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Aerospace, Volume 5, Issue 3 (September 2018)

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Open AccessArticle Aerodynamic Design of a Laval Nozzle for Real Gas Using Hodograph Method
Received: 31 July 2018 / Revised: 31 August 2018 / Accepted: 3 September 2018 / Published: 10 September 2018
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Abstract
We propose an approach for the design of the subsonic part of plane and axisymmetric Laval nozzles for real gases. The proposed approach is based on the hodograph method and allows one to solve the inverse design problem directly. Real gas effects are
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We propose an approach for the design of the subsonic part of plane and axisymmetric Laval nozzles for real gases. The proposed approach is based on the hodograph method and allows one to solve the inverse design problem directly. Real gas effects are taken into consideration using the chemical equilibrium model. We present nozzle contours computed with the proposed method for a stoichiometric methane-air mixture. Results confirm that real gas effects have a strong influence on the nozzle shape. The described method can be used in the design of nozzles for rocket engines and for high-enthalpy wind tunnels. Full article
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Open AccessArticle Natural Frequencies of Rectangular Laminated Plates—Introduction to Optimal Design in Aeroelastic Problems
Received: 7 August 2018 / Revised: 28 August 2018 / Accepted: 2 September 2018 / Published: 10 September 2018
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Abstract
Free vibration (or eigenvalue analysis) is a prerequisite for aeroelastic analysis. For divergence analysis, slope influence coefficients (rotation at point i due to unit load at point j) are calculated using free vibration mode shapes and corresponding frequencies. The lowest eigenvalue is
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Free vibration (or eigenvalue analysis) is a prerequisite for aeroelastic analysis. For divergence analysis, slope influence coefficients (rotation at point i due to unit load at point j) are calculated using free vibration mode shapes and corresponding frequencies. The lowest eigenvalue is of interest and gives the divergence speed. The present paper considers the maximization problem of eigenfrequencies for composite panels. The influence of boundary conditions and constant or variable stiffnesses on optimization results are investigated herein. A new convenient set of design variables is employed in the analysis. The computations are carried out with the use of the Rayleigh–Ritz method and Finite Element analysis (2D quadrilateral and 3D solid elements). Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle Fast and Robust Flight Altitude Estimation of Multirotor UAVs in Dynamic Unstructured Environments Using 3D Point Cloud Sensors
Received: 10 August 2018 / Revised: 30 August 2018 / Accepted: 4 September 2018 / Published: 6 September 2018
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Abstract
This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the
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This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the conventional sensors such as laser altimeters, barometers, or accelerometers, which have several limitations when used individually. Our proposed algorithm includes two stages: in the first stage, a fast clustering of the measured 3D point cloud data is performed, along with the segmentation of the clustered data into horizontal planes. In the second stage, these segmented horizontal planes are mapped based on the vertical distance with respect to the point cloud sensor frame of reference, in order to provide a robust flight altitude estimation even in presence of several static as well as dynamic ground obstacles. We validate our approach using the IROS 2011 Kinect dataset available in the literature, estimating the altitude of the RGB-D camera using the provided 3D point clouds. We further validate our approach using a point cloud sensor on board a UAV, by means of several autonomous real flights, closing its altitude control loop using the flight altitude estimated by our proposed method, in presence of several different static as well as dynamic ground obstacles. In addition, the implementation of our approach has been integrated in our open-source software framework for aerial robotics called Aerostack. Full article
(This article belongs to the collection Unmanned Aerial Systems)
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Open AccessFeature PaperArticle Effect of Ramie Fabric Chemical Treatments on the Physical Properties of Thermoset Polylactic Acid (PLA) Composites
Received: 13 July 2018 / Revised: 28 August 2018 / Accepted: 30 August 2018 / Published: 2 September 2018
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Abstract
Ramie fabric-reinforced thermoset polylactic acid (PLA) composites were prepared by using heat pressing technology. Fabrics were treated with alkali, silane, and alkali–silane respectively, expecting an improvement of the interface between the fabric and the matrix. Scanning electron microscopy (SEM) results indicated that after
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Ramie fabric-reinforced thermoset polylactic acid (PLA) composites were prepared by using heat pressing technology. Fabrics were treated with alkali, silane, and alkali–silane respectively, expecting an improvement of the interface between the fabric and the matrix. Scanning electron microscopy (SEM) results indicated that after alkali treatment, impurities on the fiber surface were removed and its diameter became finer. After the silane, and alkali–silane treatments, the contact angles of the ramie fibers increased by 14.26%, and 33.12%, respectively. The contact angle of the alkali–silane treated fiber reached 76.41°; this is beneficial for the adhesion between ramie fiber and the PLA. The research revealed that the tensile strength of the fiber increased after the alkali and silane treatments. A slight decrease was noticed on the tensile strength of fibers treated with alkali–silane. After all, three chemical treatments were done, the flexure strength of the ramie fabric-reinforced PLA composites, improved in all cases. Among the three treatments, the alkali–silane treatment demonstrated the best result, as far as the flexure strength and modulus of the fabricated composites were concerned. On the other hand, water absorption of the related composites decreased by 23.70%, which might contribute to the closer contact between the ramie fiber and the matrix. The ramie fabric-reinforced PLA composites, prepared in this study, can meet the standard requirements of aircraft interior structures and have favorable application foreground. Full article
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Open AccessArticle Unsteady Lifting Line Theory Using the Wagner Function for the Aerodynamic and Aeroelastic Modeling of 3D Wings
Received: 18 July 2018 / Revised: 23 August 2018 / Accepted: 24 August 2018 / Published: 1 September 2018
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Abstract
A method is presented to model the incompressible, attached, unsteady lift and pitching moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner theory and lifting line theory through the unsteady Kutta–Joukowski theorem.
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A method is presented to model the incompressible, attached, unsteady lift and pitching moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner theory and lifting line theory through the unsteady Kutta–Joukowski theorem. The results are a set of closed-form linear ordinary differential equations that can be solved analytically or using a Runge–Kutta–Fehlberg algorithm. The method is validated against numerical predictions from an unsteady vortex lattice method for rectangular and tapered wings undergoing step or oscillatory changes in plunge or pitch. Further validation is demonstrated on an aeroelastic test case of a rigid rectangular finite wing with pitch and plunge degrees of freedom. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle Conceptual Advanced Transport Aircraft Design Configuration for Sustained Hypersonic Flight
Received: 30 June 2018 / Revised: 22 August 2018 / Accepted: 24 August 2018 / Published: 1 September 2018
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Abstract
The conceptual aircraft design and its integration with a combined cycle engine for hypersonic cruise at Mach 8 is documented in this paper. The paper describes the process taken to develop a hypersonic aircraft from a conceptual approach. The discussion also includes the
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The conceptual aircraft design and its integration with a combined cycle engine for hypersonic cruise at Mach 8 is documented in this paper. The paper describes the process taken to develop a hypersonic aircraft from a conceptual approach. The discussion also includes the design and CFD analysis of the integrated combined cycle engine. A final conceptual hypersonic transport aircraft with an integrated combined cycle engine was achieved through this study. According to the analysis carried out, the aircraft is able to take-off and land at the airports it is intended to be used and will be able to generate enough thrust to sustain hypersonic cruise at an altitude of 30 km. Full article
(This article belongs to the Special Issue Aeroengine)
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Open AccessReview Turbine Blade Tip External Cooling Technologies
Received: 13 July 2018 / Revised: 12 August 2018 / Accepted: 13 August 2018 / Published: 26 August 2018
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Abstract
This article provides an overview of gas turbine blade tip external cooling technologies. It is not the intention to comprehensively review all the publications from past to present. Instead, selected reports, which represent the most recent progress in tip cooling technology in open
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This article provides an overview of gas turbine blade tip external cooling technologies. It is not the intention to comprehensively review all the publications from past to present. Instead, selected reports, which represent the most recent progress in tip cooling technology in open publications, are reviewed. The cooling performance on flat tip and squealer tip blades from reports are compared and discussed. As a generation conclusion, tip clearance dimension and coolant flow rate are found as the most important factors that significant influence the blade tip thermal performance was well as the over tip leakage (OTL) flow aerodynamics. However, some controversial trends are reported by different researchers, which could be attributed to various reasons. One of the causes of this disagreement between different reports is the lacking of unified parametric definition. Therefore, a more appropriate formula of blowing ratio definition has been proposed for comparison across different studies. The last part of the article is an outlook of the new techniques that are promising for future tip cooling research. As a new trend, the implementation of artificial intelligence techniques, such as genetic algorithm and neural network, have become more popular in tip cooling optimization, and they will bring significantly changes to the future turbine tip cooling development. Full article
(This article belongs to the Special Issue Cooling/Heat Transfer)
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Open AccessArticle On the Wake Properties of Segmented Trailing Edge Extensions
Received: 14 July 2018 / Revised: 3 August 2018 / Accepted: 15 August 2018 / Published: 21 August 2018
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Abstract
Changes in the amount and the distribution of mean and turbulent quantities in the free shear layer wake of a 2D National Advisory Committee for Aeronautics (NACA) 0012 airfoil and an AR 4 NACA 0012 wing with passive segmented rigid trailing edge (TE)
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Changes in the amount and the distribution of mean and turbulent quantities in the free shear layer wake of a 2D National Advisory Committee for Aeronautics (NACA) 0012 airfoil and an AR 4 NACA 0012 wing with passive segmented rigid trailing edge (TE) extensions were investigated at the University of Dayton Low Speed Wind Tunnel (UD-LSWT). The TE extensions were intentionally placed at zero degrees with respect to the chord line to study the effects of segmented extensions without changing the effective angle of attack. Force based experiments were used to determine the total lift coefficient variation of the wing with seven segmented trailing edge extensions distributed across the span. The segmented trailing edge extensions had a negligible effect on the lift coefficient, but showed a measurable decrement in the sectional and total drag coefficient. Investigation of turbulent quantities (obtained through Particle Image Velocimetry (PIV)) such as Reynolds stress, streamwise and transverse root-mean square (RMS) in the wake, reveal a significant decrease in magnitude when compared to the baseline. The decrease in the magnitude of turbulent parameters was supported by the changes in coherent structures obtained through two-point correlations. Apart from the reduction in drag, the lower turbulent wake generated by the extensions has implications in reducing structural vibrations and acoustic tones. Full article
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Open AccessArticle On Four New Methods of Analytical Calculation of Rocket Trajectories
Received: 15 June 2018 / Revised: 20 July 2018 / Accepted: 27 July 2018 / Published: 15 August 2018
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Abstract
The calculation of rocket trajectories is most often performed using purely numerical methods that account for all relevant parameters and provide the required results. There is a complementary need for analytical methods that make more explicit the effect of the various rocket and
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The calculation of rocket trajectories is most often performed using purely numerical methods that account for all relevant parameters and provide the required results. There is a complementary need for analytical methods that make more explicit the effect of the various rocket and atmospheric parameters of the trajectory and can be used as test cases with unlimited accuracy. The available analytical methods take into account (i) variable rocket mass due to propellant consumption. The present paper includes four new analytical methods taking into account besides (i) also (ii) nonlinear aerodynamic forces proportional to the square of the velocity and (iii) exponential dependence of the mass density with altitude for an isothermal atmospheric layer. The four new methods can be used in “hybrid analytical-numerical” approach in which: (i) the atmosphere is divided into isothermal rather than homogeneous layers for greater physical fidelity; and (ii) in each layer, an exact analytical solution of the equations of motion with greater mathematical accuracy than a numerical approximation is used. This should allow a more accurate calculation of rocket trajectories while discretizing the atmosphere into a smaller number of layers. The paper therefore concentrates on four analytical methods of calculation of rocket trajectories in an isothermal atmospheric layers using new exact solutions of the equations of motion beyond those currently available in the literature. The four methods are developed first for the simpler case of a vertical climb and will be subsequently extended to the practically more relevant case of a gravity turn. Full article
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Open AccessReview Cost-Effectiveness of Structural Health Monitoring in Fuselage Maintenance of the Civil Aviation Industry
Received: 6 June 2018 / Revised: 21 July 2018 / Accepted: 7 August 2018 / Published: 13 August 2018
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Abstract
Although structural health monitoring (SHM) technologies using sensors have dramatically been developed recently, their capability should be evaluated from the perspective of the maintenance industry. As a first step toward utilizing sensors, the objective of the paper is to investigate the possibility of
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Although structural health monitoring (SHM) technologies using sensors have dramatically been developed recently, their capability should be evaluated from the perspective of the maintenance industry. As a first step toward utilizing sensors, the objective of the paper is to investigate the possibility of using sensors for inspecting the entire fuselage during C-check. First, we reviewed various sensors for their detection range, detectable damage size, and installed weight, which revealed that the piezoelectric wafer active sensor (PWAS) is the most promising sensor for aircraft SHM. Second, we performed a case study of inspecting the fuselage of Boeing-737NG using PWAS. To maintain the same detecting capability of manual inspection in C-check, we estimated the total number of sensors required. It turned out that utilizing sensors can reduce the maintenance downtime and thus, maintenance cost. However, even with a very conservative estimate, the lifetime cost was significantly increased due to the weight of sensor systems. The cost due to the weight increase was an order of magnitude higher than the cost saved by using SHM. We found that a large number of sensors were required to detect damage at unknown locations, which was the main cause of the weight increase. We concluded that to make SHM cost-effective, it would be necessary either to improve the current sensor technologies so that a less number of sensors are used or to modify the aircraft design concept for SHM. Full article
(This article belongs to the Special Issue Civil and Military Airworthiness: Recent Developments and Challenges)
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Open AccessArticle Adaptive Feedforward Control for Gust-Induced Aeroelastic Vibrations
Received: 7 July 2018 / Revised: 30 July 2018 / Accepted: 3 August 2018 / Published: 10 August 2018
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Abstract
This paper demonstrates the implementation of an adaptive feedforward controller to reduce structural vibrations on a wing typical section. The aeroelastic model includes a structural nonlinearity, which is modelled in a polynomial form. Aeroelastic vibrations are induced by several gusts and atmospheric turbulence,
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This paper demonstrates the implementation of an adaptive feedforward controller to reduce structural vibrations on a wing typical section. The aeroelastic model includes a structural nonlinearity, which is modelled in a polynomial form. Aeroelastic vibrations are induced by several gusts and atmospheric turbulence, including the discrete “one-minus-cosine” and a notably good approximation in the time-domain to the von Kármán spectrum. The control strategy based on the adaptive feedforward controller has several advantages compared to the standard feedback controller. The controller gains, which are updated in real-time during the gust encounter, are found solving a minimization problem using the finite impulse responses as basis functions. To make progress with the application in aeroelasticity, a single-input single-output controller is designed measuring the wing torsional deformation. For both deterministic and random atmospheric shapes, the controller was found successful in alleviating the aeroelastic vibrations. The impact of the control action on the unmeasured structural modes was found minimal. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle A Cooperative Co-Evolutionary Optimisation Model for Best-Fit Aircraft Sequence and Feasible Runway Configuration in a Multi-Runway Airport
Received: 16 July 2018 / Revised: 4 August 2018 / Accepted: 5 August 2018 / Published: 9 August 2018
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Abstract
A careful arrival and departure sequencing of aircraft can reduce the inter-arrival/departure time, thereby opening up opportunities for new landing and/or take-off slots, which may increase the runway throughput. This sequence when serviced with a suitable runway configuration may result in an optimal
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A careful arrival and departure sequencing of aircraft can reduce the inter-arrival/departure time, thereby opening up opportunities for new landing and/or take-off slots, which may increase the runway throughput. This sequence when serviced with a suitable runway configuration may result in an optimal aircraft sequence with a runway configuration that can process the maximum number of aircraft within a given time interval. In this paper, we propose a Cooperative Co-evolutionary Genetic Algorithm (CCoGA) to find the combined solution of a best-fit sequence with a feasible runway configuration for a given traffic demand at an airport. The aircraft sequence and the runway configuration are modelled as individual species, which can cooperatively interact with each other. Therefore, we computationally evolve the best possible combination of aircraft sequence (arrival and departure) and the feasible runway configuration. The proposed CCoGA algorithm is evaluated for Chicago O’Hare International Airport runway layout and resulting configurations. Arrival and departure traffic demand is modelled through a Poisson distribution. Two different arrival/departure sequencing methods, i.e., constraint position shifting with one, two and N-position shifting and first come first serve, are modelled. Runway configuration and traffic sequence (arrivals and departure) are modelled as two species, which are evolved co-operatively, through the CCoGA algorithm, to achieve the optimal traffic sequencing with a feasible runway configuration. Time-space diagrams are presented for the best-evolved population of arrival-departure sequence and runway configuration to illustrate the possibility of using available departure slots between arrivals to maximize capacity. Arrival-departure capacity envelopes are then presented to illustrate the trade-off between the arrivals and departures, given a runway configuration for each sequencing method. Results demonstrate the high mutual dependence between arrival-departure sequence and the runway configuration, as well as its effect on overall runway capacity. The results also demonstrate the viability of using evolutionary computation-based methods for modelling and evaluating complex problems in the air transport domain. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Simulation and Experimental Evaluation of a Flexible Time Triggered Ethernet Architecture Applied in Satellite Nano/Micro Launchers
Received: 13 July 2018 / Revised: 4 August 2018 / Accepted: 7 August 2018 / Published: 9 August 2018
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Abstract
The success of small satellites has lead to the study of new technologies for the realization of Nano and Micro Launch Vehicle (NMLV) in order to make competitive launch costs. The paper has the objective to define and experimentally investigate the performance of
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The success of small satellites has lead to the study of new technologies for the realization of Nano and Micro Launch Vehicle (NMLV) in order to make competitive launch costs. The paper has the objective to define and experimentally investigate the performance of a communication system for NMLV interconnecting the End Systems as On-Board Computer (OBC), telemetry apparatus, Navigation Unit...we propose a low cost Ethernet-based solution able to provide the devices with high interconnection bandwidth. To guarantee hard delays to the Guide, Navigation and Control applications we propose some architectural changes of the traditional Ethernet network with the introduction of a layer implemented in the End Systems and allow for the lack of any contention on the network links. We show how the proposed solution has comparable performance to the one of TTEthernet standard that is a very expensive solution. An experimental test-bed equipped with Ethernet switches and Hercules boards by Texas Instruments is also provided to prove the feasibility of the proposed solution. Full article
(This article belongs to the Special Issue Verification Approaches for Nano- and Micro-Satellites)
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Open AccessArticle Experimental Study of the Aerodynamic Interaction between the Forewing and Hindwing of a Beetle-Type Ornithopter
Received: 28 June 2018 / Revised: 30 July 2018 / Accepted: 6 August 2018 / Published: 8 August 2018
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Abstract
Beetles have attracted attention from researchers due to their unique combination of a passively flapping forewing and an actively flapping hindwing during flight. Because the wing loads of beetles are larger than the wing loads of other insects, the mechanism of beetle flight
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Beetles have attracted attention from researchers due to their unique combination of a passively flapping forewing and an actively flapping hindwing during flight. Because the wing loads of beetles are larger than the wing loads of other insects, the mechanism of beetle flight is potentially useful for modeling a small aircraft with a large weight. In this paper, we present a beetle-type ornithopter in which the wings are geometrically and kinematically modeled after an actual beetle. Furthermore, the forewing is designed to be changeable between no-wing, flapping-wing, or fixed-wing configurations. Micro-electro-mechanical systems (MEMS) differential pressure sensors were attached to both the forewing and the hindwing to evaluate the aerodynamic performance during flight. Whether the forewing is configured as a flapping wing or a fixed wing, it generated constant positive differential pressure during forward flight, whereas the differential pressure on the hindwing varied with the flapping motion during forward flight. The experimental results suggest that beetles utilize the forewing for effective vertical force enhancement. Full article
(This article belongs to the Special Issue Bio-Inspired Aerospace System)
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Open AccessArticle Continued Experimental Study on the Friction Contact between a Labyrinth Seal Fin and a Honeycomb Stator: Slanted Position
Received: 2 June 2018 / Revised: 21 July 2018 / Accepted: 2 August 2018 / Published: 7 August 2018
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Abstract
Labyrinth seals are a state-of-the-art sealing technology to prevent and control leakage flows at rotor–stator interfaces in turbomachinery. Higher pressure ratios and the economical use of cooling air require small clearances, which lead to potential rubbing events. The use of honeycomb liners allows
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Labyrinth seals are a state-of-the-art sealing technology to prevent and control leakage flows at rotor–stator interfaces in turbomachinery. Higher pressure ratios and the economical use of cooling air require small clearances, which lead to potential rubbing events. The use of honeycomb liners allows for minimal leakage by tolerating rub events to a certain extent. A previous study within an EU project investigated the complex contact conditions of honeycomb liners, with the idealized contact of a seal fin and a single parallel metal foil representing the honeycomb double foil section. In the present work, the results for the slanted foil position are shown and compared to the previous results. The variation of rub velocity, incursion speed, incursion rate, and seal geometry in a test rig allows for the identification of the influence on contact forces, temperatures, and wear. For the slanted position, significantly lower friction temperatures are observed, leading to a higher ratio of abrasive wear. Overall, the rub test results demonstrate strong interactions between the contact forces, friction temperatures, and wear. Full article
(This article belongs to the Special Issue Secondary Air Systems in Gas Turbine Engines)
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Open AccessArticle Life Cycle Assessment of Ramie Fiber Used for FRPs
Received: 15 June 2018 / Revised: 28 July 2018 / Accepted: 31 July 2018 / Published: 3 August 2018
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Abstract
With the depletion of natural resources and the deterioration of environment, natural fiber based biomaterials are attracting more and more attentions. Natural fibers are considered to be renewable, biodegradable, and ecofriendly, and have been applied to be used as alternative reinforcements to traditional
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With the depletion of natural resources and the deterioration of environment, natural fiber based biomaterials are attracting more and more attentions. Natural fibers are considered to be renewable, biodegradable, and ecofriendly, and have been applied to be used as alternative reinforcements to traditional glass fibers for polymer based composites (GFRP). Natural fiber reinforced polymer (NFRP) composites have been found to be manufactured as secondary structures or interior parts of aircrafts or automobiles. In this paper, a cradle-to-gate life cycle assessment (LCA) study was performed to demonstrate the possible advantages of ramie fiber on environmental impacts and to provide fundamental data for the further assessment of ramie fiber reinforced polymers (RFRP) and its structures. By collecting the material inventories of the production process of ramie fiber, the environmental impacts of ramie fiber (characterized by eight main impact categories, which are climate change, terrestrial acidification, freshwater eutrophication, human toxicity potential, ozone depletion, photochemical oxidant creation, freshwater ecotoxicity, and fossil depletion) were calculated and compared with that of glass fiber. Found if spinning process is ignored within the production of the ramie fiber, ramie fiber exhibits better ozone depletion and they have almost the same values of climate change and terrestrial acidification in terms of glass fiber. However, if the spinning process is included, ramie fiber only performs better in terms of ozone depletion. And degumming and carding and spinning processes are the processes that cause more pollution. Full article
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Open AccessArticle Robust Optimization of Airplane Passenger Seating Assignments
Received: 26 June 2018 / Revised: 17 July 2018 / Accepted: 23 July 2018 / Published: 1 August 2018
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We present a method that reduces the time it takes to complete the passenger boarding of an airplane. In particular, we describe a two-stage mixed integer programming (MIP) approach, which assigns passengers to seats on an airplane based on the number of bags
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We present a method that reduces the time it takes to complete the passenger boarding of an airplane. In particular, we describe a two-stage mixed integer programming (MIP) approach, which assigns passengers to seats on an airplane based on the number of bags they carry aboard the plane. The first stage is an MIP that assigns passengers to seats to minimize the time to complete the boarding of the plane. The second-stage MIP also determines seating assignments, while constraining the total boarding time to that determined by the stage-one MIP and maximizing weighted slack times to provide a more robust assignment. Numerical results show that this two-stage approach results in lower average boarding times than the one-stage approach, when the time it takes passengers to walk and sit in their seats is random. Experiments indicate that the magnitude of the improvement is not very sensitive to variations in the slack time weights. Full article
(This article belongs to the collection Air Transportation—Operations and Management)
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Open AccessArticle Computational Study of Propeller–Wing Aerodynamic Interaction
Received: 12 April 2018 / Revised: 9 July 2018 / Accepted: 18 July 2018 / Published: 25 July 2018
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Abstract
Kestrel simulation tools are used to investigate the mutual interference between the propeller and wing of C130J aircraft. Only the wing, nacelles, and propeller geometries are considered. The propulsion system modelled is a Dowty six-bladed R391 propeller mounted at inboard or outboard wing
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Kestrel simulation tools are used to investigate the mutual interference between the propeller and wing of C130J aircraft. Only the wing, nacelles, and propeller geometries are considered. The propulsion system modelled is a Dowty six-bladed R391 propeller mounted at inboard or outboard wing sections in single and dual propeller configurations. The results show that installed propeller configurations have asymmetric blade loadings such that downward-moving blades produce more thrust force than those moving upward. In addition, the influence of installed propeller flow-fields on the wing aerodynamic (pressure coefficient and local lift distribution) are investigated. The installed propeller configuration data are compared with the non-installed case, and the results show that propeller effects will improve the wing’s lift distribution. The increase in lift behind the propeller is different at the left and right sides of the propeller. In addition, the propeller helps to delay the wing flow separation behind it for tested conditions of this work. Finally, the results show the capability of Kestrel simulation tools for modeling and design of propellers and investigates their effects over aircraft during conceptual design in which no experimental or flight test data are available yet. This will lead to reducing the number of tests required later. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Numerical Continuation of Limit Cycle Oscillations and Bifurcations in High-Aspect-Ratio Wings
Received: 5 July 2018 / Revised: 18 July 2018 / Accepted: 20 July 2018 / Published: 24 July 2018
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Abstract
This paper applies numerical continuation techniques to a nonlinear aeroelastic model of a highly flexible, high-aspect-ratio wing. Using continuation, it is shown that subcritical limit cycle oscillations, which are highly undesirable phenomena previously observed in numerical and experimental studies, can exist due to
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This paper applies numerical continuation techniques to a nonlinear aeroelastic model of a highly flexible, high-aspect-ratio wing. Using continuation, it is shown that subcritical limit cycle oscillations, which are highly undesirable phenomena previously observed in numerical and experimental studies, can exist due to geometric nonlinearity alone, without need for nonlinear or even unsteady aerodynamics. A fully nonlinear, reduced-order beam model is combined with strip theory and one-parameter continuation is used to directly obtain equilibria and periodic solutions for varying airspeeds. The two-parameter continuation of specific bifurcations (i.e., Hopf points and periodic folds) reveals the sensitivity of these complex dynamics to variations in out-of-plane, in-plane and torsional stiffness and a ‘wash out’ stiffness coupling parameter. Overall, this paper demonstrates the applicability of continuation to nonlinear aeroelastic analysis and shows that complex dynamical phenomena, which cannot be obtained by linear methods or numerical integration, readily exist in this type of system due to geometric nonlinearity. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle Effect of Paper or Silver Nanowires-Loaded Paper Interleaves on the Electrical Conductivity and Interlaminar Fracture Toughness of Composites
Received: 19 June 2018 / Revised: 17 July 2018 / Accepted: 17 July 2018 / Published: 19 July 2018
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Abstract
The effect of plant-fiber paper or silver nanowires-loaded paper interleaves on the electrical conductivity and interlaminar fracture toughness of composites was studied. Highly conductive paper was prepared by surface-loaded silver nanowires. The percolation threshold appeared at about 0.4 g/m2. The surface
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The effect of plant-fiber paper or silver nanowires-loaded paper interleaves on the electrical conductivity and interlaminar fracture toughness of composites was studied. Highly conductive paper was prepared by surface-loaded silver nanowires. The percolation threshold appeared at about 0.4 g/m2. The surface resistivity reached 2.3 Ω/sq when the areal density of silver nanowires was 0.95 g/m2. After interleaving the conductive papers in the composite interlayers, in-plane electrical conductivity perpendicular to the fiber direction was increased by 171 times and conductivity through thickness direction was increased by 2.81 times. However, Mode I and Mode II interlaminar fracture toughness decreased by 67.3% and 66.9%, respectively. Microscopic analysis showed that the improvement of conductivity was attributable to the formation of an electrical conducting network of silver nanowires which played a role in electrical connection of carbon fiber plies and the interleaving layers. However, the density of the highly packed flat plant fibers impeded the infiltration of resin. The parallel distribution of flat fibers to the carbon plies, and poor resin-fiber interface made the interlaminar fracture occur mainly at the interface of plant fibers and resin inside the interleaves, resulting in a decline of the interlaminar fracture toughness. The surface-loading of silver nanowires further impeded the infiltration of resin in the densely packed plant fibers, resulting in further decline of the fracture toughness. Full article
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Open AccessArticle A Hybrid Reduced-Order Model for the Aeroelastic Analysis of Flexible Subsonic Wings—A Parametric Assessment
Received: 30 April 2018 / Revised: 25 June 2018 / Accepted: 9 July 2018 / Published: 17 July 2018
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Abstract
A hybrid reduced-order model for the aeroelastic analysis of flexible subsonic wings with arbitrary planform is presented within a generalised quasi-analytical formulation, where a slender beam is considered as the linear structural dynamics model. A modified strip theory is proposed for modelling the
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A hybrid reduced-order model for the aeroelastic analysis of flexible subsonic wings with arbitrary planform is presented within a generalised quasi-analytical formulation, where a slender beam is considered as the linear structural dynamics model. A modified strip theory is proposed for modelling the unsteady aerodynamics of the wing in incompressible flow, where thin aerofoil theory is corrected by a higher-fidelity model in order to account for three-dimensional effects on both distribution and deficiency of the sectional air load. Given a unit angle of attack, approximate expressions for the lift decay and build-up are then adopted within a linear framework, where the two effects are separately calculated and later combined. Finally, a modal approach is employed to write the generalised equations of motion in state-space form. Numerical results were obtained and critically discussed for the aeroelastic stability analysis of a uniform rectangular wing, with respect to the relevant aerodynamic and structural parameters. The proposed hybrid model provides sound theoretical insights and is well suited as an efficient parametric reduced-order aeroelastic tool for the preliminary multidisciplinary design and optimisation of flexible wings in the subsonic regime. Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Sound Absorption Characterization of Natural Materials and Sandwich Structure Composites
Received: 19 June 2018 / Revised: 3 July 2018 / Accepted: 5 July 2018 / Published: 11 July 2018
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Abstract
Natural fiber and wood are environmentally friendly materials with multiscale microstructures. The sound absorption performance of flax fiber and its reinforced composite, as well as balsa wood, were evaluated using the two-microphone transfer function technique with an impedance tube system. The microstructures of
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Natural fiber and wood are environmentally friendly materials with multiscale microstructures. The sound absorption performance of flax fiber and its reinforced composite, as well as balsa wood, were evaluated using the two-microphone transfer function technique with an impedance tube system. The microstructures of natural materials were studied through scanning electrical microscope in order to reveal their complex acoustical dissipation mechanisms. The sound absorption coefficients of flax fiber fabric were predicted using a double-porosity model, which showed relatively accurate results. The integrated natural materials sandwich structure was found to provide a superior sound absorption performance compared to the synthetic-materials-based sandwich structure composite due to the contribution of their multiscale structures to sound wave attenuation and energy dissipation. It was concluded that the natural-materials-based sandwich structure has the potential of being used as a sound absorption structure, especially at high frequency. Full article
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Open AccessReview Flip-Chip (FC) and Fine-Pitch-Ball-Grid-Array (FPBGA) Underfills for Application in Aerospace Electronics—Brief Review
Received: 31 May 2018 / Revised: 27 June 2018 / Accepted: 28 June 2018 / Published: 8 July 2018
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Abstract
In this review, some major aspects of the current underfill technologies for flip-chip (FC) and fine-pitch-ball-grid-array (FPBGA), including chip-size packaging (CSP), are addressed, with an emphasis on applications, such as aerospace electronics, for which high reliability level is imperative. The following aspects of
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In this review, some major aspects of the current underfill technologies for flip-chip (FC) and fine-pitch-ball-grid-array (FPBGA), including chip-size packaging (CSP), are addressed, with an emphasis on applications, such as aerospace electronics, for which high reliability level is imperative. The following aspects of the FC and FPGGA technologies are considered: attributes of the FC and FPBGA structures and technologies; underfill-induced stresses; the roles of the glass transition temperature (Tg) of the underfill materials; some major attributes of the lead-free solder systems with underfill; reliability-related issues; thermal fatigue of the underfilled solder joints; warpage-related issues; attributes of accelerated life testing of solder joint interconnections with underfills; and predictive modeling, both finite-element-analysis (FEA)-based and analytical (“mathematical”). It is concluded particularly that the application of the quantitative assessments of the effect of the fabrication techniques on the reliability of solder materials, when high reliability is imperative, is critical and that all the three types of research tools that an aerospace reliability engineer has at his/her disposal, should be pursued, when appropriate and possible: experimental/testing, finite-element-analysis(FEA) simulations, and the “old-fashioned” analytical (“mathematical”) modeling. These two modeling techniques are based on different assumptions, and if the computed data obtained using these techniques result in the close output information, then there is a good reason to believe that this information is both accurate and trustworthy. This effort is particularly important for high-reliability FC and FPBGA applications, such as aerospace electronics, as the aerospace IC packages become more complex, and the requirements for their failure-free operations become more stringent. Full article
(This article belongs to the Special Issue Challenges in Reliability Analysis of Aerospace Electronics)
Open AccessArticle Analysis of Coherent Structures in an Under-Expanded Supersonic Impinging Jet Using Spectral Proper Orthogonal Decomposition (SPOD)
Received: 5 June 2018 / Revised: 21 June 2018 / Accepted: 26 June 2018 / Published: 6 July 2018
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Abstract
The spatiotemporal dynamics of the coherent structures in an under-expanded supersonic impinging jet are studied using a spectral proper orthogonal decomposition technique. For this analysis, a large eddy simulation of an under-expanded supersonic impinging jet at a pressure ratio of 3.4 and a
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The spatiotemporal dynamics of the coherent structures in an under-expanded supersonic impinging jet are studied using a spectral proper orthogonal decomposition technique. For this analysis, a large eddy simulation of an under-expanded supersonic impinging jet at a pressure ratio of 3.4 and a stand-off distance of 2 jet diameters at a Reynolds number of 50,000 is performed. The mean flow fields illustrate some striking features of this flow, such as an oblique shock, a stand-off shock, a Mach disk, and a recirculation bubble. The spectral proper orthogonal decomposition method is applied to time-resolved three-dimensional flow fields. The accumulative energy of modes within each azimuthal mode number reveals that the first three azimuthal modes contain most of the energy of the flow. The spectra of these azimuthal modes show that the flow exhibits a low-ranked behaviour with discrete frequencies at the optimal symmetric azimuthal mode while other two azimuthal modes have negligible contributions in this behaviour. Three peaks are observed in the spectra of the optimal symmetric azimuthal mode. The spatial fields of the streamwise velocity and pressure of these peaks show that the complex structures are consequences of the under-expansion, Mach disk, and the impingement. Strong hydrodynamic instabilities exist in the shear layer of the jet in the optimal azimuthal mode at each of these dominant frequencies. High-amplitude acoustic waves are also present in the near-field of the jet. These acoustic waves are strong at the nozzle lip, suggesting that a feedback loop linking these two processes exists for dominant frequencies in the optimal mode. High cross-spectrum density of near-field pressure fluctuations and streamwise velocity fluctuations near the nozzle lip at these frequencies confirms the hydro-acoustic coupling, which is necessary to close the feedback loop. Full article
(This article belongs to the Special Issue Under-Expanded Jets)
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Open AccessArticle Why and How to Avoid the Flipped Quaternion Multiplication
Received: 17 May 2018 / Revised: 20 June 2018 / Accepted: 28 June 2018 / Published: 5 July 2018
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Abstract
Over the last decades quaternions have become a crucial and very successful tool for attitude representation in robotics and aerospace. However, there is a major problem that is continuously causing trouble in practice when it comes to exchanging formulas or implementations: there are
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Over the last decades quaternions have become a crucial and very successful tool for attitude representation in robotics and aerospace. However, there is a major problem that is continuously causing trouble in practice when it comes to exchanging formulas or implementations: there are two quaternion multiplications commonly in use, Hamilton’s multiplication and its flipped version, which is often associated with NASA’s Jet Propulsion Laboratory. This paper explains the underlying problem for the popular passive world-to-body usage of rotation quaternions, and promotes an alternative solution compatible with Hamilton’s multiplication. Furthermore, it argues for discontinuing the flipped multiplication. Additionally, it provides recipes for efficiently detecting relevant conventions and migrating formulas or algorithms between them. Full article
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Open AccessArticle Transient Temperature Effects on the Aerothermoelastic Response of a Simple Wing
Received: 23 May 2018 / Revised: 27 June 2018 / Accepted: 29 June 2018 / Published: 2 July 2018
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Abstract
Aerothermoelasticity plays a vital role in the design and optimisation of hypersonic aircraft. Furthermore, the transient and nonlinear effects of the harsh thermal and aerodynamic environment a lifting surface is in cannot be ignored. This article investigates the effects of transient temperatures on
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Aerothermoelasticity plays a vital role in the design and optimisation of hypersonic aircraft. Furthermore, the transient and nonlinear effects of the harsh thermal and aerodynamic environment a lifting surface is in cannot be ignored. This article investigates the effects of transient temperatures on the flutter behavior of a three-dimensional wing with a control surface and compares results for transient and steady-state temperature distributions. The time-varying temperature distribution is applied through the unsteady heat conduction equation coupled to nonlinear aerodynamics calculated using 3rd order piston theory. The effect of a transient temperature distribution on the flutter velocity is investigated and the results are compared with a steady-state heat distribution. The steady-state condition proves to over-compensate the effects of heat on the flutter response, whereas the transient case displays the effects of a constantly changing heat load by varying the response as time progresses. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle EASA’s “Open” Category for Military UAS: Opportunities and Limitations in the Field of Airworthiness
Received: 31 May 2018 / Revised: 22 June 2018 / Accepted: 25 June 2018 / Published: 1 July 2018
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Abstract
The European Aviation Safety Agency (EASA) plans to establish a sole risk-based set of regulations for drones to grant access to European airspace, thus opening a multibillion-euro market. One part of this new regulation set is the so-called “open” category, imposing only a
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The European Aviation Safety Agency (EASA) plans to establish a sole risk-based set of regulations for drones to grant access to European airspace, thus opening a multibillion-euro market. One part of this new regulation set is the so-called “open” category, imposing only a minimum set of regulations. The EASA’s approach presents a strong converse to traditional and prescriptive airworthiness regulations. For decades, unmanned aircraft systems (UAS) have been state-of-the-art assets in military forces. Aiming at the fulfilment of complex missions in extreme environments, in different theatres of operation, and with different partners, military UAS need to be reliable, safe, and interoperable. Therefore, NATO established internationally accepted airworthiness standards. However, these standards might be too severe to be adhered to by small, commercial, off-the-shelf UAS in the up-to-25 kg category, preventing the military from benefiting from the now fast-growing civil drone market. Based on a sound literature review, the paper presents the EASA’s upcoming regulations for civil UAS and discusses if they are applicable to military UAS. Possible opportunities, challenges, and limitations of applying the approach for the military are shown. Full article
(This article belongs to the Special Issue Civil and Military Airworthiness: Recent Developments and Challenges)
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Open AccessArticle Autonomous Door and Corridor Traversal with a 20-Gram Flapping Wing MAV by Onboard Stereo Vision
Received: 30 March 2018 / Revised: 24 May 2018 / Accepted: 15 June 2018 / Published: 25 June 2018
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Abstract
Autonomous flight of Flapping Wing Micro Air Vehicles (FWMAVs) is a major challenge in the field of robotics, due to their light weight and their flapping-induced body motions. An FWMAV is presented weighing a mere 20 g while all its sensors and processing
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Autonomous flight of Flapping Wing Micro Air Vehicles (FWMAVs) is a major challenge in the field of robotics, due to their light weight and their flapping-induced body motions. An FWMAV is presented weighing a mere 20 g while all its sensors and processing for autonomous flight are onboard. The navigation is based on a 4-g stereo vision camera with onboard processing. Three basic navigational tasks are demonstrated, namely obstacle avoidance, door traversing and corridor following. The presented combination of sensors and control routines is shown to allow flight in common unprepared environments like corridors and offices. The algorithms do not depend on prior classification or learning of the environment or control logic and work in any unprepared environment with vertical texture. While some failure cases remain, this work forms an important step towards very small autonomous indoor MAV. Full article
(This article belongs to the Special Issue Bio-Inspired Aerospace System)
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Open AccessArticle Use of Cost-Adjusted Importance Measures for Aircraft System Maintenance Optimization
Received: 28 May 2018 / Revised: 20 June 2018 / Accepted: 21 June 2018 / Published: 24 June 2018
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Abstract
The development of an aircraft maintenance planning optimization tool and its application to an aircraft component is presented. Various reliability concepts and approaches have been analyzed, together with objective criteria which can be used to optimize the maintenance planning of an aircraft system,
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The development of an aircraft maintenance planning optimization tool and its application to an aircraft component is presented. Various reliability concepts and approaches have been analyzed, together with objective criteria which can be used to optimize the maintenance planning of an aircraft system, subsystem or component. Wolfram® Mathematica v10.3 9 (Witney, UK) has been used to develop the novel optimization tool, the application of which is expected to yield significant benefits in selecting the most appropriate maintenance intervention based on objective criteria, in estimating the probability of nonscheduled maintenance and in estimating the required number of spare components for both scheduled and nonscheduled maintenance. As such, the results of the application of the tool can be used to assist the risk planning process for future system malfunctions, providing safe projections to facilitate the supply chain of the end user of the system, resulting in higher aircraft fleet operational availability. Full article
(This article belongs to the Special Issue Civil and Military Airworthiness: Recent Developments and Challenges)
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Open AccessArticle Failure Estimates for SiC Power MOSFETs in Space Electronics
Received: 27 April 2018 / Revised: 7 June 2018 / Accepted: 20 June 2018 / Published: 22 June 2018
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Abstract
Silicon carbide (SiC) power metal-oxide-semiconductor field effect transistors (MOSFETs) are space-ready in terms of typical reliability measures. However, single event burnout (SEB) due to heavy-ion irradiation often occurs at voltages 50% or lower than specified breakdown. Failure rates in space are estimated for
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Silicon carbide (SiC) power metal-oxide-semiconductor field effect transistors (MOSFETs) are space-ready in terms of typical reliability measures. However, single event burnout (SEB) due to heavy-ion irradiation often occurs at voltages 50% or lower than specified breakdown. Failure rates in space are estimated for burnout of 1200 V devices based on the experimental data for burnout and the expected heavy-ion linear energy transfer (LET) spectrum in space. Full article
(This article belongs to the Special Issue Challenges in Reliability Analysis of Aerospace Electronics)
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