Journal of Aerospace Engineering

The electric solar wind sail (E-sail) is an innovative propellantless concept for interplanetary space propulsion that uses the natural solar wind as a thrust source with the help of long, artificially charged tethers. The characteristic property of an E-sail based spacecraft is that the propulsive acceleration scales as the inverse Sun-spacecraft distance, and the thrust vector can be varied within about 30 deg away from radial direction. The aim of this paper is to estimate the transfer times required to fulfill a mission toward the near-Earth asteroid 1998 KY26. In doing so the propulsive acceleration of the E-sail, at a reference distance from the Sun, is used as a performance parameter so that the numerical results are applicable to E-sails of different sizes and different payload masses. The paper shows that the flight time scales nearly linearly with the inverse of the spacecraft maximum propulsive acceleration at 1 astronomical unit from the Sun, when the acceleration is greater than $0.3{\mathrm{mm}/\mathrm{s}}^2$. For smaller propulsive accelerations the relationship for the flight time is more involved, because the transfer trajectory is complex and more than one revolution around the Sun is necessary to accomplish the mission. The numerical analysis involves a sample return mission in which the total flight time is parametrically correlated with the starting date for a given E-sail propulsion system.

To define load spectra of main rotor blades in this study computational fluid dynamics (CFD) software is used. The aim of the present investigation is the development of a CFD computation procedure capable of accurately simulating the flow around a full helicopter especially around main rotor blades. For this purpose the complete helicopter configuration including fuselage, main rotor and tail rotor computer-aided design (CAD) models are used in CFD modeling and determination of loads. Primary attention in this investigation is focused on defining loads of main rotor blades because metal trailing edge segments of these blades were replaced with a new segments made from honeycomb composite materials. As critical structural parts with respects to strength here are glued joints between metal and composite segments of trailing edge are considered. For precise stress analysis of these segments, including glued joints, the finite element method is used.

This paper describes the development of a three-axis attitude control system for nanosatellites and CubeSats, based on commercial electronics and capable to work autonomously for attitude stabilization or controlled from Earth to perform real-time orientation maneuvers. The system contains three microreaction wheels and related drivers, three magnetorquers with their control circuits, three magnetometers, and control electronics. The system is completely independent from the host spacecraft, with all systems included in its structure. For autonomous attitude control, an external sensor is required, providing the orientation of a reference source, such as the sun, eventually evaluated based on solar array outputs, Earth, or stars. The communication interface is based on a serial link and can be used to transfer commands, parameters, and housekeeping data. Miniaturization of the system components and of the whole assembly are among the main innovations introduced with respect to traditional attitude control system implementations, creating a complete system suitable even for one-unit (1U) CubeSats. The complete system is as small as a 52-mm side cube, weighing 150 g. The development phases of the system are described, from the definition of the design parameters to the realization of the working prototype, focusing on the system miniaturization, electronics design, and functional tests.

This article explores the boundary layer flow of Casson fluid in a thin liquid film over an impulsively moved plate with heat transfer. Viscous dissipation is considered. Mathematical formulation is presented using conservation laws of mass, momentum, and energy. Small-time series solutions for velocity and temperature are constructed. Effects of embedded physical parameters in the velocity and temperature profiles are analyzed. Numerical values of skin friction coefficient and local Nusselt number are computed and analyzed. It is found that the Casson fluid parameter decreases the temperature. Further, it is noted that effects of Casson fluid and film thickness parameters on the velocity and temperature are qualitatively similar.

This paper presents a novel design methodology to be used in the evaluation of the main features of advanced unconventional airship configuration. Similar to the process used in aircraft design, the concept of volume fractions (VF) is introduced to estimate airship weights, dimensions, and performances, in an early design phase. The paper presents the complete methodology, with tables and constants to help unconventional airship designers with preliminary design considerations. Volumes and weights of candidate solutions are obtained through an iterative method within a user-friendly tool requiring graphical and straightforward mathematical operations. The solutions are ranked based on procedures aiming at satisfying customer needs and expectations provided as inputs. A case study highlighting a step-by-step methodology process is presented, and the approach followed to select the final solution is documented. The method is easy to use and implement, rapidly providing a significant amount of data. A parametric approach is used such that the evolution in materials and technology, new configurations, and modern power and energetic solutions can be considered by simply performing a parameter sweep to perform sensitivity analysis.

Numerical investigations on the performance of the miniature centrifugal compressor in a SR-30 minijet engine are conducted in this study. A numerical framework is built on the basis of the grid independence and wall treatment sensitivity studies. The simulation results show that the compressor pressure ratio and isentropic efficiency is 2.65% and 70.1%, respectively, at 80,000 rpm. The experiments on the SR-30 engine were conducted at a testing rig for minijet engines. It is found that at 80,000 rpm, the experimental results of the compressor exit temperature is about a 9.2% difference from the simulation results and the difference in the pressure ratio is less than 4%. The compressor isentropic efficiency and pressure ratio are evaluated as a function of mass flow rate. Both the isentropic efficiency and pressure ratio show peak values at a specific mass flow rate. Continuously increasing or decreasing the mass flow rate leads to drops in both the pressure ratio and efficiency. Furthermore, the compressor surge and choke phenomena are discussed according to the mass flow rate range. Flow distribution in the impeller inlet area is mapped to illustrate the surge and choke phenomena.

In this article, the peristaltic flow of an Eyring-Powell fluid in a curved channel is modeled. Anapproach utilizing along wavelength and low Reynolds number is employed for the analysis in a wave frame. A series solution is obtained. Results for stream function, longitudinal velocity, pressure gradient, and pressure rise are plotted and analyzed. The pressure rise per wavelength is examined numerically. It is noted that results for aplane channel and viscous fluid can be deduced as the limiting cases of the present work. A comparison of flow between the planarand curved channel is also shown.

Different from the current studies on the impulsive rendezvous which are mainly normal propellant-optimal or time-optimal designs, the safety-optimal impulsive rendezvous with consideration of practical trajectory uncertainties is investigated in this paper. An optimization model for safety-optimal rendezvous is established based on the Clohessy-Wiltshire (C-W) equations, which employs one new, recently proposed quantitative performance index of the rendezvous trajectory safety as the objective function. A real-coded genetic algorithm is adopted to locate the optimal solution. The safety index and the optimization approach are tested by several rendezvous problems with different numbers of impulses and different approach directions. The practical application value of the safety-optimal rendezvous trajectory is demonstrated by comparing with the traditional propellant-optimal and time-optimal rendezvous trajectories.

This paper proposes a visual perception system for a tethered space robot’s (TSR) automatic rendezvous from 100 to 0.15 m. The core problem, tracking the entire contour of noncooperative moving targets in real time, is emphasized in this work. Given numerous challenges in a dynamic scene, a novel feature tracking algorithm is developed, i.e., the monocular real-time robust feature tracking algorithm (MRRFT). To generate a robust target model, improved speeded-up robust features (SURF) are used to extract features from a marked target box. The tracker then uses the pyramid Kanade-Lucas-Tomasi (P-KLT) matching algorithm and eliminates mismatched points by a statistical method. The greedy snake algorithm is applied to obtain the exact location of the target box and to update it automatically. A discrete feature filter and an adaptive feature updating strategy are also designed to enhance robustness. A three-dimensional (3D) simulation and a semiphysical system are developed to evaluate the method. Numerous experiments demonstrate that the tracker can stably track satellite models with simple structures with improved accuracy and time savings than good features to track (GFTT)+P-KLT or scale invariant feature transform (SIFT)+P-KLT.

Ribs and edges are the typical deformable aluminum components of the horizontal stabilizer. Riveting is the most common method of joining ribs and edges. Riveting bulging is unavoidable but extremely undesirable in the aircraft assembly. When the bulging effects of rivets coupling, there will be deformation in the aircraft’s structure. Riveting sequence is one important approach to eliminate the coupling effect of the bulging and control the deformation of the aircraft structure. Riveting sequence study of horizontal stabilizer assembly was conducted using finite element method. A riveting equivalent unit is proposed and employed to analyze the deviation induced by different riveting sequences. Equivalent unit for riveting brings a good balance between accuracy and the computational efficiency in finite element analyzing. The results have shown that different riveting sequence results in different dimensional quality, and an optimal riveting sequence of the trailing edge is obtained. It will enhance the understanding of the compliant components assembly with riveting and help systematically improving the precision control efficiency in civil aircraft assembly.

The development of reliable and computationally efficient analysis capabilities for aeroelasticity represents one of the most intriguing challenges of modern times. In this paper, an automatic procedure for flutter clearance assessment under damage has been set up. The whole procedure is efficient in managing flutter calculations when a stiffness or inertia change occurs in a substructure of the aircraft, where the change is meant to be caused by a damage occurring during flight. The efficiency is reached by means of a substructuring approach. The procedure has been set up on a business jet in which damage cases on a trunk of the horizontal tail are processed. The method has the advantage to be effectively used when flutter occurrence has to be evaluated on a statistical basis because of its computational efficiency and reliability. Statistical quantities such as cumulative density function and probability density function related to flutter speed by means of hit or miss Monte Carlo simulations have been calculated in order to show the potentiality of the method when approaching a stochastic analysis. The damage database that has been processed by Monte Carlo is not significant from a statistical point of view. Nevertheless, the aim of the paper is to set up the procedure, which is deemed a useful tool to quickly assess flutter clearance under damage, especially for military aircrafts, subjected to the extent of damages that can effect the aeroelastic performance. It has been estimated that a statistical significant number of cases (71,428 cases) would require 80 h of computational time with a laptop of moderate performance.

In an effort to assess motor and propeller performance for small unmanned aerial vehicles (UAVs), a car-top test module has been developed. This device allows for characterization of propeller and motor combinations in mean flow without the investment that is inherent with wind tunnel testing. Additionally, propulsion systems can be tested for reliability in real-world environments without risk to an airframe. Measurements of the propeller efficiency, thrust coefficient, power coefficient, and temperature of the motor and the electronic speed controller as initial parameters of interest are reported. Thrust at different advance ratios is compared to data from wind tunnel testing in order to gauge the accuracy of this technique. The module performed well in its intended role, and it is recommended that similar devices be used for time-critical or low-cost applications.