Transactions on Aerospace Research Feed

Suborbital Spaceflight Regulation: A Case-Based Commentary on Managing Risk Beyond the Learning Period

Wed, 18 Mar 2026 00:00:00 GMT

This study presents a qualitative, case-based risk assessment to evaluate participant safety and regulatory accountability in suborbital spaceflight. Currently, the suborbital flight sector is operating under a regulatory “learning period” moratorium that offers minimal oversight from the Federal Aviation Administration’s Office of Commercial Space Transportation (FAA-AST). A qualitative Bowtie-based case study is presented herein, applying the ICAO risk matrix and the ALARP (As Low As Reasonably Practicable) methodology to a representative loss-of-pressurization scenario in Blue Origin’s suborbital operations. This approach demonstrates that structured qualitative risk-management frameworks can effectively assess catastrophic hazards with limited empirical data and reduce risks to acceptable levels without imposing excessive costs on operators. To address existing safety and regulatory gaps, this study recommends: (1) establishing a defined regulatory framework with mandatory vehicle certification and legal protections for participants; (2) the adoption of risk-management methodologies such as ALARP and CBA by commercial operators; (3) developing FAA-AST– directed medical screening and training programs for spaceflight participants; (4) incorporating personal safety equipment, including breathing apparatus; and (5) fostering collaboration with established aerospace institutions such as NASA. Overall, the findings highlight the need for near-term policy action to support a safe, sustainable, and accountable evolution of suborbital space tourism.

The Influence of a Hybrid Turboelectric Power Plant Energy System on the Performance and Emissions of A Passenger Aircraft

Wed, 18 Mar 2026 00:00:00 GMT

This study investigates how the architecture and key parameters of a hybrid turboelectric power plant (HTEPP) energy system influence the performance and environmental characteristics of a light regional passenger aircraft. Three HTEPP configurations are analyzed: (i) kerosene and liquid hydrogen supplied to both the combustion chamber and a fuel cell (FC), (ii) kerosene supplied to the combustion chamber with hydrogen supplied only to the FC, and (iii) kerosene supplied to the combustion chamber with hydrogen produced onboard via kerosene reforming for FC supply. A 20-seat aircraft concept derived from the L-410UVP-E family is developed and upgraded to accommodate the HTEPP, using the AI-450S-2 L-410UVP-E family is developed and upgraded to accommodate the HTEPP, using the AI-450S-2 turboprop engine and AI-P500V5 propellers. The study applies a semi-empirical aerodynamic method and a modular simulation framework (“Integration 2.2”) to estimate mission power demand, subsystem mass/volume characteristics, payload–range capability, and gross harmful emissions consistent with ICAO Annex 16 methodology. Results show that range gains from the HTEPP are modest due to mass penalties, whereas emissions reductions are more pronounced: approximately 21.1% for Scheme 1, 16.2% for Scheme 2, and 10.3% for Scheme 3. Turbine inlet gas temperature decreases by about 6–8% across all schemes, implying potential durability benefits. The findings highlight the central role of energy-management strategy and hybridization degree in determining feasible architectures and performance trade-offs for regional hybrid-electric aircraft.

Numerical Investigation of a Nested Double Annular Combustion Chamber Configuration for Rotating Detonation Engine Applications

Wed, 18 Mar 2026 00:00:00 GMT

Rotating Detonation Engines (RDEs) utilize supersonic combustion to enhance propulsion efficiency while enabling simplified engine architectures. However, in a conventional annular RDE, the central plug reduces thrust density compared to alternative propulsion concepts. To address this limitation, a nested double annular combustion chamber is proposed. This study evaluates the feasibility and performance of the configuration using two-dimensional axisymmetric computational fluid dynamics (CFD) simulations in ANSYS Fluent. Comparative numerical analyses of single- and double-chamber models were conducted under identical mass flux conditions. The results indicate that the proposed double-chamber configuration achieves comparable performance and can even outperform the single-chamber annular RDE by up to 2.26% in thrust per chamber area. These findings provide valuable insight into the potential of nested annular RDE configurations for improving thrust density and propulsion system compactness in future propulsion applications.

A Dynamic Predictive Likelihood Framework for Anticipatory Adaptive Nested Optimization in Airline Seat Reservation Control

Wed, 18 Mar 2026 00:00:00 GMT

This study develops a novel dynamic framework for anticipatory and adaptive airline seat inventory control under stochastic customer demand. The proposed approach integrates predictive likelihood estimation, nested protection-level optimization, and adaptive decision updating within a unified mathematical structure. Demand arrivals are modeled over a discrete booking horizon divided into multiple decision epochs, allowing continuous revision of protection levels and booking limits as new information becomes available. Unlike classical static approaches such as Littlewood's rule and EMSR heuristics, the proposed model combines global non-nested optimization with local nested protection-level adjustment based on predictive likelihood functions of customer demand. The framework enables real-time updating of allocation decisions while maintaining consistency with capacity constraints and revenue dominance conditions. In addition, a statistical procedure based on Weibull modeling of reservation times is introduced to detect structural changes in customer demand or competitive pricing strategies through minimization of misrecognition probability. Numerical simulations demonstrate that the proposed dynamic approach improves expected revenue relative to non-nested allocation and heuristic EMSR methods under representative parameter settings. The results suggest that predictive likelihood-based adaptive optimization provides a rigorous and computationally tractable alternative to heuristic seat allocation rules.

Uncertainty-Aware Robustness Analysis of Blended-Wing-Body Cabin Evacuation Under the Faa 90-Second Requirement (14 CFR § 25.803)

Wed, 18 Mar 2026 00:00:00 GMT

Blended-wing-body (BWB) aircraft are currently being explored for potential efficiency gains, but emergency evacuation remains a key certification feasibility requirement for wide, non-cylindrical cabins under the FAA 90 s rule (14 CFR §25.803). This study reframes evacuation compliance as a probabilistic safety assessment problem and develops an uncertainty-aware pipeline for certification-style robustness evidence. Evacuation is posed as a limit-state problem, g(θ) = 90 - T(θ), where T is evacuation time under uncertainty in behavioral and flow parameters. Monte Carlo simulation propagates bounded aleatory variability and evidence-tagged epistemic assumptions across a predefined stressor matrix (S0–S7) to estimate the distribution of T. Compliance is reported as PoC = P(T ≤ 90 s) with 95% confidence intervals and tail-risk metrics (T95,T99); Morris screening identifies dominant contributors to failure probability Pf = 1 - PoC and extreme delays. Baseline conditions meet the 90 s requirement, whereas topology/capacity disruptions – especially exit loss and compound stress – drive PoC toward zero and inflate upper-tail percentiles, indicating discharge-capacity limits. Reduced visibility and degraded crew effectiveness primarily thicken the right tail, yielding partial compliance but elevated Pf at 90 s. Robust layout screening (D1–D9) shows that exit-demand redistribution and capacity-preserving geometry recover safety margin with limited structural penalty growth‥

Analytical Modelling and Parametric Optimization of Hybrid Hydrogen-Electric Propulsion for Long-Endurance UAVs

Sat, 14 Mar 2026 00:00:00 GMT

This study presents a clear and analytically explicit framework for exploring hybrid hydrogen–electric propulsion in micro-to-small fixed-wing unmanned aerial vehicles (UAVs). By combining classical lift–drag relationships with a first-principles energy balance, the model expresses flight endurance and range through simple, closed-form relations involving hydrogen mass, battery capacity, and cruise speed. Unlike approaches that rely on computationally intensive CFD simulations or extensive hardware testing, the framework is entirely physics-based, enabling fast, transparent, and reproducible performance estimation during early design stages. A parametric design-space analysis examines how mass allocation between hydrogen and battery storage influences endurance and range. Under idealized, constant-mass and constant-efficiency assumptions, the analytical model predicts that balanced hybrid configurations can yield theoretical endurance values approaching 70 hours and ranges on the order of 3700 km, representing a substantial improvement relative to battery-only operation. Contour-based visualization illustrates trade–offs associated with hybridization ratios and cruise conditions, providing intuitive insight into system-level behaviour. Owing to its simplicity, interpretability, and open analytical structure, the framework serves as a practical conceptual-design tool for UAV sizing, propulsion planning, and sustainable long-endurance flight studies. The model supports early-stage decision-making by offering a physics-grounded means of exploring hybrid UAV performance trends prior to more detailed analyses.

History of the Development of Aviation Structures in Latvia

Wed, 24 Dec 2025 00:00:00 GMT

This article presents a comprehensive overview of the historical development of aviation structures in Latvia, tracing the evolution of aviation science, engineering, and technological innovation across three key periods: the pre–First World War era, the years of independent Latvia (1918–1940), and the post–Second World War period up to the late twentieth century. The study examines the contributions of Riga’s scientific centers, their leading researchers, and the scientific schools that emerged around them, highlighting both theoretical advances and their industrial applications. The analysis is based on published materials, archival documents, original technical solutions developed through research and invention, as well as information provided by former heads and staff members of Riga’s aviation research institutions that operated until 1992. Particular attention is given to early aircraft design efforts in Riga, the interwar aviation industry and its designers, the post-war rise of specialized research laboratories and automated control systems, and the work of student design bureaus in developing experimental aircraft and unconventional air vehicles. This article will be of interest to researchers, engineers, students of aviation universities, and anyone interested in the history of aviation science and technology.

Justification of Performance of the Hybrid Propulsion Systems Architecture for A Transport Airship

Wed, 24 Dec 2025 00:00:00 GMT

This study investigates key strategies for reducing the energy and financial costs of air transportation and argues that a substantial decrease in fuel use per ton-kilometer can significantly enhance Europe’s energy independence. To achieve this, the paper proposes an air transport system based on a large transport airship equipped with a hybrid propulsion system powered by solid oxide fuel cells (SOFCs). The proposed propulsion architecture integrates a gas turbine engine (GTE), an auxiliary generator, an SOFC stack, a steam reformer, electric motors, and a battery subsystem. Specially designed propellers ensure the aerodynamic performance required for efficient long-range transport. The auxiliary GTE provides compressed air for SOFC operation and preheats both the fuel cells and the reformed fuel mixture, enabling stable power generation under varying flight conditions. The study outlines methods for the parametric integration of hybrid propulsion systems with the aerodynamic design of a transport airship and identifies the key performance advantages of this configuration. The results can be applied to the development of next-generation hybrid airships with high payload capacity, long endurance, or high-altitude operating requirements, offering a viable pathway toward sustainable, low-emission aerial transport.

A Poisson-Process Model for Cumulative Delamination Damage in Composite Materials

Wed, 24 Dec 2025 00:00:00 GMT

This study presents a probabilistic model for cumulative damage in composite materials undergoing delamination. The model assumes the presence of numerous weak microvolumes (WMVs) in which fatigue damage can initiate and accumulate. Defect nucleation is described as a Poisson process whose rate does not depend on specimen size. The cumulative distribution function of the fatigue life of each microvolume is obtained using the Poisson formulation, and the overall delamination behavior is interpreted as a brittle-type failure mechanism governed by nodal attachment points in honeycomb structures. Numerical implementation is demonstrated through Excel-based inverse comparison and R-based simulation methods. The results show that Poisson-driven damage evolution provides a viable approach for estimating residual undamaged area and for modelling avalanche-type delamination growth. The methodology offers a foundation for future experimental verification and refinement of stochastic models for composite damage propagation.

Formalization of Hindsight Indicators and Characteristics for Assessing Foresight of Transport and Passenger Aircraft

Wed, 24 Dec 2025 00:00:00 GMT

This study develops a unified methodological framework for assessing the prospective development of passenger and transport aircraft through the formalization of hindsight indicators and the rational evaluation of technical characteristics. A hierarchical representation of the aircraft as a complex technical system (CTS) is constructed, enabling the decomposition of subsystem properties and the definition of rational benchmark values for key parameters. A comparative method based on the degree of rationality is proposed to evaluate the technical perfection of existing and future aircraft and to identify subsystem-level weaknesses, reserves, and integrative effects. To support foresight analysis, a transport-system indicator (NTS) is introduced and applied to a curated dataset of current and advanced aircraft projects. Interpolated hindsight envelopes are derived, defining the feasible domain of flight-performance combinations achieved by state-of-the-art designs. The method allows quantitative determination of whether a proposed future aircraft represents a continuation of existing technological trajectories or a potential breakthrough. The results demonstrate that rationality-based indicators, combined with hierarchical CTS structuring and hindsight-derived envelopes, provide a systematic approach for guiding early-stage design decisions, prioritizing research directions, and evaluating the plausibility of prospective configurations in both civil and prospective hybrid-propulsion aircraft development.

Computational Determination of Dynamic Stability Derivatives

Wed, 24 Dec 2025 00:00:00 GMT

Dynamic stability derivatives are essential for flight dynamics analysis, simulation, and control design, but their experimental determination is often costly and technically demanding. This paper investigates three CFD-based approaches for determining dynamic stability derivatives in compressible, viscous flow: (i) steady-flow simulations in a non-inertial (moving) reference frame for rotational derivatives, (ii) the Forced Oscillation Method (FOM) with prescribed harmonic motion, and (iii) the Indicial Response Method (IRM) based on step-response histories in angle of attack or pitch rate. All methods are implemented in ANSYS Fluent using the Moving Reference Frame and Dynamic Mesh capabilities and are applied to the Basic Finner missile (high-speed, low-α regime) and the SZD-9 Bocian glider (low-speed, 0° ≤ α ≤ 20°). For the Finner model, the computed pitch-damping sum (cmα + cmq) agrees with experimental data within the observed scatter, with both FOM and IRM showing consistent behavior except at M = 1.2, where a discontinuity is present in both simulations and measurements. For the glider, roll-damping derivatives Clp from the Moving Reference Frame and FOM approaches agree in attached flow, diverge in partially separated conditions, and reconverge in fully separated flow. The results identify flow regimes where each method can be used with higher confidence and highlight conditions requiring increased caution and additional validation.

A Simplified Graphical Method for Weight-And-Balance Determination in the Cessna 172R

Wed, 24 Dec 2025 00:00:00 GMT

Weight-and-balance (W&B) verification remains a critical yet often neglected component of safe general aviation operations. Many pilots rely on informal estimation or omit W&B calculations entirely, contributing to numerous accidents involving aircraft operated outside approved center-of-gravity (CG) and weight limits. This study presents a new W&B performance control method – the Computer Second Paper Operation (C2PO) system – developed for the Cessna 172R. The method eliminates the need to calculate individual station moments or total moments, reducing procedural complexity and decreasing preflight preparation time. Using a geometrically derived planar grid based on incremental CG changes for all loading stations, the C2PO chart allows pilots to determine CG using only basic arithmetic. The tool was constructed through a combination of analytical procedures and encoded in Excel and Visio to include every possible loading configuration. Compared with standard computational procedures, the method reduces calculation time by 43.83% while maintaining an accuracy of 0 to 0.15 inches. By offering a fast, intuitive, and calculator-free alternative, the C2PO method aims to improve pilot compliance, promote consistent preflight W&B checks, and reduce accidents caused by improper aircraft loading.

Kinematic Design and Control Analysis of A Subsonic Ejector Nozzle with Omni-Directional Thrust Vectoring for Afterburning Turbofan Engines

Wed, 24 Dec 2025 00:00:00 GMT

This paper presents the development and analysis of a kinematic scheme for a subsonic ejector nozzle equipped with omni-directional thrust vector control (TVC) for an afterburning turbofan engine intended for advanced maneuverable aircraft. The study examines existing thrust-vectoring nozzle concepts, identifies their limitations, and evaluates the applicability of known design solutions to next-generation turbofan configurations. A new kinematic scheme is proposed that builds on the variable-geometry subsonic nozzle of the AI-222-25F engine and integrates an ejector section and multiaxis flap actuation system. Detailed geometric modeling and kinematic analysis are performed for two perpendicular rotation planes, allowing the derivation of analytical relationships between control-ring orientation and flap deflection. An analytical method is introduced for computing hydraulic-cylinder strokes based on the normal-vector angle of the control ring, ensuring precise mapping between commanded thrust-vector angles and actuator motion. The resulting nozzle configuration achieves omnidirectional thrust-vector deflection of 15° and a 1.33× throat-diameter variation. The study provides a foundation for integrating the proposed nozzle into an aircraft layout and for future refinement considering structural constraints, thermal loads, and material selection.

Study of the Impact of Prolonged Operation on Residual Deformations in the Airframe Structure of an Aircraft

Wed, 24 Dec 2025 00:00:00 GMT

Purpose The study aims to quantitatively assess the accumulation of residual deformations in the aircraft airframe during long-term operation, using the An-24 regional aircraft as a representative case. Methods Levelling data obtained during maintenance were statistically processed using regression and correlation analysis. Polynomial trend models were combined with probability distribution parameters (mean, standard deviation, skewness) to describe geometric deviations of wing control sections across different intervals of flight hours, service life, and landings. Results The analysis revealed that 25–32% of wing geometry variations are explained by accumulated flight hours, while the remaining deviations result from other operational factors such as hard landings, turbulence, and maintenance practices. Residual deformations manifested as systematic changes in wing incidence and dihedral angles, with probability estimates showing a nonlinear increase in the risk of exceeding permissible limits. Practical implications The findings improve monitoring of structural geometry through systematic levelling, enhance the reliability of residual life prediction, and support the development of preventive maintenance strategies aimed at ensuring long-term airworthiness and flight safety.

Analysis and Determination of Technological Trends of the Development of an Afterburning Chamber of Turbofan Engines

Wed, 24 Dec 2025 00:00:00 GMT

This study identifies global technological and parametric trends in afterburner design for turbofan engines used in combat aircraft. A sample of 22 third-, fourth-, and fifth-generation aircraft was assembled, and propulsion systems were grouped by Maximum Afterburning (Max AB) thrust: <50 kN, 50–100 kN, and >100 kN. Three efficiency criteria were developed: (i) K 1, relating thrust-to-weight to total air mass flow; (ii) K 2, integrating thrust-to-weight with specific fuel consumption at Max AB; and (iii) K 3, an integral system indicator combining engine thrust, fuel efficiency, number of engines, aircraft maximum speed, combat load, and takeoff weight. Normalized values (0–1) and trends versus development year were analyzed. Results show clear, but non-linear, improvements across generations. Low- and medium-thrust classes exhibit the steepest gains, while the high-thrust class improves more moderately due to platform-level constraints (e.g., weight growth) and stealth-driven afterburner/nozzle compromises that can reduce pressure recovery and K 1. Despite these trade-offs, modern designs achieve higher integrated efficiency (K 3) via better balances of thrust, fuel economy, and payload/speed. Convergence of normalized indicators suggests proximity to practical technological limits for afterburning sections under current constraints. The methodology provides a quantitative basis for comparing AES concepts and supports future work on variable-cycle/adaptive systems and low-observability-compatible combustor/nozzle solutions.

Expert-Based Risk Assessment for Flight Safety Using Kendall's W and Pearson's Chi-Square

Fri, 31 Oct 2025 00:00:00 GMT

This paper presents a practical method for quantitative assessment of flight safety risk based on expert evaluation and statistical analysis. The approach addresses one of the key challenges in civil aviation: monitoring and managing safety performance under conditions of uncertainty and numerous interrelated risk factors. The proposed model integrates expert judgments with quantitative indicators to evaluate and rank potential hazards affecting flight operations. Using Kendall's coefficient of concordance (W) and the Pearson chi-square test, the method assesses the degree of agreement among experts and determines the statistical significance of identified risk factors. A numerical example demonstrates the application of the model, showing how it can reveal the most influential contributors to flight risk – particularly human and psychological factors – even when overall expert agreement is low. The results highlight that, despite limited consensus, such analysis allows safety managers to identify and prioritize critical factors within the Flight Safety Management System (SMS). The proposed method is simple, computationally accessible, and well suited for rapid evaluation in operational environments where timely decisions are essential. It complements existing risk-based systems such as FORAS by offering a structured, expert-driven framework for monitoring, comparing, and improving flight safety performance.

Methodology for Reducing the Negative Impact of Non-Conformance in Technical Personnel Activity in the System of Continuing Airworthiness of Aircraft

Fri, 31 Oct 2025 00:00:00 GMT

This paper presents a mathematical model for managing the human factor in the system of continuing airworthiness. The model is based on the entropy evaluation of deviations in technical personnel activities, such as errors and violations recorded during maintenance operations. Using 10 years of statistical data from the “Safety” automated control system on Tu-154 aircraft maintenance (1995–2005), over 100 individual deviations were analyzed and grouped into 20 complex indicators. These were further consolidated into five generalized factors reflecting key areas of organizational performance. Entropy measures were then used to rank these factors according to their contribution to risks affecting continuing airworthiness. The outcome of this analysis is the development of a Human Factor Control System (HFCS) for application within an Maintenance and Repair Organization, ensuring the required level of continuing aircraft airworthiness. The HFCS provides a structured framework for prioritizing management actions, particularly under conditions of limited organizational resources.

Analysis of Eddy Current Probe Signal Model for Structural Monitoring of Aircraft Materials

Fri, 31 Oct 2025 00:00:00 GMT

We develop a physico-mathematical model of the “eddy current probe – test object” (ECP–TO) system that analytically describes current dynamics in coupled probe circuits while accounting for key physical and electrical parameters. The model, derived from the characteristic equation of transformer-type configurations for nonmagnetic and magnetic targets, explains when the measured response is harmonic or damped harmonic as a function of excitation mode and system parameters, thereby revealing additional informative features for material evaluation. We validate the model numerically using finite element (FEM) simulations (COMSOL, Magnetic Fields, frequency domain) and introduce a digital signal-processing workflow that extracts instantaneous amplitude- and phase-time characteristics during scanning. Experiments on aluminum alloy specimens demonstrate sensitivity to small conductivity variations and identify optimal excitation frequencies for reliable subsurface defect detection; in the tested configuration, an “infinitely deep crack” was detectable to 15.3 mm at 50 Hz. The combined analytical–numerical–experimental approach supports sensitivity-driven ECP design, accelerates inspection parameter selection, and facilitates integration with structural health monitoring (SHM) systems for aerospace structures.

Conceptual Design and Validation of a Hydrogen Training Airplane

Fri, 31 Oct 2025 00:00:00 GMT

This study presents the conceptual design and stability assessment of an ultralight hydrogen-electric training aircraft. Building on a Minimum Viable Product (MVP) approach, the analysis first examines design requirements and trends in existing two-seat trainers. A conceptual design process is then applied, with adaptations for the integration of a hydrogen propulsion system comprising a fuel cell stack, electric motor, battery, and high-pressure hydrogen storage. Four alternative configurations for propulsion system placement were proposed and compared; the integrated nose-mounted layout was identified as the most promising. Stability and controllability analyses demonstrated that, despite relatively high moments of inertia and sensitivity in control forces, the aircraft remains stable and controllable across the flight envelope. The results confirm the technical feasibility of hydrogen propulsion integration in the ultralight training segment, while also highlighting the need for further aerodynamic validation, prototype testing, and regulatory development to support the future certification of hydrogen-powered aircraft.

Aerodynamic Design Methodology for Air Propellers of Swarm UAVs under Variable Mission Payloads

Fri, 31 Oct 2025 00:00:00 GMT

This study presents an aerodynamic design methodology for fixed- and variable-pitch air propellers (APs) for swarm unmanned aerial vehicles (UAVs), based on vortex theory. The methodology integrates design calculations with system analysis, mathematical modeling, and parametric simulations to evaluate aerodynamic and flight characteristics under diverse operational scenarios. The results demonstrate that UAV flight range and endurance are strongly influenced by payload configuration, flight altitude, and velocity, with bomb load having a particularly significant impact. Verification calculations confirm that one of the most critical factors in improving UAV performance is the design of mission-specific propellers. To address this, we propose a modular approach in which UAVs are equipped with sets of interchangeable APs, each optimized for distinct combat tasks and payloads. This approach enables flexible mission adaptation while maintaining efficiency across flight regimes, providing a practical pathway toward enhancing the performance of tactical swarm UAVs.