Wing Research Articles

Helicopter rotor in a propeller slipstream: Aerodynamic and rotor blade flapping responses

During helicopter air-to-air refueling the helicopter's rotor can engage the tanker aircraft's wing and flap end tip vortices and the slipstream of its propellers. The tip vortices represent a swirl around an axis that is essentially parallel to the rotor longitudinal axis. The slipstream of the propellers includes a strong air jet downstream that can cover a significant amount of the helicopter's main rotor. This phenomenon was recently treated analytically for a rigid rotor by means of blade-element momentum theory and the rotor control angles required to reject the disturbance were computed. In this article, the rotor blade flapping is introduced as degree of freedom. It is shown that the rotor coning is affected by the slipstream position with respect to the rotor hub. Without retrim, the largest amount of coning and cyclic flapping occurs for slipstream positions on the retreating side of the rotor.

Preparation and investigation of high-performance flexible and transparent Ag/PDMS substrate with the bionic structure of cicada wings

In this study, an efficient, homogeneous, flexible and transparent Ag/Polydimethylsiloxane (PDMS) substrate with an orderly three-dimensional nanopillar structure was proposed. Ag NPs were thermally deposited on the flexible bionic PDMS support obtained by a two-step replication of cicada wings. Scanning electron microscope images reveal when the deposition time was 50 min, Ag NPs of proper size densely covered the entire PDMS nanopillar surface in the Ag-50/PDMS substrate. Both the gaps between the Ag NPs and those between the nanopillars acted as efficient electric field amplifiers. The enhancement factor (EF) of the Ag-50/PDMS substrate was calculated to be 2.89 × 107 by using crystal violet as the probe molecule. The Ag-50/PDMS substrate also exhibited good uniformity and reproducibility with a relative standard deviation of 1.46% and 11.45% respectively. The detection capability of the proposed flexible and transparent Ag-50/PDMS substrate in practical applications was demonstrated by the in-situ detection of 0.1 ppm malachite green on fish surfaces, indicating its great potential in the field of food monitoring.

Static Structural Testing of Composite Wing Structure for Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicles

Static Structural Testing of Composite Wing Structure for Vertical Takeoff and Landing (VTOL) Unmanned Aerial Vehicles

Towards extending the aircraft flight envelope by mitigating transonic airfoil buffet

In the age of globalization, commercial aviation plays a central role in maintaining our international connectivity by providing fast air transport services for passengers and freight. However, the upper limit of the aircraft flight envelope, i.e., its operational limit in the high-speed (transonic) regime, is usually fixed by the occurrence of transonic aeroelastic effects. These harmful structural vibrations are associated with an aerodynamic instability called transonic buffet. It refers to shock wave oscillations occurring on the aircraft wings, which induce unsteady aerodynamic loads acting on the wing structure. Since the structural response can cause severe structural damage endangering flight safety, the aviation industry is highly interested in suppressing transonic buffet to extend the flight envelope to higher aircraft speeds. In this contribution, we demonstrate experimentally that the application of porous trailing edges substantially attenuates the buffet phenomenon. Since porous trailing edges have the additional benefit of reducing acoustic aircraft emissions, they could prospectively provide faster air transport with reduced noise emissions.

A high-performance, sensitive, low-cost LIG/PDMS strain sensor for impact damage monitoring and localization in composite structures

Health monitoring of composite structures in aircraft is critical, as these structures are commonly utilized in weight-sensitive areas and innovative designs that directly impact flight safety and reliability. Traditional monitoring methods have limitations in monitoring area, strain limit, and signal processing. In this paper, a multifunctional sensor has been developed using acid-treated laser-induced graphene (A-LIG) with a multi-layer three-dimensional conductive network. Compared to untreated laser-induced graphene, the sensitivity of A-LIG sensor is increased by 100%. Furthermore, PDMS is used to fill the pores, which improves the fatigue performance of the A-LIG sensor. To obtain clear monitoring results, a data conversion algorithm is provided to convert the electrical signal obtained by the sensor into a strain field contour cloud map. The impact test of the A-LIG/PDMS sensor on the carbon fiber panel of the aircraft wing box segment verifies the effectiveness of its strain sensing. This work introduces a novel approach to fabricating flexible sensors with improved sensitivity, extended strain range, and cost-effectiveness. The sensor exhibits high sensitivity (gauge factor, GF ≈ 387), is low hysteresis (∼53 ms), and has a wide working range (up to 47%), and a highly stable and reproducible response over multiple test cycles (>18 000) with good switching response. It presents a promising and innovative direction for utilizing flexible sensors in the field of aircraft structural health monitoring.

Chaotic snap-through vibrations of bistable asymmetric deployable composite laminated cantilever shell under foundation excitation and application to morphing wing

The realization of the dynamic snap-through behaviors provides the new design ideas in the fields of the morphing aircraft and piezoelectric energy harvesting. This paper studies 1:2 internal resonance, nonlinear vibrations and chaotic snap-through phenomena of the bistable asymmetric composite laminated (BSCL) cantilever shell with the lower-frequency and higher-frequency primary resonances for the first time. The transverse foundation excitation subjects to the fixed end of the bistable cantilever shell. The perturbation analysis of two-degrees-of-freedom nonlinear ordinary differential equations is carried out by using the first-order approximate multiple scale method. The analytical results of the frequency-amplitude and force-amplitude response curves are obtained under the small foundation excitation. The obtained results reveal that the BSCL cantilever shell exhibits the double-jumping characteristics when 1:2 internal and primary resonances occur. There is a continuous energy exchange back and forth between two modes of the bistable laminated cantilever shell. As the foundation excitation increases, the BSCL cantilever shell exhibits saturation phenomenon. Numerical simulations are finished to further investigate the effects of the large excitation on the chaotic, quasi-periodic and snap-through vibrations for the BSCL cantilever shell. The vibration experiment is carried out to investigate the internal resonance and dynamic snap-though motions of the BSCL cantilever shell. Using the snap-though behaviors of the BSCL cantilever shell, we obtain the morphing structure of the aircraft wing.

Neural network based position control of an underactuated flapping wing aircraft considering the aerodynamic damping

Neural network based position control of an underactuated flapping wing aircraft considering the aerodynamic damping

Analytical Modeling of Riveting Squeezing Force Considering Non-Uniform Deformation of Rivets in Aeronautical Structures.

Analytical modeling of the squeezing force for aircraft wings and fuselage panels in the existing literature usually assumes uniform deformation of the rivets, while in reality, the deformation of the rivets is non-uniform. To achieve high-quality squeezing force modeling, this paper introduces Coulomb's friction and four critical adjustments to the original equation: the non-uniform rivet/sheet interference along the sheet's hole axial ordinate; the barreling effect when calculating the driven head's volume; the spring-back of the driven head's dimensions; the modified height of the driven head; and the modified sheet-hole expanded diameter considering the convex structure of the driven head. The calculated values of the proposed new model demonstrate an improved level of accuracy, particularly under squeeze ratios commonly encountered in the aerospace industry.

Catastrophic Aeroelasticity and Aircraft Wing Catastrophes

Catastrophic Aeroelasticity and Aircraft Wing Catastrophes

Overview of research status and key technologies of bionic flapping wing aircraft

Overview of research status and key technologies of bionic flapping wing aircraft

Aircraft Designed for Cargo Transportation and Investigation of its Benefits

In this study, an Octorotor UAV capable of carrying 10 desi/2 kg cargo was designed. It is an eight-rotor rotary wing aircraft and its body consists of eight arms connected to each other by two moving mechanisms. When requested in emergency situations, the fastest intervention can be provided by aircrafts. The auxiliary battery and generator system carried by the aircraft is to provide enough energy to reach the nearest electric charging station for the stranded vehicles. In cases such as disasters, the rapid delivery of health supplies can also be provided by this method. The aircraft designed for this purpose has a rotary wing and a feature that can change its body structure according to different load and weather conditions. The shape change improves its performance compared to conventional aircraft and increases its ability to fulfil its mission. For this purpose, the design of a shape-changing aircraft was realized.

Aero-Structural Comprehensive Nonprobabilistic Reliability-Based Optimization Method for High Aspect Ratio Wings

An aero-structural comprehensive reliability-based optimization method is proposed to construct the optimization framework of designing the high aspect ratio wing. There are three parts included in this method. 1) The ideal cruising shape is obtained by optimizing the geometrical parameters in the cruising conditions, where only the aerodynamic shape optimization is involved and the structural deformation is not considered. 2) The jig-shape optimization method is presented, where the aerodynamic performance of the wing structure with deformation is improved by adjusting the twist angle along the span direction to make sure that the shape with the aeroelastic deformation approaches the ideal cruising shape. 3) A nonprobabilistic reliability-based structural optimization is conducted by updating the thickness of composite layer, where the dispersion of mechanical properties of composite materials is considered and a nonprobabilistic reliability index according to strength and stiffness constraints is established. The global stiffness of the wing structure is changed after jig-shape optimization and structural optimization, and the jig-shape and structural scheme are modified alternately. The previously mentioned process needs to be repeated until the changes in the jig-shape and structural scheme in the iterations can be ignored. Finally, the effectiveness of this method has been verified through the numerical example followed by some conclusions.

Bi-direction and flexible multi-mode morphing wing based on antagonistic SMA wire actuators

This work evaluates the viability of a cutting-edge flexible wing prototype actuated by Shape Memory Alloy (SMA) wire actuators. Such flexible wings have garnered significant interest for their potential to enhance aerodynamic efficiency by mitigating noise and delaying flow separation. SMA actuators are particularly advantageous due to their superior power-to-weight ratio and adaptive response, making them increasingly favored in morphing aircraft applications. Our methodology begins with a detailed delineation of the fishbone camber morphing wing rib structure, followed by the construction of a multi-mode morphing wing segment through 3D-printed rib assembly. Comprehensive testing of the SMA wire actuators’ actuation capacity and efficiency was conducted to establish their operational parameters. Subsequent experimental analyses focused on the bi-directional and reciprocating morphing performance of the fishbone wing rib, which incorporates SMA wires on the upper and lower sides. These experiments confirmed the segment’s multi-mode morphing abilities. Aerodynamic assessments have demonstrated that our design substantially improves the Lift-to-Drag ratio (L/D) when compared to conventional rigid wings. Finally, two phases of flight tests demonstrated the feasibility of SMA as an aircraft actuator and the validity of flexible wing structures to adjust the aircraft attitude, respectively.

Current Status and Development Trends of Morphing Wing of Aircraft

Abstract:: Aircraft morphing wings, also known as adaptive wings or shape-variable wings, represent a revolutionary development in the field of aerospace engineering. Inspired by the adaptability observed in birds and insects during flight, researchers have been exploring potential applications of morphing wing technology to enhance the performance and efficiency of aircraft. This innovative technology holds the promise of improving aerodynamic efficiency, reducing fuel consumption, and enhancing overall flight maneuverability. This manuscript aims to explore and analyze the potential applications and effects of morphing wing technology for aircraft. Furthermore, this paper aims to gain an in-depth understanding of the principles and implications of morphing wing technology for aircraft and to assess its potential advantages in terms of flight performance, handling characteristics, and energy efficiency. Based on different driving mechanisms, patents related to aircraft morphing wings were systematically categorized and summarized, highlighting the most typical intra-wing and extra-wing deformations. Through an examination of patents related to aircraft morphing wings, various morphing wing technologies' unique characteristics were summarized. A comparative analysis of different deformation methods revealed their respective strengths and limitations. The paper concludes with a summary of current technical challenges facing morphing wing technology and a forward-looking exploration of its future trends and directions. Categorizing aircraft morphing wings into intra-wing and extra-wing deformations based on the method of deformation, this paper elaborates on the operational principles, advantages, and limitations of these two categories. Compared to traditional fixed wings, morphing wings exhibit superior flight performance, and it is anticipated that more patents will be developed in the future.

Design and validation of the evolved version of the tactical separation system

Purpose The small air transport (SAT) domain is gaining increasing interest over the past decade, based on its perspective relevance in enabling efficient travel over a regional range, by exploiting small airports and fixed wing aircraft with up to 19 seats (EASA CS-23 category). To support its wider adoption, it is needed to enable single pilot operations. Design/methodology/approach An integrated mission management system (IMMS) has been designed and implemented, able to automatically optimize the aircraft path by considering trajectory optimization needs. It takes into account both traffic scenario and weather actual and forecasted condition and is also able to select best destination airport, should pilot incapacitation occur during flight. As part of the IMMS, dedicated evolved tactical separation system (Evo-TSS) has been designed to provide elaboration of both surrounding and far located traffic and subsequent traffic clustering, to support the trajectory planning/re-planning by the IMMS. Findings The Clean Sky 2-funded project COAST (Cost Optimized Avionics SysTem) successfully designed and validated through flight demonstrations relevant technologies enabling affordable cockpit and avionics and supporting single pilot operations for SAT vehicles. These technologies include the TSS in its baseline and evolved versions, included in the IMMS. Originality/value This paper describes the TSS baseline version and the basic aspects of the Evo-TSS design. It is aimed to outline the implementation of the Evo-TSS dedicated software in Matlab/Simulink environment, the planned laboratory validation campaign and the results of the validation exercises in fast-time Matlab/Simulink environment, which were successfully concluded in 2023.

Tailoring 3D Star-Shaped Auxetic Structures for Enhanced Mechanical Performance

Auxetic lattice structures are three-dimensionally designed intricately repeating units with multifunctionality in three-dimensional space, especially with the emergence of additive manufacturing (AM) technologies. In aerospace applications, these structures have potential for use in high-performance lightweight components, contributing to enhanced efficiency. This paper investigates the design, numerical simulation, manufacturing, and testing of three-dimensional (3D) star-shaped lattice structures with tailored mechanical properties. Finite element analysis (FEA) was employed to examine the effect of a lattice unit’s vertex angle and strut diameter on the lattice structure’s Poisson’s ratio and effective elastic modulus. The strut diameter was altered from 0.2 to 1 mm, while the star-shaped vertex angle was adjusted from 15 to 90 degrees. Laser powder bed fusion (LPBF), an AM technique, was employed to experimentally fabricate 3D star-shaped honeycomb structures made of Ti6Al4V alloy, which were then subjected to compression testing to verify the modelling results. The effective elastic modulus was shown to decrease when increasing the vertex angle or decreasing the strut diameter, while the Poisson’s ratio had a complex behaviour depending on the geometrical characteristics of the structure. By tailoring the unit vertex angle and strut diameter, the printed structures exhibited negative, zero, and positive Poisson’s ratios, making them applicable across a wide range of aerospace components such as impact absorption systems, aircraft wings, fuselage sections, landing gear, and engine mounts. This optimization will support the growing demand for lightweight structures across the aerospace sector.

Component-based wing structure reconfiguration and analysis on the fly

To facilitate the structural design of an aircraft wing, we propose a simulation technique that can not only readily reshape a wing structure, but also rapidly yet accurately analyze its responses. For swift wing reconfiguration, we express a wing geometry with respect to shape parameters, such as a taper ratio, a half wingspan, and a sweep angle, by geometric parameterization. For rapid yet accurate analysis, we simulate a large-sized wing structure using small-sized common components whose solution spaces are shrunken by port-reduced static condensation reduced basis element (PR-SCRBE) approximation. As a result, we can easily modify both the shape and topology of a wing structure in the context of repetitive analysis. For demonstration, we construct six exemplary wing structures by assembling deformed duplicates of five common wing components. With the six wing structures, we examine the accuracy and efficiency of linear elastostatic PR-SCRBE analyses in predicting displacements and stresses compared with the corresponding finite element (FE) analyses. Regarding accuracy, the six PR-SCRBE analyses yield displacements and stresses with average relative errors of less than 0.01% and 2.79%, respectively. As for efficiency, the six PR-SCRBE analyses evaluate displacements and stresses with average speedups of 12.58 and 11.56, respectively. In conclusion, the proposed approach for wing reconfiguration and analysis may produce rapid yet accurate structural predictions, thereby considerably assisting the structural design of an aircraft wing.

Aerostructural Wing Optimization Using a Structural Surrogate in a Coupled Adjoint Formulation

As the number of disciplines included in the multidisciplinary design-optimization process continues to increase, it is envisioned that some of the disciplinary tools will take the form of surrogate models, whereas others remain physics-based, depending on the requirements and stage of the design process. To simulate this in the context of an aerostructural optimization of an aircraft wing, the work presented herein features a high-fidelity aerodynamic flow solver, while a surrogate is employed to model the wing structure. This approach includes the evaluation of the sensitivities of both the aerodynamic and structural disciplines, using a coupled-adjoint formulation to enable gradient-based optimization. An important aspect of the method is that the surrogate is trained only once, prior to the optimization, and held fixed throughout. The surrogate in effect parameterizes the structural design process, and outputs the weight and stiffness of an optimized structure, given inputs of geometry parameters and sizing loads. To minimize the number of surrogate inputs and enable the representation of the entire structural design space, parameterized loads are used to build the surrogate. The method is applied to the optimization of the NASA Common Research Model, illustrating the effectiveness of the new approach.

Aircraft Wing Morphing Using Auxetic Structures

Cellular materials exhibit two key properties: structures and mechanisms. This allows for the design of structures using cellular materials while effectively controlling both stiffness and flexibility, based on the connectivity of the struts. This study aims to explore the in-plane flexible properties of cellular materials dominated by bending under macroscopic deformation. Additionally, it seeks to establish a method for designing a passive morphing airfoil with flexible cellular cores. The investigation focuses on airfoils featuring re-entrant and S-shaped cellular cores, analyzing their behavior under static loads by examining the deformation of the cellular cores subjected to aerostatic loads. In the context of the airfoil's deformation with flexible cellular cores under aerostatic loading, shear emerges as the predominant deformation mode for the cores of the airfoil. Wings of conventional aircraft are optimized for only a few conditions, not for the entire flight envelope. Therefore, it is necessary to develop the morphing airfoil with smart structures for the next generation of excellent aircraft. In this project, this was made possible using, re-entrant and S-shaped auxetic structures as a member of the meta- material family, with negative Poisson's ratio to enable an effortless passive morphing mechanism as it has high flexibility along in-plane direction (chord-wise). The 3D CAD Models of Re-entrant and S-shaped auxetic airframes were designed and analyzed. Initially, Static Structural analysis is performed on both airframes to observe the structure’s behavior, and design modification and optimization are performed in different iterations. With a reduction in maximum equivalent stress by 20%, the Re-entrant airframe exhibits lower stress and hence more flexibility. The wings were modeled with a span of 1m using auxetic airframes, air pressure was generated using CFD analysis with MACH 0.45. Finally, the fluid-structure interaction was done by importing the air pressure and performing static structural analysis for the structural performance of wings using auxetic airframes. It was found that Re-entrant auxetic wing showed an increase of 9.99% in load carrying capacity, accompanied by a decrease of 389 grams of weight when compared to S-shaped auxetic wing. Considering the deformation of the airframe with flexible cellular cores under a load, the re-entrant honeycomb core shows the highest flexibility in shear and causes lower stress than the S-auxetic cores. This implies that the re-entrant honeycomb core has the potential for passive morphing.

Development of Anisogrid Lattice Composite Structures for Fighter Wing Applications

This paper presents research on the use of anisogrid lattice structures in fighter wing applications. While the anisogrid lattice structure has been widely used in spacecraft structures, its implementation in main aircraft structures is still limited. The study is aimed at investigating the feasibility of utilizing an anisogrid lattice structure in fighter wing design. The analysis and optimization focus on determining the optimal weight of the composite wing structure, considering static, buckling, and flutter failure constraints. Various lift distributions, including triangular, Schrenk, and constant, are applied to evaluate the structure’s response to static failure caused by aerodynamic loads. The anisogrid structure design incorporates inclined lattice elements between ribs and spars, with spar arrangement in the wing box featuring an anisogrid configuration. The anisogrid lattice structure is expected to produce higher bending and torsional stiffness compared to conventional orthogonal structures, producing better flutter and buckling characteristics. The optimized wing structure successfully meets static, buckling, and flutter load requirements at speeds below 500 m/s. The study showcases triangular, Schrenk, and constant load distributions resulting in half-wing masses of 504, 571, and 707 kg, respectively. The results show that flutter and buckling loads are no longer the critical loads in wing structural design but static load.