Search Results (955)

Flutter constrains the design of modern high-aspect-ratio wings, yet the combined influence of planform geometry, aspect ratio (AR) and structural flexibility is rarely assessed within a single consistent framework. This work presents a unified, physics-based reduced-order comparison of rectangular, trapezoidal and elliptical planforms under both rigid and flexible representations, intended as a screening tool for preliminary design rather than as a quantitatively predictive methodology for specific aircraft. A two-degree-of-freedom plunge–pitch typical section with quasi-steady (Theodorsen-based) aerodynamics is cast in state-space form, and flutter is identified through eigenvalue continuation by combined frequency coalescence and damping sign change. For rectangular and trapezoidal wings, increasing AR or reducing stiffness consistently advances flutter onset: at a fixed AR of 7.1, stiffening alone raises the critical speed by approximately 43 m/s (from 105 to 148 m/s, ≈+41%). In contrast, within the reduced-order model the elliptical planform inverts this trend: with sufficient stiffness, frequency coalescence is suppressed, and from the stiffened baseline (AR ≈ 4.75) raising AR to 5.6 keeps the wing flutter-free across the investigated velocity range, whereas lowering AR to 3.9 reintroduces hard flutter at 155 m/s. These model-based comparative tendencies indicate that AR and structural flexibility are strongly coupled design drivers and that elliptical loading is comparatively flutter-resistant, providing an efficient basis for early-stage configuration screening. Full article

In the present work, an alternative methodology was developed for the rapid prediction of pressure distributions over wings of low-speed aircraft. A hybrid neural network architecture, named “MARTHA” (Model for Airloads Reconstruction using a Trained Hybrid Architecture), was presented, which is composed of a Multilayer Perceptron and the decoder of an Autoencoder. Three compact representation models—Principal Component Analysis (PCA), Autoencoder (AE), and Variational Autoencoder (VAE)—were systematically evaluated to determine the optimal dimensionality reduction architecture; the AE was selected based on its superior reconstruction accuracy and training stability. The main feature of MARTHA is that it provides predictions of the differential pressure coefficient field in the form of monochrome images, where the pixel intensity directly represents the normalized pressure value. One of the main objectives of developing MARTHA was to create a rapid surrogate model that can approximate vortex lattice method (VLM) simulations in preliminary design and optimization tasks, particularly when thousands of wing configurations need to be evaluated. The key feature of the proposed model is its ability to predict the pressure distribution for trapezoidal wings of various geometries 10¹–10⁴ times faster than numerical models, while maintaining accuracy (R² = 0.9998). The data obtained are presented in a convenient format for their further use in CAE systems of strength analysis. To assess the practical utility of the proposed model, implementation cases were carried out using the finite element software ANSYS 18.2 for three wing configurations not present in the training dataset. The pressure fields predicted by MARTHA were mapped onto the wing meshes, and linear static structural analyses were performed. The obtained Von Mises stress distributions showed good agreement with the corresponding distributions obtained using numerical models. Full article

The maneuvering flight of future aircraft which employ morphing variable camber wings (VCWs) requires rapid and accurate aerodynamic regulation. However, the dynamic lift responses during fast morphing deflection exhibit unsteady hysteresis effects, hindering shape and flight control performance. This study proposes a novel modeling and feedforward compensation algorithm based on the Prandtl–Ishlinskii (PI) model to identify and mitigate such unsteady hysteresis effects from a control perspective. First, unsteady lift responses of a two-dimensional trailing-edge VCW under periodic and non-periodic morphing motions are analyzed, and the influences of morphing trajectories on lift characteristics are investigated. The results reveal that the maximum lift decreases significantly as the morphing frequency increases. Under point-to-point non-periodic morphing conditions, pronounced hysteretic lift responses are observed and are strongly influenced by the morphing trajectories. A forward model mapping “morphing trajectory-lift response” is developed using PI hysteresis operators and log(t)-creep operators, identified using time-domain data from two-dimensional computational fluid dynamics (CFD) calculations. From this, an inverse model of the “expected lift response-compensated morphing trajectory” is derived using a hysteresis compensation function. Simulations indicate that periodic lift hysteresis is effectively compensated, yielding a quasi-steady linear relationship. For fast terminal morphing, compensated trajectories enable lift to reach targets rapidly, smoothly, and stably without lag. Robustness is validated for varying lift targets and terminal times. This work offers new insights into fast morphing-wing and high-maneuverability control of future smart aircraft. Full article

Flying-wing aircraft are more susceptible to wind disturbance due to their smaller wing loading, making gust alleviation critical for flight performance and safety. Conventional control surfaces may exhibit insufficient manipulation efficiency on such configurations, motivating the adoption of active flow control, particularly circulation control (CC) due to its favorable control efficiency. This paper presents an Active Disturbance Rejection Control (ADRC) framework for gust load alleviation (GLA) of flying-wing aircraft equipped with CC actuators, which enables real-time estimation and compensation of both gust disturbance and practical uncertainties and is validated through closed-loop wind-tunnel experiments under various sinusoidal gust conditions. An unsteady aerodynamic model with experimental data is established and simulations are performed for further investigation of alleviation performance and response characteristics under a wide range of gust conditions. Results show that both ADRC and PID exhibit degraded performance at higher gust frequencies and larger gust ratios, but ADRC achieves higher alleviation efficiency across the tested conditions. Furthermore, ADRC maintains satisfactory performance with actuator delays up to 0.04 s and outperforms PID under measurement noise and Dryden turbulence. These findings validate the effectiveness and robustness of ADRC for GLA, underscoring its practical potential for active flow control systems. Full article

In aerospace applications, structural vibration can cause fatigue accumulation and shorten the service life of aircraft. This makes vibration suppression based on Macro Fiber Composite (MFC) piezoelectric composites an important research topic. Considering the asymmetric high-voltage operating range of the M-8557-P1 MFC from −500 V to 1500 V and its capacitive impedance characteristics within the 1000 Hz operating frequency band, this paper designs a laboratory prototype of a high-voltage driver. The prototype adopts a voltage–current dual closed-loop structure and a current-tracking PWM control strategy. Under the tested laboratory conditions, the prototype exhibited a relatively fast transient response and a certain dynamic driving capability for capacitive loads. Based on the laboratory prototype, an auxiliary signal-conditioning module and a digital control module equipped with an active control algorithm were further developed. These modules were integrated with the laboratory prototype to form a high-voltage closed-loop control system for MFC piezoelectric sensing and actuation. Ground laboratory tests were conducted on a high-aspect-ratio unmanned aerial vehicle wing. The experimental results show that, when the dominant vibration frequency is approximately 3.6 Hz, the response converges to a steady state within 4.77 s after control is applied. In the steady state, the root-mean-square displacement decreases from 15.57 mm to 4.28 mm, corresponding to a reduction of 72.52%. This result demonstrates the effectiveness of the active vibration control system under this representative application scenario. Full article

An oblique wing aircraft can continuously vary its wing sweep angle, making it attractive for high-altitude unmanned aerial vehicle (UAV) relay missions that require stable attitude, altitude, and speed for antenna pointing and air-to-ground link consistency. The present work focuses on flight-platform stability as an enabling layer for UAV relay operation rather than on direct optimization of link-level communication metrics. During sweep transitions, however, sweep-dependent mass properties, aerodynamic loads, and control effectiveness introduce coupled attitude disturbances. This study develops a six-degree-of-freedom nonlinear multi-body model using Kane’s formalism to retain products of inertia, center-of-gravity variation, and sweep-dependent control effectiveness in a compact control-oriented form. A minimum-control-energy allocation method is formulated to coordinate the aileron and differential all-moving horizontal tail when aileron roll authority decreases at large sweep angles. An inner/outer-loop sliding-mode controller with auto-throttle is then designed for attitude, altitude, and speed regulation. Closed-loop simulations of 0–30° and 30–60° sweep maneuvers show that altitude and speed remain close to their commands while attitude deviations remain bounded. A 15% aerodynamic-coefficient perturbation case further indicates bounded closed-loop responses under the considered model uncertainty. Full article

This paper presents a generic stochastic simulation framework for evaluating the operational feasibility of solar-powered unmanned aerial vehicles (UAVs) executing an invariant trajectory in high-variability climates. Unlike conventional approaches relying on idealised irradiance conditions, the proposed framework combines a modified ASHRAE radiation model corrected for local bias and variability with a semi-Markov process modelling stochastic transitions between cloud and sunlight states using parametrised state duration times. The environmental model is further extended with diurnal temperature variation and standard atmosphere effects. UAV motion is represented using a rigid body flight dynamics model combined with a cascaded trajectory tracking controller and an energy subsystem incorporating a lithium-ion battery model. Warsaw (Dfb climate) is used as a representative Central European test case characterised by frequent radiation deficits and highly variable atmospheric conditions. The simulations quantify the influence of environmental uncertainty and selected battery capacities on mission success probability across different solar-to-wing area ratios, with the mission entry at 70% initial battery state of charge and no additional manoeuvre losses or external atmospheric perturbations. The evaluations were conducted for a fixed mission start at solar noon on 15 July and were supplemented by an optimised mission scheduling analysis to establish upper flight-time limits. The results demonstrate the strong sensitivity of solar-assisted UAV operations to stochastic cloud conditions and support the design and mission planning for low-altitude long-endurance aircraft. Full article

To improve the speed and accuracy of airborne inertial navigation systems during ground initial alignment, this paper proposes a rapid self-alignment method suitable for fixed-wing aircraft during the taxi-to-takeoff phase on the runway. This approach leverages pre-surveyed runway heading data to transform the velocity vector calculated in the navigation frame to the runway frame. By utilizing the geometric constraint that the aircraft’s actual position during ground taxiing must remain within the runway boundaries and closely follow the runway centerline, the proposed method employs a dedicated Kalman filter to achieve rapid initial alignment. Both simulations and flight tests demonstrate that the proposed method can achieve rapid initial alignment within 30 s during the runway taxiing phase, with attitude, velocity, and position accuracy levels comparable to those of GNSS-aided in-motion alignment. This method eliminates the need for external aiding equipment and can serve as an emergency initial alignment solution for airborne inertial navigation systems under GNSS outage conditions, effectively enhancing the aircraft’s autonomy and rapid response capability. Full article

With the development of morphing aircraft, understanding the fluid–structure interaction (FSI) mechanisms of multibody systems composed of rigid and flexible components has become increasingly important. The coupled motion and deformation of such systems in a flow field give rise to complex nonlinear FSI problems. Here, we propose a fluid–multibody–structure interaction framework that couples a finite volume Navier–Stokes solver, a multibody dynamics solver, and radial basis function interpolation for fluid–structure data transfer. The framework is validated using a benchmark case and subsequently applied to simulations of a two-segment flexible beam and a three-dimensional continuously variable-sweep wing. The results show that the presence of joints and structural flexibility substantially affects the FSI response: hinge location markedly alters the FSI characteristics of the multibody flexible-beam system, while increasing the sweep angle during continuous morphing reduces the aerodynamic force coefficients and structural flexibility induces persistent fluctuations in aerodynamic loads. A key contribution of the proposed framework is its ability to capture both active morphing motions and passive aeroelastic deformations simultaneously. Compared with approaches based on inviscid, incompressible aerodynamic models, the present high-fidelity flow solver can better resolve complex flow phenomena during morphing. This framework provides a useful numerical tool for investigating FSI mechanisms in morphing aircraft. Its current limitations include the computational cost of global radial basis function interpolation for large multibody systems and its applicability being restricted to low-Mach-number flows. Full article

Low-altitude general aviation aircraft and unmanned aerial vehicles (UAVs) are widely deployed for complex operational tasks, yet low-altitude gusts and crosswind disturbances induce severe airspeed fluctuations, leading to variable lift, unstable flight altitude, and perturbed pitch attitude. Such aerodynamic fluctuations degrade flight smoothness and increase pilot control workload. To mitigate lift and altitude instability under unsteady incoming flow, this paper proposes a novel passive trailing-edge winglet configuration capable of self-regulating wing angle of attack (AOA) without active flight control systems. A quasi-static aerodynamic equilibrium analytical model based on moment balance about the wing pivot axis is established, combined with validated Computational Fluid Dynamics (CFD) simulations to characterize the passive AOA adjustment mechanism and quantify lift variations under velocity perturbations. Results demonstrate that the integrated wing-winglet layout generates passive aerodynamic feedback moments to automatically adjust the wing AOA when freestream speed varies. For airspeed disturbances within ±10% of the cruise velocity (102 m/s, 0.3 Ma), the total lift fluctuation of the wing-winglet assembly is suppressed within ±1.01%, whereas conventional fixed-wing configurations experience lift deviations between −16% and +22% under identical disturbance conditions. Notably, the present study only verifies quasi-static aerodynamic equilibrium under steady inflow; dynamic flight stability, unsteady aerodynamic effects, and stall-limit performance remain unexamined and require further investigation. The core novelty of this design lies in the passive negative-feedback aerodynamic moment generated by the trailing-edge winglet, which decouples fuselage attitude from wing pitching motion and stabilizes equilibrium lift under mild low-altitude gust perturbations. Full article

Section-load calibration is used in aircraft wing-box testing. This study evaluates a fixed-position quasi-static load-calibration and identification procedure for one 7050 aluminum wing-box test section instrumented with surface-bonded fiber Bragg grating (FBG) sensors. A multi-point FBG network was arranged on the skins and webs using finite-element-guided sensor placement to construct bending-, shear-, and torsion-related response features; strain-free reference FBGs provided temperature compensation. All experiments used the same specimen geometry, fixed-root boundary condition, sensor layout, and four actuator positions. Conditions 1–6 were used for regression calibration, whereas Conditions 7 and 8 were held out for interpolation-type validation within the same loading configuration. The maximum/average relative errors were 6.53%/1.51% for bending moment, 2.62%/0.86% for shear force, and 4.04%/1.23% for torsional moment. These results apply only to local laboratory calibration of the tested configuration and do not establish transfer to other geometries, boundary conditions, sensor layouts, loading positions, environmental conditions, or dynamic loading. Full article

Aircraft wing ribs form the skeletal backbone of the wing. They maintain the aerodynamic profile and transfer structural loads from the skin to the spars. Conventional manufacturing processes struggle to produce complex geometries, making these components difficult and expensive to manufacture. Recent advances in additive manufacturing (AM) address these limitations. Additive manufacturing enables the production of complex geometries that significantly reduce weight. Most designers use the standard Ashby method to identify the strongest or lightest metal. However, they often overlook whether the material will behave as expected during additive printing. This research focuses on Multi-Objective Material Selection for the design of the additive manufacturability of aircraft wing ribs using aluminium-based alloys. A key innovation in this research is the formulation of hybrid performance indices (HPIs). These indices go beyond the traditional Ashby methodology. They mathematically couple structural efficiency metrics with a weighted Processability Factor. The structural metrics include specific density, stiffness, specific strength, and Embodied-Energy-Strength-to-Embodied-Energy Index. The Processability Factor accounts for local material availability, thermal conductivity, printability, recyclability and material cost. This dual evaluation assesses both structural integrity and manufacturing risk simultaneously. The process produces an Additive Pareto Optimal set of candidate materials. This helps engineers predict and prevent issues like warping and residual stress before printing begins. The framework also emphasises sustainability. It prioritises materials that minimise waste and considers embodied energy in the selection process. The framework identifies high-performance aluminium alloys that are specifically optimised for the additive manufacturing of aircraft wing ribs. It provides a definitive ranking based on their ability to withstand aerodynamic loads while remaining easy to print. This data-driven approach replaces trial and error with a clear selection matrix for the early design stage. It ensures that the chosen alloy is both structurally sound and manufacturable for aerospace applications. Full article

This study focuses on the longitudinal dynamic stability of swifts in cruising forward flight, which is critical for their high maneuverability but remains insufficiently investigated. Understanding longitudinal dynamic stability is the essential prerequisite for revealing the physical mechanism underlying their maneuverability: it is the dynamic stability characteristics that determine how the flight state responds to disturbances and control inputs, thereby laying a foundation for subsequent flight control during agile maneuvers. Conventional studies mostly adopt steady or quasi-steady assumptions, which cannot accurately reflect the influence of periodic body vibration. This study combines CFD numerical simulation and dynamic modeling to systematically analyze the unsteady dynamic stability of swifts. A bio-inspired dynamic model is established using the BE3357B airfoil with a 5° sweep angle, and the flapping-wing motion is decomposed into three degrees of freedom: sweeping, pitching, and flapping. Numerical reliability is assessed through grid independence and time-step independence verification. Aerodynamic force and moment trimming are performed on fixed-DOF and free-DOF models, where the latter considers coupled heaving–pitching motion and adjusted trim parameters. Stability analysis is conducted using three aerodynamic derivative methods: fixed velocity, forced oscillation, and Floquet. By solving small perturbation equations, eigenvalues and eigenmodes are obtained. All three methods identify two stable modes: a short-period mode with damping coefficient 0.1236–0.1870 and oscillation period 0.1121 s–0.1380 s, and a long-period mode with damping coefficient 0.2456–0.6203 and damping half-life 3.5803 s–4.8890 s, verifying stability under periodic vibration and unsteady aerodynamic coupling. Flow field results show clear distinct dynamic pressure and drag fluctuation characteristics between the downstroke and the upstroke. The unsteady stability framework provides a theoretical reference for analyzing the longitudinal stability of biomimetic flapping-wing aircraft and offers useful insight for future bird-inspired flight dynamics studies. Full article

The frequency-domain flutter analysis method requires a linear model as input; however, when a telescopic actuator is applied to morphing aircraft, traditional frequency-domain flutter analysis methods face challenges in addressing issues involving contact nonlinearity. To enable classical frequency-domain methods to handle this type of nonlinearity, this paper presents an equivalent linearization modeling method for morphing aircraft wing structures. The proposed modeling method uses rod elements as the equivalent linearization elements and avoids the need to handle node correspondence issues. The model is parameterized by the rod element’s elastic modulus, contact surface distance, and element length coefficient. Upon completion of the equivalent modeling, flutter analysis can be performed by the PK method. The proposed modeling method increases modeling efficiency while maintaining the accuracy of the model. A simulation study of a typical hypersonic telescopic wing structure is conducted. The effects of angle of attack and altitude on flutter characteristics are analyzed. The proposed modeling method effectively captures both the static and dynamic characteristics of the original structure. The flutter Mach number decreases with increasing extension length, and it increases with altitude and angle of attack. The flutter frequency decreases with increasing extension length, angle of attack, and altitude. Full article

Vertical take-off and landing (VTOL) configurations incur a structural weight penalty that reduces payload fraction and endurance compared to conventional fixed-wing and multirotor aircraft of comparable gross weight. To extend the endurance of VTOL UAVs, this work presents the design, analysis and control of a novel unmanned tilt trirotor aircraft with tandem wings, named Gong-H, featuring VTOL capability and high aerodynamic efficiency. A prototype of this aircraft was built with the rotor system mounted between tandem wings with a high wing coverage rate, which can achieve a more compact structure than other VTOL aircraft. The control forces and torques are provided not only by the rotor system in VTOL flight mode and the two tandem wings in cruise mode, but also by both the rotor system and wings in transition mode. Additionally, Computational Fluid Dynamics (CFD) simulations are conducted to optimize the wing configuration to improve the efficiency of cruise mode. Moreover, an airspeed-scheduled hybrid control framework based on incremental nonlinear dynamic inversion (INDI) and PID is adopted for different flight modes to improve the robustness of control and the stability of flight mode switching. Hover experiments confirm improved power efficiency compared to tilt quadrotor configuration, which extends endurance time and increases range. Additionally, complete flight cycle field experiments were conducted to demonstrate the aerodynamic feasibility of the prototype, including VTOL flight, cruise flight, and transition flight modes. Control surface redundancy tests and comparative INDI-PID validation under asymmetric disturbances further verify the practical robustness of the control framework. This work provides a design concept of VTOL aircraft and a practical solution for VTOL applications. Full article