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Aerospace, Volume 8, Issue 5 (May 2021) – 25 articles

Cover Story (view full-size image): The global surface pressure was measured on a 7-degree half-angle circular cone/flare model at a nominally zero angle of attack using pressure-sensitive paint (PSP). The mean and fluctuating surface pressures were measured with a temperature-corrected, high-frequency-response (10 kHz) anodized-aluminum pressure-sensitive paint (AA-PSP) allowing for novel, global calculations of skewness and coherence. The skewness indicated the mean locations of the separation and reattachment shock feet as well as their fluctuations over the course of the test. The coherence indicated that the separation and reattachment shock feet fluctuate about their mean location at the same frequency as one another but at 180 degrees out of phase. This results in a large-scale ‘breathing motion’ of the separated region characteristic of large separation bubbles. View this paper.
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Article
Threat Evaluation of Air Targets Based on the Generalized λ-Shapley Choquet Integral of GIFSS
Aerospace 2021, 8(5), 144; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050144 - 20 May 2021
Viewed by 527
Abstract
Fast and accurate threat evaluation (TE) of incoming air targets has a great influence on air defense. In this paper, two new generalized intuitionistic fuzzy soft set (GIFSS) methods are proposed for threat evaluation of air targets. Firstly, the threat evaluation index system [...] Read more.
Fast and accurate threat evaluation (TE) of incoming air targets has a great influence on air defense. In this paper, two new generalized intuitionistic fuzzy soft set (GIFSS) methods are proposed for threat evaluation of air targets. Firstly, the threat evaluation index system is reasonably constructed by analyzing the relative kinematics between the targets and assets, apart from that between the targets and interceptors, which is more reasonable and practical. Secondly, after the threat indexes (TI) are properly obtained, two new aggregation operators for GIFSS are put forward based on the generalized λ-Shapley Choquet integral. The proposed operators not only depict the correlations among the evaluation index but also consider the importance of them globally. Finally, the effectiveness and superiority of the proposed methods are verified through a numerical simulation including four air targets in different index systems. Full article
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Article
Radiation Risks in a Mission to Mars for a Solar Particle Event Similar to the AD 993/4 Event
Aerospace 2021, 8(5), 143; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050143 - 20 May 2021
Cited by 1 | Viewed by 515
Abstract
Within the past decade, evidence of excess atmospheric 14C production in tree rings, coupled with an increase in annually resolved measurements of 10Be in Arctic and Antarctic ice cores, have indicated that an extremely large solar particle event (SPE) occurred in AD 993/4. The production of cosmogenic nuclei, such as 36Cl in consonance with 10Be, indicate that the event had a very energetic “hard” particle spectrum, comparable to the event of February 1956. Herein, we estimate the potential radiation risk to male and female crew members on a mission to Mars that would occur from such an SPE. Critical organ doses and effective doses are calculated and compared with NASA space radiation limits for an SPE comparable to the AD 993/4 event, occurring during the transit phase to Mars, or while the crew members are operating on the surface of Mars. Aluminum shielding, similar in thickness to a surface lander, a spacecraft, and a storm shelter area within the spacecraft, are assumed for the transit phase. For surface operations, including the shielding provided by the atmosphere of Mars, shielding comparable to a spacesuit, enclosed rover, and a surface habitat are assumed. The results of our simulations indicate that such an event might have severe consequences for astronauts in transit to Mars. However, on the surface of Mars, the atmosphere provides some protection against an event similar to the 993/4 SPE. In general, the results show that additional shielding may be required for some of the assumed shielding scenarios. Full article
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Article
Thermochemistry of Combustion in Polyvinyl Alcohol + Hydroxylammonium Nitrate
Aerospace 2021, 8(5), 142; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050142 - 20 May 2021
Viewed by 457
Abstract
A mixture of polyvinyl alcohol (PVA) and hydroxylammoniun nitrate (HAN) forms a gummy solid known as a plastisol, which is ionically conducting. When an electrostatic potential of 200 V DC is applied across the plastisol, it ignites. Combustion ceases upon removal of the [...] Read more.
A mixture of polyvinyl alcohol (PVA) and hydroxylammoniun nitrate (HAN) forms a gummy solid known as a plastisol, which is ionically conducting. When an electrostatic potential of 200 V DC is applied across the plastisol, it ignites. Combustion ceases upon removal of the applied voltage. The products of PVA + HAN combustion are known to include the molecular gases carbon monoxide, carbon dioxide, water, nitrogen, and hydrogen. When the electric field within the plastisol is spatially uniform, combustion occurs preferentially at the anode. The fact that HAN is an ionic conductor suggests that the mechanism of combustion is electrolytic in origin. Consistent with the preference for combustion at the anode and the known gaseous products, we consider two reaction mechanisms. One involves atomic oxygen as the oxidizing agent at the anode and hydroxyl radical as the oxidizing agent at the cathode. The other involves ozone as the oxidizing agent at the anode and hydrogen peroxide as the oxidizing agent at the cathode. Each mechanism is applied to a scenario where the products are rich in the carbon oxides and to a second scenario where the products are poor in the carbon oxides. In the rich case, the heat of the overall reaction is −808.33 kJ per mole of HAN consumed and the electrical energy is converted to thermal energy with an efficiency of 4.2%. In the poor case, the corresponding figures are −567 kJ per mole of HAN and efficiency is 2.9%. The combustion reactions at the electrodes are uniformly exothermic with the exception of the reaction involving hydrogen peroxide at the cathode. When the products are poor in the carbon oxides, this reaction is actually endothermic. Full article
(This article belongs to the Special Issue Alternative Propellants for Space Propulsion)
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Review
GKS and UGKS for High-Speed Flows
Aerospace 2021, 8(5), 141; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050141 - 19 May 2021
Cited by 1 | Viewed by 554
Abstract
The gas-kinetic scheme (GKS) and the unified gas-kinetic scheme (UGKS) are numerical methods based on the gas-kinetic theory, which have been widely used in the numerical simulations of high-speed and non-equilibrium flows. Both methods employ a multiscale flux function constructed from the integral [...] Read more.
The gas-kinetic scheme (GKS) and the unified gas-kinetic scheme (UGKS) are numerical methods based on the gas-kinetic theory, which have been widely used in the numerical simulations of high-speed and non-equilibrium flows. Both methods employ a multiscale flux function constructed from the integral solutions of kinetic equations to describe the local evolution process of particles’ free transport and collision. The accumulating effect of particles’ collision during transport process within a time step is used in the construction of the schemes, and the intrinsic simulating flow physics in the schemes depends on the ratio of the particle collision time and the time step, i.e., the so-called cell’s Knudsen number. With the initial distribution function reconstructed from the Chapman–Enskog expansion, the GKS can recover the Navier–Stokes solutions in the continuum regime at a small Knudsen number, and gain multi-dimensional properties by taking into account both normal and tangential flow variations in the flux function. By employing a discrete velocity distribution function, the UGKS can capture highly non-equilibrium physics, and is capable of simulating continuum and rarefied flow in all Knudsen number regimes. For high-speed non-equilibrium flow simulation, the real gas effects should be considered, and the computational efficiency and robustness of the schemes are the great challenges. Therefore, many efforts have been made to improve the validity and reliability of the GKS and UGKS in both the physical modeling and numerical techniques. In this paper, we give a review of the development of the GKS and UGKS in the past decades, such as physical modeling of a diatomic gas with molecular rotation and vibration at high temperature, plasma physics, computational techniques including implicit and multigrid acceleration, memory reduction methods, and wave–particle adaptation. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics on High-Speed and Non-Equilibrium Flows)
Article
Planning of Aircraft Fleet Maintenance Teams
Aerospace 2021, 8(5), 140; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050140 - 19 May 2021
Viewed by 475
Abstract
This paper addresses a support information system for the planning of aircraft maintenance teams, assisting maintenance managers in delivering an aircraft on time. The developed planning of aircraft maintenance teams is a computer application based on a mathematical programming problem written as a [...] Read more.
This paper addresses a support information system for the planning of aircraft maintenance teams, assisting maintenance managers in delivering an aircraft on time. The developed planning of aircraft maintenance teams is a computer application based on a mathematical programming problem written as a minimization one. The initial decision variables are positive integer variables specifying the allocation of available technicians by skills to maintenance teams. The objective function is a nonlinear function balancing the time spent and costs incurred with aircraft fleet maintenance. The data involve technicians’ skills, hours of work to perform maintenance tasks, costs related to facilities, and the aircraft downtime cost. The realism of this planning entails random possibilities associated with maintenance workload data, and the inference by a procedure of Monte Carlo simulation provides a proper set of workloads, instead of going through all the possibilities. The based formalization is a nonlinear integer programming problem, converted into an equivalent pure linear integer programming problem, using a transformation from initial positive integer variables to Boolean ones. A case study addresses the use of this support information system to plan a team for aircraft maintenance of three lines under the uncertainty of workloads, and a discussion of results shows the serviceableness of the proposed support information system. Full article
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Article
Three-Surface Model with Redundant Longitudinal Control: Modeling, Trim Optimization and Control in a Preliminary Design Perspective
Aerospace 2021, 8(5), 139; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050139 - 17 May 2021
Viewed by 589
Abstract
Notwithstanding the interest in the three-surface concept shown by aircraft designers, this configuration was not thoroughly investigated in conjunction with the adoption of two-elevator surfaces, on both canard and tail. In fact, the inclusion of an additional elevator produces a redundant longitudinal control [...] Read more.
Notwithstanding the interest in the three-surface concept shown by aircraft designers, this configuration was not thoroughly investigated in conjunction with the adoption of two-elevator surfaces, on both canard and tail. In fact, the inclusion of an additional elevator produces a redundant longitudinal control which can be specifically exploited to target trim optimization. The same redundancy can be also employed to improve the flying qualities of the three-surface aircraft. In this paper, after introducing a simple flight mechanics model, ideal for preliminary design and analyses, the advantages of this configuration are explored. Firstly, the problem of finding the elevator deflections of canard and tail for minimum drag in trim is formulated and solved. Secondarily, the updating of a two-surface back-tailed airplane into an equivalent three-surface one is demonstrated, showing the potential improvement in cruise performance. Finally, the controls are employed through a smart control law for achieving better flying qualities. Full article
(This article belongs to the Special Issue Aircraft Modelling for Design, Simulation and Control)
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Article
Numerical Aspects of Particle-in-Cell Simulations for Plasma-Motion Modeling of Electric Thrusters
Aerospace 2021, 8(5), 138; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050138 - 15 May 2021
Viewed by 752
Abstract
The present work is focused on a detailed description of an in-house, particle-in-cell code developed by the authors, whose main aim is to perform highly accurate plasma simulations on an off-the-shelf computing platform in a relatively short computational time, despite the large number [...] Read more.
The present work is focused on a detailed description of an in-house, particle-in-cell code developed by the authors, whose main aim is to perform highly accurate plasma simulations on an off-the-shelf computing platform in a relatively short computational time, despite the large number of macro-particles employed in the computation. A smart strategy to set up the code is proposed, and in particular, the parallel calculation in GPU is explored as a possible solution for the reduction in computing time. An application on a Hall-effect thruster is shown to validate the PIC numerical model and to highlight the strengths of introducing highly accurate schemes for the electric field interpolation and the macroparticle trajectory integration in the time. A further application on a helicon double-layer thruster is presented, in which the particle-in-cell (PIC) code is used as a fast tool to analyze the performance of these specific electric motors. Full article
(This article belongs to the Special Issue Advances in Computational Methodologies for Aerospace Propulsion)
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Article
Time-Fixed Glideslope Guidance for Approaching the Proximity of an Asteroid
Aerospace 2021, 8(5), 137; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050137 - 15 May 2021
Viewed by 495
Abstract
The guidance and control problem of spacecraft approaching an asteroid using constant continuous thrust is studied in this work. The range of interest is from hundreds of kilometers to several kilometers, in which relative measurements of much higher accuracy than based on Earth [...] Read more.
The guidance and control problem of spacecraft approaching an asteroid using constant continuous thrust is studied in this work. The range of interest is from hundreds of kilometers to several kilometers, in which relative measurements of much higher accuracy than based on Earth can be used to facilitate further hovering or landing operations. Time-fixed glideslope guidance algorithm is improved by introducing a substitute of an existing control parameter and combined with elliptical relative orbital dynamics to rendezvous the spacecraft with a prescribed location in the proximity of a given asteroid. A vast range of values for the control parameters are explored and suitable combinations are found. To fully validate the robustness and accuracy of the proposed control algorithm, Monte Carlo simulations are done with the navigational error and implementation error considered. Full article
(This article belongs to the Special Issue Spacecraft Trajectory Design and Optimization)
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Article
Eeloscope—Towards a Novel Endoscopic System Enabling Digital Aircraft Fuel Tank Maintenance
Aerospace 2021, 8(5), 136; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050136 - 12 May 2021
Viewed by 629
Abstract
In this research article, a novel endoscopic system, which is suited to perform a digital inspection of the aircraft wing fuel tanks, is introduced. The aim of this work is to specifically design and develop an assisting system, called `Eeloscope’, to allow accessing [...] Read more.
In this research article, a novel endoscopic system, which is suited to perform a digital inspection of the aircraft wing fuel tanks, is introduced. The aim of this work is to specifically design and develop an assisting system, called `Eeloscope’, to allow accessing and diving through an aircraft kerosene tank in a minimally invasive matter. Currently, mechanics often suffer from the harsh working environment and the arduous maintenance duties within the tank. To address such challenges and derive a tailored solution, an adapted Design Thinking (DT) process is applied. The resulting system enables a fully digital inspection and generation of 3-dimensional structural inspection data. Consequently, devices such as the Eeloscope will facilitate a more efficient and continuous inspection of fuel tanks to increase the transparency regarding the condition of hardly accessible aircraft structures and provide a work relief for mechanics at the same time. Full article
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Article
A Modified Dynamic Programming Approach for 4D Minimum Fuel and Emissions Trajectory Optimization
Aerospace 2021, 8(5), 135; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050135 - 11 May 2021
Viewed by 570
Abstract
4D flight trajectory optimization is an essential component to improve flight efficiency and to enhance air traffic capacity. this technique not only helps to reduce the operational costs, but also helps to reduce the environmental impact caused by the airliners. This study considers [...] Read more.
4D flight trajectory optimization is an essential component to improve flight efficiency and to enhance air traffic capacity. this technique not only helps to reduce the operational costs, but also helps to reduce the environmental impact caused by the airliners. This study considers Dynamic Programming (DP), a well-established numerical method ideally suited to solve 4D flight Trajectory Optimization Problems (TOPs). However, it bears some shortcomings that prevent the use of DP in many practical real-time implementations. This paper proposes a Modified Dynamic Programming (MDP) approach that reduces the computational effort and overcomes the drawbacks of the traditional DP. In this paper, two numerical examples with fixed arrival times are presented, where the proposed MDP approach is successfully implemented to generate optimal trajectories that minimize aircraft fuel consumption and emissions. Then the obtained optimal trajectories are compared with the corresponding reference commercial flight trajectory for the same route in order to quantify the potential benefit of reduction of aircraft fuel consumption and emissions. Full article
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Article
Load-Identification Method for Flexible Multiple Corrugated Skin Using Spectra Features of FBGs
Aerospace 2021, 8(5), 134; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050134 - 09 May 2021
Viewed by 636
Abstract
Flexible corrugated skins are ideal structures for morphing wings, and the associated load measurements are of great significance in structural health monitoring. This paper proposes a novel load-identification method for flexible corrugated skins based on improved Fisher discrimination dictionary learning (FDDL). Several fiber [...] Read more.
Flexible corrugated skins are ideal structures for morphing wings, and the associated load measurements are of great significance in structural health monitoring. This paper proposes a novel load-identification method for flexible corrugated skins based on improved Fisher discrimination dictionary learning (FDDL). Several fiber Bragg grating sensors are pasted on the skin to monitor the load on multiple corrugated crests. The loads on different crests cause nonuniform strain fields, and these discriminative spectra are recorded and used as training data. The proposed method involves load-positioning and load-size identification. In the load-size-identification stage, a classifier is trained for every corrugated crest. An interleaved block grouping of samples is introduced to enhance the discrimination of dictionaries, and a two-resolution load-size classifier is introduced to improve the performance and resolution of the grouping labels. An adjustable weight is introduced to the FDDL classification scheme to optimize the contribution from different sensors for different load-size classifiers. With the proposed method, the individual loads on eight crests can be identified by two fiber Bragg grating sensors. The positioning accuracy is 100%, and the mean error of the load-size identification is 0.2106 N, which is sufficiently precise for structural health monitoring. Full article
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Article
Development of a Flexible and Expandable UTM Simulator Based on Open Sources and Platforms
Aerospace 2021, 8(5), 133; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050133 - 08 May 2021
Viewed by 541
Abstract
In order to study air traffic control of UAS’s (Unmanned Aerial Systems) in very low altitudes, the UTM (UAS Traffic Management) simulator has to be as flexible and expandable as other research simulators because relevant technologies and regulations are not matured enough at [...] Read more.
In order to study air traffic control of UAS’s (Unmanned Aerial Systems) in very low altitudes, the UTM (UAS Traffic Management) simulator has to be as flexible and expandable as other research simulators because relevant technologies and regulations are not matured enough at this stage. Available approaches using open sources and platforms are investigated to be used in the UTM simulator. The fundamental rationale for selection is availability of necessary resources to build a UTM simulator. Integration efforts to build a UTM simulator are elaborated, using Ardupilot, MavProxi, Cesium, and VWorld, which are selected from the thorough field study. Design requirements of a UTM simulator are determined by analyzing UTM services defined by NASA (National Aeronautics and Space Administration) and Eurocontrol. The UTM simulator, named eUTM, is composed of three components: UOS (UTM Operating System), UTM, and multiple GCSs (Ground Control Stations). GCSs are responsible for generation of flight paths of various UASs. UTM component copies functions of a real UTM such as monitoring and controlling air spaces. UOS provides simulation of environment such as weather, and controls the whole UTM simulator system. UOS also generates operation scenarios of UTM, and resides on the same UTM computer as an independent process. Two GCS simulators are connected to the UTM simulator in the present configuration, but the UTM simulator can be expanded to include up to 10 GCS simulators in the present design. In order to demonstrate the flexibility and expandability of eUTM simulator, several operation scenarios are realized and typical deconfliction scenarios among them are tested with a deconfliction algorithm. During the study, some limits are identified with applied open sources and platforms, which have to be resolved in order to obtain a flexible and expandable UTM simulator supporting relevant studies. Most of them are related to interfacing individual sources and platforms which use different program languages and communication drivers. Full article
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Article
Design and Optimization of a Large Turboprop Aircraft
Aerospace 2021, 8(5), 132; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050132 - 06 May 2021
Viewed by 745
Abstract
This paper proposes a feasibility study concerning a large turboprop aircraft to be used as a lower environmental impact solution to current regional jets operated on short/medium hauls. An overview of this market scenario highlights that this segment is evenly shared between regional [...] Read more.
This paper proposes a feasibility study concerning a large turboprop aircraft to be used as a lower environmental impact solution to current regional jets operated on short/medium hauls. An overview of this market scenario highlights that this segment is evenly shared between regional turboprop and jet aircraft. Although regional jets ensure a large operative flexibility, they are usually not optimized for short missions with a negative effect on block fuel and environmental impact. Conversely, turboprops represent a greener solution but with reduced passenger capacity and speed. Those aspects highlight a slot for a new turboprop platform coupling higher seat capacity, cruise speed and design range with a reduced fuel consumption. This platform should operate on those ranges where neither jet aircraft nor existing turboprops are optimized. This work compares three different solutions: a high-wing layout with under-wing engines installation and both two- and three-lifting-surface configurations with low-wing and tail tips-mounted engines. For each concept, a multi-disciplinary optimization was performed targeting the minimum block fuel on a 1600 NM mission. Optimum solutions were compared with both a regional jet such as the Airbus A220-300 operated on 1600 NM and with a jet aircraft specifically designed for this range. Full article
(This article belongs to the Special Issue Aircraft Design (SI-3/2021))
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Project Report
Towards a Circular Economy in the Aviation Sector Using Eco-Composites for Interior and Secondary Structures. Results and Recommendations from the EU/China Project ECO-COMPASS
Aerospace 2021, 8(5), 131; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050131 - 05 May 2021
Viewed by 845
Abstract
Fiber reinforced polymers play a crucial role as enablers of lightweight and high performing structures to increase efficiency in aviation. However, the ever-increasing awareness for the environmental impacts has led to a growing interest in bio-based and recycled ‘eco-composites’ as substitutes for the [...] Read more.
Fiber reinforced polymers play a crucial role as enablers of lightweight and high performing structures to increase efficiency in aviation. However, the ever-increasing awareness for the environmental impacts has led to a growing interest in bio-based and recycled ‘eco-composites’ as substitutes for the conventional synthetic constituents. Recently, the international collaboration of Chinese and European partners in the ECO-COMPASS project provided an assessment of different eco-materials and technologies for their potential application in aircraft interior and secondary composite structures. This project summary reports the main findings of the ECO-COMPASS project and gives an outlook to the next steps necessary for introducing eco-composites as an alternative solution to fulfill the CLEAN SKY target. Full article
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Article
The Use of Machine Learning for the Prediction of the Uniformity of the Degree of Cure of a Composite in an Autoclave
Aerospace 2021, 8(5), 130; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050130 - 05 May 2021
Viewed by 568
Abstract
The difference in the degree of cure of the composite in an autoclave is one of the main characterization parameters of the uniformity of the degree of cure of the composite material. Therefore, it is very important to develop an effective method for [...] Read more.
The difference in the degree of cure of the composite in an autoclave is one of the main characterization parameters of the uniformity of the degree of cure of the composite material. Therefore, it is very important to develop an effective method for predicting the difference in the curing degree of a composite autoclave to improve the uniformity of the curing degree of the composite materials. We researched five machine learning models: a fully connected neural network (FCNN) model, a deep neural network (DNN) model, a radial basis function (RBF) neural network model, a support vector regression (SVR) model and a K-nearest neighbors (KNN) model. We regarded the heating rate, holding time and holding temperature of the composite material’s two holding-stage cure profile as input parameters and established a rapid estimation model of the maximum curing degree difference at any time during the molding process. We simulated the molding process of the composite material in an autoclave to obtain the maximum difference in the curing degree as the test sample data to train five machine learning models and compared and verified the different models after the training. The results showed that the RBF neural network model had the best prediction effect among the five models and the RBF was the most suitable algorithm for this model. Full article
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Article
Methods of Identifying Correlated Model Parameters with Noise in Prognostics
Aerospace 2021, 8(5), 129; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050129 - 05 May 2021
Cited by 1 | Viewed by 621
Abstract
In physics-based prognostics, model parameters are estimated by minimizing the error or maximizing the likelihood between model predictions and measured data. When multiple model parameters are strongly correlated, it is challenging to identify individual parameters by measuring degradation data, especially when the data [...] Read more.
In physics-based prognostics, model parameters are estimated by minimizing the error or maximizing the likelihood between model predictions and measured data. When multiple model parameters are strongly correlated, it is challenging to identify individual parameters by measuring degradation data, especially when the data have noise. This paper first presents various correlations that occur during the process of model parameter estimation and then introduces two methods of identifying the accurate values of individual parameters when they are strongly correlated. The first method can be applied when the correlation relationship evolves as damage grows, while the second method can be applied when the operating (loading) conditions change. Starting from manufactured data using the true parameters, the accuracy of identified parameters is compared with various levels of noise. It turned out that the proposed method can identify the accurate values of model parameters even with a relatively large level of noise. In terms of the marginal distribution, the standard deviation of a model parameter is reduced from 0.125 to 0.03 when different damage states are used. When the loading conditions change, the uncertainty is reduced from 0.3 to 0.05. Both are considered as a significant improvement. Full article
(This article belongs to the Special Issue Fault Detection and Prognostics in Aerospace Engineering)
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Article
Effect of Two-Head Flared Hole on Film Cooling Performance over a Flat Plate
Aerospace 2021, 8(5), 128; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050128 - 04 May 2021
Viewed by 717
Abstract
Film cooling is commonly utilized in turbine blades to decrease the temperature of the air stream from the combustion chamber that contacts directly with the blades. The shape of a cylindrical hole (CH) with the geometrical variations at inlet and outlet ports was [...] Read more.
Film cooling is commonly utilized in turbine blades to decrease the temperature of the air stream from the combustion chamber that contacts directly with the blades. The shape of a cylindrical hole (CH) with the geometrical variations at inlet and outlet ports was examined using the 3D Reynolds-averaged Navier–Stokes equations (RANS) with a shear stress transport (SST k − ω) turbulence model to study the effect of the two-head flared hole on film cooling effectiveness (FE) at high accuracy with a small y+ value. To assess the effect of the changes, each geometry of the hole was changed one after another while the other parameters were kept invariable at the test value (cylindrical hole). The numerical laterally averaged film cooling effectiveness (ηl) of the CH case was validated and compared to the experimental data. The simulation results with the two-head flared hole indicated that most of these shape changes increase the FE as compared to the CH case. In particular, the maximum spatially averaged film cooling effectiveness (ηs) with hole shape expanded along the flow direction at the outlet port reached 60.787% in comparison to the CH case. Full article
(This article belongs to the Special Issue Advances in Aerothermal Engineering)
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Article
InnoCube—A Wireless Satellite Platform to Demonstrate Innovative Technologies
Aerospace 2021, 8(5), 127; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050127 - 04 May 2021
Viewed by 611
Abstract
A new innovative satellite mission, the Innovative CubeSat for Education (InnoCube), is addressed. The goal of the mission is to demonstrate “the wireless satellite”, which replaces the data harness by robust, high-speed, real-time, very short-range radio communications using the SKITH (SKIpTheHarness) technology. This [...] Read more.
A new innovative satellite mission, the Innovative CubeSat for Education (InnoCube), is addressed. The goal of the mission is to demonstrate “the wireless satellite”, which replaces the data harness by robust, high-speed, real-time, very short-range radio communications using the SKITH (SKIpTheHarness) technology. This will make InnoCube the first wireless satellite in history. Another technology demonstration is an experimental energy-storing satellite structure that was developed in the previous Wall#E project and might replace conventional battery technology in the future. As a further payload, the hardware for the concept of a software-based solution for receiving signals from Global Navigation Satellite Systems (GNSS) will be developed to enable precise position determination of the CubeSat. Aside from technical goals this work aims to be of use in the teaching of engineering skills and practical sustainable education of students, important technical and scientific publications, and the increase of university skills. This article gives an overview of the overall design of the InnoCube. Full article
(This article belongs to the Special Issue Small Satellite Technologies and Mission Concepts)
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Article
A Hybrid Incremental Nonlinear Dynamic Inversion Control for Improving Flying Qualities of Asymmetric Store Configuration Aircraft
Aerospace 2021, 8(5), 126; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050126 - 02 May 2021
Viewed by 790
Abstract
Highly maneuverability fighter aircrafts are equipped with various weapons for successful air-to-air and air-to-ground missions. The aircraft has abrupt transient response due to ejection force generated when store of one wing is launched and the movement of lateral center-of-gravity (YCG) changing by the [...] Read more.
Highly maneuverability fighter aircrafts are equipped with various weapons for successful air-to-air and air-to-ground missions. The aircraft has abrupt transient response due to ejection force generated when store of one wing is launched and the movement of lateral center-of-gravity (YCG) changing by the mass distribution of both wings after launched. Under maintaining 1 g level flight with manual trim system in the asymmetric store configuration, the aircraft causes unexpected roll motion for the pure longitudinal maneuver because the change of AoA and airspeed changes the amount of trim for level flight of the aircraft. For this reason, the pilot should continuously use the roll control stick input to maintain level flight. This characteristic increases the pilot’s workload and adversely affects the flying qualities of the aircraft, which is a major cause of deteriorating mission efficiency for combat maneuver. In this paper, we propose a hybrid control that combines model- and sensor-based Incremental Nonlinear Dynamic Inversion (INDI) control based mathematical model of the supersonic advanced trainer to minimize the transient response of the aircraft when the store is launched and to effectively reduce the unexpected roll motion that occurs for the pure longitudinal maneuvering in the asymmetric store configuration. As a result of the frequency- and time-domain evaluation, the proposed control method can effectively reduce the transient response for store launch and minimize unexpected roll motion for the pure longitudinal maneuver. Therefore, this control method can effectively improve flying qualities and mission efficiency by reducing the pilot’s workload in the operation of the asymmetric store configuration. Full article
(This article belongs to the Special Issue Aerospace Guidance, Navigation and Control)
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Article
An Explosion Based Algorithm to Solve the Optimization Problem in Quadcopter Control
Aerospace 2021, 8(5), 125; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050125 - 27 Apr 2021
Viewed by 535
Abstract
This paper presents an optimization algorithm named Random Explosion Algorithm (REA). The fundamental idea of this algorithm is based on a simple concept of the explosion of an object. This object is commonly known as a particle: when exploded, it will randomly disperse [...] Read more.
This paper presents an optimization algorithm named Random Explosion Algorithm (REA). The fundamental idea of this algorithm is based on a simple concept of the explosion of an object. This object is commonly known as a particle: when exploded, it will randomly disperse fragments around the particle within the explosion radius. The fragment that will be considered as a search agent will fill the local space and search that particular region for the best fitness solution. The proposed algorithm was tested on 23 benchmark test functions, and the results are validated by a comparative study with eight well-known algorithms, which are Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Genetic Algorithm (GA), Differential Evolution (DE), Multi-Verse Optimizer (MVO), Moth Flame Optimizer (MFO), Firefly Algorithm (FA), and Sooty Tern Optimization Algorithm (STOA). After that, the algorithm was implemented and analyzed for a quadrotor control application. Similarly, a comparative study with the other algorithms stated was done. The findings reveal that the REA can yield very competitive results. It also shows that the convergence analysis has proved that the REA can converge more quickly toward the global optimum than the other metaheuristic algorithms. For the control application result, the REA controller can better track the desired reference input with shorter rise time and settling time, lower percentage overshoot, and minimal steady-state error and root mean square error (RMSE). Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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Article
Tightly Coupled Integrated Navigation Algorithm for Hypersonic Boost-Glide Vehicles in the LCEF Frame
Aerospace 2021, 8(5), 124; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050124 - 23 Apr 2021
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Abstract
According to the trajectory characteristics of hypersonic boost-glide vehicles, a tightly coupled integrated navigation algorithm for hypersonic vehicles based on the launch-centered Earth-fixed (LCEF) frame is proposed. First, the strapdown inertial navigation mechanization algorithm and discrete update algorithm in the LCEF frame are [...] Read more.
According to the trajectory characteristics of hypersonic boost-glide vehicles, a tightly coupled integrated navigation algorithm for hypersonic vehicles based on the launch-centered Earth-fixed (LCEF) frame is proposed. First, the strapdown inertial navigation mechanization algorithm and discrete update algorithm in the LCEF frame are introduced. Subsequently, the attitude, velocity, and position error equations of strapdown inertial navigation in the LCEF frame are introduced. The strapdown inertial navigation system/global positioning system (SINS/GPS) pseudo-range and pseudo-range rate measurement equations in the LCEF frame are derived. Further, the tightly coupled SINS/GPS integrated navigation filter state equation and the measurement equation are presented. Finally, the tightly coupled SINS/GPS integrated navigation algorithm is verified in the hardware-in-the-loop (HWIL) simulation environment. The simulation results indicate that the precision of tightly coupled integrated navigation is better than that of loosely coupled integrated navigation. Moreover, even when the number of effective satellites is less than four, tightly coupled integrated navigation functions well, thus verifying the effectiveness and feasibility of the algorithm. Full article
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Article
Global Skewness and Coherence for Hypersonic Shock-Wave/Boundary-Layer Interactions with Pressure-Sensitive Paint
Aerospace 2021, 8(5), 123; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050123 - 22 Apr 2021
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Abstract
The global surface pressure was measured on a 7° half-angle circular cone/flare model at a nominally zero angle of attack using pressure-sensitive paint (PSP). These experiments were conducted to illustrate fast PSP’s usefulness and effectiveness at measuring the unsteady structures inherent to hypersonic shock-wave/boundary-layer interactions (SWBLIs). Mean and fluctuating surface pressure was measured with a temperature-corrected, high-frequency-response (≈10 kHz) anodized-aluminum pressure-sensitive paint (AA-PSP) allowing for novel, global calculations of skewness and coherence. These analyses complement traditional SWBLI data-reduction methodologies by providing high-spatial-resolution measurements of the mean and fluctuating locations of the shock feet, as well as the frequency-dependent measure of the relationship between characteristic flow features. The skewness indicated the mean locations of the separation and reattachment shock feet as well as their fluctuations over the course of the test. The coherence indicated that the separation and reattachment shock feet fluctuate about their mean location at the same frequency as one another, but 180 degrees out of phase. This results in a large-scale ‘breathing motion’ of the separated region characteristic of large separation bubbles. These experimental findings validate the usefulness of AA-PSP, and associated data-reduction methodologies, to provide global physical insights of unsteady SWBLI surface behavior in the hypersonic flow regime. Similar methodologies can be incorporated in future experiments to investigate complex and novel SWBLIs. Full article
(This article belongs to the Special Issue Hypersonics: Emerging Research)
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Article
Sources of Onboard Fumes and Smoke Reported by U.S. Airlines
Aerospace 2021, 8(5), 122; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050122 - 22 Apr 2021
Viewed by 863
Abstract
This paper describes the relative frequency of reports of oil and hydraulic fluid fumes in the ventilation supply air (“fume events”) compared to other types of fumes and smoke reported by U.S. airlines over 10 years. The author reviewed and categorized 12,417 fume/smoke [...] Read more.
This paper describes the relative frequency of reports of oil and hydraulic fluid fumes in the ventilation supply air (“fume events”) compared to other types of fumes and smoke reported by U.S. airlines over 10 years. The author reviewed and categorized 12,417 fume/smoke reports submitted to the aviation regulator to comply with the primary maintenance reporting regulation (14 CFR § 121.703) from 2002–2011. The most commonly documented category of onboard fumes/smoke was electrical (37%). Combining the categories of “bleed-sourced”, “oil”, and “hydraulic fluid” created the second most prevalent category (26%). The remaining sources of onboard fumes/smoke are also reported. To put the data in context, the fume event reporting regulations are described, along with examples of ways in which certain events are underreported. These data were reported by U.S. airlines, but aviation regulations are harmonized globally, so the data likely also reflect onboard sources of fumes and smoke reported in other countries with equivalent aviation systems. The data provide insight into the relative frequency of the types of reported fumes and smoke on aircraft, which should drive design, operational, and maintenance actions to mitigate onboard exposure. The data also provide insight into how to improve current fume event reporting rules. Full article
(This article belongs to the Special Issue Aircraft Design (SI-3/2021))
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Article
Accuracy of Noise-Power-Distance Definition on Results of Single Aircraft Noise Event Calculation
Aerospace 2021, 8(5), 121; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050121 - 21 Apr 2021
Viewed by 531
Abstract
Aircraft performance and noise database together with operational weights (depending on flight distances) and operational procedures (including low noise procedures) significantly influence results of noise exposure contour maps assessment in conditions of real atmosphere. Current recommendations of the Standard SAE-AIR1845A allow the definition [...] Read more.
Aircraft performance and noise database together with operational weights (depending on flight distances) and operational procedures (including low noise procedures) significantly influence results of noise exposure contour maps assessment in conditions of real atmosphere. Current recommendations of the Standard SAE-AIR1845A allow the definition of flight profiles via solutions of balanced motion equations. However, differences are still supervised between the measured sound level data and calculated ones, especially in assessing the single flight noise events. Some of them are well explained by differences between balanced flight parameters (thrust and velocity first of all) and monitored ones by the traffic control system. Statistical data were gathered to make more general view on these differences and some proposal to use them in calculations has been proven. Besides, the real meteorological parameters provide inhomogeneous atmosphere conditions always, which are quite different from the main assumptions of the SAE-AIR1845A, stipulating inaccuracies of sound level calculations. Full article
(This article belongs to the Collection Aviation Sustainability)
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Article
β-Band Analysis from Simulated Flight Experiments
Aerospace 2021, 8(5), 120; https://0-doi-org.brum.beds.ac.uk/10.3390/aerospace8050120 - 21 Apr 2021
Viewed by 478
Abstract
Several safety-related improvements are applied every year to try to minimize the total number of civil aviation accidents. Fortunately, these improvements work well, reducing the number of accident occurrences. However, while the number of accidents due to mechanical failures has decreased, the number [...] Read more.
Several safety-related improvements are applied every year to try to minimize the total number of civil aviation accidents. Fortunately, these improvements work well, reducing the number of accident occurrences. However, while the number of accidents due to mechanical failures has decreased, the number of accidents due to human errors seems to grow. On that basis, this work presents a contribution regarding the brain’s β-band activities for different levels of volunteers’ expertise on flight simulator, i.e., experienced, mid-level and beginner, in which they acted as pilots in command during several simulated flights. Spectrogram analysis and statistical measurements of each volunteer’s brain’s β-band were carried out. These were based on seven flight tasks: takeoff, climb, cruise flight, descent, approach, final approach and landing. The results of the proposed experiment showed that the takeoff, approach and landing corresponded to the highest brain activities, i.e., close to 37.06–67.33% more than the brain activity of the other flight tasks: when some accidents were about to occur, the intensities of the brain activity were similar to those of the final approach task. When the volunteers’ expertise and confidence on flight simulation were considered, it was shown that the highest brain magnitudes and oscillations observed of more experienced and confident volunteers were on average close to 68.44% less, compared to less experienced and less confident volunteers. Moreover, more experienced and confident volunteers in general presented different patterns of brain activities compared to volunteers with less expertise or less familiarity with fight simulations and/or electronic games. Full article
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