Modern Passenger Aircraft Research Articles

Acoustical properties of the new sandwich structures for aircraft cabin interiors with integrated vacuum insulation

AbstractAny modern passenger aircraft must provide a high level of comfort for passengers who spend considerable time inside the cabin. The cabin's climate and interior noise levels contribute to this comfort. Vacuum insulation panels (VIP) have been explored as insulation materials to improve these factors due to their extremely low thermal conductivity. When integrating VIPs into the aircraft cabin's interior, it was discovered that the thermal conductivity of the entire sandwich structure was 3–6 times lower than conventional structures. This finding has generated much interest in using VIPs for aircraft cabin insulation. This article delves into the acoustic properties of these new structures featuring integrated VIPs. Tests were carried out to analyze the sound insulation capabilities of these structures. The results showed that the new interior structures exhibited promising acoustic properties.

RELIABILITY OF HYDROPNEUMODRIVES FOR METAL CUTTING EQUIPMENT

The reliability of hydropneumodrives largely determines the safety of machine tools, metal cutting equipment, the movement of transport vehicles, and the flight of modern passenger aircraft, and their failures can in some cases lead to accidents. The design stage is crucial in ensuring reliability. The main tasks of reliability research and calculation at this stage can be divided into three groups. First, it is a justification of reliability requirements for the main elements of the hydraulic pneumatic actuator (the task of reliability norming). This task is solved at an early stage of design and involves the preliminary development of the unit structure and justification of design principles. Secondly, it is to ensure the reliability of the elements and the unit as a whole. This group of tasks includes research and quantitative assessment of the efficiency of possible ways to ensure reliability; selection of basic design characteristics, statistical reserves of durability and longevity, stability reserves and other indicators; comparative analysis of options and selection of optimal designs. Thirdly, these are control calculations of the unit's reliability according to the design documentation. Algorithms for the distribution of normalised reliability indices at the design stage for hydropneumodrives implemented by the standard positional structure method and the minimisation method are obtained. Algorithms allow already at the early stages of hydropneumodrive design to normalise reliability indices, which makes it possible to obtain optimal solutions of reliability issues at the subsequent stages of development of the drive life cycle. The methods of calculation and determination of design relations for finding quantitative characteristics of failure-free indices of designed hydropneumodrives, implemented by the method of standard positional structure and the method of minimisation, are selected, which allows designing highly reliable hydropneumodrives for new metal cutting equipment. Evaluation of reliability indicators of hydropneumodrives at the stage of preliminary design allows to make a rational choice of structural scheme and parameters, to select appropriate materials and elements of scheme realisations.

Closed-Loop Recycling and Remanufacturing of Polymeric Aircraft Parts

The aviation industry is facing the challenge of reducing fossil fuels and emissions. Fuel efficiency is improved by making efficient powerplant systems and lighter aircraft. Modern passenger aircraft utilize polymeric and polymeric composite materials to achieve lighter structures without compromising strength. The European Union already has legislation to prevent landfilling and to increase the use of recyclable materials in the automotive industry. While older-generation aircraft, made mainly from metallic materials, are easily dismantled and recycled into other uses, such a process does not yet exist for aircraft made from composite materials. In the coming years, the industry will have to answer the question of how retired polymeric composite aircraft structures are to be recycled. One solution to increase the life cycle of polymeric and polymeric composite parts would be closed-loop recycling. In this paper, a perspective of the closed-loop recycling of polymeric aircraft parts is discussed. The technical aspects of recyclability and the different business models for the remanufacture of a finger pinch shroud certified for use in Airbus A350-900 passenger aircraft are investigated. The results show that closed-loop recycling is possible for polymeric aircraft parts. Future studies could include studying an LCA between virgin and recycled materials for a certain part.

Конструкторско-технологическое проектирование деталей из слоистого тканевого композита

The article considers the features of solving the problem of designing complex shape constructions made from layered fabric composites considering the triad "material-technology-construction". Based on the developed models, the design problem is formulated in terms of non-linear mathematical programming. The novelty is the approach to choosing the main design variables by dividing the digital model of the product into structural and technological groups, which pro-vide a quick and visual search for a rational distribution of material in the structure using a genetic optimization algo-rithm. The proposed approach is a development of the “precision design” methodology. It ensures the technological feasibility of composite items with a layered structure and their high weight return with minimal modifications at the early stages of design. The application of the technique is shown on the example of solving the problem of designing a composite bracket for the spoiler hinge of a modern passenger aircraft. Comparison of the designed bracket made of a layered fabric composite with a metal counterpart showed a significant reduction in the weight of the bracket.

Automatic cabin virtualization based on preliminary aircraft design data

Preliminary aircraft design and cabin design are essential and well-established steps within the product development cycle for modern passenger aircraft. In practice, the execution usually takes place sequentially, with the preliminary design defining a basic cabin layout and the detail implementation following in a subsequent step. To enable higher fidelity assessment of the cabin early in the design process—for example by means of virtual reality applications—this paper proposes an interface, which can derive detailed 3D geometry of the fuselage from preliminary design data provided in the Common Parametric Aircraft Configuration Schema (CPACS). This is a key step towards integration of cabin analysis and preliminary design in automated collaborative aircraft design chains, not only in terms of passenger comfort, but also manufacturability or crash safety. Like the TiGL Geometry Library for CPACS, the interface presented acts as a parameter engine, which translates data from CPACS into CAD geometry using the Open Cascade Technology library. However, the scope of TiGL is expanded significantly, albeit with an explicit focus on the fuselage, by including more details such as extruded frame and stringer profiles and floor structures. Furthermore, advanced knowledge management techniques are employed to detect and augment missing data. For virtual reality applications, triangulated representations of the CAD geometry can be provided in established exchange formats, creating an interface to common visualization platforms. Additionally, a new evolution of the cabin definition schema in CPACS is presented, to incorporate models of cabin components such as seats or sidewall panels enabling immersive virtual mock-ups.

Simulation of Nose Landing Gear Shimmy with Flexible Airframe Considered

Shimmy stability of the nose landing gear of an aircraft is studied in this paper. Firstly, Shimmy model was built considering the dynamic characteristics of the airframe. Then the critical damping, critical velocity and frequency range of the shimmy are obtained by introducing relevant parameters into the shimmy model. The research shows that the problem of shimmy is a tire type shimmy caused by insufficient damping of dampers and brings coupled resonance with the vibration mode of the airframe, which can be avoided by increasing the damping of the shimmy. At the same time, the influence of airframe dynamics and tire stiffness on the shimmy characteristics of the landing gear is also studied. With the increase of tire torsion and lateral stiffness, the critical velocity, maximum critical damping value and shimmy frequency of the landing gear increase. However, the elasticity of the airframe makes the frequency of the aircraft landing gear lower and the stable region of the shimmy smaller, so that the phenomenon of shimmy is more likely to occur. Therefore, the influence of airframe dynamic characteristics can not be ignored when studying the shimmy stability of the landing gear of a modern large passenger aircraft.

IMPROVING THE AERODYNAMICS OF A TRANSPORT AIRCRAFT WING USING A DELTA PLANFORM WINGTIP LEADING EDGE EXTENSION

The article explores the possibility of improving the aerodynamic properties of a supercritical-airfoil wing, typical for a modern passenger aircraft, using delta planform passive devices of large relative areas, installed along the leading edge at the wing tip. Delta extensions of various configurations were considered to be used as wingtip devices, potentially improving or completely replacing classical R. Whitcomb winglets. As a result of two- and three-dimensional CFD simulations performed on DLR-F4 wing-body prototype, the potential advantage of these devices was confirmed, particularly when they are installed in a combination with an elliptical planform, largely swept, raked winglet in terms of reducing the induced drag and increasing the aerodynamic lift-to-drag ratio at flight angles of attack. The growth in lift-to-drag ratio applying these devices owes it solely to the drop in drag, without increasing the lift force acting on the wing. In comparison to the classical winglets that lead to a general increase in lifting and lateral forces acting on the wing structure, resulting in a weight penalty, the Wingtip Ledge Edge Triangular Extension (WLETE) yields the same L/D ratio increase, but with a much smaller increase in the wing loading. A study has been made of the characteristics of the local (modified) airfoil in the WLETE zone in a two-dimensional flow context, and a quantitative analysis has been conducted of the influence of WLETE on both the profile and induced drag components, as well as its influence on the overall lift coefficient of the wing. The resulted synthesis of the WLETE influence on the wing L/D ratio will consist of its influence on each of these components. A comparison of the efficiency of using delta extensions against classical winglets was carried out in a multidisciplinary way, where in addition to the changes in aerodynamic coefficients of lift and drag, the increments of magnitude and distribution of the loads acting on the wing console were studied along with the maximum resulted structural stress. The study of the growth of structural stress on the wing structure after installing WLETE, confirmed the results obtained from CFD simulations that these delta extensions do not increase and do not change the distribution of total forces and moments acting on the wing console.

INCREASING THE QUALITY OF DRILLING HOLES IN FIBER REINFORCEMENT COMPOSITE MATERIALS

Problems. Fiber reinforcement polymer composite materials (FRP) are used in many areas of modern machine building, mostly in aircraft and aerospace industries. Millions of high-quality holes in FRP details are necessary for production of a modern passenger aircraft, to provide reliable bolt and rivet connections. Drilling is a key-machining operation for the production of holes in FRP.Comparing metal-containing materials drilling, FRP drilling is accompanied by the appearance of specific defects, such as delamination, uncut fibers, the damages of FRP’s matrix from the holes surface and thermal destruction. The listed defects adversely affect the reliability of bolt and rivet joints between parts of FRP, which determines the relevance of this study.The aim of the study. Determination of the influence of the support cutting edges of the developed drill with superhard materials on the holes surfaces quality of carbon fiber reinforcement plastics (CFRP) samples.Research methodology. The goals were achieved by experimental investigations on drilling CFRP samples by the designed drill bits and drill bit from SECO (Sweden) with similar cutting conditions. The drilling process was accompanied by the registration the axial force of cutting, torque and the acoustic emission signal. The analysis of the registered signals allowed to study the features of support cutting edges of the developed drill. The quality of the drilled holes surfaces was analyzed by determining the roughness using Alicona Infinite Focus (Austria) optical microscope. Conclusions were made according to the results of experimental studies.Conclusions. Analyzed data are shown, that the developed drill provides twice the lower roughness of the holes surfaces than the drill SECO, according to the same level of the wear of the main cutting edges. These results are mainly due to the work of the support cutting edges of the developed drill on a reversing feed.

New real-time heuristics for electrical load rebalancing in aircraft

The concept of more electric aircraft leads to increases in the amount of electrical loads, as well as the power consumed in the aircraft of the future. To utilize the power feeders, more symmetric, load balancing methods can be applied to swap loads between different phases of an alternating current (AC) feeder, or even between different power feeders. If the load balancing system reacts to measurement data during the flight in real time, the cable power losses and return network power losses, too, are reduced. In addition, the rate of power management interventions decreases. The load balancing problem in three-phase systems is a mixed-integer nonlinear nondifferentiable optimization problem, which is typically solved by elaborate and time-consuming nonreal-time optimization algorithms. The AC loads in aircraft have different power factors, which result in currents described by complex numbers. To determine a load swapping scheme in real time starting from a given load allocation with sparse swapping, new heuristics are presented. One heuristic is specially designed to solve the phase swapping problem by shifting single-phase loads between phases of a feeder. Another heuristic, based on the first one, is enhanced to more than one three-phase feeder and considers the swapping of single-phase and three-phase loads. The heuristics are tested by simulations of a comprehensive case study based on real measurement data from a modern passenger aircraft. To prove the efficiency of the new concepts, a test bench has been built, and several experiments successfully conducted.

The life of a composite: Turning materials data into materials knowledge

Composite materials have experienced a boom in popularity over the last 40 years, thanks in large part to their weight saving advantages. Modern passenger aircraft, for example, may contain up to 50% composite materials, up from only 6% in the 1980s, and this trend seems set to continue. Compared to conventional materials, such as the aluminium alloys used in aerospace, composites can offer outstanding mechanical properties at lower density. However, engineering with composites can also be both expensive and time consuming, with development and qualification costs for new materials in the tens of millions, and time from conception to implementation measured in years. Engineering organizations continue to optimize composite performance, achieving further weight reductions, but also look to do so at lower cost, and with faster time to market.

Experimental investigation of personal air supply nozzle use in aircraft cabins

To study air passengers' use of individual air supply nozzles in aircraft cabins, we constructed an experimental chamber which replicated the interior of a modern passenger aircraft. A series of experiments were conducted at different levels of cabin occupancy. Survey data were collected focused on the reasons for opening the nozzle, adjusting the level of air flow, and changing the direction of the air flow. The results showed that human thermal and draft sensations change over time in an aircraft cabin. The thermal sensation response was highest when the volunteers first entered the cabin and decreased over time until it stablized. Fifty-one percent of volunteers opened the nozzle to alleviate a feeling of stuffiness, and more than 50% adjusted the nozzle to improve upper body comfort. Over the period of the experiment the majority of volunteers chose to adjust their the air flow of their personal system. This confirms airline companies' decisions to install the individual aircraft ventilation systems in their aircraft indicates that personal air systems based on nozzle adjustment are essential for cabin comfort. These results will assist in the design of more efficient air distribution systems within passenger aircraft cabins where there is a need to optimize the air flow in order to efficiently improve aircraft passengers' thermal comfort and reduce energy use.

Composites poised to transform airline economics

Modern passenger aircraft that represent a quantum leap in composites adoption, and a commensurate improvement in airline economics, are now entering service or will soon be doing so. Freelance journalist George Marsh reviews the progress of the leaders of this new wave in commercial air transport.

Investigation of the role for noise canceling headphones to assist speech recall in noise

There are many situations where it is necessary to hear, understand and be able to recall spoken information in less than ideal listening conditions. For example within an aircraft cabin where, despite improvements in modern passenger aircraft, noise generated from aircraft engines and aerodynamic airflow make it difficult to hear important on-board safety announcements such as the preflight safety brief. The benefits of headphones that incorporate active noise control in such environments are the focus of a series of research studies. In this paper, we discuss the techniques developed to investigate the use of active noise control headphones on the intelligibility and recall of speech generated outside the headsets in noise typical of that in a commercial aircraft cabin. The initial studies were directed towards assessing the effects on the recall for safety announcements. These studies have been extended to investigate if there are any benefits for those for which English is a second language. The results suggest that the use of active noise control headphones can minimize communication errors in a range of situations and this paper will discuss the methodology adopted and summarize the outcomes.

Continuation Analysis of Aircraft Ground Loads During High-Speed Turns

The current lateral ground loads requirement for an aircraft during a high-speed turn was written in the middle of the last century when relatively small aircraft with tricycle landing gear arrangements started to emerge. This requirement is known to be conservative when applied to large modern passenger aircraft. Nonlinearities (such as tire forces) have a significant effect at the edge of operating envelopes, placing a renewed interest on analysis methods that can classify the dynamics in these regions. In this paper, a continuation analysis is used to assess the loads that can be generated for different aircraft configurations during high-speed turns and to compare the results to the original requirement. A comparison is made between test results from a Federal Aviation Admistration study and continuation results, where all of the significant test data points are located within an envelope constructed from a continuation analysis. Continuation analysis, therefore, provides a conservative estimate of the maximum lateral load factors. These values are, however, less than the value prescribed in the regulation.

Mathematical description of nonstationary aerodynamic characteristics of a passenger aircraft model in longitudinal motion at large angles of attack

Aerodynamic loads in problems of flight dynamics of passenger aircraft in stalled flow regimes are described using a mathematical model that includes an ordinary linear first-order differential equation. A procedure for determining the parameters of the mathematical model is proposed which is based on approximating experimental frequency characteristics with the frequency characteristics of the linearized mathematical model. The mathematical model was verified by tests of a modern passenger aircraft model in a wind tunnel.

An experimental study of sound generated by flows around cylinders of different cross-section

The sound radiated by rigid cylinders placed transversely in a uniform stream has been measured in an anechoic wind tunnel over a range of Mach numbers ( M = 0.09 – 0.2 ). The cylinders have different cross-sections, e.g., circular, square, rectangular, elliptic, and circular with lateral ribs or knurled surfaces. Different length to diameter ratios of the cylinders are also investigated. Results are presented as narrow band spectra, measured in the far field (acoustic as well as geometric). All spectra are presented with dimensionless (scaled) axes, as well as the original dimensional scales. It is shown that elliptic cross-sections are less noisy, compared to all other cylinders, but noise abatement techniques such as lateral ribs and knurled surfaces can also reduce tonal radiated noise. Two practical applications of these experiments are the reduction of radiated noise from pantographs of high-speed railway trains, and from the landing gear of modern passenger aircraft.

Analysis of Residual Stresses Around ‘Dimpled’ Cold-Expanded Holes in Aluminium Alloy Plates

A traditional approach to increasing fatigue resistance of many assemblies involves the creation of regions of compressive residual stress. For example, riveting holes used in modern passenger aircraft are currently subjected to cold expansion using split mandrel tools. The method is relatively expensive and not entirely problem-free. In the present study we consider a method of creating residual stresses around drilled holes referred to as ‘dimpling’, that itself is a variation of a novel technique known as the StressWaveTM process. An experimental procedure is described for the creation of localised regions of significant plastic deformation and residual stress by ‘dimpling’, allowing the production of cold-worked and residually-stressed specimens. The overall aims of this study were to determine thickness-average residual stresses by two different techniques, namely, one destructive technique (Sachs boring) and one non-destructive (high energy X-ray diffraction); and to compare the results. In Sachs boring experiments the variation of strain gauge readings with increasing diameter of the central hole was recorded. A classical elastic-ideally plastic axisymmetric model for plane stress conditions was used in the analysis. Energy dispersive synchrotron X-ray diffraction experiments were performed for non-destructive assessment of residual elastic strains. The two different stress evaluation techniques used in this project led to consistent results. Good correlation was found between the stresses obtained from X-ray diffraction results and those deduced from Sachs boring experiments.

Analyzing Cockpit Interfaces Using Formal Methods

Modern passenger aircraft are highly automated, and problems at the interface between the automation and the pilot are implicated in several accidents. I use a simple example taken from the autopilot of a widely used aircraft type to demonstrate how formal methods can be used to analyze some aspects of these interfaces, and to expose potential problems.This example serves to illustrate the wider thesis that formal methods can find application in domains outside those traditionally associated with it, provided only that the phenomena of interest can be modeled effectively in discrete mathematics.

First A340 Model in the High‐Speed Wind Tunnel

HIGH lift, minimum drag and good controlability are among the aerodynamic requirements imposed on modern passenger aircraft. These performance characteristics are particularly relevant to the future long range version of the Airbus, the A340 four‐engine wide‐body aircraft incorporating a new wing design.