Flight Loads Research Articles

Global air freight flow data for aviation policy modelling

Models of air freight are often constrained by a lack of available data. This study brings together different sources of air freight supply and demand data to address this gap. To study air freight operations, we combine schedules, flight tracking data and country-level databases of passenger and freight movements to produce estimates of global flight segment-level capacity and load factors in freighter aircraft and passenger holds for 2019–2021. To study true origin-ultimate destination air freight demand, a freight mode choice model by commodity group is developed for 2019 to fill gaps in mode information in international and national trade datasets, and estimates are made for 2019 and 2021. Initial comparisons of supply and demand data demonstrate that air freight journeys differ significantly from passenger journeys, typically including more flight legs (roughly, around 2, compared to 1.2 for passengers) and greater leg distances (2.2–2.5 times average passenger distance), with significant asymmetry in commodity flows and operations to and from individual countries and regions. These differences persist in 2021, despite COVID-19 induced shifts towards carrying more air freight in freighter aircraft. This research forms a first step towards making available an integrated database of estimated global air freight flows by commodity.

Crack Growth Analytical Model Considering the Crack Growth Resistance Parameter Due to the Unloading Process

Crack growth analysis is essential for probabilistic damage tolerance assessment of aeroengine life-limited parts. Traditional crack growth models directly establish the stress ratio–crack growth rate or crack opening stress relationship and focus less on changes in the crack tip stress field and its influence, so the resolution and accuracy of maneuvering flight load spectral analysis are limited. To improve the accuracy and convenience of analysis, a parameter considering the effect of unloading amount on crack propagation resistance is proposed, and the corresponding analytical model is established. The corresponding process for acquiring the model parameters through the constant amplitude test data of a Ti-6AL-4V compact tension specimen is presented. Six kinds of flight load spectra with inserted load pairs with different stress ratios and repetition times are tested to verify the accuracy of the proposed model. All the deviations between the proposed model and test life results are less than 10%, which demonstrates the superiority of the proposed model over the crack closure and Walker-based models in addressing relevant loading spectra. The proposed analytical model provides new insights for the safety of aeroengine life-limited parts.

Multistable Composite Laminate Grids as a Design Tool for Soft Reconfigurable Multirotors

Adaptive‐morphology multirotors exhibit superior versatility and task‐specific performance compared to traditional multirotors owing to their functional morphological adaptability. However, a notable challenge lies in the contrasting requirements of locking each morphology for flight controllability and efficiency while permitting low‐energy reconfiguration. A novel design approach is proposed for reconfigurable multirotors utilizing soft multistable composite laminate airframes. These airframes show kinematically determinate morphologies corresponding to multiple minima in their elastic potential energy landscape. By varying design parameters, the methodology allows for tuning the energy landscape characteristics governing each morphology's structural stability and reconfiguration energetics. The airframe, composed of multistable composite laminate grids, is optimized to maximize rigidity under flight loads and minimize reconfiguration work. The 130‐g reconfigurable multirotor design demonstrates self‐locking properties in an open and a folded configuration, enabling a 48% reduction in width‐span without compromising stability during flight. Soft pneumatic actuators, actuated using a tethered compressed air supply, enable reversible reconfiguration on the ground between open and folded configurations. The design resolves the conflicting requirements of high‐stiffness to lock each flight configuration and low‐actuation work for reconfigurability. By exploiting soft yet multistable structures, the approach combines the stability observed in rigid‐linked reconfigurable multirotors with the low‐effort reconfigurability of soft multirotors, offering new methods for designing adaptive‐morphology multirotors.

Research on the measurement method of flight load of flap drive mechanism

Research on the measurement method of flight load of flap drive mechanism

Research on torque measurement in flight test for all-moving horizontal tail based on spiral driver

PurposeTorque is one of the main loads acting on the aircraft wing, the horizontal tail and the vertical tail. In flight load measurement, due to the significant influence of the bending moment and the shear force on the strain gauge, the accuracy of torque measurement is usually low. Therefore, aircraft torque measurement is difficult. Based on the characteristics of a certain type of horizontal tail, a measurement method for the torque with high accuracy was proposed in this paper.Design/methodology/approachA new simplified torque measurement method for the all-moving horizontal tail was proposed based on the spiral driver. The feasibility of the method and key points of the tests were analyzed and studied through a virtual load calibration test.FindingsBased on the results of the real load calibration test, the torque load equation with high accuracy was established, and the torque measurement was achieved in load flight tests.Research limitations/implicationsHowever, the proposed method is based on the structure of the spiral driver. If there is generally no spiral driver at the aircraft wings and vertical tails, then the appropriate torque measurement method needs to be derived according to the specific object.Originality/valueThe research in this paper provides a new idea for the torque measurement of aircraft structures, which can be used for the torque measurement of subsequent aircraft types.

SHM System Architecture based on Ultrasonic Guided Waves for Aircraft Application Scenarios

Structural health monitoring (SHM) based on ultrasonic guided waves is a novel technology using permanently attached actuator and sensor networks, data acquisition and data evaluation systems to enable in-service inspection of aircraft structures. A modular and decentralized SHM system is presented that can be adapted to various aircraft application scenarios. The central element of the SHM system is a robust sensor array based on piezocomposite technology that can be efficiently integrated into the manufacturing process of CFRP structures (via co-bonding). The sensor array consists of integrated piezoceramic transducers, temperature sensors, electrical cables and integrated electronic components. The decentralized system architecture of the individual electronic components reduces the installation and cabling effort during the assembly of aircraft structures as well as the system weight. Integration and installation aspects as well as various system architectures are discussed using an Airbus A350 door surround structure. Furthermore, an outlook of damage detection under representative flight loads is given.

Fatigue behavior of an airfoil with tolerable exfoliation cracks induced by dynamic corrosion: Experimental and numerical assessment

Pitting corrosion creates preferential sites for cracks formation by the exfoliation process, which grow due to the continuous action of flight loads, even those of constant amplitude (CA). Whether the find-fix protocol must repair all defects, some may go unnoticed due to their sizes or locations in the aircraft. For this reason, it is necessary to study the fatigue behavior of airfoils with defects (cracks), analyzing their growth rates and the affectation on residual strength. This research work studied experimental and numerically fatigue performance of an airfoil with initial defects caused by dynamic corrosion. Intentionally, single-edge cracks (SECs) formation was induced in three wing skin regions: leading and trailing edges and central zone. The pre-corroded airfoil was subjected to alternate drag and lift forces to assess the crack growth and take validation data as deflection and the load level. The low stress intensity factor (SIF) estimated by means of a 3D finite element (FE) numerical model indicated that cracks did not propagate. Even though the stress level in the crack tip remained under the fatigue limit, giving rise to infinity life, the degraded material residual strength was considerably reduced. Also, the estimations obtained from an FE 1D model considering the damage factor and the mechanical properties loss in the crack region corroborated the infinity life behavior. Numerical and experimental results could determine an allowable flaw size under CA load conditions. However, the load variation play an important role increasing crack growth rate up to six times.

Study of Local Strength of Tail Rotor Blade under Ground and Flight Loads

Study of Local Strength of Tail Rotor Blade under Ground and Flight Loads

Horizontal Tail Flight Load Prediction Method for Large UAVs based on Machine Learning

In today’s rapidly developing large UAVs field, flight safety and reliability are essential considerations. Flight load is one of the important factors affecting the load capacity of large UAVs, so the research on load prediction technology can improve flight safety and the reliability of air transportation. This paper first introduces the collection and processing method of flight load data, then uses the machine learning method-BP neural network to predict flight load, establishes the BP neural network model to predict flight load with flight parameters, and optimizes the model according to error analysis. Finally, the accuracy and practicability of the model are verified by analysing the fitting of the training set and the test set, and the error distribution of the true value of shear, bending moment, torque and the absolute percentage of the predicted value, and the model is evaluated.

Analysis of Flight Loads during Symmetric Aircraft Maneuvers Based on the Gradient-Enhanced Kriging Model

The analysis of flight loads during symmetric aircraft maneuvers is an essential but computationally intensive task in aircraft design. The significant structural elastic deformation in modern aircraft further complicates this work, adding to the computational demands. Therefore, improving the analysis efficiency of flight loads during maneuvers is crucial for accelerating design interactions and shortening the development cycle. This study explores a method for analyzing flight loads in the time domain during maneuvers of elastic aircraft by introducing a database of high-precision rigid-body aerodynamic loads. Furthermore, it combines the gradient-enhanced Kriging model to efficiently predict elastic flight loads during longitudinal maneuvers. The results indicate that the proposed surrogate-based method has high fitting accuracy with significantly improved computational efficiency, providing a new approach for efficient analysis of flight loads during aircraft maneuvers.

Qualification test campaign of RFA one fairing engineering model

The fairing is an important element of the rocket as it protects the payload from the external environment during the most aggressive phases of the flight. A test campaign was developed with the aim of qualifying the fairing structure of the RFA One. This test is intended to simulate the quasi-static loads of the most critical phase during flight. A FEA model was developed to identify the most critical phase of flight and to identify the quasi-static reactions that replicate the flight loads. Based on these reactions, the loads and test levels were defined. The test results were compared with the FEA data to correlate and improve the model. The static test was successfully performed at acceptance and qualification Level 2. The load and strain results indicate that the DLL was achieved and exceeded by a factor of 1.11, while the fairing maintained its functionality and key performance. This paper presents the most relevant results of the test, discusses the results compared with the FEA model and summarizes some lessons drawn from the test campaign.

Design, Manufacturing, and Testing of a Metallic Fuselage Panel Incorporating New Alloys and Environmentally Friendly Technologies

Within the ecoTECH project, a new fuselage section was designed based on an existing business jet panel, aiming to incorporate innovative technologies and environmentally friendly approaches. The Metallic Fuselage Panel Demonstrator developed in this project integrates the most promising technologies previously developed in the areas of manufacturing methods, including mechanical milling and friction stir welding, as well as surface treatments such as sol-gel and thin film sulphuric acid anodizing, along with a Chrome-free primer applied on a new Al-Cu-Li alloy structure. Two types of full-scale testing were performed to mature the newly developed technologies and assess the performance of the demonstrator. The first was a Static Full-Scale Test Demonstrator, designed and manufactured to undergo static full-scale testing. This testing evaluated the structural integrity and performance of the panel under various load conditions, representative of an operational aircraft, including compression, shear, pressure, tension, and combinations of these forces. The second type of testing conducted concerned endurance. Similar to the static test demonstrator, this demonstrator was subjected to fatigue to assess its durability and long-term performance by simulating representative flight loading spectrum of a business jet aircraft and providing valuable insights into the panel’s ability to withstand prolonged operational conditions. The successful completion of these phases in the ecoTECH project represents a significant milestone, demonstrating the effective integration of innovative manufacturing methods and environmentally friendly surface treatments for new aluminum alloys in the development of innovative environmentally friendly technologies. The project’s outcomes contribute to the advancement of sustainable and efficient technologies in the aerospace industry, providing a foundation for the future development of aircraft structures with improved performance, durability, and reduced environmental impact.

Doomed from the start, understanding the importance of boundary conditions in modal testing

Modal survey tests are commonly performed in the aerospace industry to validate the structural dynamics behavior of the finite element model used in the flight loads predictions for both hardware structural capability and expected crew loads. During the planning phase, great effort is spent on the selection of accelerometer locations to properly capture the modes and satisfy orthogonality conditions. The same due diligence is not always spent on the design of the test’s setup and boundary conditions. Logistical and programmatic concerns may influence the technical approach taken, which, unfortunately, may result in test modes that are strongly coupled with boundary condition fixturing. The purpose of the paper is to present case studies of modal survey tests that were performed where the boundary condition influenced the test results. Additionally, best practices will be presented.

Construction of flight planning and loading courses under the new generation transportation system

Facing the development of the new generation of air transportation, the Civil Aviation Administration of China has successively promulgated the CCAR-121-R5-R7 version of the "Certification Rules for the Operation of Large Aircraft Public Air Transport Carriers". With the introduction of the latest national regulations, existing teaching materials and teaching content are no longer suitable for student training needs. Through the construction of industry-university collaborative education projects, analyze the connotation and extension of flight planning and loading courses, compile new teaching materials for flight planning and loading courses, establish a good teaching team for flight planning and loading courses, and form flight planning and loading courses. The course's on-campus teachers and industry experts have jointly created an online and offline teaching model, and established an assessment system that combines standard answer exams and non-standard answer exams for flight planning and loading.

On the effects of rotor induced vibrational stability on helicopter flight dynamics

This article investigates vibrational stabilization effects in rotorcraft flight dynamics. This study is motivated by recent results in flapping-wing flight, which showed that the time-varying aerodynamic and inertial loads due to the insect wing periodic motion induce a vibrational stabilization mechanism in hover. The dynamics of flapping-wing flyers and rotary-wing vehicles are both described by time-periodic systems so vibrational stabilization mechanisms can also have an effect on stability characteristics of rotary-wing vehicles. The article extends the use of the harmonic decomposition method to vibrational stability analysis of rotorcraft. Two cases are considered: vibrational stability due blade imbalance at hover, and vibrational stability due to number-of-blades-per-rotor-revolution (Nb\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N_b$$\\end{document}/rev) in high-speed forward flight. Results show that while vibrations induced by rotor blade imbalance do not stabilize the hovering dynamics of a helicopter, these vibrations can still have a significant effect on the hovering dynamics. Rotor blade imbalance results in a symmetric effect on the roll and pitch axes, in that it tends to decrease the frequency of the subsidence modes of the hovering cubic, while the unstable oscillatory modes tend to increase in frequency and decrease in damping (destabilizing effect). On the other hand, the yaw/heave dynamics are relatively unaffected compared to the lateral and longitudinal axes. Moreover, Nb\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$N_b$$\\end{document}/rev rotor loads in forward flight are shown to reduce the damping of the coupled roll/pitch oscillation mode.

Integrated design of lateral-directional control law and vertical tail load for civil aircraft

According to new requirements of airworthiness regulation CS25.353, the advanced lateral-directional P-Beta control law design is studied in this paper. The LQR method based on the tracking command model is used to design the lateral-directional control law parameters. At the same time, the vertical tail load model of aircraft for yaw maneuver is introduced into the lateral-directional control law design model. The aim is to build the integrated design of control law and flight load. Finally, the simulation results show that the P-Beta control law can not only improve Dutch roll damping and coordination turn characteristics, but it can also reduce the yaw maneuver load by 18.5%. Thus, the structure weight of the aircraft’s vertical tail can be reduced.

МЕТОД ПРОЕКТУВАННЯ ТА ПАРАМЕТРИЧНОГО МОДЕЛЮВАННЯ СИЛОВОЇ НЕРВЮРИ КРИЛА ЛІТАКА ТРАНСПОРТНОЇ КАТЕГОРІЇ

The creation of any structural element begins with the design of basic geometric parameters. In the article, the method of designing and determining the main elements of the structure of the main ribs of the wing with conditions of static strength were reviewed, and a method of three-dimensional parametric modeling was developed. The rib is one of the most important elements of the wing, which act significant flight loads, and the main ribs additionally act concentrated forces. The article analyzed the design features of the rib design of the wing of the transport category aircraft. An analysis of the current loads on the main rib was performed, shear and bending diagrams were determined. During realize high-lift devices, the aerodynamic flow of the wing changes significantly, which leads to a change in the stress-strain state of the wing. This relates not only to the increase in lift due to a change in the curvature of the wing and an increase in the wing area, but also due to a change in the position of the center of pressure relative to the chord of the wing. Therefore, to determine the loads, the aerodynamic characteristics, obtained by the numerical method in the ANSYS program, were used. In order to remain competitive, the aviation company needs to ensure the high quality of the manufactured equipment, its quick modernization and modification or change of the model series. The use of CAD/CAM/CAE/PLM systems at all stages of the life cycle of aviation parts, including the design and production stages, can significantly improve the quality of the created parts and reduce the cost of performing work related to design and production, while maintaining high rates of work. The method of three-dimensional parametric modeling of the main machined wing rib was developed using the Siemens NX computer integrated system, which allows to significantly reduce the stage of modeling typical elements of the aircraft airframe structure using the created three-dimensional parametric model of a typical structural element

Structural comparison of conventional and chiral auxetic morphed aircraft rib

Abstract Tri-chiral structures are auxetic structures that show negative Poisson’s ratio. This effect is due to their microstructure and geometric sequence. They are used in the development of novel products as they show improved damping and energy absorption properties. While traditional manufacturing methods remain dysfunctional, the development of additive manufacturing technology provides opportunities for new studies in various industries such as aviation, textile, and automotive. In this study, passive airfoil morphing application was applied and a comparative study was carried out. A two-stage study was conducted. First, the tri-chiral pattern was fabricated by an FDM 3D printer with PLA+ and subjected to the in-plane compression test. Stress–strain curves of the tri-chiral structure were generated. Then, it was used in airfoil morphing applications. Morphed airfoil was also manufactured and a compression test was applied. Secondly, the aerostatic loads of the aircraft were calculated. Both conventional and chiral morphed ribs’ behaviors under flight loads were examined using the FEM and results were compared. The weight difference was calculated. In addition, eigenfrequency and eigenvectors of traditional and chiral ribs were computed and transverse vibration frequencies were expressed. Despite being more than 50 % lighter, chiral morphed rib was found to be stiffer than conventional rib.

Thoughts on the Importance of Similitude and Multi-Axial Loads When Assessing the Durability and Damage Tolerance of Adhesively-Bonded Doublers and Repairs

Adhesively bonded doublers and adhesively bonded repairs are extensively used to extend the operational life of metallic aircraft structures. Consequently, this paper focuses on the tools needed to address sustainment issues associated with both adhesively bonded doublers and adhesively bonded repairs to (metallic) aircraft structures, in a fashion that is consistent with the building-block approach mandated in the United States Air Force (USAF) airworthiness certification standard MIL-STD-1530D and also in the United States (US) Joint Services Structural Guidelines JSSG-2006. In this context, it is shown that the effect of biaxial loads on cohesive crack growth in a bonded doubler under both constant amplitude fatigue loads and operational flight loads can be significant. It is also suggested that as a result, for uniaxial tests to replicate the cohesive crack growth seen in adhesively bonded doublers and adhesively bonded repairs under operational flight loads, the magnitude of the applied load spectrum may need to be continuously modified so as to ensure that the crack tip similitude parameter in the laboratory tests reflects that seen in the full-scale aircraft.

On the Dynamic Behavior of Wings Incorporating Floating Wingtip Fuel Tanks

Recent studies have shown that semi-aeroelastic hinge devices can enable larger aircraft wingspans. Such a device would be folded on the ground to meet airport width restrictions, locked during cruise for optimal aerodynamic performance, and released during maneuvers to alleviate flight loads. In contrast, this paper uses a wind tunnel experiment to study the aeroelastic behavior of floating wingtip fuel tanks. This device consists of a freely floating wingtip with an additional mass attached in the form of a liquid-filled fuel tank. The static aeroelastic results show that altering the fuel tank’s filling level and position allows the wingtip to float at an optimal angle for aerodynamic efficiency across various angles of attack and fuel masses. Additionally, this paper shows that, with careful selection of the mass distribution of the wingtip, dynamic load alleviation comparable to the semi-aeroelastic hinge concept can be achieved during turbulence and one-minus-cosine encounters. Furthermore, the effect of fluid motion is shown to reduce incremental loads during random turbulence encounters by up to 10%; however, it has a negligible impact on the response to one-minus-cosine encounters. Such results are also confirmed by a numerical model incorporating a simple reduced-order fluid sloshing model.