Abstract: This article presents the design, manufacturing and wind tunnel tests conducted on a 1:4 scaled Vertical Take Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV). A brief description of the VTOL model, identifying characteristic dimensions, along with the manufacturing process for the scale model and the measurement equipment is presented. Results of the wind tunnel experiments are conducted varying both angle of attack and sideslip angle for a wide rage of the angles, and several wind tunnel speeds, thus allowing to characterize the full flight envelope for all three flight phases of the VTOL-UAV: axial, transition and cruise flight phases. A description of the wind tunnel measuring setup and the methodology used is presented, along with the subsequent analysis and corrections considered for all the data obtained, presenting a discussion about the results and its comparison with numerical analysis obtained with CFD studies. Finally, some conclusions and recommendations are made with the main objective of establishing a basis for future tests. PubDate: 2020-12-04 DOI: 10.1007/s42496-020-00070-2
Abstract: A new analytical solution in the form of asymptotic series is proposed and studied for Mode III crack problems with spring boundary conditions, which are, in the mathematically-oriented literature, referred to as Robin boundary conditions. Under the assumption of antiplane shear loading, the corresponding elastic problem reduces to the Laplace equation for the out-of-plane displacement. Numerical solutions for benchmark problems are obtained, applying the Finite Element Method, to verify this asymptotic approximation. In particular, two problems are studied, Neumann–Robin and Dirichlet–Robin. Both are used to define a partially damaged adhesive interface in which the Linear Elastic Interface Model is applied. The numerical solution is obtained using the software FEniCS, for which the variational formulation of the problem is developed. Then, it is compared to the analytical expressions proposed for the problem, computing a normalized error. Finally, a convergence analysis is presented. Several parameters, such as the stress singularity or another error measure, are used to analyse two different ways to refine the mesh. PubDate: 2020-11-18 DOI: 10.1007/s42496-020-00068-w
Abstract: The transitional flow around the SD7003 airfoil at \(\alpha = 8^\circ\) , \({\text { Re }}= 60,000\) and \({\text { Ma }}= 0.2\) was investigated employing p-adaptive large eddy simulations in a Discontinuous Galerkin (DG) framework. This test case is particularly challenging since a laminar separation bubble (LSB) with transition and reattachment of the turbulent boundary layer has been observed. The results obtained with the dynamic anisotropic model have been compared with experimental measurements and other numerical results available in literature. The polynomial adaptivity technique confirmed its capability to correctly represent the flow with a great saving in the computational cost. The results are close to experimental measurements thanks to the capability of the subgrid model to capture the energy backscatter from the subgrid scales. Starting from the statistically steady state flow field obtained, the viscous, parallel, Blade-Vortex Interaction (BVI) has been studied in the same numerical framework. A modelled vortex has been superimposed to the developed flow around the SD7003 airfoil and the dynamic p-adaptivity has been successfully employed to capture its advection over time. The loads have been recorded and compared with a reference simulation without the vortex. While the drag rapidly comes back to its steady-state value, the transients for lift and moment coefficients are longer because of the effect of the vortex on the LSB. PubDate: 2020-11-16 DOI: 10.1007/s42496-020-00065-z
Abstract: Asteroid mining is one of the most promising private space ventures of the near future. Near-Earth Asteroids (NEAs), i.e. those with perihelion at less than 1.3 AU from the Sun, are among the best candidates for such venture. In preparation of mining expeditions, it is likely that prospector missions will be carried out well in advance so to assess the accessibility, potential for revenues and possible critical issues of target asteroids. This work is concerned with the problem of the feasibility of a single spacecraft prospector mission capable of visiting as many NEAs as possible in one shot, focusing on Apollo-class asteroids only. The search of possible trajectories is done assuming a chemically propelled spacecraft with realistic specific impulse and propellant mass ratio, so to allow for a credible mission design with a reasonable, cost-effective total duration. In order to restrict the number of possible trajectories, only those that lie in the plane of the ecliptic are examined; such trajectories can be reached from the Earth without expensive plane change maneuvers. The search for a maximum number of encounters is thus restricted to those occurring where the asteroid orbit crosses the ecliptic. A deterministic building blocks approach is adopted, dividing the optimization problem in two parts: a local optimization for possible target determination; and a global optimization for the choice of the overall trajectory. It is found that the combined approach leads to the identification of viable trajectories, able to perform a number of encounters that depends on the launch epoch; as an example, in one test case two different sets of 21 NEA’s each were identified that could be reached with a single launch, with a slightly different propellant expenditure. It is concluded that the method is well suited to perform feasibility studies of NEA missions with good accuracy and moderate computational cost. PubDate: 2020-11-12 DOI: 10.1007/s42496-020-00067-x
Abstract: The present paper provides an investigation of the effects of linear slosh dynamics on aeroelastic stability and response of flying wing configuration. The proposal of this work is to use reduced order model based on the theory of the equivalent mechanical models for the description of the sloshing dynamics. This model is then introduced into an integrated modeling that accounts for both rigid and elastic behavior of flexible aircraft. The formulation also provides for fully unsteady aerodynamics modeled in the frequency domain via doublet lattice method and recast in time-domain state-space form by means of a rational function approximation. The case study consists of the so-called body freedom flutter research model equipped with a single tank, partially filled with water, located underneath the center of mass of the aircraft. The results spotlight that neglecting such sloshing effects considering the liquid as a frozen mass may overshadow possible instabilities, especially for mainly rigid-body dynamics. PubDate: 2020-11-10 DOI: 10.1007/s42496-020-00064-0
Abstract: The European Space Agency Venus Express mission (VEX) was sent to Venus in 2005 to unveil the unsolved mysteries regarding its atmosphere, the plasma environment and its temperatures. Radio occultation experiments performed by VeRa radio science instrument probed the planet’s atmosphere by studying the frequency shift on the radio signal sent by the spacecraft to Earth-based ground stations. This study carries out the calibration of the radio frequencies within a radio occultation experiment in order to correct the main sources of error as: thermal noise, spacecraft clock, spacecraft trajectory, and plasma noise. Any uncalibrated effects will bias the retrieval of atmospheric properties. A comparison of the occultation experiments between Venus and Mars is presented, both from the engineering and scientific point of view, through the analysis of Venus Express and Mars Global Surveyor (MGS) occultations data, highlighting stronger calibrations required for VEX, the extreme, hostile, thick Venus’ atmosphere, and a friendly, thin Mars’ atmosphere. This investigation analyzes Venus Express data recorded by the NASA Deep Space Network in 2014, and the results are compatible to previous studies of Venus atmosphere with VEX between 2006 and 2009. PubDate: 2020-11-09 DOI: 10.1007/s42496-020-00066-y
Abstract: This paper aims to describe the analysis of the performance of an electro-optical space-based sensor for space surveillance purposes and space debris detection in the geostationary (GEO) ring. Such sensor is considered to be operating on a dawn–dusk Sun-synchronous, circular low Earth orbit at an altitude of 630 Km, while its optical characteristics have been taken from those of the Space-Based Visible (SBV) sensor. Two main simulations have been carried out through the use of the MATLAB software. The first simulation deals with the detection capability of the sensor, which is discussed in terms of detectable visual magnitude when the target of the observation is a diffuse sphere orbiting in the geostationary (GEO) orbit; its minimum detectable size is then determined. In addition, the relative geometry between the Sun, the sensor and the target has also been studied along with the configurations which can limit the visibility of the sensor over the target. The second simulation has been used to evaluate the performance of the sensor in terms of number of detectable GEO targets and duration of the observation when a certain pointing strategy is adopted. In such strategy, two SBV-like sensors are placed on the same orbit, thus creating a constellation in which each sensor points towards a fixed location in the inertial space. These locations have been chosen to be the geosynchronous pinch points. PubDate: 2020-11-05 DOI: 10.1007/s42496-020-00063-1
Abstract: This paper considers a feedback control law that achieves attitude stabilization for Earth-pointing spacecraft using only magnetorquers as torque actuators. The control law is proportional derivative (PD)-like with matrix gains, and it guarantees asymptotic stability. The PD matrix gains are determined through the numerical solution of a periodic linear quadric regulator problem. A case study shows the effectiveness of the considered control law, and specifically of the gain selection method, in a simplified simulation scenario. PubDate: 2020-10-23 DOI: 10.1007/s42496-020-00062-2
Abstract: The problem of prediction of heat flux at throat of liquid rocket engines still constitutes a challenge, because of the little experimental information. Such a problem is of obvious importance in general, and becomes even more important when considering reusable engines. Unfortunately, only few indirect experimental data are available for the validation of throat heat flux prediction. On the numerical side, a detailed solution would require a huge resolution and codes able to solve at the same time combustion, boundary layer with possible finite-rate reactions, expansion up to at least sonic speed, and in some cases radiative heat flux. Therefore, it is important to validate, with the few experimental data available in the literature, simplified CFD approaches whose aim is to predict heat flux in the nozzle in affordable times. Results obtained by different numerical models based on a RANS approach show the correctness and quality of the approximations made, indicating the main phenomena to be included in modeling for the correct prediction of throat heat flux. PubDate: 2020-10-07 DOI: 10.1007/s42496-020-00060-4
Abstract: Cycler mission architectures consider the use of a large space vehicle that cycles continuously between Earth and Mars, describing a near-ballistic path that includes flybys at the two planets. While this large spacecraft can be equipped with the life support system appropriate for a long interplanetary flight with a crew, taxi vehicles of reduced size are sufficient to ensure the connection between the interplanetary vehicle and each planet. This study employs the relations of Keplerian motion and proposes a global exploration methodology capable of identifying the entire set of cycling paths belonging to two distinct families, without any need of solving the Lambert’s problem. This result is achieved by reducing the problem to the solution of a single nonlinear equation with only an unknown quantity, constrained to a proper interval, directly related to feasibility of the cycler. Some well-known solutions are found as special cases, together with further remarkable cycling trajectories, which often exhibit very interesting features, i.e. limited time of flight or reduced hyperbolic velocities. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00050-6
Abstract: The determination of minimum-propellant-consumption trajectories represents a crucial issue for the purpose of planning robotic and human missions to the Moon in the near future. This work addresses the problem of identifying minimum-fuel orbit transfers from a specified low Earth orbit (LEO) to a low Moon orbit (LMO), under the assumption of employing high-thrust propulsion. The problem at hand is solved in the dynamical framework of the circular restricted three-body problem. First, the optimal two-dimensional LEO-to-LMO transfer is determined. Second, three-dimensional transfers are considered, in a dynamical model that includes the Cassini’s laws of lunar motion. The propellant consumption associated with three-dimensional transfers turns out to be relatively insensitive to the final orbit inclination and exceeds only marginally the value of the globally optimal two-dimensional orbit transfer. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00046-2
Abstract: In a famous report about the induced drag of multiplanes, L. Prandtl conceived the Best Wing System: the lifting system having the minimum induced drag among all the other ones, for assigned wingspan and lift. The resulting shape was a box-wing, asymptotically equivalent to a multiplane having infinite wings. At the end of the report, he gave the performance of this optimal lifting system (in terms of dimensionless induced drag and vertical gap) through a curve, without presenting the method he used. Nowadays, modern computational aerodynamics show an excellent agreement between the numerical results and Prandtl’s prevision. The first part of the paper aims at clarifying which method Prandtl used for the Best Wing System only. In the second part of the paper, starting from Prandtl’s different approach for the biplane and triplane problem, we propose a simple model for the evaluation of the induced drag of multiplanes, using notions an aerodynamicist of 1920s likely had. We show that the limit multiplane having infinitely many wings, under the ansatz of elliptic lift distribution on the outermost wings and constant lift distribution on the innermost ones, matches the Best Wing System curve. This leads to a simple but interesting interpretation of the actual results. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00058-y
Abstract: The present paper deals with the take-off performance analysis of PrandtlPlane aircraft. The PrandtlPlane is a Box-Wing configuration based on Prandtl’s “Best Wing System” concept, which minimizes the induced drag once wingspan and lift are given. The take-off dynamics is simulated implementing the non-linear equations of motion in a numerical tool, which adopts a Vortex Lattice Method solver to evaluate the aerodynamics characteristics taking also ground effects into account. The take-off analysis is performed for both a PrandtlPlane and a reference monoplane, with the aim of comparing the performance of the two different architectures. The preliminary results show the potential advantages of the PrandtlPlane, such as runway length reduction and improved passenger comfort. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00056-0
Abstract: EDEN ISS is an H2020 project aimed at testing key technologies for plant cultivation in large-scale closed environments for a future implementation in space habitats. In this light, a Future Exploration Greenhouse has been designed, developed and deployed at the highly isolated German Neumayer III Antarctic Station to simulate the harsh conditions of an extra planetary outpost mission and test a typical space operation scenario. The greenhouse has been equipped with all the systems to control the environmental parameters (temperature, relative humidity, light intensity, etc.), and to accommodate and feed the plants during their lifecycle. A camera system has been implemented for plant status assessment via remote image analysis. A command and data handling system provides the capability to configure the experimental set points via software, and can be controlled by remote operators. A Mission Control Centre has been realized at DLR for remote monitoring and control of the facility. The MCC receives all the telemetry and the images and can make them available to other centres, which have been included in the operations loop to provide expert support to the on-site operator. This paper describes the facility and its capabilities as platform for fresh food production experiments in an extreme environment. It is an extended version of a paper presented at the AIDAA Congress 2019, in the Technical Session “Red Planet Exploration”. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00051-5
Abstract: This paper illustrates the historical and technical evolution of the Italian aerospace sector through the activities of A.I.D.A.A., the Italian Association of Aeronautics and Astronautics in the period from 1920 to 2020. A.I.D.A.A. celebrates 100 years of life since the founding of its first historical nucleus, A.I.D.A., the Italian Association of Aerotechnics, in 1920, a long period, a century which has seen great changes, both political and social, and two World Wars. These changes have involved all sectors, civilian and military, including the aerospace sector. To facilitate the analysis, this period has been divided into three stages: the first from 1920 to 1951 with the foundation of A.I.D.A., the Italian Association of Aerotechnics, the second from 1951 to 1969 with the constitution of A.I.R., the Italian Rockets Association, affiliated with A.I.D.A. and the third from 1969 to 2020 with the current name A.I.D.A.A., the Italian Association of Aeronautics and Astronautics and the astronautical sector. The main activities carried forward by A.I.D.A.A. are illustrated, in particular the National and International Congresses which best represent the Association since they express not only the quality and level of Italian scientific aerospace research but they also indicate the lines along which research will develop in the near future. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00059-x
Abstract: This paper proposes a novel approach to build refined shell models. The focus is on the free vibrations of composite panels, and the node-dependent-kinematics is used to select shell theories node-wise. The methodology shown in this work can provide at least two sets of information. First, it optimizes the use of shell models by indicating the minimum number of refined models to use. Then, it highlights which areas of the structures are more vulnerable to non-classical effects. Moreover, by varying various problem features, e.g., boundary conditions, thickness, and stacking sequence, the influence of those parameters on the modelling strategy is evaluated. The results suggest the predominant influence of thickness and boundary conditions and the possibility to improve the quality of the solution via the proper use of the refinement strategy. PubDate: 2020-09-01 DOI: 10.1007/s42496-020-00045-3
Hybrid journal (It can contain Open Access articles)
