Journal of Aerospace Engineering

The effects of active separation control on a highly loaded subsonic compressor stator cascade were numerically studied by comparing the behavior of different devices: continuous jet actuator (CJA), zero-net mass-flux synthetic jet actuator (SJA), and plasma actuator (PA). For the jet actuator modeling, a suction/blowing type boundary condition was used, imposing a time-constant velocity for the CJA case and a prescribed sinusoidal time-varying velocity for the SJA case. For the PA case, the body force, which represents the effect of the plasma actuator on the flow, was added to the momentum equations in the computational fluid dynamics (CFD) code. The PA is slightly more efficient for the reduction of flow separation in the region just downstream of the blade actuators. However, at the same mechanical power delivered by the actuator to the fluid, the SJAs are more advantageous than the CJAs and slightly outperform plasma actuator application from the pressure loss reduction and pressure rise viewpoints. The fluidic jets have low power requirements, whereas the power consumption would be prohibitive for the PA configuration that shows low fluid mechanic efficiency.

Aircraft engines usually contain a lot of pipes and cables whose routing design greatly affects engine performance and reliability. In this paper a pipe routing approach for aircraft engines based on ant colony optimization is proposed, which contains improvements in three aspects. First, constraints over aircraft engine pipe routing are formulated and classified with respect to nine aspects. Second, a fan annual mesh of the layout space is developed, and two-mesh division is conducted to store and update environmental information about the layout space. Every unit obtained by the layout space modeling has been assigned a potential value to meet constraints and represent different areas in the layout space. Third, an improved ant colony optimization is developed for pipe routing, which includes the classification of ant colony, rank mechanism updating rule of pheromone intensity, and a dynamic updating rule of heuristic information. Every ant can search for 26 adjacent units in random directions and across layers. Simulation results show that the proposed pipe routing approach is effective.

A finite-element-based computational model is used to investigate the effects of bore cracking on stress distributions in solid rocket motors (SRMs) at various storage temperatures. Capabilities of a rocket-motor health-monitoring system are assessed based on the assumption that the proposed stress sensors are evenly distributed along the circumference of the inside of the motor case. A quantitative relationship is obtained between the crack depth and the sensor data to inversely estimate the size of bore cracks in the motor. It is shown that the proposed type of sensing system can detect critical bore cracks in SRMs.

The strong variations in lift that occur with changes in forward speed lead to one of the fundamental difficulties in aircraft design: how to provide sufficient lift at landing and take-off without having oversized wings for cruise conditions. This fundamental problem is generally tackled using two approaches. First, by providing flaps and other high-lift devices, extra lift can be generated during landing and take-off, albeit at the cost of extra drag and complexity. Second, by using long and smooth runways, higher landing and take-off speeds can be tolerated, closing the gap between these speeds and those of operational flight. Even so, it is common for aircraft flying in the cruise condition to be operating with rather small main wing angles of attack (AoAs) compared with those at stall, implying that smaller wings would be desirable if acceptable landing and take-off could be achieved. A number of designers have attempted to tackle this problem with various forms of powered lift augmentation. This paper re-examines the idea of the Custer wing duct, also known as a channel wing, here applied to small unmanned air vehicles (UAVs). Such aircraft are generally not operated from long smooth runways and rarely have complex high-lift systems in their wings. It is shown that by using suitable ducts around the propellers, startlingly good take-off and landing performance can be achieved, and that suitable ducts can be readily incorporated into small UAVs with the use of 3D printing (selective laser sintering) for their manufacture. Computational fluid dynamics (CFD) analysis, wind tunnel tests, and flight trials of a Custer channel wing UAV are described.

A high-speed manufacturing process for multiwalled carbon nanotube (MWNT) buckypaper is presented, and its application as an embedded strain sensor for composite materials is demonstrated. This manufacturing method enables the production of sizable carbon nanotube (CNT) membranes with significantly reduced processing time and less manufacturing complexity than other contemporary techniques. The use of surfactants and chemical functionalization of MWNTs was completely avoided in this method because functionality of carbon nanotubes can be hampered by such surface treatments. Microstructure, mechanical properties, and piezoresistive response of the fabricated buckypaper were characterized, and its sensitivity as a strain sensor was analyzed. Stable piezoresistive response could be achieved at low strains, and a high sensitivity to strain was observed when buckypaper was embedded in glass fiber epoxy laminates for strain sensing.

A computational modeling and simulation study is carried out to gain insight and formulate strategy for the design and tailoring of panel-like space structure that can withstand space debris impact without penetration. To represent a generic engineering structure, the impacted panel structure is modeled as a set of bonded plates. The analysis is based on fundamental principles, which are elaborated and numerically simulated. The objective is to identify optimum configuration in terms of loading, structural dimensions, material properties, and composite layup. The analyses are based on dynamic response with emphasis on the elastic region. The direct numerical simulation is carried out in parallel for the analysis, synthesis, parametric study, and optimization. Simulation results of impact loading by a spherical rigid body at certain velocity perpendicular to the panel show how fiber-metal laminates can be structurally tailored to achieve a nonpenetrating impact.

The problem of axisymmetric magnetohydrodynamic (MHD) flow of third-grade fluid between the stretching-shrinking sheets has been modeled. Suitable transformations are considered to reduce the partial differential equations into the ordinary differential equations. The resulting nonlinear differential system for both the cases, stretching and shrinking, is solved by the homotopy analysis method (HAM). The radial and axial velocities are displayed and discussed. Considering both stretching and shrinking phenomena, the skin friction coefficient is tabulated and analyzed.

The stagnation point flow of a Jeffrey nanofluid towards a stretching surface is addressed in the presence of Newtonian heating. The fluid is electrically conducting in the presence of an applied magnetic field. Appropriate transformations reduce the nonlinear partial differential system to an ordinary differential system. The governing nonlinear system is computed for convergent solutions. Results of velocity, temperature, and concentration fields are calculated in series forms. Effects of different parameters on velocity, temperature, and concentration profiles are shown and analyzed. The skin friction coefficient as well as Nusselt and Sherwood numbers are also computed and examined.

A 32.8-kg unmanned aerial vehicle (UAV) is employed as a case study to assess the accuracy of the empirical techniques used in predicting aerodynamic performance. Despite the prevalent use of empirical methods for the design of new UAV airframes, it remains difficult to quantify the uncertainty in their use, even for traditional aircraft configurations. In this study, a collection of common methods is applied for developing a simple mathematical model for predicting various performance metrics, including thrust required for level, ascending, or turning flight. The calculated performance is compared directly against actual aircraft performance.

This paper reports the heat and mass transfer effects in three-dimensional flow of a Maxwell fluid over a stretching surface with convective boundary conditions. Analysis is carried out in the presence of mass transfer with first-order chemical reactions, and with Soret and Dufour effects. Convergent series solutions to the resulting nonlinear problems were developed. It is found that the roles of Deborah and Biot parameters on the Nusselt number were opposite; however, the Sherwood number was qualitatively similar for both Biot and Deborah numbers. Also, variations of Prandtl and Biot numbers on the Nusselt and Sherwood numbers were similar.

A modern class of micro aerial vehicles (MAVs) uses deformable membrane wings (DMWs), which comprise rigid or rigidizable structural elements that guarantee stiffness, as well as flexible membranes that provide an aerodynamic shape, all in a compact and lightweight form. To contribute to the body of knowledge about DMWs, this paper presents extensive numerical simulations, accompanied by experiments that substantiate the findings pertinent to the aerodynamics and static aeroelastic behavior of these unconventional wings. The performance characteristics of canonical, untapered, and untwisted rectangular DMWs are studied using a parametric physical-based two-dimensional (2D) fluid structure interaction (FSI) model adopting a two-way coupled FSI algorithm. The effect of geometrical, material, and flow properties is investigated, and the results obtained show that the material Young’s modulus is the most influential parameter affecting the aerodynamic characteristics of the studied DMWs, with their higher rigidity and lower excess length ratio producing a higher lift-to-drag ratio. The validation of the computational modeling is carried out using a dedicated experimental setup tested in a low-speed wind tunnel facility. Numerical investigations show reasonably good agreement with the performed experiments and provide a wealth of information on the aerodynamic and aeroelastic behavior of this class of wings.

To avoid the mathematical singularity of polar converting in bank-to-turn (BTT) guidance and to provide the specified terminal impact angle, a BTT guidance law with impact-angle constraint (BTT-GL/IA) is presented. Considering the influence of the impact-angle control and target maneuver to the miss-distance, a new form zero-effort miss-distance with impact angle (ZEM/IA) is introduced. Referring to the Lyapunov-like approach used to drive the guidance law in the prior literature, a Lyapunov function is constructed in terms of ZEM/IA. Based on the Lyapunov stability theorem, a negative definite function is designed, and the BTT-GL/IA is derived. Next, BTT-GL/IA is implemented in another form with the variables as the line-of-sight angle and its rate, which are easily measured by the seeker. When using BTT-GL/IA, the guidance law tends to maintain smooth and continuously-varied body acceleration and roll-angle commands while satisfying the impact position and angle constraints. The problem of a mathematical singularity in normal BTT polar converting logic is avoided. Finally, both the maneuverable and stationary targets with different impact-angle constraints are considered in numerical simulations. Through various simulation results, the effectiveness and practicality of the BTT-GL/IA are demonstrated.

This paper addresses the coordination problem of distributed spacecraft systems with time-invariant communication topologies. In order to estimate the neighbor spacecraft’ relative states which are not able to be measured directly, estimating processes are established on each spacecraft by utilizing an unscented Kalman filtering approach with measuring principles of both the pseudorange and the carrier phase. Based on such estimations, a distributed consensus protocol is proposed to address the coordinated motion problem of distributed spacecraft. The effectiveness of the proposed approach is demonstrated through numerical simulations, with a low-Earth-orbit satellites flying scenario.

The relatively low fabrication precision of CFRP (carbon fiber-reinforced plastics) is an obstacle to the bimaterial specimens’ repeatability and reproducibility. A solution could be found by fabricating certain metallic specimens to fit the CFRP in order to obtain the exact experimental states of the bimaterial beam and accomplish the repeatability and reproducibility of the composite tests. The paper investigates the effect of spring-in distortion on a bimaterial beam’s ultimate tensile strength by the designed experiments. Typical assembling process of the bimaterial beam containing spring-in distortion is analyzed. Bimaterial specimens are designed to represent the typical spring-in distortion. Tension tests are carried out based on available standards to determine the CFRP’s behaviors in the numerical model. Correlation analysis between the real assembling state and the experimental assembling state is conducted in detail. Based on the verified numerical model of the experimental bimaterial beam, the numerical model of the real bimaterial beam is constructed. The effect of spring-in distortion on a bimaterial beam’s ultimate tensile strength is obtained. The reported work presents a solution of fabricating certain metallic specimens to obtain the exact states of the bimaterial beam containing spring-in distortion. It will enhance the understanding of the composite components’ assembly and help to systematically improve the composites’ assembling efficiency in the civil aircraft industry.

A novel take-off and landing system using ground-based power is proposed in the EU-FP7 project GABRIEL. The main feature of this system is the complete removal of the landing gear from civil aircraft. The proposed system has the potential to reduce aircraft weight, emissions, and noise. A feasibility study of the structural design of the connection mechanism between aircraft and ground system has been performed by simulating the landing procedure on a moving ground system. One of the key challenges is the landing on a moving ground system under high crosswind conditions. The main focus in the current research is the calculation of the critical dynamic loads on both aircraft and ground system for a wide range of landing conditions (sink rate, velocity differences between aircraft and ground system, etc.). For comparison, conventional landing procedures with a traditional landing (TL) gear have also been simulated. The aerodynamics of the aircraft is represented by an accurate empirical model. The results of the simulations are a set of load cases and operational constraints that can be used for the structural design of the ground system and modifications to the aircraft. Eight critical load cases (combinations of vertical sink rate, horizontal velocity difference, and crosswind) are identified. These can be used instead of the traditional landing load cases specified in the certification specifications.

This paper proposes an efficient framework for multiobjective optimization of the fuselage step on a large amphibious aircraft using a combination of computational aerodynamic and hydrodynamic methods. Both cruise drag and water take-off resistance and distance are calculated to evaluate the effects of the two key parameters, the longitudinal location and the depth of the step. A Reynolds-averaged Navier-Stokes (RANS) model was used for the calculation of cruise drag of the wing body configuration. Water take-off resistance and distance required for the baseline configuration were calculated using a volume of fluid method for hydrodynamic calculation and RANS method for aerodynamic calculation, respectively. A drag breakdown method was adopted to improve the efficiency of the hydraulic calculations. The method can achieve an accuracy of less than 5% difference compared to fully viscous calculations with only half of the computational time. The optimization is achieved using a combination of design of experiment and the response surfaces method. The optimized step configuration achieved an 18% improvement in take-off distance while maintaining similar cruise performance. The proposed method is generic and can be used in the optimizations of other components such as wings and fuselage geometries of amphibious aircraft.

This paper describes a novel approach for vision-based passive navigation of unmanned aerial vehicles (UAVs) suitable for use in outdoor environments. The researchers chose a number of coordinate points on a flat earth model as waypoints. At each waypoint, a number of objects were chosen as landmarks which provided a unique polygonal constellation. Features of these landmarks and waypoints were computed in advance and stored in the database. A 6 degree of freedom kinematic model of a UAV flew from one waypoint to the next waypoint in a detailed simulation which included real aerial imagery. An image of the terrain was captured while approaching the waypoint. An illumination, scale, and rotation invariant algorithm was used to extract landmarks and waypoint features. These features were compared with those in the database. Position drift was computed at each waypoint and used to update the current position of the UAV prior to heading towards the next waypoint. The drift calculated by the vision-based algorithm was used to estimate the error caused primarily by wind and thus estimate the wind speed and direction. Experiments with both computer generated images and real images taken from the UAV flight trial have demonstrated the technique in the presence of wind and Gaussian noise. These results show accuracy of the drift computation algorithm and reliability of the feature matching algorithm under various environmental conditions. These algorithms were compared against other popular algorithms in the field and demonstrate higher performance.

The use of solar radiation pressure for station-keeping at a sub-$L_2$ Sun-Earth/Moon collinear libration point is presented. Numerical halo and Lissajous reference trajectories are generated for the sub-$L_2$ libration point. Owing to the instability of these orbits, active station-keeping is required to prevent spacecraft escape after orbit insertion. The control inputs for solar sail control include area variation and solar sail pitch and roll angle variations. A nonlinear higher order control method is developed to utilize solar radiation pressure to minimize the trajectory tracking error. The stability of the proposed controllers is established using the Lyapunov theory. The performance of the proposed controllers is tested through numerical simulation of the governing nonlinear equations of motion and is applied for station-keeping in the elliptical restricted three-body problem. It is shown that underactuated control is able to keep the spacecraft motion bounded, but the tracking error remains high. The fully actuated control is able to provide accurate station-keeping for both halo and Lissajous trajectories. The numerical results demonstrate the effectiveness of the proposed control technique for precise station-keeping using solar radiation pressure at a sub-$L_2$ libration point.

Miniature aerial vehicles (MAVs) are finding applications in a number of civilian domains in which their autonomous operations are desirable. Applications of miniature aerial vehicles in different areas are growing exponentially due to technological advancement in areas such as computing, sensing, and communication, and due to advantages offered by these vehicles in terms of safe and economic operations. Due to the drive to keep cost of MAVs low, or lack of available technology and accurate sensors, exact measurement of pertinent signals and states of these kinds of nonlinear systems is not always possible. This necessitates the development of algorithmic tools such as observers that can be used to enhance the performance of sensors and measurement devices. The more complex a control system becomes, the more difficult it becomes to measure the states of the system accurately, which inherently makes the development of observers more challenging. In this paper, state observer and control system design for a small coaxial helicopter are presented. The states are observed with three different methods and compared for designing a classical pole-placement controller (based on a linearized model of the plant) and applied to a coaxial helicopter. The observer design methods used in this paper are based on Kalman filter and full- and reduced-order Luenberger observers. Numerical simulations have been carried out to illustrate the proposed techniques. Comparison of the three proposed methods confirms the intuitive notion that, in case of noisy systems, using Kalman filter method yields more accurate results as compared with the Luenberger methods.

An attempt is made in this work to develop an observer-based modal ${\mathrm{H}}_2$-optimal controller for active vibration control of laminated composite plates subjected to external excitation. Collocated piezoelectric patches are used as distributed sensors (polyvinylidene fluoride, PVDF) and actuators (interdigitated electrode-piezofiber composites, IDE-PFC) along with multiple point observers. The structural modal model is developed based on finite-element methodology and is coded in a MATLAB environment. Optimal positioning of the sensor/actuator pairs is evaluated based on the ${\mathrm{H}}_2$ norm of the sensor/actuator for a few selected structural modes and the piezo patches are accordingly placed. Response analysis is then carried out for both open- and closed-loop systems, and the effectiveness of the developed model is established. Piezoelectric actuation voltage is also calculated based on the closed-loop performance of the developed system.

Curvic couplings are extensively used in aerospace machinery, such as helicopter, aero-engine, or other aircrafts. The aim of this paper is to reveal new insights into the behavior of bolted joint with curvic couplings according to the bolt geometry and physical parameters by an analytical model. The different cases are focused mainly on the different geometry characters of the bolt. The analytical results show that the compression stiffness of both the curvic and the ring part of the disc has some relationship with the curvic rotation. The curvic rotation angle and the curvic compression stiffness show a slight difference during the tightening regardless of the bolt structural parameters. However, the stiffness of the other disc parts present a more obvious difference in tightening because of the various bolt structural parameters.

This paper proposes a negative Gaussian curvature cable dome and examines its feasibility. First, the paper studies its configuration and demonstrates that it satisfies the original definition of the cable dome in geometric concept. Second, the paper studies the feasible prestress of this new form of cable dome and provides a Newton iteration method and a simple displacement superposition to update prestress and geometry, respectively. Next, the paper builds an illustrative numerical model and determines its feasible prestress after changing its geometry using the proposed method. Last, its static advantage is compared with the corresponding Geiger dome and cable net structure, and its modal properties are analyzed. The results indicate that this new form is feasible not only in geometric concept but also in mechanical concept, and the method proposed in the paper is efficient and accurate for the design of feasible prestress for this new form. The negative Gaussian curvature cable dome has better rigidity than the corresponding cable net structure and better stability than the Geiger dome.

The zero-propellant maneuver (ZPM) is an advanced space station large-angle attitude maneuver technique using control momentum gyroscopes (CMGs), and rapid path planning (RPP) enhances its performance. This paper proposes a novel trajectory optimization technique—the RPP method—to generate the ZPM path. The core of the RPP method is the reconstruction of a continuous-time feasible solution upon the rapid computation of the nonlinear programming (NLP) problem. The method maintains the sparsity of the transcribed NLP and achieves the continuous-time feasibility of the solution with a small number of discretization points. Thus, rapid acquisition of a suboptimal solution may be achieved. The performance of the RPP method is demonstrated by showing that continuous-time feasible ZPM paths with high performance index may be obtained rapidly.

This paper proposes a new trajectory optimization approach that can directly handle the range safety for launch operations. An analytic solution for an instantaneous impact point (IIP) of a vehicle is introduced and used to describe the constraints of the optimization problem in an explicit way. A quadratic formula that can address various types of range safety requirements is proposed. Based on the aforementioned elements, the launch trajectory optimization problem with explicit IIP constraints is mathematically defined. The validity of the proposed trajectory optimization is demonstrated through two case studies using realistic launch vehicle data and range safety issues.