effectively handles simultaneous actuator and sensor faults with arbitrary nonlinear dynamics caused by environmental effects, model uncertainties and external disturbances. A nonlinear disturbance observer is incorporated for accurate sensor fault detection and estimation, thereby enhancing the robustness of the control system. The integration of the radial basis function neural network enables an adaptive estimation of the faults, ensuring accurate fault compensation and system stability under challenging conditions. The observer is optimised to minimise the deviation of the closed-loop dynamics eigenvalues from the assigned eigenvalues and to approach unity observer steady-state gain. The stability of the control architecture is mathematically proven using Lyapunov analysis, and the performance of the approach is validated through numerical simulations on a six Degrees of Freedom fixed-wing unmanned aerial vehicles model. The results show superior performance and robustness to challenging fault scenarios. This research provides a comprehensive fault management solution that enhances the safety and reliability of unmanned aircraft operations in extreme environments.
Open Access
Fault diagnosis across aircraft systems using image recognition and transfer learning
(MDPI, 2025-03-02) Jia, Lilin; Ezhilarasu, Cordelia Mattuvarkuzhali; Jennions, Ian K.
With advances in machine learning, the fault diagnosis of aircraft systems is becoming more efficient and accurate, which makes condition-based maintenance possible. However, current fault diagnosis algorithms require abundant and balanced data to be trained, which is difficult and expensive to obtain for aircraft systems. One solution is to transfer the diagnostic knowledge from one system to another. To achieve this goal, transfer learning was explored, and two approaches were attempted. The first approach uses relational similarity between the source and target domain features to enable the transfer between two different systems. The results show it only works when transferring from the fuel system to ECS but not to APU. The second approach uses image recognition as the intermediate domain linking the distant source and target domains. Using a deep network pre-trained with fuel system images or the ImageNet dataset finetuned with a small amount of target system data, an improvement in accuracy is found for both target systems, with an average of 6.90% in the ECS scenario and 5.04% in the APU scenario. This study outlines a pioneering approach that transfers knowledge between completely different systems, which is a rare transfer learning application in fault diagnosis.
Open Access
Does cutting airport slots reduce climate impact? the case of Amsterdam airport
(Elsevier, 2025-06) Suau-Sanchez, Pere; Dobruszkes, Frédéric; Mattioli, Giulio
This study evaluates the effectiveness of airport slot reductions as a strategy for mitigating greenhouse gas (GHG) emissions, focusing on Amsterdam Schiphol Airport. Following the Dutch Government's decision to reduce slots from 500,000 to 440,000, we analyse various risk scenarios using the D'Hondt method for proportional slot allocation and the Fuel Estimation in Air Transportation (FEAT) model to estimate fuel consumption. Strategies include proportional slot cuts, prioritising short-haul flights, and shifting to rail alternatives. Results show that short-term emissions reductions are modest and do not scale with slot reductions unless long-haul flights are significantly curtailed. Moreover, aircraft up-gauging could lead to increased emissions if airline behaviour is not addressed. Our findings challenge the effectiveness of slot reductions as a climate strategy, highlighting the importance of targeting long-haul flights and adopting comprehensive policies to achieve substantial emissions reductions. The study offers critical insights for sustainable aviation policy development.
Open Access
A review of hydrogen micromix combustion technologies for gas turbine applications
(Elsevier, 2025-05-13) Singh, Gaurav; Schreiner, B. Deneys J.; Sun, Xiaoxiao; Sethi, Vishal
Hydrogen micromix combustion is a promising technology for gas turbines, introducing rapid, miniaturized air-fuel mixing, significantly reducing combustion zone length and nitrogen oxides (NOx) emissions. This review evaluates the state-of-the-art hydrogen micromix combustion technologies, focusing on injector performance, flashback characteristics, and NOx reduction strategies. Injector designs are categorized based on premixing and flame stabilization techniques. While stationary gas turbines approach Technology Readiness Level (TRL) 9, aviation applications remain below TRL 4. This review identifies key design principles and predictive modelling challenges and presents a development roadmap for advancing hydrogen micromix combustion technology for aviation from TRL 4 to TRL 9 by 2040.
Open Access
Energy optimization strategies for automatic tiltrotor electric vertical takeoff and landing aircraft
(AIAA, 2025-03-25) Kang, Namuk; Lu, Linghai; Whidborne, James F.
Open Access
Pilots’ training backgrounds affecting the attribution of event causal factors and airline safety management
(Elsevier, 2025-05) Chan, Wesley Tsz-Kin; Li, Wen-Chin; Braithwaite, Graham
For safety management in diverse aviation operators, it is necessary to investigate how different cultural factors interact in flight operations. Whilst prior studies have evaluated between-group cultural differences, there remains a research gap on whether within-group subcultural differences challenge the assimilation of people into the safety culture of the wider group. Cultural differences in how causal factors are perceived in the context of systemic safety deficiencies can affect the implementation of safety management strategies. In the present study, pilots from airline-sponsored, self-funded, and ex-military initial training backgrounds were invited to categorise an identical set of aircraft accident causal factors using the Human Factors Analysis and Classification System (HFACS). Results from 121 participants found significant differences amongst the three groups in the attribution of human factors conditions to organisational-level and supervisory-level categories. Significant associations amongst HFACS categories also differed amongst the three professional groups, with a considerable number of same-level associations found between ‘Preconditions for Unsafe Acts’ at the same level. Familiarity with organizational cultures was considered to impact the perception of causal factors. The finding of same-level associations presents a new contribution to the theoretical basis of the HFACS taxonomy, calling for a conceptual change in the directionality of causal sequences. The results suggest that the direction of safety remedies for different parts of the organisation is dependent on perceived relevance, which differs amongst subcultural groups. Findings are relevant to industry, particularly international airlines with diverse employee subcultural groups, for the implementation of safety management systems.
Open Access
Unsteady flow interactions and ground plane proximity in a coupled compact intake-fan in crosswind
(Association Aéronautique et Astronautique de France (3AF), 2025-04-01) Lobuono, Luca; MacManus, David G.; Hueso Rebassa, Josep; Christie, Robert
The assessment of the crosswind flow separation mechanisms and resulting distortion for compact intakes can be a key contributor for the design of viable large civil aeroengines. Under crosswind conditions, the intake aerodynamics are strongly influenced by both the fan and the ground plane. However, the impact of key design parameters, such as ground clearance, on the intake flow distortion is not fully understood. This study investigates the effects of a large variation in ground clearance on the intake-fan unsteady aerodynamics using an Unsteady Reynolds-Averaged Navier-Stokes fully coupled with a rotating fan stage. The work includes an assessment of the unsteady swirl distortion and the unsteady peak distortion events. The findings show that increased ground clearance can have adverse effects for the considered compact intake design. Gross separation can occur at lower crosswind velocities and arise at the intake lower section due to mass flow redistribution. When the ground clearance is increased, the gross separation on the windward side of the intake occurs at a greater crosswind velocity but exhibits greater levels of unsteady intake flow distortion. Overall, intake designs should be assessed at the expected ground clearance as the distortion and the onset of separation can vary substantially.
Open Access
Cluster-based tracking method for the identification and characterisation of vortices
(Association Aéronautique et Astronautique de France (3AF), 2025-03-26) Ibanez, Claudia; Migliorini, Matteo; Giannouloudis, Alexandros; Tejero, Fernando; Zachos, Pavlos K.
An unsupervised, flow-agnostic and automatic cluster-based tracking algorithm for the segmentation of vortex-dominated flows has been successfully developed. It combines the Rortex method and density-based clustering algorithms. The Rortex method differs shear from rotation and overcomes the sensitivity to user-defined thresholds that characterises current practice of vortex identification methods. The algorithm is demonstrated with experimental Stereoscopic Particle Image Velocimetry data from two cases; a high-Reynolds (≈ 106) vortex generated by a half-delta wing, and distorted flow in a scaled-model of a civil aero-engine intake under cross-wind conditions. The approach is a successful method for the segmentation of complex vortical flows under a wide range of conditions.
Open Access
Creating more viable safety recommendations in accident investigation by revising the human factors intervention matrix (HFIX)
(Elsevier, 2025-05-01) Chan, Wesley Tsz-Kin; Li, Wen-Chin; Yeun, Richard; Wang, Thomas
Open Access
Use of Bayesian Networks to understand sustainability requirements
(MDPI, 2025-03-13) Spinelli, Andrea; Kipouros, Timoleon
Sustainability is a key requirement in contemporary engineering design, but it is difficult to quantify due to its multidimensionality. We propose the application of Bayesian Networks for modeling the cause and effect of engineering systems and their environment. Emphasis is placed on capturing the impact on sustainability indicators of design decisions. These include the performance of the system, its economic viability in terms of cost, and its environmental and societal impacts. The method leverages data from simulation models, enabling the designer to perform assumption-free inferences on the variables at play.
Open Access
Integrated power and thermal management system in a parallel hybrid-electric aircraft: an exploration of passive and active cooling and temperature control
(MDPI, 2025-03-13) Ouyang, Zeyu; Nikolaidis, Theoklis; Jafari, Soheil; Pontika, Evangelia
Hybrid-electric aircraft (HEAs) represent a promising solution for reducing fuel consumption and emissions. However, the additional heat loads generated by the electrical propulsion systems in HEAs can diminish these benefits. To address this, an integrated power and thermal management system (IPTMS) is essential to mitigate these challenges by optimizing the interaction between thermal management and power management. This paper presents a preliminary IPTMS design for a parallel HEA operating under International Standard Atmosphere (ISA) conditions. The design includes an evaluation of active cooling, passive cooling, and active temperature control strategies. The IPTMS accounts for heat loads from the engine system, including the generators, shaft bearings, and power gearboxes, as well as from the electrical propulsion system, such as motors, batteries, converters, and the electric bus. This study investigates the impact of battery power (BP) contribution to cooling power on required coolant pump power and induced ram air drag. A comparison of IPTMS performance under 0% and 100% BP conditions revealed that the magnitude of battery power contribution to cooling power does not significantly impact the thermal management system (TMS) performance due to the large disparity between the total battery power (maximum 950 kW) and the required cooling power (maximum 443 W). Additionally, it was determined that the motor-inverter loop accounts for 95% of the pump power and 97% of the ram air drag. These findings suggest that IPTMS optimization should prioritize the thermal domain, particularly the motor-inverter loop. This study provides new insights into IPTMS design for HEAs, paving the way for further exploration of IPTMS performance under various operating conditions and refinement of cooling strategies.
Open Access
Control allocation problem transformation approaches for over-actuated vectored thrust VTOLs
(Elsevier, 2025-06-01) Enenakpogbe, Emmanuel; Whidborne, James F.; Lu, Linghai
One main challenge of vectored thrust VTOLs is actuator thrust control saturation because it may lead to undesired behaviour and loss of control if the control channels are not prioritised. Another challenge of vectored thrust VTOLs is that the vectored thrust results in non-linear effector mapping preventing the direct use of standard linear control allocation approaches. Linear control allocation approaches have lower online computational and complexity burden, and have simplier requirements for fault tolerance and reconfigurability than nonlinear control allocation approaches. This paper proposes three real-time control allocation approaches for transforming a nonlinear control allocation problem to a linear problem so that classical linear control allocation approaches can then be used. The approaches which addresses the two main challenges of the particular VTOL configuration are then tested using three selected flight test manoeuvres on a generic over-actuated vectored thrust three degrees of freedom planar VTOL with no aerodynamics. The first approach transfers the non-linearity from the effector mapping to the computation of the actuator limits by formulating the real controls in cartesian form and then converts the physical actuator limits from polar to cartesian form. The second approach transforms the non-linear effector mapping to a linear mapping via numerical linearisation of the non-linear effector mapping in real-time. The third approach is similar to second approach except an extra step which transforms the virtual controls from cartesian to polar before performing an analytical linearisation resulting in a different and more complicated linear Effector mapping. The results demonstrate the effectiveness of the proposed control allocation schemes to allocate remaining control authority to higher priority and critical control channels in order to maintain operational safety and stability during certain flight conditions while there is limited control authority.
Open Access
Use of non-intrusive flow diagnostics for aero-engine inlet flow distortion measurements in an industrial wind-tunnel
(AIAA, 2025-01-06) Piovesan, Tommaso; Zachos, Pavlos K.; MacManus, David; Michaelis, Dirk; van Rooijen, Bart; Sheaf, Christopher; Arzoglou, Dimitris
In crosswind conditions, aero-engine intakes experience unsteady flow distortions at the fan face, typically caused by the ingestion of ground vortices and flow separation. These distortions can negatively impact both intake performance and the compatibility of the downstream propulsion system. Understanding the aerodynamics of these flows is crucial for developing next-generation aircrafts with propulsion systems integrated more closely with the airframe. Optical measurement techniques provide detailed datasets in both space and time to support this understanding, but several challenges limit their widespread use in propulsion integration testing. This study demonstrates a novel application of non-intrusive flow diagnostics in an industrial setting for propulsion integration testing. Optical measurements were conducted within an aspirated intake configuration and, later, within a fully coupled fan-intake propulsion system representative of a modern high-bypass aero-engine. Several innovative solutions were developed to improve the integration of optical systems into industrial settings and enhance data acquisition efficiency. The analysis of the results yielded significant contributions about the unsteady interactions within civil intakes at crosswind and high incidence conditions, which are expected to have a notable impact on the development of future, closely integrated propulsion systems architectures able to meet the specified NetZero targets.
Open Access
Experimental investigation of unsteady fan-intake interactions using time-resolved stereoscopic particle image velocimetry
(Elsevier, 2025-07) Migliorini, Matteo; Zachos, Pavlos K.; MacManus, David G.; Giannouloudis, Alexandros
Understanding engine response to unsteady intake flow distortion is a crucial requirement to de-risk the development of novel aircraft configurations. This is more critical for configurations with highly embedded engines. Recent advances in non-intrusive, laser-based flow diagnostics demonstrated the ability to measure unsteady flows in convoluted intakes with high resolution in time and space. This work presents novel non-intrusive, unsteady flow measurements ahead of a fan rotor coupled to a convoluted diffusive intake. The fan rotor caused a local increase of the maximum levels of swirl intensity at the blade tip region, as well as flow re-distribution at the interface plane between the fan and the inlet duct compared to the baseline configuration with no fan in place. This contributed to the reduction of the overall swirl angle unsteadiness across the main flow distortion frequencies. This research presents a notable advance in unsteady fan-intake interaction characterisation. The work shows that high-resolution optical measurements offer notably better understanding of these complex aerodynamic interactions and have the potential to be part of larger scale, industrial testing programmes for future product development and certification.
Open Access
Off-design performance control and simulation for gas turbine engines with sequential combustors
(SAGE, 2025-12-31) Li, Yi-Guang; Liu, Yang
A gas turbine engine with a sequential combustion system has the potential to offer high cycle efficiency at moderate turbine entry temperatures. Consequently, it has one more degree of power setting control, which offers more flexible but also more complex control of engine off-design operations. In this paper, a novel simulation method for off-design thermodynamic performance of sequential combustion gas turbines has been introduced and a novel performance control schedule for part-load operations at various ambient conditions have been proposed aiming to keep the relative workloads between the two turbine sections constant. The proposed control schedule is simple and can be adapted easily. By applying the off-design performance control schedule to a model industrial gas turbine engine with two sequential combustors, the performance of the model engine is simulated at different part-load and at different ambient conditions. The results show that by applying the proposed off-design performance control schedule, the model sequential combustion gas turbine engine could operate effectively at different part-load operating conditions and at different ambient conditions with both turbine sections keeping nearly constant workload distributions.

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