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Aerospace, Volume 6, Issue 1 (January 2019)

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Cover Story (view full-size image) In the Clean Sky Program, the authors were involved in ambitious research aimed at the design and [...] Read more.
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Open AccessArticle A Generalized State-Space Aeroservoelastic Model Based on Tangential Interpolation
Received: 27 November 2018 / Accepted: 11 January 2019 / Published: 15 January 2019
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Abstract
In this work, a new approach for the generation of a generalized state-space aeroservoelastic model based on tangential interpolation is presented. The resulting system of differential algebraic equations (DAE) is reduced to a set of ordinary differential equations (ODE) by residualization of the [...] Read more.
In this work, a new approach for the generation of a generalized state-space aeroservoelastic model based on tangential interpolation is presented. The resulting system of differential algebraic equations (DAE) is reduced to a set of ordinary differential equations (ODE) by residualization of the non-proper part of the transfer function matrix. The generalized state-space is of minimal order and allows for the application of the force summation method (FSM) for the aircraft loads recovery. Compared to the classical rational function approximation (RFA) approach, the presented method provides a minimal order realization with exact interpolation of the unsteady aerodynamic forces in tangential directions, avoiding any selection of poles (lag states). The new approach is applied first for the generation of an aerodynamic model for the bidimensional unsteady incompressible flow in the time domain. Next, an application on the generation of an aeroservoelastic model for loads evaluation of the flutter reduced order assessment (FERMAT) model under atmospheric disturbances is done, showing an excellent agreement with the reference model in the frequency domain. The proposed aeroservoelastic model of minimal order is suited for loads analysis and multivariable control design, and an application to a gust loads alleviation (GLA) strategy is shown. Full article
(This article belongs to the Special Issue Aeroelasticity)
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Open AccessArticle Correlation Analysis of Separation Shock Oscillation and Wall Pressure Fluctuation in Unstarted Hypersonic Inlet Flow
Received: 3 October 2018 / Revised: 14 December 2018 / Accepted: 6 January 2019 / Published: 10 January 2019
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The flow field in a hypersonic inlet model at a design point of M = 6 has been studied experimentally. The focus of the current study is to present the time-resolved flow characteristics of separation shock around the cowl and the correlation between [...] Read more.
The flow field in a hypersonic inlet model at a design point of M = 6 has been studied experimentally. The focus of the current study is to present the time-resolved flow characteristics of separation shock around the cowl and the correlation between the separation shock oscillation induced by the unstart flow and the wall pressure fluctuation when the inlet is in a state of unstart. High-speed Schlieren flow visualization is used to capture the transient shock structure. High-frequency pressure transducers are installed on the wall around both the cowl and isolator areas to detect the dynamic pressure distribution. A schlieren image quantization method based on gray level detection and calculation is developed to analyze the time-resolved spatial structure of separation shock. Results indicate that the induced separation shock oscillation and the wall pressure fluctuation are closely connected, and they show the same frequency variation characteristics. The unsteady flow pattern of the “little buzz” and “big buzz” modes are clarified based on time-resolved Schlieren images of separation shock. Furthermore, the appropriate location of the pressure transducers is determined on the basis of the combined analysis of fluctuating wall-pressure and oscillating separation shock data. Full article
(This article belongs to the Special Issue Aerodynamic Design of Next Generation High-Speed Aircrafts)
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Open AccessArticle Assessing the Critical Multifunctionality Threshold for Optimal Electrical, Thermal, and Nanomechanical Properties of Carbon Nanotubes/Epoxy Nanocomposites for Aerospace Applications
Received: 17 December 2018 / Revised: 30 December 2018 / Accepted: 7 January 2019 / Published: 10 January 2019
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Abstract
Epoxy composites are widely used in primary aerospace structures, where high impact damage properties are necessary. However, challenges appear when multiple functionalities, including electrical and thermal conductivity, are needed in parallel with increased mechanical properties. The current study aims at the assessment of [...] Read more.
Epoxy composites are widely used in primary aerospace structures, where high impact damage properties are necessary. However, challenges appear when multiple functionalities, including electrical and thermal conductivity, are needed in parallel with increased mechanical properties. The current study aims at the assessment of a critical concentration of multiwalled carbon nanotubes (MWCNTs), incorporated in epoxy resin, which will indicate a threshold for optimal electrical, thermal and mechanical properties. For the evaluation of this optimal concentration, electrical conductivity, thermal stability and nanomechanical properties (Young modulus and nanohardness) have been assessed, for epoxy nanocomposites with 0 to 15 parts per hundred resin per weight (phr) MWCNTs. Percolation theory was applied to study the electrical conductivity for different contents of MWCNTs in the epoxy nanocomposite system. Thermogravimetric analysis was employed for the assessment of the epoxy composites’ thermal properties. Nanohardness and elastic modulus were measured, and the hardness versus modulus index was calculated. Emphasis was given to the dispersion of MWCNTs in the epoxy matrix, which was assessed by both microscopy techniques and X-ray micro–computed tomography. A correlation between the optimum dispersion and MWCNTs content in terms of electrical conductivity, thermal stability, and nanomechanical properties revealed a threshold concentration at 3 phr, allowing the manufacturing of aerospace structures with multifunctional properties. Full article
(This article belongs to the Special Issue 8th EASN-CEAS Workshop on Manufacturing for Growth and Innovation)
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Open AccessEditorial Acknowledgement to Reviewers of Aerospace in 2018
Published: 8 January 2019
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Abstract
Rigorous peer-review is the corner-stone of high-quality academic publishing. [...] Full article
Open AccessEditorial Special Issue “Computational Aerodynamic Modeling of Aerospace Vehicles”
Received: 3 January 2019 / Accepted: 7 January 2019 / Published: 8 January 2019
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Abstract
Aerospace, an open access journal operated by MDPI, has published a Special Issue on the Computational Aerodynamic Modeling of Aerospace Vehicles. [...] Full article
(This article belongs to the Special Issue Computational Aerodynamic Modeling of Aerospace Vehicles)
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Open AccessArticle Effects of Nozzle Pressure Ratio and Nozzle-to-Plate Distance to Flowfield Characteristics of an Under-Expanded Jet Impinging on a Flat Surface
Received: 2 December 2018 / Revised: 27 December 2018 / Accepted: 4 January 2019 / Published: 6 January 2019
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Abstract
The current work experimentally investigates the flowfield characteristics of an under-expanded turbulent jet impinging on a solid surface for various nozzle-to-plate distances 2.46Dj, 1.64Dj, and 0.82Dj (Dj is the jet hydraulic diameter), and [...] Read more.
The current work experimentally investigates the flowfield characteristics of an under-expanded turbulent jet impinging on a solid surface for various nozzle-to-plate distances 2.46 D j , 1.64 D j , and 0.82 D j ( D j is the jet hydraulic diameter), and nozzle pressure ratios (NPRs) ranging from 2 to 2.77 . Planar particle image velocimetry (PIV) measurements were performed in the central plane of the test nozzle and near the impingement surface. From the obtained PIV velocity vector fields, flow characteristics of under-expanded impinging jets, such as mean velocity, root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. Comparisons of statistical profiles obtained from PIV velocity measurements were performed to study the effects of the impingement surface, nozzle-to-plate distances, and NPRs to the flow patterns. Finally, proper orthogonal decomposition (POD) analysis was applied to the velocity snapshots to reveal the statistically dominant flow structures in the impinging jet regions. Full article
(This article belongs to the Special Issue Under-Expanded Jets)
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Open AccessArticle Comparative Environmental and Cost Analysis of Alternative Production Scenarios Associated with a Helicopter’s Canopy
Received: 9 November 2018 / Revised: 17 December 2018 / Accepted: 28 December 2018 / Published: 3 January 2019
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Abstract
In the present work the carbon footprint and the financial viability of different materials, manufacturing scenarios, as well as recycling scenarios, associated with the production of aeronautical structural components are assessed. The materials considered were carbon fiber reinforced epoxy and carbon fiber reinforced [...] Read more.
In the present work the carbon footprint and the financial viability of different materials, manufacturing scenarios, as well as recycling scenarios, associated with the production of aeronautical structural components are assessed. The materials considered were carbon fiber reinforced epoxy and carbon fiber reinforced PEEK (polyetheretherketone). The manufacturing techniques compared were the autoclave, resin transfer molding (RTM) and cold diaphragm forming (CDF). The recycling scenarios included mechanical recycling and pyrolysis. For this purpose, Life Cycle Analysis (LCA) and Life Cycle Costing (LCC) models were developed and implemented for the case of a helicopter’s canopy production. The results of the study pointed out that producing the canopy by using carbon fiber reinforced thermosetting composites and involving RTM as the manufacturing process is the optimal route both in terms of environmental and financial efficiency. The environmental and financial efficiency of the scenarios including thermoplastic composites as the material of choice is impaired from both the high embodied energy and raw material cost of PEEK. The scenarios investigated do not account for potential benefits arising from the recyclability and the improved reusability of thermoplastic matrices as compared to thermosetting ones. This underlines the need for a holistic aircraft structural optimization approach including not only performance and weight but also cost and environmental criteria. Full article
(This article belongs to the Special Issue 8th EASN-CEAS Workshop on Manufacturing for Growth and Innovation)
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Open AccessArticle The Miniature Optical Communication Transceiver—A Compact, Power-Efficient Lasercom System for Deep Space Nanosatellites
Received: 28 November 2018 / Revised: 22 December 2018 / Accepted: 24 December 2018 / Published: 31 December 2018
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Abstract
Optical communication is becoming more prevalent in orbit due to the need for increased data throughput. Nanosatellites, which are satellites that typically weigh less than 10 kg, are also becoming more common due to lower launch costs that enable the rapid testing of [...] Read more.
Optical communication is becoming more prevalent in orbit due to the need for increased data throughput. Nanosatellites, which are satellites that typically weigh less than 10 kg, are also becoming more common due to lower launch costs that enable the rapid testing of technology in a space environment. Nanosatellites are cheaper to launch than their larger counterparts and may be a viable option for communicating beyond Earth’s orbit, but have strict Size, Weight, and Power (SWaP) requirements. The Miniature Optical Communication Transceiver (MOCT) is a compact optical transceiver designed to provide modest data rates to SWaP constrained platforms, like nanosatellites. This paper will cover the optical amplifier characterization and simulated performance of the MOCT amplifier design that produces 1 kW peak power pulses and closes three optical links which include Low Earth Orbit (LEO) to Earth, LEO to LEO, and Moon to Earth. Additionally, a benchtop version of the amplifier design was constructed and was able to produce amplified pulses with 1.37 W peak power, including a 35.7% transmit optics loss, at a pump power of 500 mW. Finally, the modulator, seed laser, amplifier, receiver, and time-to-digital converter were all used together to measure the Bit Error Ratio (BER), which was 0.00257 for a received optical peak power of 176 nW. Full article
(This article belongs to the Special Issue Space-based Laser Communications)
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Open AccessArticle Electro-Actuation System Strategy for a Morphing Flap
Received: 5 November 2018 / Revised: 17 December 2018 / Accepted: 20 December 2018 / Published: 28 December 2018
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Abstract
Within the framework of the Clean Sky-JTI (Joint Technology Initiative) project, the design and technological demonstration of a novel wing flap architecture were addressed. Research activities were carried out to substantiate the feasibility of morphing concepts enabling flap camber variation in compliance with [...] Read more.
Within the framework of the Clean Sky-JTI (Joint Technology Initiative) project, the design and technological demonstration of a novel wing flap architecture were addressed. Research activities were carried out to substantiate the feasibility of morphing concepts enabling flap camber variation in compliance with the demanding safety requirements applicable to the next generation green regional aircraft. The driving motivation for the investigation on such a technology was found in the opportunity to replace a conventional double slotted flap with a single slotted camber-morphing flap assuring similar high lift performances—in terms of maximum attainable lift coefficient and stall angle—while lowering emitted noise and system complexity. The actuation and control logics aimed at preserving prescribed geometries of the device under variable load conditions are numerically and experimentally investigated with reference to an ‘iron-bird’ demonstrator. The actuation concept is based on load-bearing actuators acting on morphing ribs, directly and individually. The adopted un-shafted distributed electromechanical system arrangement uses brushless actuators, each rated for the torque of a single adaptive rib of the morphing structure. An encoder-based distributed sensor system generates the information for appropriate control-loop and, at the same time, monitors possible failures in the actuation mechanism. Further activities were then discussed in order to increase the TRL (Technology Readiness Level) of the validated architecture. Full article
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Aerospace EISSN 2226-4310 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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