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Abstract: Abstract Passengers’ safety in unconventional situations, such as those of an emergency landing, has become more and more important due to the increase of air traffic. To improve passengers’ safety, certification authorities have imposed specific crashworthiness requirements in airworthiness regulations as defined in Title 14 of Federal Regulations Code—Part 25 for transport aircraft. Over the years, a series of drop tests were carried out to evaluate the structural performance of the airframe and seats and their effects on the occupants. However, the development of a single test is not only time-consuming but also very expensive. In this context, computer modelling and simulation have become increasingly popular for efficient and quick investigations on aircraft’s dynamic behaviour. This study aims to develop a numerical procedure to assess passengers’ safety during a crash landing and optimize the occupant lumbar load for which the impacts of different seat cushion foams are analysed. The experimental data have been collected as part of the research project, which involved the Department of Industrial Engineering Federico II on a drop test of a full-scale fuselage section equipped with two Anthropomorphic Test Devices (ATDs). The finite element model of the test article is generated through the pre/post-processor LS-PREPOST® and is solved using the non-linear explicit dynamic finite element code LS-DYNA®. The parametric study confirms the importance of choosing the appropriate foam material of the aeronautical seat cushion, as it has been observed that DAX 55 foams resulted in a lumbar load peak reduced by 20.6% with reference to the conventional polyurethane foam. PubDate: 2022-04-29
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Abstract: Abstract This work presents the experimental results of launching of Fénix I-2 “Alejandro Pedroza Meléndez” (F2APM), a Mexican manufacture single-stage solid propellant rocket motor from Cabo Tuna Range in Charcas, San Luis Potosí, México. The solid fuel sounding rocket motor was KN-Sorbitol propellant type. The rocket performed its flight at perfect weather and visibility conditions, reaching a maximum altitude of about 6 000 m. Engine and flight trajectory showed very good agreement with the theoretical data measurement obtained from captive-fired experiment. At burnt-out, locked-in resonance increased drag limiting the maximum vertical reach. PubDate: 2022-04-29
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Abstract: Abstract Impact testing is a critical activity for many aerospace activities. Data on impacts can be employed to evaluate materials survivability, operations safety, and, if possible, to plan prompt maintenance. A classical impact testing facility usually employs Light-Gas Guns (LGGs) to evaluate the effect of collisions in a controlled laboratory environment. In particular, single stage LGGs are relatively simple in their working principle, as they consist in a pressurized gas reservoir and a barrel with a projectile placed in front of the experiment target. When the shot command is executed, the gas from the reservoir accelerates the projectile through the barrel; in first approximation, its velocity is related to the reservoir pressure, the barrel geometry, and the projectile velocity. In this context, The Malta College of Arts, Science and Technology (MCAST) and the Centre of Studies and Activities for Space CISAS “Giuseppe Colombo” of the University of Padova have started a collaboration to develop a single stage LGG impact facility in Malta. In this paper, the conceptual evaluation and the development of the facility is introduced. First, the potential application of such facility in the framework of Malta aviation market as well as the business opportunities in the emerging space sector are presented. In a second part of this work, the LGG main design drivers are defined and a preliminary evaluation of the achievable projectile velocities is performed. PubDate: 2022-03-21
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Abstract: Abstract Recent years have seen an increasing interest towards similitude methods. In fact, the possibility of testing a scaled model, instead of a full-scale prototype, leads to many advantages: financial and time savings, easier experimental setups, etc. However, similitudes have drawbacks, too, mainly due to non-scalable effects and partial similitude, which prevent from an accurate reconstruction of the prototype response. For these reasons, an alternative method which can bypass these limitations is needed. A new method, called VOODOO (Versatile Offset Operator for the Discrete Observation of Objects), is herein proposed: it is based on the definition of a transformation matrix which links the outputs of a given linear systems to those belonging to another system, which may be a scaled model. The responses are acquired on a discrete number of points for both the systems. This work aims at investigating the method’s strengths and limitations of the method. The results show that, although VOODOO exhibits some lack of accuracy in off-design conditions due to the loss of spatial correlation, it is able to overcome some major restrictions that affect all similitude methods. PubDate: 2022-03-09
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Abstract: Abstract The prediction of dynamic crushing behavior of aerospace-grade composites is a hard challenge for researchers. At coupons scale, such behavior implies the understanding of the initiation and propagation of the elementary damage mechanisms. Many results of the research confirm that the modulus and strength of composites increases with strain-rate. This paper presents the improvement of the constitutive model UL-Crush by adding dynamic stiffness modulus and strengths. The improved tool uses new approach by updating the stiffness and the strength values depending on strain-rates. In addition, parameter sensitivity investigations were conducted to assess the specific energy absorption capabilities of different material configurations. A new on-axis compression fixture was designed and manufactured to carry out tests of plain weave fabric composites, under quasi-static (QS) and low-velocity compression using MTS Insight 100 loading frame and drop tower CEAST Instron9340 facility. Two types of cross-section geometries were used: flat-plate and Hat-Shape coupons. Four types of triggering mechanism were adopted, including saw teeth, chamfer45°, steeple and corrugated, to ensure a continuous and stable crushing mode of failure. Detailed parameter sensitivity investigations were performed, including dimension scale, stacking sequences, trigger types and strain-rates. It was shown that the crush response is strain-rate dependent, and dynamic load decreases absorbed energy, which is indicative of microstructure disintegrating. Globally, big dimension scale, corrugated trigger, [0/45/45/0]s layup and decreasing strain-rate are the parameters to enhance the energy absorption capability of composite coupons. It has been observed that the improved numerical tool UL-Crush was able to significantly capture most crush mechanisms, reasonably correlate with experiments, and give an accurate dynamic response for crashworthy structures. PubDate: 2022-03-03 DOI: 10.1007/s42496-022-00108-7
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Abstract: Abstract Sustainable air transportation requires aerodynamically efficient airplanes. Thus, reduction of drag is of paramount importance. From a pure induced drag perspective, this goal can be achieved by the adoption of nonplanar configurations such as C-Wings, Joined Wings or with other design options such as wingtip devices (winglets). Under the assumption of inviscid flow with wake aligned with the freestream velocity, several winglet designs are investigated and general properties are demonstrated. In particular, under optimal conditions, given a closed simply connected wingtip region bounded by a curve, any winglet design geometrically included in that region will be less efficient than the winglet whose lifting line is represented by the bounding curve. Moreover, closed winglets are characterized by undetermined optimal aerodynamic load but unique and global minimum for the induced drag. Finally the Box Winglet and several variations of it are proposed as effective forms to reduce induced drag. PubDate: 2022-03-01 DOI: 10.1007/s42496-022-00110-z
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Abstract: Abstract This paper presents the development of a rotorcraft conceptual design tool able to incorporate handling qualities assessment at an early design stage. After a first conventional sizing, performed utilizing NASA’s NDARC software, a linearized model of the rotorcraft flight mechanics is built. The linear model is augmented by a simplified control system, designed according to structured \(H_{\infty }\) techniques, to determine augmentation requirements, rather than design the actual flight control system. ADS-33 Bandwidth and Phase-Delay standards are exploited to objectively assess the handling qualities of the current design and to drive an iterative redesign process aimed at enhancing the handling qualities ratings. The rotorcraft parameters resulting from the augmented sizing are subsequently used to automatically generate a real-time capable multibody model, which can be used for the subjective evaluation of its handling qualities via piloted flight simulation. The tool capabilities are demonstrated by designing a conventional lightweight helicopter of the class of the Airbus Helicopters BO105. PubDate: 2022-02-03 DOI: 10.1007/s42496-022-00107-8
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Abstract: Abstract Advances in lasers, optics and electronics for Satellite’s optical communication are opening the possibility of very high performance near Earth space links with data rate up to several Gbps. Being the divergence of the laser beam typically of tens of \(\mu\) rad, an extremely high precision pointing is needed to correctly establish and maintain data optical link. In particular, the relative motion between the satellite and the ground station shall be accurately evaluated to estimate how to correct pointing angles for future orbital locations. This correction is made via a point-ahead mirror (PAM) mechanism, which deviates the laser beam by an angle called point-ahead angle (PAA). The purpose of this paper is evaluate the possibility of accurately estimate the point-ahead angle in advance using the two-line elements sets for the orbiting satellite, which are available before the ground station overpass. The study evaluated TLE-based orbital evolution of Sentinel-6 satellite, comparing the results with the high precision data obtained by laser ranging from the crustal dynamics data information system (CDDIS). The maximum error observed between the estimated and measured point-ahead angles was less than 1 \(\mu\) rad, demonstrating the possibility of this point-ahead correction technique for LEO orbiting satellites. PubDate: 2022-02-02 DOI: 10.1007/s42496-022-00106-9
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Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The objective of the present work is the computational micromechanical analysis of unidirectional fiber-reinforced composites, considering defects. The micromechanical model uses refined beam theories based on the Carrera unified formulation (CUF) and involves using the component-wise (CW) approach, resulting in a high-fidelity model. Defects are introduced in the representative volume element (RVE) in the form of matrix voids by modifying the material properties of a certain quantity of the Gauss points associated with the matrix. The quantity of Gauss points thus modified is based on the required void volume fraction, and the resulting set is prescribed a material property with negligible stiffness to model voids. Two types of void distribution are considered in the current work—randomly distributed voids within the matrix and voids clustered in a region of the RVE. The current study investigates the influence of the volume fraction of voids present in the matrix and their distribution throughout the RVE domain on the macroscale mechanical response. Material nonlinearity is considered for the matrix phase. Numerical assessments are performed to investigate the influence of the volume fraction and the distribution of the voids on the macroscopic response. PubDate: 2021-11-08 DOI: 10.1007/s42496-021-00103-4
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Abstract: Abstract This paper proposes a new reconfigurable control strategy for the attitude control of a Low Earth Orbit (LEO) micro-satellite equipped with reaction control wheels and reaction control thrusters (used as a secondary actuation system). Control laws are combined with control allocation algorithms that enable the optimal allocation of control effort in case of reaction wheels saturation and/or faults as well as when control limits are reached (e.g. maximum torques provided by reaction wheels). This allows to effectively use the redundancy of the actuators set and guarantee robust stability and control of the satellite attitude. The effectiveness of the proposed strategy has been assessed through a numerical analysis that includes several simulation scenarios, where different initial conditions have been set and also the fault of a reaction wheel has been simulated. Simulations have shown the ability of the control architecture to effectively manage several control issues (i.e. maximum achievable torques, reaction wheel saturation and faults) through the allocation of control effort among all the available control effectors. PubDate: 2021-11-06 DOI: 10.1007/s42496-021-00102-5
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Abstract: Abstract The aim of this paper is to analyze optimal trajectories of a solar sail-based spacecraft in missions towards the outer Solar System region. The paper proposes a simplified approach able to estimate the minimum flight time required to reach a given (sufficiently high) heliocentric distance. In particular, the effect of a set of solar photonic assists on the overall mission performance is analyzed with a simplified numerical approach. A comparison with results taken from the existing literature show the soundness of the proposed approach. PubDate: 2021-10-22 DOI: 10.1007/s42496-021-00100-7
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Abstract: Abstract This article presents the aerodynamic design of the airfoil of the gust generator system being developed in the GUDGET project and conceived to generate high-amplitude gusts in a transonic wind tunnel. The system is made of vanes creating a flow deviation in turn by flapping around a rotational axis or by blowing air though a suitable sonic jet located close to the vane trailing edge. The airfoil shape optimization has been carried out using a design of experiment technique (DOE) and response surface optimization along with URANS CFD. The computational model has been preliminarily validated using data provided by ONERA for the baseline design at a lower Mach number ( \(\hbox {M}=0.73\) ) and then compared with the one actually required by GUDGET in the test chamber ( \(\hbox {M}=0.82\) ). All the cases have been optimized at a frequency of 40 Hz and then investigated at a frequency of 80Hz. PubDate: 2021-10-07 DOI: 10.1007/s42496-021-00098-y
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Abstract: Abstract Boundary Avoidance Tracking (BAT) theory has emerged as a novel theory in the area of Handling Qualities (HQ). The HQ of the aircraft in a given environment greatly influences the cognitive load of the pilot. Advancement in eye gaze tracking technologies has enabled non-invasive estimation of cognitive load of pilots, even in combat aircraft cockpits. This research is aimed to investigate BAT theory using a COTS-based eye gaze tracker to record ocular parameters like fixations and saccades to study the effects of boundary size/limits on the cognitive load of the pilot. The statistical model involved three independent variables, namely aircraft flying qualities, secondary task, and boundary size. Initially, experiments were conducted in two stages on a fixed-base variable-stability HQ research flight simulator. Further, the study was extended to inflight tests involving flights in Hawk and Jaguar aircraft maneuvering in high G conditions and undertaking various training combat missions. Both studies found statistically significant correlation between boundary size/limit and ocular parameters, in particular, the rate of fixations. The results proved the application and effectiveness BAT theory in HQ Stress Testing to elevate pilot gain, during flight testing of flight control system for a new aircraft program. PubDate: 2021-09-17 DOI: 10.1007/s42496-021-00094-2
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Abstract: Abstract There is an increasing trend for the usage of electrically powered equipment in the aviation industry. In this paper, a Reliability Centered Maintenance (RCM) analysis application is performed for Electro-Mechanical Actuators (EMA). We consider a new model for criticality classification for individual failure modes for the Reliability Centered Maintenance analysis stages using the Analytic Hierarchy Process (AHP) method. AHP method is used as a new tool for motor, electrical/electronic, and mechanical/structural failures in EMAs. A predictive maintenance planning model is also offered for Class A and B parts designated for electro-mechanical actuators. PubDate: 2021-08-10 DOI: 10.1007/s42496-021-00089-z
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