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  Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 120 journals)
Showing 1 - 30 of 30 Journals sorted by number of followers
AIAA Journal     Hybrid Journal   (Followers: 1191)
SpaceNews     Free   (Followers: 825)
Journal of Spacecraft and Rockets     Hybrid Journal   (Followers: 771)
Journal of Propulsion and Power     Hybrid Journal   (Followers: 610)
Acta Astronautica     Hybrid Journal   (Followers: 495)
Advances in Space Research     Full-text available via subscription   (Followers: 457)
Aviation Week     Full-text available via subscription   (Followers: 437)
Aerospace Science and Technology     Hybrid Journal   (Followers: 427)
IEEE Transactions on Aerospace and Electronic Systems     Hybrid Journal   (Followers: 384)
Journal of Aircraft     Hybrid Journal   (Followers: 335)
Control Systems     Hybrid Journal   (Followers: 314)
IEEE Aerospace and Electronic Systems Magazine     Full-text available via subscription   (Followers: 282)
Journal of Navigation     Hybrid Journal   (Followers: 278)
Aircraft Engineering and Aerospace Technology     Hybrid Journal   (Followers: 261)
Gyroscopy and Navigation     Hybrid Journal   (Followers: 258)
Journal of Guidance, Control, and Dynamics     Hybrid Journal   (Followers: 204)
Space Science International     Open Access   (Followers: 200)
Space Science Reviews     Hybrid Journal   (Followers: 97)
International Journal of Aerospace Engineering     Open Access   (Followers: 82)
Progress in Aerospace Sciences     Full-text available via subscription   (Followers: 80)
Advances in Aerospace Engineering     Open Access   (Followers: 69)
Journal of Aerospace Engineering     Full-text available via subscription   (Followers: 69)
Propulsion and Power Research     Open Access   (Followers: 68)
Aerospace     Open Access   (Followers: 60)
Space Safety Magazine     Free   (Followers: 51)
Space Research Today     Full-text available via subscription   (Followers: 48)
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering     Hybrid Journal   (Followers: 46)
International Journal of Aeroacoustics     Hybrid Journal   (Followers: 40)
IEEE Transactions on Circuits and Systems I: Regular Papers     Hybrid Journal   (Followers: 39)
International Journal of Aerodynamics     Hybrid Journal   (Followers: 37)
Canadian Aeronautics and Space Journal     Full-text available via subscription   (Followers: 34)
Journal of Aerospace Information Systems     Hybrid Journal   (Followers: 34)
International Journal of Aerospace Sciences     Open Access   (Followers: 32)
Journal of Aeronautics & Aerospace Engineering     Open Access   (Followers: 31)
Space Policy     Hybrid Journal   (Followers: 30)
CEAS Aeronautical Journal     Hybrid Journal   (Followers: 29)
Journal of Space Weather and Space Climate     Open Access   (Followers: 27)
Aviation Psychology and Applied Human Factors     Hybrid Journal   (Followers: 27)
Russian Aeronautics (Iz VUZ)     Hybrid Journal   (Followers: 24)
Egyptian Journal of Remote Sensing and Space Science     Open Access   (Followers: 24)
Artificial Satellites     Open Access   (Followers: 23)
International Journal of Aerospace Psychology     Hybrid Journal   (Followers: 23)
Journal of Aerospace Information Systems     Hybrid Journal   (Followers: 22)
Annual of Navigation     Open Access   (Followers: 22)
Chinese Journal of Aeronautics     Open Access   (Followers: 21)
Nonlinear Dynamics     Hybrid Journal   (Followers: 20)
Aerospace Medicine and Human Performance     Full-text available via subscription   (Followers: 19)
Journal of Aerospace Engineering & Technology     Full-text available via subscription   (Followers: 18)
Journal of Aerodynamics     Open Access   (Followers: 18)
Aerospace Scientific Journal     Open Access   (Followers: 18)
Journal of Wind Engineering and Industrial Aerodynamics     Hybrid Journal   (Followers: 17)
Aviation     Open Access   (Followers: 17)
International Journal of Space Structures     Full-text available via subscription   (Followers: 17)
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription   (Followers: 17)
Proceedings of the Human Factors and Ergonomics Society Annual Meeting     Hybrid Journal   (Followers: 16)
Fatigue of Aircraft Structures     Open Access   (Followers: 15)
International Journal of Satellite Communications Policy and Management     Hybrid Journal   (Followers: 13)
Frontiers in Astronomy and Space Sciences     Open Access   (Followers: 12)
Elsevier Astrodynamics Series     Full-text available via subscription   (Followers: 12)
Aeronautical Journal, The     Hybrid Journal   (Followers: 12)
International Journal of Crashworthiness     Hybrid Journal   (Followers: 12)
Journal of Airline and Airport Management     Open Access   (Followers: 12)
International Journal of Micro Air Vehicles     Full-text available via subscription   (Followers: 11)
Journal of Aviation Technology and Engineering     Open Access   (Followers: 11)
International Journal of Space Science and Engineering     Hybrid Journal   (Followers: 11)
Air Force Magazine     Full-text available via subscription   (Followers: 11)
COSPAR Colloquia Series     Full-text available via subscription   (Followers: 11)
International Journal of Space Technology Management and Innovation     Full-text available via subscription   (Followers: 10)
Aviation in Focus - Journal of Aeronautical Sciences     Open Access   (Followers: 10)
Journal of Aircraft and Spacecraft Technology     Open Access   (Followers: 9)
Population Space and Place     Hybrid Journal   (Followers: 9)
Journal of Aeronautical Materials     Open Access   (Followers: 9)
International Journal of Aviation Management     Hybrid Journal   (Followers: 9)
Transportmetrica A : Transport Science     Hybrid Journal   (Followers: 9)
Journal of the Astronautical Sciences     Hybrid Journal   (Followers: 9)
Advances in Aerospace Science and Technology     Open Access   (Followers: 8)
Air Medical Journal     Hybrid Journal   (Followers: 8)
Journal of Space Safety Engineering     Hybrid Journal   (Followers: 8)
International Journal of Aviation Technology, Engineering and Management     Full-text available via subscription   (Followers: 7)
Journal of the American Helicopter Society     Full-text available via subscription   (Followers: 7)
Journal of Aerospace Technology and Management     Open Access   (Followers: 7)
International Journal of Applied Geospatial Research     Hybrid Journal   (Followers: 7)
New Space     Hybrid Journal   (Followers: 6)
Aerospace Systems     Hybrid Journal   (Followers: 6)
International Journal of Turbo and Jet-Engines     Hybrid Journal   (Followers: 6)
RocketSTEM     Free   (Followers: 6)
Civil Aviation High Technologies     Open Access   (Followers: 5)
International Journal of Aviation, Aeronautics, and Aerospace     Open Access   (Followers: 5)
REACH - Reviews in Human Space Exploration     Full-text available via subscription   (Followers: 5)
International Journal of Sustainable Aviation     Hybrid Journal   (Followers: 5)
Aviation Advances & Maintenance     Open Access   (Followers: 5)
Cosmic Research     Hybrid Journal   (Followers: 5)
Unmanned Systems     Hybrid Journal   (Followers: 5)
Space and Polity     Hybrid Journal   (Followers: 4)
Life Sciences in Space Research     Hybrid Journal   (Followers: 4)
Aerotecnica Missili & Spazio : Journal of Aerospace Science, Technologies & Systems     Hybrid Journal   (Followers: 4)
Astrodynamics     Hybrid Journal   (Followers: 4)
Investigación Pecuaria     Open Access   (Followers: 3)
Aerospace technic and technology     Open Access   (Followers: 3)
Journal of Spatial Science     Hybrid Journal   (Followers: 3)
ASTRA Proceedings     Open Access   (Followers: 3)
Journal of KONBiN     Open Access   (Followers: 3)
Problemy Mechatroniki. Uzbrojenie, lotnictwo, inżynieria bezpieczeństwa / Problems of Mechatronics. Armament, Aviation, Safety Engineering     Open Access   (Followers: 3)
npj Microgravity     Open Access   (Followers: 3)
Journal of Astrobiology & Outreach     Open Access   (Followers: 3)
Journal of Aviation/Aerospace Education & Research     Open Access   (Followers: 2)
IEEE Journal on Miniaturization for Air and Space Systems     Hybrid Journal   (Followers: 2)
Microgravity Science and Technology     Hybrid Journal   (Followers: 2)
Вісник Національного Авіаційного Університету     Open Access   (Followers: 2)
International Journal of Aeronautical and Space Sciences     Hybrid Journal   (Followers: 2)
Ciencia y Poder Aéreo     Open Access   (Followers: 2)
MAD - Magazine of Aviation Development     Open Access   (Followers: 2)
Journal of the Australasian Society of Aerospace Medicine     Open Access   (Followers: 1)
Open Aerospace Engineering Journal     Open Access   (Followers: 1)
Advances in Astronautics Science and Technology     Hybrid Journal   (Followers: 1)
Journal of Engineering and Technological Sciences     Open Access   (Followers: 1)
Technical Soaring     Full-text available via subscription   (Followers: 1)
Spatial Information Research     Hybrid Journal   (Followers: 1)
Mekanika : Jurnal Teknik Mesin i     Open Access   (Followers: 1)
Perspectives of Earth and Space Scientists i     Open Access  

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Journal Prestige (SJR): 0.305
Citation Impact (citeScore): 1
Number of Followers: 60  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2226-4310
Published by MDPI Homepage  [233 journals]
  • Aerospace, Vol. 8, Pages 58: Harmonic Forcing from Distortion in a
           Boundary Layer Ingesting Fan

    • Authors: Hans Mårtensson
      First page: 58
      Abstract: Integrating a fan with a boundary layer ingestion (BLI) configuration into an aircraft fuselage can improve propulsion efficiency by utilizing the lower momentum airflow in the boundary layer developed due to the surface drag of the fuselage. As a consequence, velocity and total pressure variations distort the flow field entering the fan in both the circumferential and radial directions. Such variations can negatively affect fan aerodynamics and give rise to vibration issues. A fan configuration to benefit from BLI needs to allow for distortion without large penalties. Full annulus unsteady computational fluid dynamics (CFD) with all blades and vanes is used to evaluate the effects on aerodynamic loading and forcing on a fan designed to be mounted on an adapted rear fuselage of a Fokker 100 aircraft, i.e., a tail cone thruster. The distortion pattern used as a boundary condition on the fan is taken from a CFD analysis of the whole aircraft with a simplified model of the installed fan. Detailed simulations of the fan are conducted to better understand the relation between ingested distortion and the harmonic forcing. The results suggest that the normalized harmonic forcing spectrum is primarily correlated to the circumferential variation of inlet total pressure. In this study, the evaluated harmonic forces correlate with the total pressure variation at the inlet for the first 12 engine orders, with some exceptions where the response is very low. At higher harmonics, the distortion content as well as the response become very low, with amplitudes in the order of magnitude lower than the principal disturbances. The change in harmonic forcing resulting from raising the working line, thus, increasing the incidence on the fan rotor, increases the forcing moderately. The distortion transfers through the fan resulting in a non-axisymmetric aerodynamic loading of the outlet guide vane (OGV) that has a clear effect on the aerodynamics. The time average aerodynamic load and also the harmonic forcing of the OGV vary strongly around the circumference. In particular, this is the case for some of the vanes at higher back pressure, most likely due to an interaction with separations starting to occur on vanes operating in unfavorable conditions.
      Citation: Aerospace
      PubDate: 2021-02-24
      DOI: 10.3390/aerospace8030058
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 59: Evaluation of the Climate Impact Reduction
           Potential of the Water-Enhanced Turbofan (WET) Concept

    • Authors: Regina Pouzolz, Oliver Schmitz, Hermann Klingels
      First page: 59
      Abstract: Aviation faces increasing pressure not only to reduce fuel burn, and; therefore, CO2 emissions, but also to provide technical solutions for an overall climate impact minimization. To combine both, a concept for the enhancement of an aircraft engine by steam injection with inflight water recovery is being developed. The so-called Water-Enhanced Turbofan (WET) concept promises a significant reduction of CO2 emissions, NOx emissions, and contrail formation. Representative missions for an A320-type aircraft using the proposed new engine were calculated. Applying a first-order one-dimensional climate assessment prospects the reduction of more than half of the Global Warming Potential over one hundred years, compared to an evolutionarily improved aero-engine. If CO2-neutrally produced sustainable aviation fuels are used, climate impact could be reduced by 93% compared to today’s aircraft. The evaluation is a first estimate of effects based on preliminary design studies and should provide a starting point for discussion in the scientific community, implying the need for research, especially on the formation mechanisms and radiation properties of potential contrails from the comparatively cold exhaust gases of the WET engine.
      Citation: Aerospace
      PubDate: 2021-02-25
      DOI: 10.3390/aerospace8030059
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 60: Generation and Mitigation Mechanism Studies
           of Nonlinear Thermoacoustic Instability in a Modelled Swirling Combustor
           with a Heat Exchanger

    • Authors: Yuze Sun, Dan Zhao, Xiaowei Zhu
      First page: 60
      Abstract: In the present work, 3D Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are performed to investigate the generation and mitigation mechanism of combustion-sustained thermoacoustic instabilities in a modelled swirl combustor. The effects of (1) swirling number SN, (2) inlet air flow rate Va and (3) inlet temperature Ti on the amplitudes and frequencies of swirling combustion-excited limit cycle oscillations are examined. It is found that the amplitude of acoustic fluctuations is increased with increasing SN and Va and decreased with the increase of Ti. The dominant frequency of oscillations is also found to increases with the increase of SN and Va. However, increasing Ti leads to the dominant frequency being decreased first and then increased. An alternative passive control method of installing an adjustable temperature heat exchanger on the combustion chamber wall is then proposed. Numerical results show that thermoacoustic oscillations could be excited and mitigated by setting the heat exchanger temperature to TH. Global and local Rayleigh indexes are applied to further reveal the excitation and attenuation effects on mechanisms. The present study is conducive to developing a simulation platform for thermoacoustic instabilities in swirling combustors. It also provides an alternative method to amplify or mitigate thermoacoustic oscillations.
      Citation: Aerospace
      PubDate: 2021-02-26
      DOI: 10.3390/aerospace8030060
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 61: Aircraft Requirements for Sustainable
           Regional Aviation

    • Authors: Dominik Eisenhut, Nicolas Moebs, Evert Windels, Dominique Bergmann, Ingmar Geiß, Ricardo Reis, Andreas Strohmayer
      First page: 61
      Abstract: Recently, the new Green Deal policy initiative was presented by the European Union. The EU aims to achieve a sustainable future and be the first climate-neutral continent by 2050. It targets all of the continent’s industries, meaning aviation must contribute to these changes as well. By employing a systems engineering approach, this high-level task can be split into different levels to get from the vision to the relevant system or product itself. Part of this iterative process involves the aircraft requirements, which make the goals more achievable on the system level and allow validation of whether the designed systems fulfill these requirements. Within this work, the top-level aircraft requirements (TLARs) for a hybrid-electric regional aircraft for up to 50 passengers are presented. Apart from performance requirements, other requirements, like environmental ones, are also included. To check whether these requirements are fulfilled, different reference missions were defined which challenge various extremes within the requirements. Furthermore, figures of merit are established, providing a way of validating and comparing different aircraft designs. The modular structure of these aircraft designs ensures the possibility of evaluating different architectures and adapting these figures if necessary. Moreover, different criteria can be accounted for, or their calculation methods or weighting can be changed.
      Citation: Aerospace
      PubDate: 2021-02-26
      DOI: 10.3390/aerospace8030061
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 62: Analysis of the Cosmic Ray Effects on
           Sentinel-1 SAR Satellite Data

    • Authors: Hakan Köksal, Nusret Demir, Ali Kilcik
      First page: 62
      Abstract: Ionizing radiation sources such as Solar Energetic Particles and Galactic Cosmic Radiation may cause unexpected errors in imaging and communication systems of satellites in the Space environment, as reported in the previous literature. In this study, the temporal variation of the speckle values on Sentinel 1 satellite images were compared with the cosmic ray intensity/count data, to analyze the effects which may occur in the electromagnetic wave signals or electronic system. Sentinel 1 Synthetic Aperture Radar (SAR) images nearby to the cosmic ray stations and acquired between January 2015 and December 2019 were processed. The median values of the differences between speckle filtered and original image were calculated on Google Earth Engine Platform per month. The monthly median “noise” values were compared with the cosmic ray intensity/count data acquired from the stations. Eight selected stations’ data show that there are significant correlations between cosmic ray intensities and the speckle amounts. The Pearson correlation values vary between 0.62 and 0.78 for the relevant stations.
      Citation: Aerospace
      PubDate: 2021-03-03
      DOI: 10.3390/aerospace8030062
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 63: A Numerical Investigation on Stress Modal
           Analysis of Composite Laminated Thin Plates

    • Authors: Yadong Zhou, Youchao Sun, Weili Zeng
      First page: 63
      Abstract: Because of the light weight and high strength, composite laminates have many advantages in aircraft structures; however, they are frequently subjected to severe dynamic loadings during flight. To understand the dynamic properties of composite laminated thin plates at the stress scale, this paper studies the stress modal analysis (SMA) of composite laminated thin plates by finite element method (FEM). Firstly, the basic theory on SMA of composite laminates was given from the classical displacement modal analysis. Secondly, a square laminated thin plate was numerically studied to obtain some distribution laws of the stress mode shapes (SMSs) from the layup and stress component perspectives. Then, based on the characteristics of SMSs in different plies, a modified layup configuration was conducted for possible lower magnitude and more uniform distributions of SMSs. Results indicate that ±45° layups can improve the performance of SMSs of the square plate, without excessively decreasing the modal frequencies. Such fact manifests that ±45° layups are critically vital for the dynamic stress reduction of the square composite laminated plates. Modal participation factor and strain energy were evaluated to assist the determination of critical modes. Lastly, the aspect ratio of the composite plate on layup design was considered. Numerical investigation in this study can serve as a preliminary step of SMSs perspective for the analysis and optimization of dynamic composite laminates.
      Citation: Aerospace
      PubDate: 2021-03-04
      DOI: 10.3390/aerospace8030063
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 64: Development of a Novel Deployable Solar Panel
           and Mechanism for 6U CubeSat of STEP Cube Lab-II

    • Authors: Shankar Bhattarai, Ji-Seong Go, Hongrae Kim, Hyun-Ung Oh
      First page: 64
      Abstract: The structural safety of solar cells mounted on deployable solar panels in the launch vibration environment is a significant aspect of a successful CubeSat mission. This paper presents a novel highly damped deployable solar panel module that is effective in ensuring structural protection of solar cells under the launch environment by rapidly suppressing the vibrations transmitting through the solar panel by constrained layer damping achieved using printed circuit board (PCB)-based multilayered thin stiffeners with double-sided viscoelastic tapes. A high-damping solar panel demonstration model with a three-pogo pin-based burn wire release mechanism was fabricated and tested for application in the 6U CubeSat “STEP Cube Lab-II” developed by Chosun University, South Korea. The reliable release function and radiation hardness assurance of the mechanism in an in-orbit environment were confirmed by performing solar panel deployment tests and radiation tests, respectively. The design effectiveness and structural safety of the proposed solar panel module were validated by launch vibration and in-orbit environment tests at the qualification level.
      Citation: Aerospace
      PubDate: 2021-03-05
      DOI: 10.3390/aerospace8030064
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 65: Spoken Instruction Understanding in Air
           Traffic Control: Challenge, Technique, and Application

    • Authors: Yi Lin
      First page: 65
      Abstract: In air traffic control (ATC), speech communication with radio transmission is the primary way to exchange information between the controller and aircrew. A wealth of contextual situational dynamics is embedded implicitly; thus, understanding the spoken instruction is particularly significant to the ATC research. In this paper, a comprehensive review related to spoken instruction understanding (SIU) in the ATC domain is provided from the perspective of the challenges, techniques, and applications. Firstly, a full pipeline is represented to achieve the SIU task, including automatic speech recognition, language understanding, and voiceprint recognition. A total of 10 technique challenges are analyzed based on the ATC task specificities. In succession, the common techniques for SIU tasks are categorized from common applications, and extensive works in the ATC domain are also reviewed. Finally, a series of future research topics are also prospected based on the corresponding challenges. The author sincerely hopes that this work is able to provide a clear technical roadmap for the SIU tasks in the ATC domain and further make contributions to the research community.
      Citation: Aerospace
      PubDate: 2021-03-05
      DOI: 10.3390/aerospace8030065
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 66: Numerical Investigation of an Optimized Rotor
           Head Fairing for the RACER Compound Helicopter in Cruise Flight

    • Authors: Patrick Pölzlbauer, Andreas Kümmel, Damien Desvigne, Christian Breitsamter
      First page: 66
      Abstract: The present work is part of the Clean Sky 2 project Full-Fairing Rotor Head Aerodynamic Design Optimization (FURADO), which deals with the aerodynamic design optimization of a full-fairing rotor head for the Rapid And Cost-Effective Rotorcraft (RACER) compound helicopter. The rotor head is a major drag source and previous investigations have revealed that the application of rotor head fairings can be an effective drag reduction measure. As part of the full-fairing concept, a new blade-sleeve fairing was aerodynamically optimized for cruise flight. Within this publication, the newly developed blade-sleeve fairing is put to test on an isolated, five-bladed rotor head and compared to an already existing reference blade-sleeve fairing, which was developed at Airbus Helicopters. Numerical flow simulations are performed with ANSYS Fluent 2019 R2 considering a rotating rotor head with cyclic pitch movement. The aerodynamic forces of the isolated rotor head are analyzed to determine the performance benefit of the newly developed blade-sleeve fairing. A drag reduction of 4.7% and a lift increase of 20% are obtained in comparison to the Airbus Helicopters reference configuration. Furthermore, selected surface and flow field quantities are presented to give an overview on the occurring flow phenomena.
      Citation: Aerospace
      PubDate: 2021-03-05
      DOI: 10.3390/aerospace8030066
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 67: Fuel Planning Strategies Considering
           Operational Uncertainties of Aerodynamic Formation Flight

    • Authors: Majed Swaid, Tobias Marks, Florian Linke, Volker Gollnick
      First page: 67
      Abstract: The operational concept of aerodynamic formation flight, also referred to as aircraft wake-surfing for efficiency (AWSE), has high potential in terms of fuel savings and climate impact mitigation. In order to implement this concept, many technological and operational challenges have to be coped with. As the fuel consumption during a mission strongly depends on a successful execution of AWSE, the existing uncertainties regarding flight planning increase. While a conservative fuel planning ensures a follower to complete the mission even in the case of a formation failure, it might result in high amounts of excess fuel and, therefore, additional fuel consumption. In this study, this issue is addressed by the adaptation of flight planning procedures to the requirements of AWSE focusing on fuel planning in particular, considered from the perspective of a designated follower aircraft of a two-aircraft formation. This trade-off is modeled as an n-action two-event decision-making problem. Each of the possible actions is represented by a combination of mission routing and a corresponding diversion airport, taking atmospheric effects (e.g., wind) into account in order to determine the resulting amount of trip fuel. The two events under consideration are a total formation failure in contrast to a complete success. Based on a scenario with a set of double origin destination pairs characterizing the formations and representative weather patterns for the North Atlantic region, each action is analyzed with regard to the expected fuel consumption and expense. Based on a set of assumed formation success probabilities, we find that the proposed method holds a savings potential to reduce the follower’s fuel consumption by 4.8% and its monetary expenses by 1.2% compared with a conventional flight planning. In order to gain a monetary profit margin applying this method, the required formation success probability is shown to vary between 92% and 96%, depending on the assumed fuel price.
      Citation: Aerospace
      PubDate: 2021-03-07
      DOI: 10.3390/aerospace8030067
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 68: Rendezvous in Cis-Lunar Space near
           Rectilinear Halo Orbit: Dynamics and Control Issues

    • Authors: Giordana Bucchioni, Mario Innocenti
      First page: 68
      Abstract: The paper presents the development of a fully-safe, automatic rendezvous strategy between a passive vehicle and an active one orbiting around the Earth–Moon L2 Lagrangian point. This is one of the critical phases of future missions to permanently return to the Moon, which are of interest to the majority of space organizations. The first step in the study is the derivation of a suitable full 6-DOF relative motion model in the Local Vertical Local Horizontal reference frame, most suitable for the design of the guidance. The main dynamic model is approximated using both the elliptic and circular three-body motion, due to the contribution of Earth and Moon gravity. A rather detailed set of sensors and actuator dynamics was also implemented in order to ensure the reliability of the guidance algorithms. The selection of guidance and control is presented, and evaluated using a sample scenario as described by ESA’s HERACLES program. The safety, in particular the passive safety, concept is introduced and different techniques to guarantee it are discussed that exploit the ideas of stable and unstable manifolds to intrinsically guarantee some properties at each hold-point, in which the rendezvous trajectory is divided. Finally, the rendezvous dynamics are validated using available Ephemeris models in order to verify the validity of the results and their limitations for future more detailed design.
      Citation: Aerospace
      PubDate: 2021-03-08
      DOI: 10.3390/aerospace8030068
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 69: Background Pressure Effects on the
           Performance of a 20 kW Magnetically Shielded Hall Thruster Operating in
           Various Configurations

    • Authors: Antonio Piragino, Farbod Faraji, Maryam Reza, Eugenio Ferrato, Annalisa Piraino, Tommaso Andreussi
      First page: 69
      Abstract: The paper reports the characterization results of a 20 kW-class magnetically shielded Hall thruster in three different configurations and operating with a centrally mounted cathode. The characterization was carried out at two different pumping speeds in SITAEL’s IV10 vacuum chamber, resulting in two different background pressure levels for each tested operating point. A linear behavior of discharge current and thrust values versus the anode mass flow rate was noticed for both pumping speeds levels and for all the three configurations. In addition, the thrust and discharge current values were always found to be lower at lower background pressure levels. From the performance levels, a preliminary estimate of the ingested mass flow rates was performed, and the values were then compared to a recently developed background flow model. The results suggested that, for this thruster and in the tested operating regimes, the change in performance due to background pressure could be ascribed not only to the ingestion of external mass flow coming from the chamber but also to other physical processes caused by the flux of residual background neutrals.
      Citation: Aerospace
      PubDate: 2021-03-09
      DOI: 10.3390/aerospace8030069
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 70: Phasing Maneuver Analysis from a Low Lunar
           Orbit to a Near Rectilinear Halo Orbit

    • Authors: Giordana Bucchioni, Mario Innocenti
      First page: 70
      Abstract: The paper describes the preliminary design of a phasing trajectory in a cislunar environment, where the third body perturbation is considered non-negligible. The working framework is the one proposed by the ESA’s Heracles mission in which a passive target station is in a Near Rectilinear Halo Orbit and an active vehicle must reach that orbit to start a rendezvous procedure. In this scenario the authors examine three different ways to design such phasing maneuver under the circular restricted three-body problem hypotheses: Lambert/differential correction, Hohmann/differential correction and optimization. The three approaches are compared in terms of ΔV consumption, accuracy and time of flight. The selected solution is also validated under the more accurate restricted elliptic three-body problem hypothesis.
      Citation: Aerospace
      PubDate: 2021-03-09
      DOI: 10.3390/aerospace8030070
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 71: Human Machine Interface Design for Monitoring
           Safety Risks Associated with Operating Small Unmanned Aircraft Systems in
           Urban Areas

    • Authors: Max Friedrich, Mark Vollrath
      First page: 71
      Abstract: The envisioned introduction of autonomous Small Unmanned Aircraft Systems (sUAS) into low-altitude urban airspace necessitates high levels of system safety. Despite increased system autonomy, humans will most likely remain an essential component in assuring safety. This paper derives, applies, and evaluates a display design concept that aims to support safety risk monitoring of multiple sUAS by a human operator. The concept comprises of five design principles. The core idea of the concept is to limit display complexity despite increasing the number of sUAS monitored by primarily visualizing highly abstracted information while hiding detailed information of lower abstraction, unless specifically requested by the human operator. States of highly abstracted functions are visualized by function-specific icons that change hue in accordance to specified system states. Simultaneously, the design concept aims to support the human operator in identifying off-nominal situations by implementing design properties that guide visual attention. The display was evaluated in a study with seven subject matter experts. Although preliminary, the results clearly favor the proposed display design concept. The advantages of the proposed design concept are demonstrated, and the next steps for further exploring the proposed display design concept are outlined.
      Citation: Aerospace
      PubDate: 2021-03-10
      DOI: 10.3390/aerospace8030071
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 72: Special Issue: Deicing and Anti-Icing of

    • Authors: Sakaue
      First page: 72
      Abstract: In-flight icing for aircrafts is a large concern for all those involved in aircraft operations. This Special Issue assembles a diverse selection of research papers on topics related to the deicing and anti-icing of aircrafts. These topics span experimental, numerical, and data science studies from droplet scale [1,2] to the system level [3–6], as summarized in Table 1. The editor is pleased to assemble 11 articles in this Special Issue. The readers will enjoy this variety of high-quality research on the deicing and anti-icing of aircrafts. [...]
      Citation: Aerospace
      PubDate: 2021-03-10
      DOI: 10.3390/aerospace8030072
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 73: Task Planning for Multiple-Satellite
           Space-Situational-Awareness Systems

    • Authors: Yutao Chen, Guoqing Tian, Junyou Guo, Jie Huang
      First page: 73
      Abstract: Space situational awareness (SSA) plays an important role in maintaining space advantages. Task planning is one of the key technologies in SSA to allocate multiple tasks to multiple satellites, so that a satellite may be allocated to supervise multiple space objects, and a space object may be supervised by multiple satellites. This paper proposes a hierarchical and distributed task-planning framework for SSA systems with focus on fast and effective task planning customized for SSA. In the framework, a global task-planner layer performs satellite and object clustering, so that satellites are clustered into multiple unique clusters on the basis of their positions, while objects are clustered into multiple possibly intersecting clusters, hence allowing for a single object to be supervised by multiple satellites. In each satellite cluster, a local task planner performs distributed task planning using the contract-net protocol (CNP) on the basis of the position and velocity of satellites and objects. In addition, a customized discrete particle swarm optimization (DPSO) algorithm was developed to search for the optimal task-planning result in the CNP. Simulation results showed that the proposed framework can effectively achieve task planning among multiple satellites and space objects. The efficiency and scalability of the proposed framework are demonstrated through static and dynamic orbital simulations.
      Citation: Aerospace
      PubDate: 2021-03-12
      DOI: 10.3390/aerospace8030073
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 74: A Review of Current Research in Subscale
           Flight Testing and Analysis of Its Main Practical Challenges

    • Authors: Alejandro Sobron, David Lundström, Petter Krus
      First page: 74
      Abstract: Testing of untethered subscale models, often referred to as subscale flight testing, has traditionally had a relatively minor, yet relevant use in aeronautical research and development. As recent advances in electronics, rapid prototyping and unmanned-vehicle technologies expand its capabilities and lower its cost, this experimental method is seeing growing interest across academia and the industry. However, subscale models cannot meet all similarity conditions required for simulating full-scale flight. This leads to a variety of approaches to scaling and to other alternative applications. Through a literature review and analysis of different scaling strategies, this study presents an overall picture of how subscale flight testing has been used in recent years and synthesises its main issues and practical limitations. Results show that, while the estimation of full-scale characteristics is still an interesting application within certain flight conditions, subscale models are progressively taking a broader role as low-cost technology-testing platforms with relaxed similarity constraints. Different approaches to tackle the identified practical challenges, implemented both by the authors and by other organisations, are discussed and evaluated through flight experiments.
      Citation: Aerospace
      PubDate: 2021-03-12
      DOI: 10.3390/aerospace8030074
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 75: Tribology in Space Robotic Actuators:
           Experimental Method for Evaluation and Analysis of Gearboxes

    • Authors: Erik Nyberg, Dídac Llopart i Cervelló, Ichiro Minami
      First page: 75
      Abstract: Liquid lubricants are critical to enable long-life operation of high-performance machinery, such as geared actuators employed in robotics. In space applications, actuator gearboxes must operate in low temperatures, where liquid lubricants face inherent problems related to low temperature rheology. Heaters are relied upon to provide acceptable gearbox temperatures. Unfortunately, heating is energy-intense and does not scale well with increasing mechanism mass and performance. Effective boundary lubrication (BL), on the other hand, can minimize problems of low temperature rheology. BL relies on tribofilm formation over conventional fluid film separation. Effective space grade boundary lubricants can potentially allow for drastically reduced amounts of oil and the accompanying rheological problems. In this work, we describe the design of a methodology to evaluate and analyze tribology of actuator gearboxes operated under cryogenic oil-starved conditions in N2 atmosphere. The devised methodology enables research pertinent to space actuator tribology by accelerated testing and advanced analysis, as demonstrated by a lubricant candidate case study. Complementary microscopy techniques are discussed, and a novel methodology devised for gear internal microstructure analysis by X-ray microtomography (XMT) is presented.
      Citation: Aerospace
      PubDate: 2021-03-13
      DOI: 10.3390/aerospace8030075
      Issue No: Vol. 8, No. 3 (2021)
  • Aerospace, Vol. 8, Pages 24: Non-Propellant Eddy Current Brake and
           Traction in Space Using Magnetic Pulses

    • Authors: Yi Zhang, Qiang Shen, Liqiang Hou, Shufan Wu
      First page: 24
      Abstract: The safety of on-orbit satellites is threatened by space debris with large residual angular velocity and the space debris removal is becoming more challenging than before. This paper explores the non-contact despinning and traction problem of high-speed rotating targets and proposes an eddy current brake and traction technology for space targets without any propellant consumption. The principle of the conventional eddy current brake is analyzed in this article and the concept of eddy current brake and traction without propellant is put forward for the first time. Secondly, according to the key technical requirements, a brand-new structure of a satellite generating artificial magnetic field is designed accordingly. Then the control mechanism of eddy current brake and traction without propellant is analyzed qualitatively by simplifying the model and conditions. Then, the magnetic pulse control method is proposed and analyzed quantitatively. Finally, the feasibility of the technology is verified by the numerical simulation method. According to the simulation results, the eddy current brake and traction technology based on magnetic pulses can make the angular speed of target decrease linearly without propellant during the process. This technology has huge advantages compared with conventional eddy current brake technology in terms of efficiency and reduced propellant consumption.
      Citation: Aerospace
      PubDate: 2021-01-20
      DOI: 10.3390/aerospace8020024
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 25: Performance and Emissions of a Microturbine
           and Turbofan Powered by Alternative Fuels

    • Authors: Radoslaw Przysowa, Bartosz Gawron, Tomasz Białecki, Anna Łęgowik, Jerzy Merkisz, Remigiusz Jasiński
      First page: 25
      Abstract: Alternative fuels containing biocomponents produced in various technologies are introduced in aviation to reduce its carbon footprint but there is little data describing their impact on the performance and emissions of engines. The purpose of the work is to compare the performance and gas emissions produced from two different jet engines—the GTM-140 microturbine and the full-size DGEN380 turbofan, powered by blends of Jet A-1 and one of two biocomponents: (1) Alcohol-to-Jet (ATJ) and (2) Hydroprocessed Esters and Fatty Acids (HEFA) produced from used cooking oil (UCO) in various concentrations. The acquired data will be used to develop an engine emissivity model to predict gas emissions. Blends of the mineral fuel with synthetic components were prepared in various concentrations, and their physicochemical parameters were examined in the laboratory. Measurements of emissions from both engines were carried out in selected operating points using the Semtech DS gaseous analyzer and the EEPS spectrometer. The impact of tested blends on engine operating parameters is limited, and their use does not carry the risk of a significant decrease in aircraft performance or increase in fuel consumption. Increasing the content of biocomponents causes a noticeable rise in the emission of CO and slight increase for some other gasses (HC and NOx), which should not, however, worsen the working conditions of the ground personnel. This implies that there are no contraindications against using tested blends for fuelling gas-turbine engines.
      Citation: Aerospace
      PubDate: 2021-01-21
      DOI: 10.3390/aerospace8020025
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 26: Synthesis and Experimental Characterization
           of a MWCNT-Filled Bio-Based Adhesive

    • Authors: Konstantinos Tserpes, Vasileios Tzatzadakis
      First page: 26
      Abstract: In the present paper, a novel epichlorohydrin/cardanol adhesive was reinforced by multi-walled carbon nanotubes (MWCNTs) and characterized experimentally. The adhesive was reinforced by MWCNTs in weight ratios (wt %) of 0.5%, 1.0% and 2.0%. The bulk properties of the reinforced adhesive were characterized through dynamic mechanical analysis tests, tension tests, and fracture toughness tests, while its shear behavior was characterized through single-lap shear tests on aluminum and composite bonded specimens. The morphology of the reinforced adhesive was characterized using scanning electron microscopy tests. Due to the high viscosity of the bio-based adhesive, special efforts were placed on the dispersion of the MWCNTs into the adhesive, which was achieved through mechanical mixing. The results from the tests show that the presence of the MWCNTs increases the glass transition temperature, the Young’s modulus and the fracture toughness of the reinforced bio-based adhesive, while it decreases its tensile strength. This contradictory finding is attributed to the formation of MWCNT agglomerates into the adhesive. For the content of 2.0 wt %, the shear strength of the reinforced adhesive is increased by 57% for the aluminum joints and by 10.4% for the composite joints. The findings of the study reveal that the reinforcement of the bio-based adhesive by MWCNTs is feasible from a manufacturing viewpoint and may increase the efficiency of the adhesive in structural applications.
      Citation: Aerospace
      PubDate: 2021-01-21
      DOI: 10.3390/aerospace8020026
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 27: Learning from Incidents: A Qualitative Study
           in the Continuing Airworthiness Sector

    • Authors: James Clare, Kyriakos I. Kourousis
      First page: 27
      Abstract: Learning from incidents (LFI) is a useful approach when examining past events and developing measures to prevent ensuing recurrence. Although the reporting of incidents in the aircraft maintenance and continuing airworthiness domain is well appointed, it is often unclear how the maximum effect of safety data can be efficaciously applied in support of LFI in the area. From semi-structured interviews, with thirty-four participants, the gathered data were thematically analyzed with the support of NVivo software. This study establishes a relationship between an incident in its lifecycle and the learning process. The main aim of this work is to elucidate factors that enable LFI. The analysis of the data revealed, for example, the benefits of a just culture and the use of formal continuation training programs in this respect. Moreover, it identified limitations inherent in current processes such as poor event causation and poorly designed learning syllabi. Additionally, aspects such as a lack of regulatory requirements for competence in the areas of learning for managers and accountable persons currently exist. This thematic analysis could be used in support of organizations examining their own processes for learning from incidents. Additionally, it can support the development of terms of reference for a continuing airworthiness regulatory working group to examine, strengthen and better apply LFI in the aviation industry.
      Citation: Aerospace
      PubDate: 2021-01-22
      DOI: 10.3390/aerospace8020027
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 28: Toward ATM Resiliency: A Deep CNN to Predict
           Number of Delayed Flights and ATFM Delay

    • Authors: Rasoul Sanaei, Brian Alphonse Pinto, Volker Gollnick
      First page: 28
      Abstract: The European Air Traffic Management Network (EATMN) is comprised of various stakeholders and actors. Accordingly, the operations within EATMN are planned up to six months ahead of target date (tactical phase). However, stochastic events and the built-in operational flexibility (robustness), along with other factors, result in demand and capacity imbalances that lead to delayed flights. The size of the EATMN and its complexity challenge the prediction of the total network delay using analytical methods or optimization approaches. We face this challenge by proposing a deep convolutional neural network (DCNN), which takes capacity regulations as the input. DCNN architecture successfully improves the prediction results by 50 percent (compared to random forest as the baseline model). In fact, the trained model on 2016 and 2017 data is able to predict 2018 with a mean absolute percentage error of 22% and 14% for the delay and delayed traffic, respectively. This study presents a method to provide more accurate situational awareness, which is a must for the topic of network resiliency.
      Citation: Aerospace
      PubDate: 2021-01-25
      DOI: 10.3390/aerospace8020028
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 29: Probabilistic Prediction of Separation Buffer
           to Compensate for the Closing Effect on Final Approach

    • Authors: Stanley Förster, Michael Schultz, Hartmut Fricke
      First page: 29
      Abstract: The air traffic is mainly divided into en-route flight segments, arrival and departure segments inside the terminal maneuvering area, and ground operations at the airport. To support utilizing available capacity more efficiently, in our contribution we focus on the prediction of arrival procedures, in particular, the time-to-fly from the turn onto the final approach course to the threshold. The predictions are then used to determine advice for the controller regarding time-to-lose or time-to-gain for optimizing the separation within a sequence of aircraft. Most prediction methods developed so far provide only a point estimate for the time-to-fly. Complementary, we see the need to further account for the uncertain nature of aircraft movement based on a probabilistic prediction approach. This becomes very important in cases where the air traffic system is operated at its limits to prevent safety-critical incidents, e.g., separation infringements due to very tight separation. Our approach is based on the Quantile Regression Forest technique that can provide a measure of uncertainty of the prediction not only in form of a prediction interval but also by generating a probability distribution over the dependent variable. While the data preparation, model training, and tuning steps are identical to classic Random Forest methods, in the prediction phase, Quantile Regression Forests provide a quantile function to express the uncertainty of the prediction. After developing the model, we further investigate the interpretation of the results and provide a way for deriving advice to the controller from it. With this contribution, there is now a tool available that allows a more sophisticated prediction of time-to-fly, depending on the specific needs of the use case and which helps to separate arriving aircraft more efficiently.
      Citation: Aerospace
      PubDate: 2021-01-26
      DOI: 10.3390/aerospace8020029
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 30: Automated Defect Detection and
           Decision-Support in Gas Turbine Blade Inspection

    • Authors: Jonas Aust, Sam Shankland, Dirk Pons, Ramakrishnan Mukundan, Antonija Mitrovic
      First page: 30
      Abstract: Background—In the field of aviation, maintenance and inspections of engines are vitally important in ensuring the safe functionality of fault-free aircrafts. There is value in exploring automated defect detection systems that can assist in this process. Existing effort has mostly been directed at artificial intelligence, specifically neural networks. However, that approach is critically dependent on large datasets, which can be problematic to obtain. For more specialised cases where data are sparse, the image processing techniques have potential, but this is poorly represented in the literature. Aim—This research sought to develop methods (a) to automatically detect defects on the edges of engine blades (nicks, dents and tears) and (b) to support the decision-making of the inspector when providing a recommended maintenance action based on the engine manual. Findings—For a small sample test size of 60 blades, the combined system was able to detect and locate the defects with an accuracy of 83%. It quantified morphological features of defect size and location. False positive and false negative rates were 46% and 17% respectively based on ground truth. Originality—The work shows that image-processing approaches have potential value as a method for detecting defects in small data sets. The work also identifies which viewing perspectives are more favourable for automated detection, namely, those that are perpendicular to the blade surface.
      Citation: Aerospace
      PubDate: 2021-01-26
      DOI: 10.3390/aerospace8020030
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 31: On Probabilistic Risk of Aircraft Collision
           along Air Corridors

    • Authors: Luís M. B. C. Campos, Joaquim M. G. Marques
      First page: 31
      Abstract: The separation of aircraft in cruising flight in air corridors is based on the assurance of an extremely low probability of collision due to position inaccuracy caused by navigation errors, atmospheric disturbances, or other factors. The appropriate standard is the International Civil Aviation Organization (ICAO) Target Level of Safety (TLS) of frequency of collision less than 5 × 10−9 per flight hour. An upper bound for the collision probability per unit distance is the probability of coincidence, in the case of aircraft flying at the same speed along parallel tracks in the same direction. This leads to the case of two aircraft flying at a constant separation, for which at least three probabilities of coincidence can be calculated: (i) the maximum probability of coincidence at the most likely point; (ii) the cumulative probability of coincidence integrated along the flight path; and (iii) the cumulative probability of coincidence integrated over all space. These three probabilities of coincidence are applied to the old standard and new reduced vertical separations of 2000 ft and 1000 ft respectively, for comparison with the ICAO TLS, and also to assess their suitability as safety metrics. The possibility is raised of complementing the ICAO TLS 5 × 10−9 per hour, which is suitable for the cumulative probability of collision, by two additional safety metrics: (i) one per hour flown squared, which is suitable for comparison with the maximum joint probability density of collision; and (ii) another times hour flown, for comparison with the three-dimensional cumulative probability of coincidence. These three metrics (i) to (iii) have distinct dimensions, give different information, and could be alternatives or supplements.
      Citation: Aerospace
      PubDate: 2021-01-27
      DOI: 10.3390/aerospace8020031
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 32: Analysis of Risk-Based Operational Bird
           Strike Prevention

    • Authors: Isabel C. Metz, Joost Ellerbroek, Thorsten Mühlhausen, Dirk Kügler, Jacco M. Hoekstra
      First page: 32
      Abstract: Bird strike prevention in civil aviation has traditionally focused on the airport perimeter. Since the risk of especially damaging bird strikes outside the airport boundaries is rising, this paper investigates the safety potential of operational bird strike prevention involving pilots and controllers. In such a concept, controllers would be equipped with a bird strike advisory system, allowing them to delay departures which are most vulnerable to the consequences of bird strikes in case of high bird strike risk. An initial study has shown the strong potential of the concept to prevent bird strikes in case of perfect bird movement prediction. This paper takes the research to the next level by taking into account the limited predictability of bird tracks. As such, the collision avoidance algorithm is extended to a bird strike risk algorithm. The risk of bird strikes is calculated for birds expected to cross the extended runway center line and to cause aircraft damage upon impact. By specifically targeting these birds and excluding birds lingering on the runway which are taken care of by the local wildlife control, capacity reductions should be limited, and the implementation remain feasible. The extrapolation of bird tracks is performed by simple linear regression based on the bird positions known at the intended take-off times. To calculate the probability of collision, uncertainties resulting from variability in bird velocity and track are included. The study demonstrates the necessity to limit alerts to potentially damaging strikes with birds crossing the extended runway center line to keep the imposed delays tolerable for airports operating at their capacity limits. It is shown that predicting bird movements based on simple linear regression without considering individual bird behavior is insufficient to achieve a safety-effect. Hence, in-depth studies of multi-year bird data to develop bird behavior models and reliable predictions are recommended for future research. This is expected to facilitate the implementation of a bird strike advisory system satisfying both safety and capacity aspects.
      Citation: Aerospace
      PubDate: 2021-01-28
      DOI: 10.3390/aerospace8020032
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 33: Analysis of Aircraft Routing Strategies for
           North Atlantic Flights by Using AirTraf 2.0

    • Authors: Hiroshi Yamashita, Feijia Yin, Volker Grewe, Patrick Jöckel, Sigrun Matthes, Bastian Kern, Katrin Dahlmann, Christine Frömming
      First page: 33
      Abstract: Climate-optimized routing is an operational measure to effectively reduce the climate impact of aviation with a slight increase in aircraft operating costs. This study examined variations in the flight characteristics among five aircraft routing strategies and discusses several characteristics of those routing strategies concerning typical weather conditions over the North Atlantic. The daily variability in the North Atlantic weather patterns was analyzed by using the European Center Hamburg general circulation model (ECHAM) and the Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model in the specified dynamics mode from December 2008 to August 2018. All days of the ten complete winters and summers in the simulations were classified into five weather types for winter and into three types for summer. The obtained frequency for each of the weather types was in good agreement with the literature data; and then representative days for each weather type were selected. Moreover, a total of 103 North Atlantic flights of an Airbus A330 aircraft were simulated with five aircraft routing strategies for each representative day by using the EMAC model with the air traffic simulation submodel AirTraf. For every weather type, climate-optimized routing shows the lowest climate impact, at which a trade-off exists between the operating costs and the climate impact. Cost-optimized routing lies between the time- and fuel-optimized routings and achieves the lowest operating costs by taking the best compromise between flight time and fuel use. The aircraft routing for contrail avoidance shows the second lowest climate impact; however, this routing causes extra operating costs. Our methodology could be extended to statistical analysis based on long-term simulations to clarify the relationship between the aircraft routing characteristics and weather conditions.
      Citation: Aerospace
      PubDate: 2021-01-28
      DOI: 10.3390/aerospace8020033
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 34: Wind-Tunnel Measurement of Differential
           Pressure on the Surface of a Dynamically Inflatable Wing Cell

    • Authors: Diego Muniz Benedetti, Carlos Alberto Gurgel Veras
      First page: 34
      Abstract: An instrumentation system for in-situ measurement of the inner-outer pressure differential at the upper and lower surfaces of dynamically inflatable wings is designed and tested, revealing important insights into the aerodynamic characteristics of inflatable airfoils. Wind tunnel tests demonstrated full capability of low-pressure differential readings in the range of 1.0–120 Pa, covering speeds from 3 to 10 m/s at angles of attack from −20 to +25°. Readings were stable, presenting coefficients of variation from 2% to 7% over the operational flight envelope. The experimental data confirmed the occurrence of a bottom leading-edge recirculation bubble, linked to the low Reynolds regime and the presence of an air intake. It supported the proposition of a novel approach to aerodynamic characterization based on local pressure differentials, which takes in account the confined airflow structure and provides lift forces estimations compatible with practical observation. The results were also compatible with data previously obtained following different strategies and were shown to be effective for parameterizing the inflation and stall phenomena. Overall, the instrumentation may be applied straightforwardly as a flight-test equipment, and it can be further converted into collapse alert and prevention systems.
      Citation: Aerospace
      PubDate: 2021-01-29
      DOI: 10.3390/aerospace8020034
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 35: Validation of a Simulation Tool for an
           Environmentally Friendly Aircraft Cargo Fire Protection System

    • Authors: Arnav Pathak, Victor Norrefeldt, Marie Pschirer
      First page: 35
      Abstract: One of the objectives of the CleanSky-2 project is to develop an Environmentally Friendly Fire Protection (EFFP) system to substitute halon for the aircraft cargo hold. For this, an aircraft demonstrator including the cargo hold was equipped with a nitrogen-based fire suppression system. The demonstrator is located in the Flight Test Facility (FTF) low-pressure vessel and can thus be subjected to realistic cruise pressure conditions and take-off and descent pressure profiles. As a design tool, a zonally refined simulation model to predict the local oxygen and nitrogen concentration distribution in the cargo hold has been developed using the Indoor Environment Simulation Suite (IESS). The model allows for fast transient simulations of the suppression system operation. This paper presents a model validation case of knockdown during cruising, followed by a holding phase and descent.
      Citation: Aerospace
      PubDate: 2021-01-30
      DOI: 10.3390/aerospace8020035
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 36: Mitigation of Non-CO2 Aviation’s Climate
           Impact by Changing Cruise Altitudes

    • Authors: Sigrun Matthes, Ling Lim, Ulrike Burkhardt, Katrin Dahlmann, Simone Dietmüller, Volker Grewe, Amund S. Haslerud, Johannes Hendricks, Bethan Owen, Giovanni Pitari, Mattia Righi, Agnieszka Skowron
      First page: 36
      Abstract: Aviation is seeking for ways to reduce its climate impact caused by CO2 emissions and non-CO2 effects. Operational measures which change overall flight altitude have the potential to reduce climate impact of individual effects, comprising CO2 but in particular non-CO2 effects. We study the impact of changes of flight altitude, specifically aircraft flying 2000 feet higher and lower, with a set of global models comprising chemistry-transport, chemistry-climate and general circulation models integrating distinct aviation emission inventories representing such alternative flight altitudes, estimating changes in climate impact of aviation by quantifying radiative forcing and induced temperature change. We find in our sensitivity study that flying lower leads to a reduction of radiative forcing of non-CO2 effects together with slightly increased CO2 emissions and impacts, when cruise speed is not modified. Flying higher increases radiative forcing of non-CO2 effects by about 10%, together with a slight decrease of CO2 emissions and impacts. Overall, flying lower decreases aviation-induced temperature change by about 20%, as a decrease of non-CO2 impacts by about 30% dominates over slightly increasing CO2 impacts assuming a sustained emissions scenario. Those estimates are connected with a large but unquantified uncertainty. To improve the understanding of mechanisms controlling the aviation climate impact, we study the geographical distributions of aviation-induced modifications in the atmosphere, together with changes in global radiative forcing and suggest further efforts in order to reduce long standing uncertainties.
      Citation: Aerospace
      PubDate: 2021-01-31
      DOI: 10.3390/aerospace8020036
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 37: Fuel Tankering: Economic Benefits and
           Environmental Impact for Flights Up to 1500 NM (Full Tankering) and 2500
           NM (Partial Tankering)

    • Authors: Laurent Tabernier, Esther Calvo Fernández, Andreas Tautz, Robin Deransy, Peter Martin
      First page: 37
      Abstract: The majority of emissions from aviation come from the combustion of the fuel required to operate each flight. Keeping the fuel consumption required for a safe flight to the absolute minimum is therefore the simplest and most effective way to ensure that emissions from that flight are kept to a minimum. In practice, however, the fuel load is determined by each aircraft operator on the basis of a number of criteria maximizing first cost efficiency, rather than fuel savings. In this context, tankering is the practice of carrying more fuel than is necessary for the safe execution of the flight to avoid or minimize refueling at the destination airport. It offers an economic advantage when there is a significant difference in fuel prices between the departure and arrival airports, but considerably increases the amount of emissions produced, because the more fuel an aircraft carries, the heavier it is, and carrying this extra weight increases its fuel consumption. This paper presents the steps followed by EUROCONTROL in conducting a first study to estimate the number of times this practice would offer an economic benefit and the amount of extra CO2 emissions that would result. This study, limited to flights up to 1500 and 2500 NM, corresponding mainly to short and medium-haul flights, estimates that, in 2018, 21% of ECAC (In this paper, ECAC refers to the geographical region defined by the 44 member states that signed the European Civil Aviation Conference) flights would perform fuel tankering beneficially. This would represent a net saving of 265 M€ per year for the airlines, but the burning of 286,000 tonnes of additional fuel (equivalent to 0.54% of ECAC jet fuel used), or 901,000 tonnes of CO2 per year. At a time when aviation is challenged for its contribution to climate change, the use of fuel tankering for economic reasons is therefore highly questionable.
      Citation: Aerospace
      PubDate: 2021-01-31
      DOI: 10.3390/aerospace8020037
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 38: Constrained Urban Airspace Design for
           Large-Scale Drone-Based Delivery Traffic

    • Authors: Malik Doole, Joost Ellerbroek, Victor L. Knoop, Jacco M. Hoekstra
      First page: 38
      Abstract: Large-scale adoption of drone-based delivery in urban areas promise societal benefits with respect to emissions and on-ground traffic congestion, as well as potential cost savings for drone-based logistic companies. However, for this to materialise, the ability of accommodating high volumes of drone traffic in an urban airspace is one of the biggest challenges. For unconstrained airspace, it has been shown that traffic alignment and segmentation can be used to mitigate conflict probability. The current study investigates the application of these principles to a highly constrained airspace. We propose two urban airspace concepts, applying road-based analogies of two-way and one-way streets by imposing horizontal structure. Both of the airspace concepts employ heading-altitude rules to vertically segment cruising traffic according to their travel direction. These airspace configurations also feature transition altitudes to accommodate turning flights that need to decrease the flight speed in order to make safe turns at intersections. While using fast-time simulation experiments, the performance of these airspace concepts is compared and evaluated for multiple traffic demand densities in terms of safety, stability, and efficiency. The results reveal that an effective way to structure drone traffic in a constrained urban area is to have vertically segmented altitude layers with respect to travel direction as well as horizontal constraints imposed to the flow of traffic. The study also makes recommendations for areas of future research, which are aimed at supporting dynamic traffic demand patterns.
      Citation: Aerospace
      PubDate: 2021-02-01
      DOI: 10.3390/aerospace8020038
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 39: Modeling and Control of a Modular Iron Bird

    • Authors: Luciano Blasi, Mauro Borrelli, Egidio D’Amato, Luigi Emanuel di Grazia, Massimiliano Mattei, Immacolata Notaro
      First page: 39
      Abstract: This paper describes the control architecture and the control laws of a new concept of Modular Iron Bird aimed at reproducing flight loads to test mobile aerodynamic control surface actuators for small and medium size aircraft and Unmanned Aerial Vehicles. The iron bird control system must guarantee the actuation of counteracting forces. On one side, a hydraulic actuator simulates the hinge moments acting on the mobile surface due to aerodynamic and inertial effects during flight; on the other side, the actuator to be tested applies an active hinge moment to control the angular position of the same surface. Reference aerodynamic and inertial loads are generated by a flight simulation module to reproduce more realistic conditions arising during operations. The design of the control action is based on a dynamic model of the hydraulic plant used to generate loads. This system is controlled using a Proportional Integral Derivative control algorithm tuned with an optimization algorithm taking into account the closed loop dynamics of the actuator under testing, uncertainties and disturbances in the controlled plant. Numerical simulations are presented to show the effectiveness of the proposed architecture and control laws.
      Citation: Aerospace
      PubDate: 2021-02-02
      DOI: 10.3390/aerospace8020039
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 40: Optimal Sizing and Operation of Airport
           Infrastructures in Support of Electric-Powered Aviation

    • Authors: Lorenzo Trainelli, Francesco Salucci, Carlo E. D. Riboldi, Alberto Rolando, Federico Bigoni
      First page: 40
      Abstract: The adoption of hybrid-electric aircraft is expected to have a considerable impact on airport operations, with the need of new infrastructural requirements to support electric-powered fleets. In particular, battery-charging requirements shall play a decisive role. Preliminary investigations useful to perform scenario studies for the future implementation of electric-powered aviation can take advantage of the ARES methodology presented here, which provides the optimal solution to the sizing of airport battery recharging infrastructures. Based on the flight schedule and on the specifications of the aircraft fleet and the charging equipment, the solution assesses the number and type of charging points, the related electrical consumption in terms of energy and power, and further information needed to guarantee the required operational level while minimizing the procurement and operating costs. The method allows considering and comparing two charging strategies: plug-in recharge and battery swapping. Energy price variation in time is also taken into account and a full description of the optimal time scheduling of recharging operations is provided. Application studies to the reconfiguration of two existing aerodromes, a General Aviation airport and a large regional hub, are discussed, showing the potential of the proposed approach.
      Citation: Aerospace
      PubDate: 2021-02-03
      DOI: 10.3390/aerospace8020040
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 41: Analysis of Continuing Airworthiness
           Occurrences under the Prism of a Learning Framework

    • Authors: James Clare, Kyriakos I. Kourousis
      First page: 41
      Abstract: In this research paper fifteen mandatory occurrence reports are analysed. The purpose of this is to highlight the learning potential incidents such as these may possess for organisations involved in aircraft maintenance and continuing airworthiness management activities. The outputs from the mandatory occurrence reports are aligned in tabular form for ease of inclusion in human factors’ continuation training material. A new incident learning archetype is also introduced, which intends to represent how reported incidents can be managed and translated into lessons in support of preventing event recurrence. This ‘learning product’ centric model visually articulates activities such as capturing the reported information, establishing causation and the iterative nature of developing a learning product.
      Citation: Aerospace
      PubDate: 2021-02-05
      DOI: 10.3390/aerospace8020041
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 42: Towards Determining the Contrail Cirrus

    • Authors: Michael Ponater, Marius Bickel, Lisa Bock, Ulrike Burkhardt
      First page: 42
      Abstract: Contrail cirrus has been emphasized as the largest individual component of aircraft climate impact, yet respective assessments have been based mainly on conventional radiative forcing calculations. As demonstrated in previous research work, individual impact components can have different efficacies, i.e., their effectiveness to induce surface temperature changes may vary. Effective radiative forcing (ERF) has been proposed as a superior metric to compare individual impact contributions, as it may, to a considerable extent, include the effect of efficacy differences. Recent climate model simulations have provided a first estimate of contrail cirrus ERF, which turns out to be much smaller, by about 65%, than the conventional radiative forcing of contrail cirrus. The main reason for the reduction is that natural clouds exhibit a substantially lower radiative impact in the presence of contrail cirrus. Hence, the new result suggests a smaller role of contrail cirrus in the context of aviation climate impact (including proposed mitigation measures) than assumed so far. However, any conclusion in this respect should be drawn carefully as long as no direct simulations of the surface temperature response to contrail cirrus are available. Such simulations are needed in order to confirm the power of ERF for assessing contrail cirrus efficacy.
      Citation: Aerospace
      PubDate: 2021-02-06
      DOI: 10.3390/aerospace8020042
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 43: In-Flight Lift and Drag Estimation of an
           Unmanned Propeller-Driven Aircraft

    • Authors: Dominique Paul Bergmann, Jan Denzel, Ole Pfeifle, Stefan Notter, Walter Fichter, Andreas Strohmayer
      First page: 43
      Abstract: The high-power density and good scaling properties of electric motors enable new propulsion arrangements and aircraft configurations. This results in distributed propulsion systems allowing to make use of aerodynamic interaction effects between individual propellers and the wing of the aircraft, improving flight performance and thus reducing in-flight emissions. In order to systematically analyze these effects, an unmanned research platform was designed and built at the University of Stuttgart. As the aircraft is being used as a testbed for various flight performance studies in the field of distributed electric propulsion, a methodology for precise identification of its performance characteristics is required. One of the main challenges is the determination of the total drag of the aircraft to be able to identify an exact drag and lift polar in flight. For this purpose, an on-board measurement system was developed which allows for precise determination of the thrust of the aircraft which equals the total aerodynamic drag in steady, horizontal flight. The system has been tested and validated in flight using the unmanned free-flight test platform. The article provides an overview of the measuring system installed, discusses its functionality and shows results of the flight tests carried out.
      Citation: Aerospace
      PubDate: 2021-02-06
      DOI: 10.3390/aerospace8020043
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 44: Physics Guided Deep Learning for Data-Driven
           Aircraft Fuel Consumption Modeling

    • Authors: Mevlut Uzun, Mustafa Umut Demirezen, Gokhan Inalhan
      First page: 44
      Abstract: This paper presents a physics-guided deep neural network framework to estimate fuel consumption of an aircraft. The framework aims to improve data-driven models’ consistency in flight regimes that are not covered by data. In particular, we guide the neural network with the equations that represent fuel flow dynamics. In addition to the empirical error, we embed this physical knowledge as several extra loss terms. Results show that our proposed model accomplishes correct predictions on the labeled test set, as well as assuring physical consistency in unseen flight regimes. The results indicate that our model, while being applicable to the aircraft’s complete flight envelope, yields lower fuel consumption error measures compared to the model-based approaches and other supervised learning techniques utilizing the same training data sets. In addition, our deep learning model produces fuel consumption trends similar to the BADA4 aircraft performance model, which is widely utilized in real-world operations, in unseen and untrained flight regimes. In contrast, the other supervised learning techniques fail to produce meaningful results. Overall, the proposed methodology enhances the explainability of data-driven models without deteriorating accuracy.
      Citation: Aerospace
      PubDate: 2021-02-08
      DOI: 10.3390/aerospace8020044
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 45: Aircraft Flight Stabilizer System by CDM
           Designed Servo State-Feedback Controller

    • Authors: Ekachai Asa, Yoshio Yamamoto
      First page: 45
      Abstract: This research presents an automatic flight control system whose advantage is its ease of modification or maintenance while still effectively meeting the system’s performance requirement. This research proposes a mixed servo state-feedback system for controlling aircraft longitudinal and lateral-directional motion simultaneously based on the coefficient diagram method or CDM as the controller design methodology. The structure of this mixed servo state-feedback system is intuitive and straightforward, while CDM’s design processes are clear. Simulation results with aircraft linear and nonlinear models exhibit excellent performance in stabilizing and tracking the reference commands for both longitudinal and lateral-directional motion.
      Citation: Aerospace
      PubDate: 2021-02-08
      DOI: 10.3390/aerospace8020045
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 46: Special Issue: Civil and Military
           Airworthiness: Recent Developments and Challenges (Volume II)

    • Authors: Kyriakos I. Kourousis
      First page: 46
      Abstract: Effective safety management has always been a key objective for the broader airworthiness sector [...]
      Citation: Aerospace
      PubDate: 2021-02-08
      DOI: 10.3390/aerospace8020046
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 47: Machine Learning and Natural Language
           Processing for Prediction of Human Factors in Aviation Incident Reports

    • Authors: Tomás Madeira, Rui Melício, Duarte Valério, Luis Santos
      First page: 47
      Abstract: In the aviation sector, human factors are the primary cause of safety incidents. Intelligent prediction systems, which are capable of evaluating human state and managing risk, have been developed over the years to identify and prevent human factors. However, the lack of large useful labelled data has often been a drawback to the development of these systems. This study presents a methodology to identify and classify human factor categories from aviation incident reports. For feature extraction, a text pre-processing and Natural Language Processing (NLP) pipeline is developed. For data modelling, semi-supervised Label Spreading (LS) and supervised Support Vector Machine (SVM) techniques are considered. Random search and Bayesian optimization methods are applied for hyper-parameter analysis and the improvement of model performance, as measured by the Micro F1 score. The best predictive models achieved a Micro F1 score of 0.900, 0.779, and 0.875, for each level of the taxonomic framework, respectively. The results of the proposed method indicate that favourable predicting performances can be achieved for the classification of human factors based on text data. Notwithstanding, a larger data set would be recommended in future research.
      Citation: Aerospace
      PubDate: 2021-02-11
      DOI: 10.3390/aerospace8020047
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 48: Tuning of a Linear-Quadratic Stabilization
           System for an Anti-Aircraft Missile

    • Authors: Witold Bużantowicz
      First page: 48
      Abstract: A description is given of an application of a linear-quadratic regulator (LQR) for stabilizing the characteristics of an anti-aircraft missile, and an analytical method of selecting the weighting elements of the gain matrix in feedback loop is proposed. A novel method of LQR tuning via a single parameter ς was proposed and tested. The article supplements and develops the topics addressed in the author’s previous work. Its added value includes the observation that the solutions obtained are symmetric pairs, and that the tuning parameter ς proposed for the designed linear-quadratic regulator enables the selection of suitable parameters for the airframe stabilizing loop for the majority of the analytical solutions of the considered Riccati equation.
      Citation: Aerospace
      PubDate: 2021-02-12
      DOI: 10.3390/aerospace8020048
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 49: Novel Aero-Engine Multi-Disciplinary
           Preliminary Design Optimization Framework Accounting for Dynamic System
           Operation and Aircraft Mission Performance

    • Authors: Alexios Alexiou, Nikolaos Aretakis, Ioannis Kolias, Konstantinos Mathioudakis
      First page: 49
      Abstract: This paper presents a modular, flexible, extendable and fast-computational framework that implements a multidisciplinary, varying fidelity, multi-system approach for the conceptual and preliminary design of novel aero-engines. In its current status, the framework includes modules for multi-point steady-state engine design, aerodynamic design, engine geometry and weight, aircraft mission analysis, Nitrogen Oxide (NOx) emissions, control system design and integrated controller-engine transient-performance analysis. All the modules have been developed in the same software environment, ensuring consistent and transparent modeling while facilitating code maintainability, extendibility and integration at modeling and simulation levels. Any simulation workflow can be defined by appropriately combining the relevant modules. Different types of analysis can be specified such as sensitivity, design of experiment and optimization. Any combination of engine parameters can be selected as design variables, and multi-disciplinary requirements and constraints at different operating points in the flight envelope can be specified. The framework implementation is exemplified through the optimization of an ultra-high bypass ratio geared turbofan engine with a variable area fan nozzle, for which specific aircraft requirements and technology limits apply. Although the optimum design resulted in double-digit fuel-burn benefits compared to current technology engines, it did not meet engine-response requirements, highlighting the need to include transient-performance assessments as early as possible in the preliminary engine design phase.
      Citation: Aerospace
      PubDate: 2021-02-12
      DOI: 10.3390/aerospace8020049
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 50: Climate Impact Mitigation Potential of
           European Air Traffic in a Weather Situation with Strong Contrail Formation

    • Authors: Benjamin Lührs, Florian Linke, Sigrun Matthes, Volker Grewe, Feijia Yin
      First page: 50
      Abstract: Air traffic contributes to anthropogenic global warming by about 5% due to CO2 emissions and non-CO2 effects, which are primarily caused by the emission of NOx and water vapor as well as the formation of contrails. Since—in the long term—the aviation industry is expected to maintain its trend to grow, mitigation measures are required to counteract its negative effects upon the environment. One of the promising operational mitigation measures that has been a subject of the EU project ATM4E is climate-optimized flight planning by considering algorithmic climate change functions that allow for the quantification of aviation-induced climate impact based on the emission’s location and time. Here, we describe the methodology developed for the use of algorithmic climate change functions in trajectory optimization and present the results of its application to the planning of about 13,000 intra-European flights on one specific day with strong contrail formation over Europe. The optimization problem is formulated as bi-objective continuous optimal control problem with climate impact and fuel burn being the two objectives. Results on an individual flight basis indicate that there are three major classes of different routes that are characterized by different shapes of the corresponding Pareto fronts representing the relationship between climate impact reduction and fuel burn increase. On average, for the investigated weather situation and traffic scenario, a climate impact reduction in the order of 50% can be achieved by accepting 0.75% of additional fuel burn. Higher mitigation gains would only be available at much higher fuel penalties, e.g., a climate impact reduction of 76% associated with a fuel penalty of 12.8%. However, these solutions represent much less efficient climate impact mitigation options.
      Citation: Aerospace
      PubDate: 2021-02-12
      DOI: 10.3390/aerospace8020050
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 51: Radio Frequency Interference Measurements for
           a Radio Astronomy Observatory Site in Indonesia

    • Authors: Sitompul, Manik, Batubara, Suhandi
      First page: 51
      Abstract: We report on the measurements of radio frequency interference (RFI) at Mount Timau, Kupang, Indonesia, which is intended to host a future radio astronomy observatory. These measurements were taken twice in October 2020 and December 2020 to obtain the RFI environment, at frequencies between 70 and 7000 MHz. Due to the limitations of the measurement data, the results presented in this paper are based on peak detection rather than statistical analysis. Based on the measurement results, the frequency interval between 70–88 MHz and 120–150 MHz is relatively quiet, and the frequency range of 150–300 MHz is relatively clear. The frequency interval of 300 to 800 MHz is relatively quiet, except at the frequency of 600 MHz. The frequency range of 800–1400 MHz is also relatively quiet. The predominant terrestrial services in this band are at 840 MHz, with an amplitude around 32 dB, and 916 MHz, with an amplitude around 12 dB, and the global system for mobile (GSM) signals around 954 MHz have an amplitude around 20 dB above the noise floor. The frequency range of 1400–7000 MHz is also relatively quiet. In this band frequency, we can see RFI at 2145 and 2407 MHz, emitted by local Wi-Fi, and at 2683 MHz, with amplitudes of 18, 40 and 15 dB, respectively, from the noise level. We conclude that, for this period, the frequency band allocated for astronomy can possibly be used for radio telescope development.
      Citation: Aerospace
      PubDate: 2021-02-17
      DOI: 10.3390/aerospace8020051
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 52: Vibration Response Aspects of a Main Landing
           Gear Composite Door Designed for High-Speed Rotorcraft

    • Authors: Maurizio Arena, Antonio Chiariello, Martina Castaldo, Luigi Di Palma
      First page: 52
      Abstract: One of the crucial issues affecting the structural safety of propeller vehicles is the propeller tonal excitation and related vibrations. Propeller rotation during flight generates vibrating sources depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust, and blade geometry. Generally, the higher energy levels generated are confined to 1st blade passing frequency (BPF) and its harmonics, while additional broadband components, mainly linked with the blade shape, the developed engine power, and the turbulent boundary layer (TBL), also contribute to the excitation levels. The vibrations problem takes on particular relevance in the case of composite structures. The laminates in fact could exert damping levels generally lower than metallic structures, where the greater amount of bolted joints allow for dissipating more vibration energy. The prediction and reduction of aircraft vibration levels are therefore significant considerations for conventional propeller aircrafts now entering the commercial market as well as for models currently being developed. In the Clean Sky 2 framework, the present study focuses on a practical case inherent to the AIRBUS-Racer program aiming to design and develop a multi-tasking fast rotorcraft. This paper defines a finite elements (FE)-based procedure for the characterization of the vibration levels of a main landing gear (MLG) composite door with respect to the expected operating tonal loads. A parametric assessment was carried out to evaluate the principal modal parameters (transfer functions and respective resonance frequencies, mode shapes, and damping coefficients) of the landing gear-door assembly in order to achieve reduced vibration levels. Based on the FE analysis results, the influence of the extra-damping, location, and number of ballast elements, the boundary conditions were investigated with respect to failure scenarios of the kinematic line opening the study towards aeroelastic evaluations. Further experimental ground test results serve as a validation database for the prediction numerical methods representative of the composite door dynamic response.
      Citation: Aerospace
      PubDate: 2021-02-19
      DOI: 10.3390/aerospace8020052
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 53: A Numerical and Experimental Investigation of
           the Convective Heat Transfer on a Small Helicopter Rotor Test Setup

    • Authors: Abdallah Samad, Eric Villeneuve, François Morency, Christophe Volat
      First page: 53
      Abstract: In-flight icing affects helicopter performance, limits its operations, and reduces safety. The convective heat transfer is an important parameter in numerical icing simulations and state-of-the-art icing/de-icing codes utilize important computing resources when calculating it. The BEMT–RHT and UVLM–RHT offer low- and medium-fidelity approaches to estimate the rotor heat transfer (RHT). They are based on a coupling between Blade element momentum theory (BEMT) or unsteady vortex lattice method (UVLM), and a CFD-determined heat transfer correlation. The latter relates the Frossling number (Fr) to the Reynolds number (Re) and effective angle of attack (αEff). In a series of experiments carried out at the Anti-icing Materials International Laboratory (AMIL), this paper serves as a proof of concept of the proposed correlations. The objective is to propose correlations for the experimentally measured rotor heat transfer data. Specifically, the Frx is correlated with the Re and αEff in a similar form as the proposed CFD-based correlations. A fixed-wing setup is first used as a preliminary step to verify the heat transfer measurements of the icing wind tunnel (IWT). Tests are conducted at a = 0°, for a range of 4.76 ´ 105 £ Re £ 1.36 ´ 106 and at 10 non-dimensional surface wrap locations −0.62 £ (S/c) £ + 0.87. Later, a rotor setup is used to build the novel heat transfer correlation, tests are conducted at two pitch angles ((q) = 0° and 6°) for a range of rotor speeds (500 RPM £ (W) £ 1500 RPM), three different radial positions ((r/R) = 0.6, 0.75 and 0.95), and 0 £ S/c £ + 0.58. Results indicate that the fixed-wing Frx at the stagnation point was in the range of literature experimental data, and within 8% of fully turbulent CFD simulations. The FrAvg also agrees with CFD predictions, with an average discrepancy of 1.4%. For the rotor, the W caused a similar increase of Frx for the tests at q = 0° and those at q = 6°. Moreover, the Frx behavior changed significantly with r/R, suggesting the αEff had a significant effect on the Frx. Finally, the rotor data are first correlated with Rem(at each S/c) for q = 0° to establish the correlation parameters, and a term for the αEff is then added to also account for the tests at q = 6°. The correlations fit the data with an error between 2.1% and 14%, thus justifying the use of a coupled approach for the BEMT–RHT and UVLM–RHT.
      Citation: Aerospace
      PubDate: 2021-02-20
      DOI: 10.3390/aerospace8020053
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 54: Configuration Study of Electric Helicopters
           for Urban Air Mobility

    • Authors: Julia A. Cole, Lauren Rajauski, Andrew Loughran, Alexander Karpowicz, Stefanie Salinger
      First page: 54
      Abstract: There is currently interest in the design of small electric vertical take-off and landing aircraft to alleviate ground traffic and congestion in major urban areas. To support progress in this area, a conceptual design method for single-main-rotor and lift-augmented compound electric helicopters has been developed. The design method was used to investigate the feasible design space for electric helicopters based on varying mission profiles and technology assumptions. Within the feasible design space, it was found that a crossover boundary exists as a function of cruise distance and hover time where the most efficient configuration changes from a single-main-rotor helicopter to a lift-augmented compound helicopter. In general, for longer cruise distances and shorter hover times, the lift-augmented compound helicopter is the more efficient configuration. An additional study was conducted to investigate the potential benefits of decoupling the main rotor from the tail rotor. This study showed that decoupling the main rotor and tail rotor has the potential to reduce the total mission energy required in all cases, allowing for increases in mission distances and hover times on the order of 5% for a given battery size.
      Citation: Aerospace
      PubDate: 2021-02-20
      DOI: 10.3390/aerospace8020054
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 55: An Ultrasonic-Based Detection of Air-Leakage
           for the Unclosed Components of Aircraft

    • Authors: Yanlin Lyu, Muhammad Jamil, Pengfei Ma, Ning He, Munish Kumar Gupta, Aqib Mashood Khan, Danil Yurievich Pimenov
      First page: 55
      Abstract: Air-leakage detection is among the most important processes at the assembly stage of unclosed components, especially for large aircraft. A series of air-leakage detecting methods are generally applied during the final assembly, nevertheless, many of them are less effective to detect the leakage at the assembly stage. The present study aims to discuss the principles of ultrasonic generation in negative pressure conditions to detect the air-leakage. An ultrasonic-based detection method is proposed and designed to detect the air-leakage of unclosed components for aircraft. A relationship between the acoustic power, sound pressure, and the leak aperture detection distance was identified and discussed. A leakage rate model related to leakage rate, leak aperture, and system pressure was implemented and confirmed through experiments. Findings have indicated that the air-leakage can be detected effectively within a detection distance of 0.8 m and a leak aperture greater or equal to 0.4 mm with this method. Besides, the leak location, leak aperture, and leakage rate was acquired in an accurate and fast way. It is an effective method of detecting the air-leakage of unclosed components at the aircraft assembly stage reducing the testing time, energy consumption, and cost for the air-leakage detection in the final assembly stage of large aircraft.
      Citation: Aerospace
      PubDate: 2021-02-20
      DOI: 10.3390/aerospace8020055
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 56: A Study on Thermal Buckling and Mode Jumping
           of Metallic and Composite Plates

    • Authors: Javier Gutiérrez Álvarez, Chiara Bisagni
      First page: 56
      Abstract: Composite plates in post-buckling regime can experience mode jumping in their buckling shape, suddenly increasing the number of half-waves. This phenomenon can be advantageous, because the shape change could be used for local morphing or structural adaptability in future aerospace structures. A study of this phenomenon under heating is here presented, combining numerical and experimental techniques. At first, a set of parametric analysis was conducted to identify composite panels that present a mode jump when heated. Three plates were selected, one in aluminum alloy 2024T3, and two in AS4/8552 composite material, with layup [30/−30/5/−5]s and [35/−35/10/−10]s. The plates were tested in a new test setup for thermal buckling based on low thermal expansion fixtures. The mode jumping was successfully obtained experimentally for both composite plates. Numerical simulations predicted the general trends for all plates, and the mode jumps for the composite plates.
      Citation: Aerospace
      PubDate: 2021-02-21
      DOI: 10.3390/aerospace8020056
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 57: Spectral Correlation for Signal Presence
           Detection and Frequency Acquisition of Small Satellites

    • Authors: Jonas Hofmann, Andreas Knopp, Chad M. Spooner, Giovanni Minelli, James Newman
      First page: 57
      Abstract: Challenges in interference-limited satellite detection arising from the low-earth orbit (LEO) and the Industrial, Scientific and Medical (ISM) frequency bands are addressed. In particular, a novel signal presence detector based on cyclostationary signal properties is proposed and analyzed for a low signal-to-noise-plus-interference ratio (SINR) regime. The performance of the proposed detector, which is applicable to various small-satellite scenarios, is evaluated on both simulated and real-world measurement data. This measurement data has been collected from the scientific satellite mission “Picosats Realizing Orbital Propagation Calibrations using Beacon Emitters” (PROPCUBE).
      Citation: Aerospace
      PubDate: 2021-02-22
      DOI: 10.3390/aerospace8020057
      Issue No: Vol. 8, No. 2 (2021)
  • Aerospace, Vol. 8, Pages 11: Evolution of Emission Species in an
           Aero-Engine Turbine Stator

    • Authors: André A.V. Perpignan, Stella Grazia Tomasello, Arvind Gangoli Rao
      First page: 11
      Abstract: Future energy and transport scenarios will still rely on gas turbines for energy conversion and propulsion. Gas turbines will play a major role in energy transition and therefore gas turbine performance should be improved, and their pollutant emissions decreased. Consequently, designers must have accurate performance and emission prediction tools. Usually, pollutant emission prediction is limited to the combustion chamber as the composition at its outlet is considered to be “chemically frozen”. However, this assumption is not necessarily valid, especially with the increasing turbine inlet temperatures and operating pressures that benefit engine performance. In this work, Computational Fluid Dynamics (CFD) and Chemical Reactor Network (CRN) simulations were performed to analyse the progress of NOx and CO species through the high-pressure turbine stator. Simulations considering turbulence-chemistry interaction were performed and compared with the finite-rate chemistry approach. The results show that progression of some relevant reactions continues to take place within the turbine stator. For an estimated cruise condition, both NO and CO concentrations are predicted to increase along the stator, while for the take-off condition, NO increases and CO decreases within the stator vanes. Reaction rates and concentrations are correlated with the flow structure for the cruise condition, especially in the near-wall flow field and the blade wakes. However, at the higher operating pressure and temperature encountered during take-off, reactions seem to be dependent on the residence time rather than on the flow structures. The inclusion of turbulence-chemistry interaction significantly changes the results, while heat transfer on the blade walls is shown to have minor effects.
      Citation: Aerospace
      PubDate: 2021-01-04
      DOI: 10.3390/aerospace8010011
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 12: Axial Flow Compressor Stability Enhancement:
           Circumferential T-Shape Grooves Performance Investigation

    • Authors: Marco Porro, Richard Jefferson-Loveday, Ernesto Benini
      First page: 12
      Abstract: This work focuses its attention on possibilities to enhance the stability of an axial compressor using a casing treatment technique. Circumferential grooves machined into the case are considered and their performances evaluated using three-dimensional steady state computational simulations. The effects of rectangular and new T-shape grooves on NASA Rotor 37 performances are investigated, resolving in detail the flow field near the blade tip in order to understand the stall inception delay mechanism produced by the casing treatment. First, a validation of the computational model was carried out analysing a smooth wall case without grooves. The comparisons of the total pressure ratio, total temperature ratio and adiabatic efficiency profiles with experimental data highlighted the accuracy and validity of the model. Then, the results for a rectangular groove chosen as the baseline case demonstrated that the groove interacts with the tip leakage flow, weakening the vortex breakdown and reducing the separation at the blade suction side. These effects delay stall inception, improving compressor stability. New T-shape grooves were designed keeping the volume as a constant parameter and their performances were evaluated in terms of stall margin improvement and efficiency variation. All the configurations showed a common efficiency loss near the peak condition and some of them revealed a stall margin improvement with respect to the baseline. Due to their reduced depth, these new configurations are interesting because they enable the use of a thinner light-weight compressor case as is desirable in aerospace applications.
      Citation: Aerospace
      PubDate: 2021-01-04
      DOI: 10.3390/aerospace8010012
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 13: Quasi-3D Aerodynamic Analysis Method for
           Blended-Wing-Body UAV Configurations

    • Authors: Pericles Panagiotou, Thomas Dimopoulos, Stylianos Dimitriou, Kyros Yakinthos
      First page: 13
      Abstract: The current study presents a low-fidelity, quasi-3D aerodynamic analysis method for Blended-Wing-Body (BWB) Unmanned Aerial Vehicle (UAV) configurations. A tactical BWB UAV experimental prototype is used as a reference platform. The method utilizes 2D panel method analyses and theoretical aerodynamic calculations to rapidly compute lift and pitching moment coefficients. The philosophy and the underlying theoretical and semi-empirical equations of the proposed method are extensively described. Corrections related to control surfaces deflection and ground effect are also suggested, so that the BWB pitching stability and trimming calculations can be supported. The method is validated against low-fidelity 3D aerodynamic analysis methods and high-fidelity, Computational Fluid Dynamics (CFD) results for various BWB configurations. The validation procedures show that the proposed method is considerably more accurate than existing low-fidelity ones, can provide predictions for both lift and pitching moment coefficients and requires far less computational resources and time when compared to CFD modeling. Hence, it can serve as a valuable aerodynamics and stability analysis tool for BWB UAV configurations.
      Citation: Aerospace
      PubDate: 2021-01-06
      DOI: 10.3390/aerospace8010013
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 14: Climate Impact Mitigation Potential of
           Formation Flight

    • Authors: Tobias Marks, Katrin Dahlmann, Volker Grewe, Volker Gollnick, Florian Linke, Sigrun Matthes, Eike Stumpf, Majed Swaid, Simon Unterstrasser, Hiroshi Yamashita, Clemens Zumegen
      First page: 14
      Abstract: The aerodynamic formation flight, which is also known as aircraft wake-surfing for efficiency (AWSE), enables aircraft to harvest the energy inherent in another aircraft’s wake vortex. As the thrust of the trailing aircraft can be reduced during cruise flight, the resulting benefit can be traded for longer flight time, larger range, less fuel consumption, or cost savings accordingly. Furthermore, as the amount and location of the emissions caused by the formation are subject to change and saturation effects in the cumulated wake of the formation can occur, AWSE can favorably affect the climate impact of the corresponding flights. In order to quantify these effects, we present an interdisciplinary approach combining the fields of aerodynamics, aircraft operations and atmospheric physics. The approach comprises an integrated model chain to assess the climate impact for a given air traffic scenario based on flight plan data, aerodynamic interactions between the formation members, detailed trajectory calculations as well as on an adapted climate model accounting for the saturation effects resulting from the proximity of the emissions of the formation members. Based on this approach, we derived representative AWSE scenarios for the world’s major airports by analyzing and assessing flight plans. The resulting formations were recalculated by a trajectory calculation tool and emission inventories for the scenarios were created. Based on these inventories, we quantitatively estimated the climate impact using the average temperature response (ATR) as climate metric, calculated as an average global near surface temperature change over a time horizon of 50 years. It is shown, that AWSE as a new operational procedure has a significant mitigation potential on climate impact. For a global formation flight scenario, we estimated the average relative change of climate response to range between 22% and 24% while the relative fuel saving effects sum up to 5–6%.
      Citation: Aerospace
      PubDate: 2021-01-08
      DOI: 10.3390/aerospace8010014
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 15: Effect of Increased Cabin Recirculation
           Airflow Fraction on Relative Humidity, CO2 and TVOC

    • Authors: Victor Norrefeldt, Florian Mayer, Britta Herbig, Ria Ströhlein, Pawel Wargocki, Fang Lei
      First page: 15
      Abstract: In the CleanSky 2 ComAir study, subject tests were conducted in the Fraunhofer Flight Test Facility cabin mock-up. This mock-up consists of the front section of a former in-service A310 hosting up to 80 passengers. In 12 sessions the outdoor/recirculation airflow ratio was altered from today’s typically applied fractions to up to 88% recirculation fraction. This leads to increased relative humidity, carbon dioxide (CO2) and Total Volatile Organic Compounds (TVOC) levels in the cabin air, as the emissions by passengers become less diluted by outdoor, dry air. This paper describes the measured increase of relative humidity, CO2 and TVOC level in the cabin air for the different test conditions.
      Citation: Aerospace
      PubDate: 2021-01-13
      DOI: 10.3390/aerospace8010015
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 16: Proof of Concept Study for Fuselage Boundary
           Layer Ingesting Propulsion

    • Authors: Arne Seitz, Anaïs Luisa Habermann, Fabian Peter, Florian Troeltsch, Alejandro Castillo Pardo, Biagio Della Corte, Martijn van Sluis, Zdobyslaw Goraj, Mariusz Kowalski, Xin Zhao, Tomas Grönstedt, Julian Bijewitz, Guido Wortmann
      First page: 16
      Abstract: Key results from the EU H2020 project CENTRELINE are presented. The research activities undertaken to demonstrate the proof of concept (technology readiness level—TRL 3) for the so-called propulsive fuselage concept (PFC) for fuselage wake-filling propulsion integration are discussed. The technology application case in the wide-body market segment is motivated. The developed performance bookkeeping scheme for fuselage boundary layer ingestion (BLI) propulsion integration is reviewed. The results of the 2D aerodynamic shape optimization for the bare PFC configuration are presented. Key findings from the high-fidelity aero-numerical simulation and aerodynamic validation testing, i.e., the overall aircraft wind tunnel and the BLI fan rig test campaigns, are discussed. The design results for the architectural concept, systems integration and electric machinery pre-design for the fuselage fan turbo-electric power train are summarized. The design and performance implications on the main power plants are analyzed. Conceptual design solutions for the mechanical and aero-structural integration of the BLI propulsive device are introduced. Key heuristics deduced for PFC conceptual aircraft design are presented. Assessments of fuel burn, NOx emissions, and noise are presented for the PFC aircraft and benchmarked against advanced conventional technology for an entry-into-service in 2035. The PFC design mission fuel benefit based on 2D optimized PFC aero-shaping is 4.7%.
      Citation: Aerospace
      PubDate: 2021-01-13
      DOI: 10.3390/aerospace8010016
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 17: The Efficacy of Operational Bird Strike

    • Authors: Isabel Metz, Joost Ellerbroek, Thorsten Mühlhausen, Dirk Kügler, Stefan Kern, Jacco Hoekstra
      First page: 17
      Abstract: Involving air traffic controllers and pilots into the bird strike prevention process is considered an essential step to increase aviation and avian safety. Prior to implementing operational measures such as real-time warning systems, it is vital to evaluate their feasibility. This paper studies the efficacy of a bird strike advisory system for air traffic control. In addition to the potential safety benefit, the possible impact on airport operations is analyzed. To this end, a previously developed collision avoidance algorithm underlying the system was tested in fast-time Monte Carlo simulations involving various air traffic and bird densities to obtain representative conclusions for different operational conditions. The results demonstrate the strong safety potential of operational bird strike prevention in case of precise bird movement prediction. Unless airports operate close to their capacity limits while bird abundance is high, the induced delays remain tolerable. Prioritization of hazardous strikes involving large individuals as well as flocks of birds are expected to support operational feasibility in all conditions.
      Citation: Aerospace
      PubDate: 2021-01-14
      DOI: 10.3390/aerospace8010017
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 18: Unmanned Aerial Vehicle Pitch Control Using
           Deep Reinforcement Learning with Discrete Actions in Wind Tunnel Test

    • Authors: Daichi Wada, Sergio A. Araujo-Estrada, Shane Windsor
      First page: 18
      Abstract: Deep reinforcement learning is a promising method for training a nonlinear attitude controller for fixed-wing unmanned aerial vehicles. Until now, proof-of-concept studies have demonstrated successful attitude control in simulation. However, detailed experimental investigations have not yet been conducted. This study applied deep reinforcement learning for one-degree-of-freedom pitch control in wind tunnel tests with the aim of gaining practical understandings of attitude control application. Three controllers with different discrete action choices, that is, elevator angles, were designed. The controllers with larger action rates exhibited better performance in terms of following angle-of-attack commands. The root mean square errors for tracking angle-of-attack commands decreased from 3.42° to 1.99° as the maximum action rate increased from 10°/s to 50°/s. The comparison between experimental and simulation results showed that the controller with a smaller action rate experienced the friction effect, and the controllers with larger action rates experienced fluctuating behaviors in elevator maneuvers owing to delay. The investigation of the effect of friction and delay on pitch control highlighted the importance of conducting experiments to understand actual control performances, specifically when the controllers were trained with a low-fidelity model.
      Citation: Aerospace
      PubDate: 2021-01-14
      DOI: 10.3390/aerospace8010018
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 19: Numerical Analysis of Flow across Brush
           Elements Based on a 2-D Staggered Tube Banks Model

    • Authors: Xiaolei Song, Meihong Liu, Xiangping Hu, Xueliang Wang, Taohong Liao, Junfeng Sun
      First page: 19
      Abstract: In order to improve efficiency in turbomachinery, brush seal replaces labyrinth seals widely in the secondary air system. A 2-d staggered tube bank model is adopted to simulate the gas states and the pressure character in brush seal, and computational fluid dynamics (CFD) is used to solve the model in this paper. According to the simulation results, the corrected formula of the Euler number and dimensionless pressure are given. The results show that gas expands when flow through the bristle pack, and the gas expansion closes to an isotherm process. The dynamic pressure increases with decreasing static pressure. The Euler number can reflect the seal performance of brush seals in leakage characteristics. Compared with increasing the number of rows, the reduction of the gap is a higher-efficiency method to increase the Euler number. The Euler number continually increases as the gap decreases. However, with the differential pressure increasing, Euler number first increases and then decreases as the number of rows increases. Finally, the pressure distribution on the surface of end rows is asymmetric, and it may increase the friction between the bristles and the back plate.
      Citation: Aerospace
      PubDate: 2021-01-15
      DOI: 10.3390/aerospace8010019
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 20: Review of State-of-the-Art Green
           Monopropellants: For Propulsion Systems Analysts and Designers

    • Authors: Ahmed E. S. Nosseir, Angelo Cervone, Angelo Pasini
      First page: 20
      Abstract: Current research trends have advanced the use of “green propellants” on a wide scale for spacecraft in various space missions; mainly for environmental sustainability and safety concerns. Small satellites, particularly micro and nanosatellites, evolved from passive planetary-orbiting to being able to perform active orbital operations that may require high-thrust impulsive capabilities. Thus, onboard primary and auxiliary propulsion systems capable of performing such orbital operations are required. Novelty in primary propulsion systems design calls for specific attention to miniaturization, which can be achieved, along the above-mentioned orbital transfer capabilities, by utilizing green monopropellants due to their relative high performance together with simplicity, and better storability when compared to gaseous and bi-propellants, especially for miniaturized systems. Owing to the ongoing rapid research activities in the green-propulsion field, it was necessary to extensively study and collect various data of green monopropellants properties and performance that would further assist analysts and designers in the research and development of liquid propulsion systems. This review traces the history and origins of green monopropellants and after intensive study of physicochemical properties of such propellants it was possible to classify green monopropellants to three main classes: Energetic Ionic Liquids (EILs), Liquid NOx Monopropellants, and Hydrogen Peroxide Aqueous Solutions (HPAS). Further, the tabulated data and performance comparisons will provide substantial assistance in using analysis tools—such as: Rocket Propulsion Analysis (RPA) and NASA CEA—for engineers and scientists dealing with chemical propulsion systems analysis and design. Some applications of green monopropellants were discussed through different propulsion systems configurations such as: multi-mode, dual mode, and combined chemical–electric propulsion. Although the in-space demonstrated EILs (i.e., AF-M315E and LMP-103S) are widely proposed and utilized in many space applications, the investigation transpired that NOx fuel blends possess the highest performance, while HPAS yield the lowest performance even compared to hydrazine.
      Citation: Aerospace
      PubDate: 2021-01-15
      DOI: 10.3390/aerospace8010020
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 21: Dynamic Characterization of a High-Altitude
           Balloon during a Flight Campaign for the Detection of ISM Radio Background
           in the Stratosphere

    • Authors: Matteo Gemignani, Salvo Marcuccio
      First page: 21
      Abstract: Sounding balloons, available at very low cost from commercial vendors and operable with minimal training, have an excellent potential as testing platforms in the near-space environment. The work reported here was motivated by the need to perform an experimental assessment of the radio frequency (RF) background present in the ISM (Industrial, Scientific and Medical) bands, namely 868 MHz (Ultra High Frequency—UHF) and 2.4 GHz (S-Band), simulating the operational environment of a Low Earth Orbit (LEO) constellation forInternet of Things (IoT) telecommunications. To this end, five balloons were flown with a dedicated RF payload. Along with the radio measurements, the flights provided a convenient opportunity to collect data on the dynamic behavior of the payload gondola. We report on the system design and the operational phase of the mission, and discuss the data collected throughout the successful flight campaign. As a result, a preliminary understanding of the gondola dynamics has been gained, including both linear accelerations and attitude oscillations. It is also concluded that the two ISM bands considered are actually suitable for IoT ground-to-LEO links.
      Citation: Aerospace
      PubDate: 2021-01-17
      DOI: 10.3390/aerospace8010021
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 22: Electric Propulsion Methods for Small
           Satellites: A Review

    • Authors: Dillon O’Reilly, Georg Herdrich, Darren F. Kavanagh
      First page: 22
      Abstract: Over 2500 active satellites are in orbit as of October 2020, with an increase of ~1000 smallsats in the past two years. Since 2012, over 1700 smallsats have been launched into orbit. It is projected that by 2025, there will be 1000 smallsats launched per year. Currently, these satellites do not have sufficient delta v capabilities for missions beyond Earth orbit. They are confined to their pre-selected orbit and in most cases, they cannot avoid collisions. Propulsion systems on smallsats provide orbital manoeuvring, station keeping, collision avoidance and safer de-orbit strategies. In return, this enables longer duration, higher functionality missions beyond Earth orbit. This article has reviewed electrostatic, electrothermal and electromagnetic propulsion methods based on state of the art research and the current knowledge base. Performance metrics by which these space propulsion systems can be evaluated are presented. The article outlines some of the existing limitations and shortcomings of current electric propulsion thruster systems and technologies. Moreover, the discussion contributes to the discourse by identifying potential research avenues to improve and advance electric propulsion systems for smallsats. The article has placed emphasis on space propulsion systems that are electric and enable interplanetary missions, while alternative approaches to propulsion have also received attention in the text, including light sails and nuclear electric propulsion amongst others.
      Citation: Aerospace
      PubDate: 2021-01-18
      DOI: 10.3390/aerospace8010022
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 23: Acknowledgment to Reviewers of Aerospace in

    • Authors: Aerospace Editorial Office Aerospace Editorial Office
      First page: 23
      Abstract: Peer review is the driving force of journal development, and reviewers are gatekeepers who ensure that Aerospace maintains its standards for the high quality of its published papers [...]
      Citation: Aerospace
      PubDate: 2021-01-19
      DOI: 10.3390/aerospace8010023
      Issue No: Vol. 8, No. 1 (2021)
  • Aerospace, Vol. 8, Pages 1: Advanced Materials and Technologies for
           Compressor Blades of Small Turbofan Engines

    • Authors: Dmytro Pavlenko, Yaroslav Dvirnyk, Radoslaw Przysowa
      First page: 1
      Abstract: Manufacturing costs, along with operational performance, are among the major factors determining the selection of the propulsion system for unmanned aerial vehicles (UAVs), especially for aerial targets and cruise missiles. In this paper, the design requirements and operating parameters of small turbofan engines for single-use and reusable UAVs are analysed to introduce alternative materials and technologies for manufacturing their compressor blades, such as sintered titanium, a new generation of aluminium alloys and titanium aluminides. To assess the influence of severe plastic deformation (SPD) on the hardening efficiency of the proposed materials, the alloys with the coarse-grained and submicrocrystalline structure were studied. Changes in the physical and mechanical properties of materials were taken into account. The thermodynamic analysis of the compressor was performed in a finite element analysis system (ANSYS) to determine the impact of gas pressure and temperature on the aerodynamic surfaces of compressor blades of all stages. Based on thermal and structural analysis, the stress and temperature maps on compressor blades and vanes were obtained, taking into account the physical and mechanical properties of advanced materials and technologies of their processing. The safety factors of the components were established based on the assessment of their stress-strength characteristics. Thanks to nomograms, the possibility of using the new materials in five compressor stages was confirmed in view of the permissible operating temperature and safety factor. The proposed alternative materials for compressor blades and vanes meet the design requirements of the turbofan at lower manufacturing costs.
      Citation: Aerospace
      PubDate: 2020-12-22
      DOI: 10.3390/aerospace8010001
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 2: Parametric Modeling of a Long-Range Aircraft
           under Consideration of Engine-Wing Integration

    • Authors: Matthias Schulze, Jens Neumann, Thomas Klimmek
      First page: 2
      Abstract: The purpose of this paper is to investigate the influence of the engine position and mass as well as the pylon stiffness on the aeroelastic stability of a long-range wide-body transport aircraft. As reference configuration, DLR’s (German Aerospace Center/Deutsches Zentrum für Luft und Raumfahrt) generic aircraft configuration DLR-D250 is taken. The structural, mass, loads, and optimization models for the reference and a modified configuration with different engine and pylon parameters are set up using DLR’s automatized aeroelastic design process cpacs-MONA. At first, the cpacs-MONA process with its capabilities for parametric modeling of the complete aircraft and in particular the set-up of a generic elastic pylon model is unfolded. Then, the influence of the modified engine-wing parameters on the flight loads of the main wing is examined. The resulting loads are afterward used to structurally optimize the two configurations component wise. Finally, the results of post-cpacs-MONA flutter analyses performed for the two optimized aircraft configurations with the different engine and pylon characteristics are discussed. It is shown that the higher mass and the changed position of the engine slightly increased the flutter speed. Although the lowest flutter speeds for both configurations occur at a flutter phenomenon of the horizontal tail-plane outside of the aeroelastic stability envelope.
      Citation: Aerospace
      PubDate: 2020-12-23
      DOI: 10.3390/aerospace8010002
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 3: Design and Optimization of Ram Air-Based
           Thermal Management Systems for Hybrid-Electric Aircraft

    • Authors: Hagen Kellermann, Michael Lüdemann, Markus Pohl, Mirko Hornung
      First page: 3
      Abstract: Ram air-based thermal management systems (TMS) are investigated herein for the cooling of future hybrid-electric aircraft. The developed TMS model consists of all components required to estimate the impacts of mass, drag, and fuel burn on the aircraft, including the heat exchangers, coldplates, ducts, pumps, and fans. To gain a better understanding of the TMS, one- and multi-dimensional system sensitivity analyses were conducted. The observations were used to aid with the numerical optimization of a ram air-based TMS towards the minimum fuel burn of a 180-passenger short-range turboelectric aircraft with a power split of up to 30 electric power. The TMS was designed for the conditions at the top of the climb. For an aircraft with the maximum power split, the additional fuel burn caused by the TMS is 0.19. Conditions occurring at a hot-day takeoff represent the most challenging off-design conditions for TMS. Steady-state cooling of all electric components with the designed TMS is possible during a hot-day takeoff if a small puller fan is utilized. Omitting the puller fan and instead oversizing the TMS is an alternative, but the fuel burn increase on the aircraft level grows to 0.29.
      Citation: Aerospace
      PubDate: 2020-12-23
      DOI: 10.3390/aerospace8010003
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 4: LEO Object’s Light-Curve Acquisition System
           and Their Inversion for Attitude Reconstruction

    • Authors: Fabrizio Piergentili, Gaetano Zarcone, Leonardo Parisi, Lorenzo Mariani, Shariar Hadji Hossein, Fabio Santoni
      First page: 4
      Abstract: In recent years, the increase in space activities has brought the space debris issue to the top of the list of all space agencies. The fact of there being uncontrolled objects is a problem both for the operational satellites in orbit (avoiding collisions) and for the safety of people on the ground (re-entry objects). Optical systems provide valuable assistance in identifying and monitoring such objects. The Sapienza Space System and Space Surveillance (S5Lab) has been working in this field for years, being able to take advantage of a network of telescopes spread over different continents. This article is focused on the re-entry phase of the object; indeed, the knowledge of the state of the object, in terms of position, velocity, and attitude during the descent, is crucial in order to predict as accurately as possible the impact point on the ground. A procedure to retrieve the light curves of orbiting objects by means of optical data will be shown and a method to obtain the attitude determination from their inversion based on a stochastic optimization (genetic algorithm) will be proposed.
      Citation: Aerospace
      PubDate: 2020-12-23
      DOI: 10.3390/aerospace8010004
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 5: A Conceptional Approach of
           Resin-Transfer-Molding to Rosin-Sourced Epoxy Matrix Green Composites

    • Authors: Sicong Yu, Xufeng Zhang, Xiaoling Liu, Chris Rudd, Xiaosu Yi
      First page: 5
      Abstract: In this concept-proof study, a preform-based RTM (Resin Transfer Molding) process is presented that is characterized by first pre-loading the solid curing agent onto the preform, and then injecting the liquid nonreactive resin with an intrinsically low viscosity into the mold to infiltrate and wet the pre-loaded preform. The separation of resin and hardener helped to process inherently high viscosity resins in a convenient way. Rosin-sourced, anhydrite-cured epoxies that would normally be regarded as unsuited to liquid composite molding, were thus processed. Rheological tests revealed that by separating the anhydrite curing agent from a formulated RTM resin system, the remaining epoxy liquid had its flowtime extended. C-scan and glass transition temperature tests showed that the preform pre-loaded with anhydrite was fully infiltrated and wetted by the liquid epoxy, and the two components were diffused and dissolved with each other, and finally, well reacted and cured. Composite laminates made via this approach exhibited roughly comparable quality and mechanical properties with prepreg controls via autoclave or compression molding, respectively. These findings were verified for both carbon and ramie fiber composites.
      Citation: Aerospace
      PubDate: 2020-12-28
      DOI: 10.3390/aerospace8010005
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 6: Target Tracking Enhancement by
           Three-Dimensional Cooperative Guidance Law Imposing Relative Interception

    • Authors: Xiaoma Liu, Yang Han, Peng Li, Hongwu Guo, Wenqi Wu
      First page: 6
      Abstract: The problem that two cooperative missiles intercept a maneuvering target while imposing a desired relative geometry is investigated in the paper. Firstly, a three-dimensional (3D) estimation model for cooperative target tracking is proposed and the observability of the missile-target range measurement is analyzed. In order to enhance the estimation performance, a two-level cooperative interception guidance architecture is proposed which combines a coordination algorithm with a novel 3D fixed-time convergent guidance law considering line of sight (LOS) angle constraints, such that the desired relative geometry can be imposed quickly and steadily by a dynamic strategy. The effectiveness and superiority of the proposed guidance law is evidenced through the numerical simulations comparing with other guidance laws.
      Citation: Aerospace
      PubDate: 2020-12-28
      DOI: 10.3390/aerospace8010006
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 7: Numerical Simulations on Unsteady Nonlinear
           Transonic Airfoil Flow

    • Authors: Diliana Friedewald
      First page: 7
      Abstract: Large-amplitude excitations need to be considered for gust load analyses of transport aircraft in cruise flight conditions. Nonlinear amplitude effects in transonic flow are, however, only marginally taken into account. The present work aims at closing this gap by means of systematic unsteady Reynolds-averaged Navier-Stokes simulations. The RAE2822 airfoil is analyzed for a variety of sinusoidal gust excitations at different transonic Mach numbers. Responses are evaluated with respect to lift and moment coefficients, their derivatives and the unsteady shock motion. A strong dependency on inflow Mach number and excitation frequency is observed. Generally, amplitude effects decrease with lower Mach numbers or higher excitation frequencies. The unsteady nonlinear simulations predict lower maximum lift values and lower lift and moment derivatives compared to their linear counterparts for lower frequencies in combination with large-amplitude excitations. For the mid-frequency range, trends are not as clear. Additionally, it is shown that the variables of harmonic distortion and maximum shock motion might not be reasonable indicators to predict a nonlinear response.
      Citation: Aerospace
      PubDate: 2020-12-29
      DOI: 10.3390/aerospace8010007
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 8: Correction: Tanaka, T., et al. Dual-Satellite
           Lunar Global Navigation System Using Multi-Epoch Double-Differenced
           Pseudorange Observations. Aerospace 2020, 7, 122

    • Authors: Toshiki Tanaka, Takuji Ebinuma, Shinichi Nakasuka
      First page: 8
      Abstract: The authors regret that this paper [1] contains typographical errors in the sentence between Equation (16) and Equation (17), as well as in Equations (18), (20), (21), (34), (36) and (37), with respect to the point that they use the wrong notations t1 − tN, while the correct notations are tk − tk+N−1 [...]
      Citation: Aerospace
      PubDate: 2020-12-30
      DOI: 10.3390/aerospace8010008
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 9: Novel 3U Stand-Alone CubeSat Architecture for
           Autonomous Near Earth Asteroid Fly-By

    • Authors: Stefano Casini, Iosto Fodde, Bert Monna, Angelo Cervone, Eberhard Gill
      First page: 9
      Abstract: The purpose of this work is to present a novel CubeSat architecture, aimed to explore Near Earth Asteroids. The fast growth in small satellite commercial-off-the-shelf technologies, which characterized the last decade of space industry, is exploited to design a 3U CubeSat able to provide a basic scientific return sufficient to improve the target asteroid dataset. An overview of the current available technologies for each subsystem is presented, followed by a component selection driven by the mission constraints. First a typical asteroid fly-by mission is introduced together with the system and performance requirements. Then each characterizing subsystem is critically analyzed, and the proposed configuration is presented, showing the mission feasibility within only 3.9 kg of wet mass and 385 m/s of total ΔV.
      Citation: Aerospace
      PubDate: 2020-12-30
      DOI: 10.3390/aerospace8010009
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 8, Pages 10: Amphibious Aircraft Developments:
           Computational Studies of Hydrofoil Design for Improvements in

    • Authors: Arjit Seth, Rhea P. Liem
      First page: 10
      Abstract: Amphibious aircraft designers face challenges to improve takeoffs and landings on both water and land, with water-takeoffs being relatively more complex for analyses. Reducing the water-takeoff distance via the use of hydrofoils was a subject of interest in the 1970s, but the computational power to assess their designs was limited. A preliminary computational design framework is developed to assess the performance and effectiveness of hydrofoils for amphibious aircraft applications, focusing on the water-takeoff performance. The design framework includes configuration selections and sizing methods for hydrofoils to fit within constraints from a flying-boat amphibious aircraft conceptual design for general aviation. The position, span, and incidence angle of the hydrofoil are optimized for minimum water-takeoff distance with consideration for the longitudinal stability of the aircraft. The analyses and optimizations are performed using water-takeoff simulations, which incorporate lift and drag forces with cavitation effects on the hydrofoil. Surrogate models are derived based on 2D computational fluid dynamics simulation results to approximate the force coefficients within the design space. The design procedure is evaluated in a case study involving a 10-seater amphibious aircraft, with results indicating that the addition of the hydrofoil achieves the purpose of reducing water-takeoff distance by reducing the hull resistance.
      Citation: Aerospace
      PubDate: 2020-12-30
      DOI: 10.3390/aerospace8010010
      Issue No: Vol. 8, No. 1 (2020)
  • Aerospace, Vol. 7, Pages 167: Constructive Aerodynamic Interference in a
           Network of Weakly Coupled Flutter-Based Energy Harvesters

    • Authors: Emmanuel Beltramo, Martín E. Pérez Segura, Bruno A. Roccia, Marcelo F. Valdez, Marcos L. Verstraete, Sergio Preidikman
      First page: 167
      Abstract: Converting flow-induced vibrations into electricity for low-power generation has received growing attention over the past few years. Aeroelastic phenomena, good candidates to yield high energy performance in renewable wind energy harvesting (EH) systems, can play a pivotal role in providing sufficient power for extended operation with little or no battery replacement. In this paper, a numerical model and a co-simulation approach have been developed to study a new EH device for power generation. We investigate the problem focusing on a weakly aerodynamically coupled flutter-based EH system. It consists of two flexible wings anchored by cantilevered beams with attached piezoelectric layers, undergoing nonlinear coupled bending–torsion limit cycle oscillations. Besides the development of individual EH devices, further issues are posed when considering multiple objects for realizing a network of devices and magnifying the extracted power due to nonlinear synergies and constructive interferences. This work investigates the effect of various external conditions and physical parameters on the performance of the piezoaeroelastic array of devices. From the viewpoint of applications, we are most concerned about whether an EH can generate sufficient power under a variable excitation. The results of this study can be used for the design and integration of low-energy wind generation technologies into buildings, bridges, and built-in sensor networks in aircraft structures.
      Citation: Aerospace
      PubDate: 2020-11-24
      DOI: 10.3390/aerospace7120167
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 168: Sensitivity Analysis and Flight Tests
           Results for a Vertical Cold Launch Missile System

    • Authors: Głębocki, Jacewicz
      First page: 168
      Abstract: In vertical cold launch the missile starts without the function of the main engine. Over the launcher, the attitude of the missile is controlled by a set of lateral thrusters. However, a quick turn might be disturbed by various uncertainties. This study discusses the problem of the influences of disturbances and the repeatability of lateral thrusters’ ignition on the pitch maneuver quality. The generic 152.4 mm projectile equipped in small, solid propellant lateral thrusters was used as a test platform. A six degree of freedom mathematical model was developed to execute the Monte-Carlo simulations of the launch phase and to prepare the flight test campaign. The parametric analysis was performed to investigate the influence of system uncertainties on quick turn repeatability. A series of ground laboratory trials was accomplished. Thirteen flight tests were completed on the missile test range. The flight parameters were measured using an onboard inertial measurement unit and a ground vision system. It was experimentally proved that the cold vertical launch maneuver could be realized properly with at least two lateral motors. It was found that the initial roll rate of the projectile and the lateral thrusters’ igniters’ uncertainties could affect the pitch angle achieved and must be minimized to reduce the projectile dispersion.
      Citation: Aerospace
      PubDate: 2020-11-28
      DOI: 10.3390/aerospace7120168
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 169: How Well Can Persistent Contrails Be

    • Authors: Klaus Gierens, Sigrun Matthes, Susanne Rohs
      First page: 169
      Abstract: Persistent contrails and contrail cirrus are responsible for a large part of aviation induced radiative forcing. A considerable fraction of their warming effect could be eliminated by diverting only a quite small fraction of flight paths, namely those that produce the highest individual radiative forcing (iRF). In order to make this a viable mitigation strategy it is necessary that aviation weather forecast is able to predict (i) when and where contrails are formed, (ii) which of these are persistent, and (iii) how large the iRF of those contrails would be. Here we study several data bases together with weather data in order to see whether such a forecast would currently be possible. It turns out that the formation of contrails can be predicted with some success, but there are problems to predict contrail persistence. The underlying reason for this is that while the temperature field is quite good in weather prediction and climate simulations with specified dynamics, this is not so for the relative humidity in general and for ice supersaturation in particular. However we find that the weather model shows the dynamical peculiarities that are expected for ice supersaturated regions where strong contrails are indeed found in satellite data. This justifies some hope that the prediction of strong contrails may be possible via general regression involving the dynamical state of the ambient atmosphere.
      Citation: Aerospace
      PubDate: 2020-12-02
      DOI: 10.3390/aerospace7120169
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 170: The Contrail Mitigation Potential of
           Aircraft Formation Flight Derived from High-Resolution Simulations

    • Authors: Simon Unterstrasser
      First page: 170
      Abstract: Formation flight is one potential measure to increase the efficiency of aviation. Flying in the upwash region of an aircraft’s wake vortex field is aerodynamically advantageous. It saves fuel and concomitantly reduces the carbon foot print. However, CO2 emissions are only one contribution to the aviation climate impact among several others (contrails, emission of H2O and NOx). In this study, we employ an established large eddy simulation model with a fully coupled particle-based ice microphysics code and simulate the evolution of contrails that were produced behind formations of two aircraft. For a large set of atmospheric scenarios, these contrails are compared to contrails behind single aircraft. In general, contrails grow and spread by the uptake of atmospheric water vapour. When contrails are produced in close proximity (as in the formation scenario), they compete for the available water vapour and mutually inhibit their growth. The simulations demonstrate that the contrail ice mass and total extinction behind a two-aircraft formation are substantially smaller than for a corresponding case with two separate aircraft and contrails. Hence, this first study suggests that establishing formation flight may strongly reduce the contrail climate effect.
      Citation: Aerospace
      PubDate: 2020-12-05
      DOI: 10.3390/aerospace7120170
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 171: Using Convolutional Neural Networks to
           Automate Aircraft Maintenance Visual Inspection

    • Authors: Anil Doğru, Soufiane Bouarfa, Ridwan Arizar, Reyhan Aydoğan
      First page: 171
      Abstract: Convolutional Neural Networks combined with autonomous drones are increasingly seen as enablers of partially automating the aircraft maintenance visual inspection process. Such an innovative concept can have a significant impact on aircraft operations. Though supporting aircraft maintenance engineers detect and classify a wide range of defects, the time spent on inspection can significantly be reduced. Examples of defects that can be automatically detected include aircraft dents, paint defects, cracks and holes, and lightning strike damage. Additionally, this concept could also increase the accuracy of damage detection and reduce the number of aircraft inspection incidents related to human factors like fatigue and time pressure. In our previous work, we have applied a recent Convolutional Neural Network architecture known by MASK R-CNN to detect aircraft dents. MASK-RCNN was chosen because it enables the detection of multiple objects in an image while simultaneously generating a segmentation mask for each instance. The previously obtained F1 and F2 scores were 62.67% and 59.35%, respectively. This paper extends the previous work by applying different techniques to improve and evaluate prediction performance experimentally. The approach uses include (1) Balancing the original dataset by adding images without dents; (2) Increasing data homogeneity by focusing on wing images only; (3) Exploring the potential of three augmentation techniques in improving model performance namely flipping, rotating, and blurring; and (4) using a pre-classifier in combination with MASK R-CNN. The results show that a hybrid approach combining MASK R-CNN and augmentation techniques leads to an improved performance with an F1 score of (67.50%) and F2 score of (66.37%).
      Citation: Aerospace
      PubDate: 2020-12-07
      DOI: 10.3390/aerospace7120171
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 172: Assessing the Climate Impact of Formation

    • Authors: Katrin Dahlmann, Sigrun Matthes, Hiroshi Yamashita, Simon Unterstrasser, Volker Grewe, Tobias Marks
      First page: 172
      Abstract: An operational measure that is inspired by migrant birds aiming toward the mitigation of aviation climate impact is to fly in aerodynamic formation. When this operational measure is adapted to commercial aircraft it saves fuel and is, therefore, expected to reduce the climate impact of aviation. Besides the total emission amount, this mitigation option also changes the location of emissions, impacting the non-CO2 climate effects arising from NOx and H2O emissions and contrails. Here, we assess these non-CO2 climate impacts with a climate response model to assure a benefit for climate not only due to CO2 emission reductions, but also due to reduced non-CO2 effects. Therefore, the climate response model AirClim is used, which includes CO2 effects and also the impact of water vapor and contrail induced cloudiness as well as the impact of nitrogen dioxide emissions on the ozone and methane concentration. For this purpose, AirClim has been adopted to account for saturation effects occurring for formation flight. The results of the case studies show that the implementation of formation flights in the 50 most popular airports for the year 2017 display an average decrease of fuel consumption by 5%. The climate impact, in terms of average near surface temperature change, is estimated to be reduced in average by 24%, with values of individual formations between 13% and 33%.
      Citation: Aerospace
      PubDate: 2020-12-08
      DOI: 10.3390/aerospace7120172
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 173: Design Space Exploration of a Jet Engine
           Component Using a Combined Object Model for Function and Geometry

    • Authors: Jakob R. Müller, Massimo Panarotto, Ola Isaksson
      First page: 173
      Abstract: The design of aircraft and engine components hinges on the use of computer aided design (CAD) models and the subsequent geometry-based analyses for evaluation of the quality of a concept. However, the generation (and variation) of CAD models to include radical or novel design solutions is a resource intense modelling effort. While approaches to automate the generation and variation of CAD models exist, they neglect the capture and representation of the product’s design rationale—what the product is supposed to do. The design space exploration approach Function and Geometry Exploration (FGE) aims to support the exploration of more functionally and geometrically different product concepts under consideration of not only geometrical, but also teleological aspects. The FGE approach has been presented and verified in a previous presentation. However, in order to contribute to engineering design practice, a design method needs to be validated through application in industrial practice. Hence, this publication reports from a study where the FGE approach has been applied by a design team of a Swedish aerospace manufacturers in a conceptual product development project. Conceptually different alternatives were identified in order to meet the expected functionality of a guide vane (GV). The FGE was introduced and applied in a series of workshops. Data was collected through participatory observation in the design teams by the researchers, as well as interviews and questionnaires. The results reveal the potential of the FGE approach as a design support to: (1) Represent and capture the design rationale and the design space; (2) capture, integrate and model novel solutions; and (3) provide support for the embodiment of novel concepts that would otherwise remain unexplored. In conclusion, the FGE method supports designers to articulate and link the design rationale, including functional requirements and alternative solutions, to geometrical features of the product concepts. The method supports the exploration of alternative solutions as well as functions. However, scalability and robustness of the generated CAD models remain subject to further research.
      Citation: Aerospace
      PubDate: 2020-12-08
      DOI: 10.3390/aerospace7120173
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 174: Validation of Numerical Models of a
           Rotorcraft Crashworthy Seat and Subfloor

    • Authors: Paolo Astori, Mauro Zanella, Matteo Bernardini
      First page: 174
      Abstract: The present work explores some critical aspects of the numerical modeling of a rotorcraft seat and subfloor equipped with energy-absorbing stages, which are paramount in crash landing conditions. To limit the vast complexity of the problem, a purely vertical impact is considered as a reference scenario for an assembly made of a crashworthy helicopter seat and a subfloor section, including an anthropomorphic dummy. A preliminary lumped mass model is used to drive the design of the experimental drop test. Some additional static and dynamic tests are carried out at the coupon and sub-component levels to characterize the seat cushion, the seat pan and the honeycomb elements that were introduced in the structure as energy absorbers. The subfloor section is designed and manufactured with a simplified technique, yet representative of this structural component. Eventually, a finite element model representing the full drop test was created and, together with the original lumped mass model, finally validated against the experimental test, outlining the advantage of using both the numerical techniques for design assistance.
      Citation: Aerospace
      PubDate: 2020-12-10
      DOI: 10.3390/aerospace7120174
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 175: Traffic Network Identification Using
           Trajectory Intersection Clustering

    • Authors: Ingrid Gerdes, Annette Temme
      First page: 175
      Abstract: The current airspace route system consists mainly of pre-defined routes with a low number of intersections to facilitate air traffic controllers to oversee the traffic. Our aim is a method to create an artificial and reliable route network based on planned or as-flown trajectories. The application possibilities of the resulting network are manifold, reaching from the assessment of new air traffic management (ATM) strategies or historical data to a basis for simulation systems. Trajectories are defined as sequences of common points at intersections with other trajectories. All common points of a traffic sample are clustered, and, after further optimization, the cluster centers are used as nodes in the new main-flow network. To build almost-realistic flight trajectories based on this network, additional parameters such as speed and altitude are added to the nodes and the possibility to take detours into account to avoid congested areas is introduced. As optimization criteria, the trajectory length and the structural complexity of the main-flow system are used. Based on these criteria, we develop a new cost function for the optimization process. In addition, we show how different traffic situations are covered by the network. To illustrate the capabilities of our approach, traffic is exemplarily divided into separate classes and class-dependent parameters are assigned. Applied to two real traffic scenarios, the approach was able to emulate the underlying route systems with a difference in median trajectory length of 0.2%, resp. 0.5% compared to the original routes.
      Citation: Aerospace
      PubDate: 2020-12-10
      DOI: 10.3390/aerospace7120175
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 176: Modelling Flexibility and Qualification
           Ability to Assess Electric Propulsion Architectures for Satellite

    • Authors: Massimo Panarotto, Olivia Borgue, Ola Isaksson
      First page: 176
      Abstract: The higher satellite production rates expected in new megaconstellation scenarios involve radical changes in the way design trade-offs need to be considered by electric propulsion companies. In relative comparison, flexibility and qualification ability will have a higher impact in megaconstellations compared to traditional businesses. For these reasons, this paper proposes a methodology for assessing flexible propulsion architectures by taking into account variations in market behavior and qualification activities. Through the methodology, flexibility and qualification ability can be traded against traditional engineering attributes (such as functional performances) in a quantitative way. The use of the methodology is illustrated through an industrial case related to the study of xenon vs. krypton architectures for megaconstellation businesses. This paper provides insights on how to apply the methodology in other case studies, in order to enable engineering teams to present and communicate the impact of alternative architectural concepts to program managers and decision-makers.
      Citation: Aerospace
      PubDate: 2020-12-11
      DOI: 10.3390/aerospace7120176
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 177: Application of the HPCMP CREATETM-AV Kestrel
           to an Integrated Propeller Prediction

    • Authors: Pooneh Aref, Mehdi Ghoreyshi, Adam Jirasek, Jürgen Seidel
      First page: 177
      Abstract: This article presents the results of a computational investigation of an integrated propeller test case using the HPCMP CREATETM-AV Kestrel simulation tools. There is a renewed interest in propeller-driven aircraft for unmanned aerial vehicles, electric aircraft, and flying taxies. Computational resources can significantly accelerate the generation of aerodynamic models for these vehicles and reduce the development cost if the prediction tools can accurately predict the aircraft/propeller aerodynamic interactions. Unfortunately, limited propeller experimental data are available to validate computational methods. An American Institute of Aeronautics and Astronautics (AIAA) workshop was therefore established to address this problem. The objective of this workshop was to generate an open access-powered wind tunnel test database for computational validation of propeller effects on the wing aerodynamics, specifically for wing-tip-mounted propellers. The propeller selected for the workshop has four blades and a diameter of 16.2 in. The wing has a root and tip chord of 11.6 and 8.6 in, respectively. Two different simulation approaches were used: one using a single grid including wind tunnel walls and the second using a subset grid overset to an adaptive Cartesian grid that fills the space between the near-body grid and wind tunnel walls. The predictions of both approaches have been compared with available experimental data from the Lockheed Martin low-speed wind tunnel to investigate the grid resolution required for accurate prediction of flowfield data. The results show a good agreement for all tested conditions. The measured and predicted data show that wing aerodynamic performance is improved by the spinning tip-mounted propeller.
      Citation: Aerospace
      PubDate: 2020-12-11
      DOI: 10.3390/aerospace7120177
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 178: Analysis of Aircraft Maintenance Related
           Accidents and Serious Incidents in Nigeria

    • Authors: Khadijah Abdullahi Habib, Cengiz Turkoglu
      First page: 178
      Abstract: The maintenance of aircraft presents considerable challenges to the personnel that maintain them. Challenges such as time pressure, system complexity, sparse feedback, cramped workspaces, etc., are being faced by these personnel on a daily basis. Some of these challenges cause aircraft-maintenance-related accidents and serious incidents. However, there is little formal empirical work that describes the influence of aircraft maintenance to aircraft accidents and incidents in Nigeria. This study, therefore, sets out to explore the contributory factors to aircraft-maintenance-related incidents from 2006 to 2019 and accidents from 2009 to 2019 in Nigeria, to achieve a deeper understanding of this safety critical aspect of the aviation industry, create awareness amongst the relevant stakeholders and seek possible mitigating factors. To attain this, a content analysis of accident reports and mandatory occurrence reports, which occurred in Nigeria, was carried out using the Maintenance Factors and Analysis Classification System (MxFACS) and Hieminga’s maintenance incidents taxonomy. An inter-rater concordance value was used to ascertain research accuracy after evaluation of the data output by subject matter experts. The highest occurring maintenance-related incidents and accidents were attributed to “removal/installation”, working practices such as “accumulation of dirt and contamination”, “inspection/testing”, “inadequate oversight from operator and regulator”, “failure to follow procedures” and “incorrect maintenance”. To identify the root cause of these results, maintenance engineers were consulted via a survey to understand the root causes of these contributory factors. The results of the study revealed that the most common maintenance-related accidents and serious incidents in the last decade are “collision with terrain” and “landing gear events’’. The most frequent failures at systems level resulting in accidents are the “engines” and “airframe structure”. The maintenance factors with the highest contribution to these accidents are “operator and regulatory oversight”, “inadequate inspection” and “failure to follow procedures”. The research also highlights that the highest causal and contributory factors to aviation incidents in Nigeria from 2006 to 2019 are “installation/removal issues”, “inspection/testing issues”, “working practices”, “job close up”, “lubrication and servicing”, all of which corresponds to studies by other researchers in other countries.
      Citation: Aerospace
      PubDate: 2020-12-11
      DOI: 10.3390/aerospace7120178
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 179: Trajectory Design of Perseus: A CubeSat
           Mission Concept to Phobos

    • Authors: Ravi teja Nallapu, Graham Dektor, Nalik Kenia, James Uglietta, Shota Ichikawa, Mercedes Herreras-Martinez, Akshay Choudhari, Aman Chandra, Stephen Schwartz, Erik Asphaug, Jekanthan Thangavelautham
      First page: 179
      Abstract: The Martian satellites Phobos and Deimos hold many unanswered questions that may provide clues to the origin of Mars. These moons are low Δv stopover sites to Mars. Some human missions to Mars typically identify Phobos and Deimos as staging bases for Mars surface exploration. Astronauts could base initial operations there in lieu of repeated voyages to and from the planet surface, to refuel transiting spacecraft, to teleoperate robotics and other critical machinery, and to develop habitable infrastructure ahead of human landings. Despite their strategic and scientific significance, there has been no successful dedicated mission to either moon. For this reason, we propose Perseus, a geological imaging CubeSat mission to Phobos. Perseus, a 27U, 54kg CubeSat will return thermal and visible images at resolutions better than currently available over most of Phobos’ surface. This includes visible images at 5m/pixel and thermal images at 25m/pixel of Phobos’ surface. The Perseus mission is nominally intended to be a co-orbital mission, where the spacecraft will encounter Phobos on its Martian orbit. However, a hyperbolic rendezvous mission concept, to image Phobos on a hyperbolic flyby, is also considered to reduce the risks associated with orbit capture and to reduce mission costs. This paper presents the preliminary feasibility, science objectives, and technological development challenges of achieving these science goals. We then formulate two rendezvous concepts as a series of three nonlinear optimization problems that span the design tree of mission concepts. The tree’s root node is the heliocentric cruise problem, which identifies the near-optimal launch and arrival windows for the Perseus spacecraft. The leaf nodes of the design tree are the two rendezvous concepts that identify near-optimal co-orbital and hyperbolic trajectories for Phobos’ reconnaissance. The design problems are solved using evolutionary algorithms, and the performance of the selected mission concepts is then examined. The results indicate that a co-orbital encounter allows about one encounter per day with about 6 min per encounter. The hyperbolic encounter, on the other hand, allows a single encounter where the spacecraft will spend about 2 min in the imaging region with respect to Phobos. The spacecraft will obtain higher resolution images of Phobos on this feasible region than have ever been seen for most of the surface. These detailed images will help identify candidate landing sites and provide critical data to derisk future surface missions to Phobos.
      Citation: Aerospace
      PubDate: 2020-12-15
      DOI: 10.3390/aerospace7120179
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 180: Deployment of Solar Sails by Joule Effect:
           Thermal Analysis and Experimental Results

    • Authors: Gianluigi Bovesecchi, Sandra Corasaniti, Girolamo Costanza, Fabrizio Paolo Piferi, Maria Elisa Tata
      First page: 180
      Abstract: Space vehicles may be propelled by solar sails exploiting the radiation pressure coming from the sun and applied on their surfaces. This work deals with the adoption of Nickel-Titanium Shape Memory Alloy (SMA) elements in the sail deployment mechanism activated by the Joule Effect, i.e., using the same SMA elements as a resistance within suitable designed electrical circuits. Mathematical models were analyzed for the thermal analysis by implementing algorithms for the evaluation of the temperature trend depending on the design parameters. Several solar sail prototypes were built up and tested with different number, size, and arrangement of the SMA elements, as well as the type of the selected electrical circuit. The main parameters were discussed in the tested configurations and advantages discussed as well.
      Citation: Aerospace
      PubDate: 2020-12-16
      DOI: 10.3390/aerospace7120180
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 181: Energy Transition in Aviation: The Role of
           Cryogenic Fuels

    • Authors: Arvind Gangoli Rao, Feijia Yin, Henri G.C. Werij
      First page: 181
      Abstract: Aviation is the backbone of our modern society. In 2019, around 4.5 billion passengers travelled through the air. However, at the same time, aviation was also responsible for around 5% of anthropogenic causes of global warming. The impact of the COVID-19 pandemic on the aviation sector in the short term is clearly very high, but the long-term effects are still unknown. However, with the increase in global GDP, the number of travelers is expected to increase between three- to four-fold by the middle of this century. While other sectors of transportation are making steady progress in decarbonizing, aviation is falling behind. This paper explores some of the various options for energy carriers in aviation and particularly highlights the possibilities and challenges of using cryogenic fuels/energy carriers such as liquid hydrogen (LH2) and liquefied natural gas (LNG).
      Citation: Aerospace
      PubDate: 2020-12-18
      DOI: 10.3390/aerospace7120181
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 182: Advanced Passenger Movement Model Depending
           On the Aircraft Cabin Geometry

    • Authors: Marc Engelmann, Tim Kleinheinz, Mirko Hornung
      First page: 182
      Abstract: The aircraft cabin and boarding procedures are steadily increasing focus points for both aircraft manufacturers and airlines, as they play a key part in the customer experience. In the German research project AVACON (AdVAnced Aircraft CONcepts), the boarding procedure is assessed using the PAXelerate boarding simulation. As the project demands an increased level of detail concerning the passenger movement model, this publication introduces an improved methodology. Additions to the model include the development of a method capable of describing the passenger walking speed in dependence of the surrounding objects, their proximity as well as the location of other passengers within the cabin. The validation of the model is performed using the AVACON research baseline and an Airbus A320. The model is then applied to an altered version of the Airbus A320 with an extended aisle and to a COVID-19 safe distance scenario. Regarding the results, an extended aisle width delivers boarding times reduced by up to 3%, whereas the COVID-19 assessment delivers a 67% increase in boarding times. Concluding, the integration of the newly developed model empowers PAXelerate to simulate a more detailed boarding process and enables a better understanding of the influence of cabin layout changes to an aircraft’s boarding performance.
      Citation: Aerospace
      PubDate: 2020-12-20
      DOI: 10.3390/aerospace7120182
      Issue No: Vol. 7, No. 12 (2020)
  • Aerospace, Vol. 7, Pages 158: Method to Characterize Potential UAS
           Encounters Using Open Source Data

    • Authors: Andrew Weinert
      First page: 158
      Abstract: As unmanned aerial systems (UASs) increasingly integrate into the US national airspace system, there is an increasing need to characterize how commercial and recreational UASs may encounter each other. To inform the development and evaluation of safety critical technologies, we demonstrate a methodology to analytically calculate all potential relative geometries between different UAS operations performing inspection missions. This method is based on a previously demonstrated technique that leverages open source geospatial information to generate representative unmanned aircraft trajectories. Using open source data and parallel processing techniques, we performed trillions of calculations to estimate the relative horizontal distance between geospatial points across sixteen locations.
      Citation: Aerospace
      PubDate: 2020-11-04
      DOI: 10.3390/aerospace7110158
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 159: Utilization of FPGA for Onboard Inference of
           Landmark Localization in CNN-Based Spacecraft Pose Estimation

    • Authors: Kiruki Cosmas, Asami Kenichi
      First page: 159
      Abstract: In the recent past, research on the utilization of deep learning algorithms for space applications has been widespread. One of the areas where such algorithms are gaining attention is in spacecraft pose estimation, which is a fundamental requirement in many spacecraft rendezvous and navigation operations. Nevertheless, the application of such algorithms in space operations faces unique challenges compared to application in terrestrial operations. In the latter, they are facilitated by powerful computers, servers, and shared resources, such as cloud services. However, these resources are limited in space environment and spacecrafts. Hence, to take advantage of these algorithms, an on-board inferencing that is power- and cost-effective is required. This paper investigates the use of a hybrid Field Programmable Gate Array (FPGA) and Systems-on-Chip (SoC) device for efficient onboard inferencing of the Convolutional Neural Network (CNN) part of such pose estimation methods. In this study, Xilinx’s Zynq UltraScale+ MPSoC device is used and proposed as an effective onboard-inferencing solution. The performance of the onboard and computer inferencing is compared, and the effectiveness of the hybrid FPGA-CPU architecture is verified. The FPGA-based inference has comparable accuracy to the PC-based inference with an average RMS error difference of less than 0.55. Two CNN models that are based on encoder-decoder architecture have been investigated in this study and three approaches demonstrated for landmarks localization.
      Citation: Aerospace
      PubDate: 2020-11-05
      DOI: 10.3390/aerospace7110159
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 160: Influence of Satellite Motion Control System
           Parameters on Performance of Space Debris Capturing

    • Authors: Mahdi Akhloumadi, Danil Ivanov
      First page: 160
      Abstract: Relative motion control problem for capturing the tumbling space debris object is considered. Onboard thrusters and reaction wheels are used as actuators. The nonlinear coupled relative translational and rotational equations of motion are derived. The SDRE-based control algorithm is applied to the problem. It is taken into account that the thrust vector has misalignment with satellite center of mass, and reaction wheels saturation affects the ability of the satellite to perform the docking maneuver to space debris. The acceptable range of a set of control system parameters for successful rendezvous and docking is studied using numerical simulations taking into account thruster discreteness, actuators constrains, and attitude motion of the tumbling space debris.
      Citation: Aerospace
      PubDate: 2020-11-06
      DOI: 10.3390/aerospace7110160
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 161: Multifidelity Sensitivity Study of Subsonic
           Wing Flutter for Hybrid Approaches in Aircraft Multidisciplinary Design
           and Optimisation

    • Authors: Marco Berci, Francesco Torrigiani
      First page: 161
      Abstract: A comparative sensitivity study for the flutter instability of aircraft wings in subsonic flow is presented, using analytical models and numerical tools with different multidisciplinary approaches. The analyses build on previous elegant works and encompass parametric variations of aero-structural properties, quantifying their effect on the aeroelastic stability boundary. Differences in the multifidelity results are critically assessed from both theoretical and computational perspectives, in view of possible practical applications within airplane preliminary design and optimisation. A robust hybrid strategy is then recommended, wherein the flutter boundary is obtained using a higher-fidelity approach while the flutter sensitivity is computed adopting a lower-fidelity approach.
      Citation: Aerospace
      PubDate: 2020-11-12
      DOI: 10.3390/aerospace7110161
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 162: Neuro-Fuzzy Network-Based Reduced-Order
           Modeling of Transonic Aileron Buzz

    • Authors: Rebecca Zahn, Christian Breitsamter
      First page: 162
      Abstract: In the present work, a reduced-order modeling (ROM) framework based on a recurrent neuro-fuzzy model (NFM) that is serial connected with a multilayer perceptron (MLP) neural network is applied for the computation of transonic aileron buzz. The training data set for the specified ROM is obtained by performing forced-motion unsteady Reynolds-averaged Navier Stokes (URANS) simulations. Further, a Monte Carlo-based training procedure is applied in order to estimate statistical errors. In order to demonstrate the method’s fidelity, a two-dimensional aeroelastic model based on the NACA651213 airfoil is investigated at different flow conditions, while the aileron deflection and the hinge moment are considered in particular. The aileron is integrated in the wing section without a gap and is modeled as rigid. The dynamic equations of the rigid aileron rotation are coupled with the URANS-based flow model. For ROM training purposes, the aileron is excited via a forced motion and the respective aerodynamic and aeroelastic response is computed using a computational fluid dynamics (CFD) solver. A comparison with the high-fidelity reference CFD solutions shows that the essential characteristics of the nonlinear buzz phenomenon are captured by the selected ROM method.
      Citation: Aerospace
      PubDate: 2020-11-13
      DOI: 10.3390/aerospace7110162
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 163: A Test Platform to Assess the Impact of
           Miniaturized Propulsion Systems

    • Authors: Fabrizio Stesina, Sabrina Corpino, Daniele Calvi
      First page: 163
      Abstract: Miniaturized propulsion systems can enable many future CubeSats missions. The advancement of the Technology Readiness Level of this technology passes through the integration in a CubeSat platform and the assessment of the impact and the interactions of the propulsion systems on the actual CubeSat technology and vice versa. The request of power, the thermal environmental, and the electromagnetic emissions generated inside the platform require careful analyses. This paper presents the upgraded design and the validation of a CubeSat test platform (CTP) that can interface a wide range of new miniaturized propulsion systems and gather unprecedented information for these analyses, which can be fused with the commonly used ground support equipment. The CTP features are reported, and the main achievements of the tests are shown, demonstrating the effective capabilities of the platform and how it allows for the investigation of the mutual interactions at system level between propulsion systems and the CubeSat technology.
      Citation: Aerospace
      PubDate: 2020-11-16
      DOI: 10.3390/aerospace7110163
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 164: Static Aeroelasticity Using High Fidelity
           Aerodynamics in a Staggered Coupled and ROM Scheme

    • Authors: Angelos Kafkas, George Lampeas
      First page: 164
      Abstract: Current technology in evaluating the aeroelastic behavior of aerospace structures is based on the staggered coupling between structural and low fidelity linearized aerodynamic solvers, which has inherent limitations, although tried and trusted outside the transonic region. These limitations arise from the assumptions in the formulation of linearized aerodynamics and the lower fidelity in the description of the flowfield surrounding the structure. The validity of low fidelity aerodynamics also degrades fast with the deviation from a typical aerodynamic shape due to the inclusion of various control devices, gaps, or discontinuities. As innovative wings tend to become more flexible and also include a variety of morphing devices, it is expected that using low fidelity linearized aerodynamics in aeroelastic analysis will tend to induce higher levels of uncertainty in the results. An obvious solution to these issues is to use high fidelity aerodynamics. However, using high fidelity aerodynamics incurs a very high computational cost. Various formulations of reduced order models have shown promising results in reducing the computational cost. In the present work, the static aeroelastic behavior of three characteristic aeroelastic problems is obtained using both a full three-dimensional staggered coupled scheme and a time domain Volterra series based reduced order model (ROM). The reduced order model’s ability to remain valid for a wide range of dynamic pressures around a specific Mach number (and Reynolds number regime if viscous flow is considered) and the capability to modify structural parameters such as damping ratios and natural frequencies are highlighted.
      Citation: Aerospace
      PubDate: 2020-11-17
      DOI: 10.3390/aerospace7110164
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 165: Evaluation of Strategies to Reduce the Cost
           Impacts of Flight Delays on Total Network Costs

    • Authors: Judith Rosenow, Philipp Michling, Michael Schultz, Jörn Schönberger
      First page: 165
      Abstract: Competitive price pressure and economic cost pressure constantly force airlines to improve their optimization strategies. Besides predictable operational costs, delay costs are a significant cost driver for airlines. Especially reactionary delay costs can endanger the profitability of such a company. These time-dependent costs depend on the number of sensitive transfer passengers. This cost component is represented by the number of missed flights and the connectivity of onward flights, i.e., the offer of alternative flight connections. The airline has several options to compensate for reactionary delays, for example, by increasing cruising speeds, shortening turnaround times, rebookings and cancellations. The effects of these options on the cost balance of airline total operating costs have been examined in detail, considering a flight-specific number of transfer passengers. The results have been applied to a 24-h rotation schedule of a large German hub airport. We found, that the fast turnaround and increasing cruise speed are the most effective strategies to compensate for passenger-specific delay costs. The results could be used in a multi-criteria trajectory optimization to find a balance between environmentally-driven and cost-index-driven detours and speed adjustments.
      Citation: Aerospace
      PubDate: 2020-11-18
      DOI: 10.3390/aerospace7110165
      Issue No: Vol. 7, No. 11 (2020)
  • Aerospace, Vol. 7, Pages 166: On the Design of Aeroelastically Scaled
           Models of High Aspect-Ratio Wings

    • Authors: Frederico Afonso, Mónica Coelho, José Vale, Fernando Lau, Afzal Suleman
      First page: 166
      Abstract: Recently, innovative aircraft designs were proposed to improve aerodynamic performance. Examples include high aspect ratio wings to reduce the aerodynamic induced drag to achieve lower fuel consumption. Such solution when combined with a lightweight structure may lead to aeroelastic instabilities such as flutter at lower air speeds compared to more conventional wing designs. Therefore, in order to ensure safe flight operation, it is important to study the aeroelastic behavior of the wing throughout the flight envelope. This can be achieved by either experimental or computational work. Experimental wind tunnel and scaled flight test models need to exhibit similar aeroelastic behavior to the full scale air vehicle. In this paper, three different aeroelastic scaling strategies are formulated and applied to a flexible high aspect-ratio wing. These scaling strategies are first evaluated in terms of their ability to generate reduced models with the intended representations of the aerodynamic, structural and inertial characteristics. Next, they are assessed in terms of their potential in representing the unsteady non-linear aeroelastic behavior in three different flight conditions. The scaled models engineered by exactly scaling down the internal structure suitably represent the intended aeroelastic behavior and allow the performance assessment for the entire flight envelope. However, since both the flight and wind tunnel models are constrained by physical and budgetary limitations, custom built structural models are more likely to be selected. However, the latter ones are less promising to study the entire flight envelope.
      Citation: Aerospace
      PubDate: 2020-11-18
      DOI: 10.3390/aerospace7110166
      Issue No: Vol. 7, No. 11 (2020)
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