Journal of Aerospace Engineering

In recent years, the study of wing-body-tail interference has gained greater significance in aerodynamics because of its importance in the modern aircraft design. One of the interference consequences is formation of downwash phenomenon. Downwash reduces the wing’s effective angle of attack and as a result reduces lift force and also produces induced drag. Downwash changes the flow field downstream of the main wing and consequently changes the aerodynamic coefficients of the airplane’s tail. These changes directly affect the stability derivatives and control coefficients of an airplane. Because of the importance of the effects of the rate of downwash on the stability derivatives of an airplane, a three-dimensional airplane with T-shape tail in incompressible and compressible subsonic flows was studied numerically in this paper. A fully structured grid was used for the whole domain around the airplane. Aerodynamic coefficients of the horizontal tail of the airplane and also the downwash and downwash rate with respect to the angle of attack of the horizontal tail were investigated. In addition, the compressibility effects on the downwash rate of the airplane’s tail were also studied in this paper.

The flow regimes associated with a $2:1$ aspect ratio, elliptical planform cavity in a turbulent flat-plate boundary layer have been systematically examined for various depth/width ratios (0.1–1.0) and yaw angles (0–90°), using a combination of wind tunnel experiments (including particle image velocimetry) and computational fluid-dynamics (CFD) simulations. For each of the three categories specified according to yaw angle, which include the symmetric flow regime (yaw angle = 0°), straight vortex regime (yaw angle = 90°), and asymmetric flow regime ($15°\le \mathrm{yaw}\mathrm{angle}\le 60°$), different flow structures are found to exist depending on cavity depth. For each combination of yaw angle and depth, the flow has been analyzed through investigation of shear layer parameters, three-dimensional (3D) vortex structure, pressure distribution and drag, and wake flow. While the elliptical cavity flows have been found to have some similarities with those of nominally two-dimensional and rectangular cavities, the 3D effects due to the low aspect ratio and curvature of the walls give rise to features exclusive to low-aspect ratio elliptical cavities, including formation of cellular structures at intermediate depths and distinct vortex structures within and downstream of the cavity. The 3D structure of the flow is most pronounced in the asymmetric regimes with large yaw angles (45 and 60°). The dominant feature in this regime is the formation of a trailing vortex that is associated with high drag.

In this paper, the effects of temperature and oxidation on cyclic-fatigue life of two dimensional (2D) woven SiC/SiC ceramic-matrix composites (CMCs) have been investigated. The relationships between fatigue life, fibers failure, interface shear stress and fibers strength degradation, temperature, and oxidation have been established using micromechanical approach. The tension-tension fatigue life $S\text{-}N$ curves of 2D SiC/SiC composite at room and elevated temperatures in moisture, argon, air, and steam have been predicted. It was found that the presence of steam causes accelerated damage evolution and degradation in fatigue life compared with that in air.

Improved guaranteed cost control and quantum adaptive control are developed in this study for a quadrotor helicopter with state delay and actuator faults. Improved guaranteed cost control is designed to eliminate disturbance effects and guarantee the robust stability of a quadrotor helicopter with state delay. The inapplicability of guaranteed cost control to the quadrotor linear model is addressed by combining guaranteed cost control with a model reference linear quadratic regulator. In the event of actuator faults, quadrotor tracking performance is maintained through quantum adaptive control. Finally, the availability of the proposed scheme is verified through numerical simulation.

This research intends to characterize numerically the impact of sweep angle on the supersonic sharp corner flows. For this purpose, the effect of sweep angle on the variations of flow parameters such as shear stress, temperature, and pressure on the corner surface and also on the shock structure is examined. To ensure the accuracy of current numerical model, validation is performed with previous researches and reasonable agreements are observed. Results indicate that the inclusion of sweep angle has a significant effect on the Mach reflection strength and thus on the flow parameters’ variations on the corner surface. It is found that the role of sweep angle in changing the flow parameters’ variations in the zones near the trailing edge is of less significance than those that are close to the leading edge. It is shown that the inclusion of sweep angle has a little effect on the separation zone size although it tends to increase slightly the separation region length along the wing span at the trailing edge. Results demonstrate that the increase in sweep angle causes the shock structure and thus the Mach stem to become closer to the wing geometry. It is also seen that an increase in sweep angle leads to an increase in the Mach stem length.

Against a background of various techniques for gust load alleviation (GLA), this paper aims at proposing an improved linear quadratic Gaussian (LQG) method, which is robust to variations of flight parameters, structural parameters, and modeling errors and suitable for application in structure/control design optimization. This new technique differs from the traditional LQG methodology by the introduction of properly constructed fictitious high-frequency noise. Furthermore, to accurately measure the stability margins of the multi-input multi-output (MIMO) controllers, a variable-structure $\mu$ analysis method is proposed. The parameters of the Dryden continuous gust model are adjusted according to the structural natural frequencies to meet the design requirements, and model reduction combined with input signal scaling is applied to reduce the controller order. Using a general transport aircraft (GTA) model, the robust performance and robust stability of the improved LQG method are compared with those of modern robust controllers, including the $H_{\infty }$ controller and the $\mu$-synthesis controller. The numerical results demonstrate the successful application of this new technique.

Bistable tape springs are suitable as deployable structures thanks to their high packaging ratio, self-deployment ability, low cost, light weight, and stiffness. A deployable booms assembly composed of four 1-m long bistable glass fiber tape springs was designed for the electromagnetically clean 3U CubeSat Small Explorer for Advanced Missions (SEAM). The aim of the present study was to investigate the deployment dynamics and reliability of the SEAM boom design after long-term stowage using onground experiments and simulations. A gravity offloading system (GOLS) was built and used for the onground deployment experiments. Two booms assemblies were produced and tested: a prototype and an engineering qualification model (EQM). The prototype assembly was deployed in a GOLS with small height, whereas the EQM was deployed in a GOLS with tall height to minimize the effects of the GOLS. A simple analytical model was developed to predict the deployment dynamics and to assess the effects of the GOLS and the combined effects of friction, viscoelastic relaxation, and other factors that act to decrease the deployment force. Experiments and simulations of the deployment dynamics indicate significant viscoelastic energy relaxation phenomena, which depend on the coiled radius and stowage time. In combination with friction effects, these viscoelastic effects decreased the deployment speed and the end-of-deployment shock vibrations.

In this paper, numerical simulations are performed to investigate the influence of aerodisk size on the drag reduction and thermal protection of highly blunted bodies flying at hypersonic speeds. The compressible, axisymmetric Navier-Stokes equations are solved with an one-equation turbulence model for free-stream Mach number of 5.75. To ensure the validity of used numerical model, results are compared with data of analytical and experimental works and good agreement is observed. Results show that an increase in the aerodisk size initially decreases the drag coefficient and then increases the drag force. It is found that that the flat-faced spike leads to a lower drag than the spherical one at low aerodisk size, whereas the reverse is observed at high aerodisk size. The findings show that the spike length plays a crucial role in the drag coefficient. Moreover, results reveal that an increase in the aerodisk size significantly reduces heat load over the cone, while the heat load of the whole assembly increases at high aerodisk size. Numerical findings exhibit that heat load of the flat-faced spike is always lower than the spherical spike. According to the numerical results, the optimum aerodisk in terms of having lower drag and heating level is obtained.

A robust unscented Kalman filter based on a multiplicative quaternion-error approach is proposed for high-precision spacecraft attitude estimation using quaternion measurements under measurement faults. The global attitude parameterization is given by a quaternion, whereas the local attitude error is defined using a generalized three-dimensional attitude representation. To guarantee quaternion normalization in the filter, the unscented Kalman filter is formulated with a multiplicative quaternion-error approach derived from the local attitude error. A standard unscented Kalman filter provides sufficiently good estimation results even for initial large error conditions. However, in the case of measurement sensor malfunctions, the unscented Kalman filter fails in providing the required estimation accuracy and may even collapse over time. The proposed algorithm uses a statistical function including measurement residuals to detect measurement faults and then uses an adaptation scheme based on a multiple scale factor so that the filter may stand robust against faulty measurements. The proposed algorithm is demonstrated for attitude estimation of a spacecraft using quaternion measurements in three measurement fault cases. The estimation performance of the proposed algorithm is also compared with those of the standard extended Kalman filter and unscented Kalman filter under the same simulation conditions.

A splitter plate is a key component of the inlet system in turbine-based combined-cycle engines, which divides the whole captured air flow into different engines, namely turbojet and ramjet. The aerodynamic force acting on the thin splitter plate with a single pivot may engender vibration and, in turn, flow-field variations at the start and end of the mode transition phase. A loosely-coupled method was used to simulate the process of fluid-structure interaction. The results showed that the deformation of the splitter plate is, in fact, a process in which the elastic restoring force struggles against the aerodynamic force under the action of damping. At turbojet mode, the splitter plate can attain the maximum displacement of 7.20 mm. The terminal shock was observed to move back and forth in the flowpath. The mass flow rate in turbojet and ramjet flowpaths varied by 5.91 and 44.34%, respectively. At ramjet mode, the inlet fell into the unstart state with a greater displacement of 8.95 mm. The mass flow rate in turbojet and ramjet flowpaths, and slot-coupled cavity varied by 1.69, 23.91, and 51.85%, respectively.

This paper studies the use of a fuzzy proportional integral derivative (PID) controller based on a genetic algorithm (GA) in a docking maneuver of two spacecraft in the space environment. The docking maneuver consists of two parts: translation and orientation. To derive governing equations for the translational phase, Hill linear equations in a local vertical–local horizontal (LVLH) frame will be used. In fuzzy PID (FPID) controller design, two fuzzy inference motors will be utilized. The single input fuzzy inference motor (SIFIM) is the first to have only one input, and for each state variable, a separate SIFIM is defined. Another fuzzy inference motor, the preferrer fuzzy inference motor (PFIM), represents the control priority order of each state variable and a supervisory role in large deviations. This FPID controller covers a servicer’s translation of a docking maneuver, which tries to dock with a stable nonrotating target. Various conflicting objective functions are distance errors from the set point and control efforts. To enter the control limit in an optimization problem, the maximal value of the thrust force is constrained. Considering these objective functions, a statistical analysis on the GA parameters will be performed, and the test with the best minimum fuel consumption and minimum deviations of the servicer from the equilibrium point will be chosen as the best test. The three-dimensional (3D) Pareto frontiers corresponding to the best test will be plotted, and the optimal points related to the objective functions will be demonstrated on them; the time response figures corresponding to these points will then be generated. The results prove that this controller shows an efficient performance in the docking maneuver of the servicer spacecraft. In comparison with similar work, a number of system performance parameters (e.g., settling time) will be improved, and overshoot (as a critical parameter in docking maneuver) will be truncated.

Towing spinning debris in space is subjected to the risk of twist, increasing the likelihood of collision. To reduce the twist potential, a twist suppression method is proposed for the viscoelastic tether in this paper. The system two-dimensional model is explored taking into account the attitude of the two end bodies and the tether slackness. The twist model describing the twist length is established to investigate the tension change during twist. The impedance based tension controller is designed to regulate tension actively by altering the tether unstretched length. Three cases where the thrust is 1 N, 2 N, and 5 N are studied to validate the feasibility of the method. It is shown that without tension control, towing removal is challenging for the system owing to the twist potential and large tension induced. However, the twist length is reduced dramatically and the relative distance of the two bodies is maintained under the tension control. It is also shown that the controller is robust to the measurement noise, and its performance is better for the lager thrust.

An adaptive predictor-corrector guidance algorithm is presented to improve the performance of atmospheric entry guidance. In the predictor, a virtual entry terminal (VET) is employed instead of an actual terminal to reduce the computational request. The VET is adaptively selected from a reference trajectory according to the vehicle’s authority to cancel disturbances; thus, it is reachable by the vehicle in different cases. In the corrector, an effective modification method for the bank angle and the angle of attack is designed. With the predictor-corrector algorithm, the vehicle is able to reach the VET. After the VET, a reference trajectory tracking law is employed to fly the vehicle to the actual entry terminal. The adaptive entry guidance method is verified using Monte Carlo simulations. A comparison with the conventional predictor-corrector algorithm shows that the computation time is significantly reduced by employing the VET in the adaptive algorithm.

The authors investigate mechanical properties of sintered lunar regolith. Using JSC-1A and DNA lunar simulants, they study the influence of changes in glass content, main plagioclase series, and ilmenite content on a defined sintering process and on the mechanical properties of resulting sintered samples. Ilmenite addition up to 20 wt% of the regolith showed a negligible effect on the sintered product. The anorthite plagioclase endmember cannot be replaced by albite, responsible for the low sintering temperature of DNA and covering up the effect of the glass phase. The vacuum environment was revealed to have a positive effect on JSC-1A sintering: the grains bond at lower temperature than in air, thus preventing the formation of additional porosity and increasing the compression strength up to 152 MPa compared with only 98 MPa for sintering JSC-1A in air.

In a wind tunnel, the Mach number in the test section is an important parameter that should be predicted quickly and accurately. In building a Mach number prediction model, large-scale and high-dimensional data is the main issue. To solve the issue, the feature subsets ensemble (FSE) method has been proposed. However, a major drawback of the FSE method is that a large number of submodels are necessarily combined. In this paper, the maximum entropy pruning (MEP) method is proposed to overcome this drawback in the FSE Mach number prediction model. The MEP method refers to finding a subset of submodels that best approximates the entire submodels, while maximizing the quadratic Rényi entropy criterion. Experiments demonstrate that, with much fewer submodels than the FSE and other Mach number models, the MEP-FSE Mach number model can improve the prediction performance (i.e., the generalization), and meet the requirements of the forecasting speed and the root mean square error (less than 0.002).

In this paper, a robust optimal controller design problem is investigated for the longitudinal dynamics of generic hypersonic vehicles. The vehicle dynamics involve parametric uncertainties, nonlinear and coupling dynamics, unmodeled uncertainties, and external atmospheric disturbances, which are considered as equivalent disturbances. A linear time-invariant robust controller is proposed with two parts: an optimal controller to achieve the desired tracking performance and a robust compensator to restrain the influence of the equivalent disturbances. The robustness properties and the optimal tracking control performance can be achieved simultaneously without compromise. Theoretical analysis and simulation results are given to demonstrate the advantages of the proposed control approach.

A two-axis gimbal-type X-band antenna used to transmit real-time image data from a satellite to a ground station is a potential source of microjitter, which can degrade image quality from high-resolution observation satellites. Activation of discontinuous stepper motors during pointing of the antenna mechanism in the azimuth and elevation directions is one of the primary sources of microjitter disturbances. It is desirable to enhance microjitter attenuation capability by isolating disturbances from stepper motor activation with a reliable technical solution not requiring major design modification of the antenna. In this study, the application of a low-torsional-stiffness spring-blade isolator on the output shaft of the stepper actuator is proposed. The spring-blade isolators were designed based on the derived torque budgets of the antenna, ensuring structural safety of the blades. The design of the spring-blade isolators was verified through structural analysis and a torque measurement test. In addition, the effectiveness of the isolators was demonstrated in a microjitter measurement test of the $\mathrm{X}$-band antenna.

This study investigates an onboard aeroengine model (OBEM)-tuning system (OTS) based on a hybrid Kalman filter, which is mostly used to estimate the aeroengine performance. The OTS structure comprises two parts. One is an OBEM, the other a linear parameter-varying Kalman filter. The Kalman filter is used as a regulator to minimize the mismatch of the measured outputs between the OBEM and the actual engine. This study describes the method and procedure used to construct the OTS. The results from the application of the technique to the aeroengine simulations are presented and compared to the conventional approach of tuner selection. The new methodology is shown to yield a significant improvement in online Kalman filter estimation accuracy.

In this paper, a novel model-free fuzzy adaptive control (MFFAC) scheme is developed to control the heading angle of fixed-wing unmanned aerial vehicles (UAVs). It is common knowledge that the aerodynamics of the heading angle of fixed-wing UAVs are difficult to accurately model and are subject to wind disturbances. Therefore, it is difficult to implement conventional model-based control to the heading angle control problem. To overcome this difficulty, the authors propose a novel data-driven control approach. First, an adaptive neuro-fuzzy inference system (ANFIS) is designed to estimate the pseudo partial derivative (PPD), which is described as an equivalent dynamic linearization (EDL) technique for unknown nonlinear systems. Secondly, an extended model-free adaptive control (MFAC) strategy is proposed to control the heading angle of fixed-wing UAVs with wind disturbances. Finally, a discrete Lyapunov-based stability analysis is presented to prove the globally asymptotic stability of the proposed control scheme. The high-fidelity semiphysical simulations illustrate that accurate and stable control is achieved in this designed control strategy.

This investigation highlights the performance of epoxy-novolac interpenetrating polymer network (IPN) adhesive bonding of surface-modified polyether imide (PEI) to titanium (Ti) under elevated temperatures and an aggressive chemical environment as well as humid conditions. The results of physical and thermomechanical properties reveal that epoxy-novolac ($4:1$) IPN adhesive is the best combination. X-ray photoelectron spectroscopic (XPS) analysis demonstrates formation of oxide functional groups due to low-pressure plasma treatment onto the surface PEI and formation of oxide as well as nitride functional groups due to anodization and plasma nitriding on the titanium surfaces. Surface energy of the anodized titanium is relatively higher in comparison to plasma-nitrided titanium due to the high polarity of oxygen compared to nitrogen, and it consequently shows higher adhesive joint strength. Epoxy-novolac ($4:1$) IPN adhesive bonding of polyether imide to titanium reveals that anodized titanium to plasma-treated polyether imide adhesive joints show higher bond strength in ambient conditions. However, when exposed to an aggressive environment, the plasma-nitrided titanium to polyether imide adhesive joint shows higher bond strength because the nitride layer is more stable than the oxide layer and consequently results in a durable interface between titanium and adhesive, leading to cohesive failure of the adhesive joints.

The aim of this work is to investigate the analytical solutions for the equations of motion of a rigid body about a fixed point through the process of decoupling Euler’s dynamic equations. This body is acted upon by a gyrostatic torque $\underline{\ell }=({\ell }_1,{\ell }_2,{\ell }_3)$ about the axes of rotation, and in the presence of a moment about the same axes, it depends on an external loading in which its components have been expressed as a harmonic function of time. The achieved analytical solutions for the equations of motion are obtained under conditions consistent with the physical nature of the body, and the uniqueness of the solution is proved. Some new theoretical applications are presented when the body is symmetric about one of its principal axes and when the body is in complete symmetry. The graphical representations for the motion of the body are represented to show the effectiveness of the physical parameters of the body. Moreover, the phase plane plots are given to ensure that the considered motion is free of chaos.