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The Mach number, angle of attack and altitude of operation for an interceptor vary widely during the course of its trajectory. As a result, the interceptor Center of Pressure (CP) locations move significantly around a given Center of Gravity (CG) location at these operating conditions. This results in an inevitable variation in aerodynamic static stability leading to stable and unstable operating regions. In order to ensure good speed of response during the interceptor homing phase, lesser static stability is desirable. Hence the requirement to handle aerodynamic instability at some other operating conditions in the interceptor envelope become inevitable. Since flexibility has a strong bearing on autopilot design, it becomes necessary to control unstable operating points in the presence of flexibility modes. Despite the static stability variation, aerodynamic design can control the level of maximum instability of the configuration. Hence the maximum static instability the autopilot can handle has to be specified for aerodynamic configuration design. This paper brings out the limitations of autopilot design in controlling an unstable interceptor with low bending mode frequencies in terms of maximum instability the autopilot design can handle, which serves as an important input for aerodynamic design.

Interceptors operate at wide range of operating conditions in terms of Mach number, altitude and angle of attack. The aerodynamic design caters for such wide operating envelope by appropriate sizing of lifting and control surfaces for meeting the normal acceleration capability requirements. The wide range of operating conditions leads to an inevitable spread in center of pressure location and hence spread in static stability. The performance of control design is a strong function of the aerodynamic static stability. The total operating envelope can be bifurcated into statically stable and unstable zones and the aerodynamic lifting surface location can be used as a control parameter to identify the neutral stability point. During the homing phase lesser static stability is desirable for good speed of response, hence the lifting surface location needs to be chosen based on the capability of control to handle instability. This paper analyses the limitations of autopilot design for the control of an unstable interceptor and brings out a method to identify the optimum aerodynamic lifting surface location for efficiently managing static margin while satisfying the control limitations and homing phase performance. This provides an input on the most appropriate lifting surface location to the aerodynamic designer during the initial CFD based aerodynamic characterisation stage itself, before commencing the rigorous wind tunnel based characterisation.

An experimental study for the characterization of 6063-O aluminum alloy and IS 2062 mild steel materials under high strain rate shear loading was conducted. A microstructural study of the tested samples was performed to understand the correlation between the microstructure and mechanical properties. Aluminum alloy 6063-O and IS 2062 mild steel specimens were subjected to shear strain rates in the range of 120-200 and 100-280 s−1, respectively. An enhancement in the shear strength is observed for both the materials tested at high strain rates. The microstructural study on the fracture surfaces of the aluminum alloy and the mild steel test coupons was carried out using scanning electron microscopy (SEM). Grain size refinement was observed with increasing strain rate indicating a strong dependence of mechanical properties on the grain size evolution during testing. Changes in microstructural properties at different shear strain rates and its effect on the mechanical properties are presented.

Lissajous curves have been used in various engineering applications such as optics, imaging, antenna scan, machining, as well as mobile robotics. In this article, we propose and analytically justify a Lissajous curve based trajectory planning strategy for aerial multi-agent systems to achieve the following objectives simultaneously: (i) Collision free paths for repeated coverage of a region while maintaining a closed sensor ring around a specified center for all time. (ii) Guaranteed detection of any stationary or moving object enclosed within the ring in finite time without the possibility of undetected escape. This leverages known and some novel properties of Lissajous curves that we establish as a part of this work. This has several potential applications in civil and military missions such as search and surveillance, repeated patrolling, target detection and capture, and the proposed strategy meets all these objectives simultaneously. We validate the proposed strategy through simulations and experiments using differential drive ground robots. We also demonstrate the applicability of this strategy for aerial surveillance through a Software-In-Loop-Simulation for quadrotors.

A surface to air missile (SAM) typically operates at a wide range of Mach numbers, angles of attack and altitudes. This leads to an inevitable significant variation in center of pressure (CP) location. In addition, the propulsion burning changes the Center of Gravity (CG) location. The variation in CP and CG locations results in high variation in aerodynamic static stability in the flight envelope. The high variation of static stability makes operating at statically unstable regions inevitable and needs to be tackled through the missile on-board algorithm. The control design poses a requirement of high autopilot bandwidth to tackle the static instability, which leads to unrealistic actuator bandwidth requirements. Here, we propose a novel technique to handle the high static instability outside the purview of control design without burdening the control requirements. In this paper, the highly unstable operating conditions are avoided through judicious design of mid-course guidance. This paper also presents design of this guidance scheme through higher order sliding mode technique.

A real-time vision-based edge detection algorithm is used for reliable fault identification and it also helps to accurately know the extent of fault. Partial loss of vertical tail of a high performance fighter aircraft is considered for this purpose. A geometric method is used to characterize the identified damage by calculating percentage loss of vertical tail area and shift in aerodynamic center. Analytical estimation technique is used for stability and control derivatives identification. It is parametrized further to obtain the state matrix which can be stored off-line to improve real-time computation.

In this paper, a method to design the reduced-order sliding-mode control is proposed for the robust output tracking of an arbitrary signal for nonminimum-phase systems. The main contributions in this paper include the design of the reduced-order switching function that ensures the asymptotic tracking of an arbitrary reference signal during sliding motion, the design of the reduced-order sliding-mode controller that enforces the sliding motion in finite time, and the computation of bounds on stable and virtually stable zero dynamics that is required for the output tracking. To show the effectiveness of the proposed design method, results of implementation on the experimental setup of an inverted pendulum system are also presented here.

Investigations on the effect of intensity of incident pressure wave applied through the striker bar on the specimen force histories and stress wave attenuation during split Hopkinson pressure bar (SHPB) tensile testing are presented. Details of the tensile SHPB along with Lagrangian x-t diagram of the setup are included. Studies were carried out on aluminum alloy 7075 T651 and IS 2062 mild steel. While testing specimens using the tensile SHPB setup, it was observed that the force calculated from the transmitter bar strain gauge was smaller than the force obtained from the incident bar strain gauge. This mismatch between the forces in the incident bar and the transmitter bar is explained on the basis of stress wave attenuation in the specimens. A methodology to obtain force histories using the strain gauges on the specimen during SHPB tensile testing is also presented. Further, scanning electron microscope images and photomicrographs are given. Correlation between the microstructure and mechanical properties is explained. Further, uncertainty analysis was conducted to ascertain the accuracy of the results.

Fixed wing mini aerial vehicles (MAVs) are miniaturized version of conventional fixed wing aircraft. These are used for various applications such as traffic monitoring, aerial videography and photography, search and rescue operations etc. The launching of MAVs can be done using several mechanisms such as hydraulic, pneumatic, para-sail, bungee etc. In this paper bungee launch of MAV is considered. A mathematical formulation including forces acting on MAV at the time of bungee launch is derived considering the longitudinal model of MAV. During launch MAV experiences an extra force created due to tension in elastic bungee which may result in overshoots and loop formations in trajectory, which increases the chances of crash. Thus it is required to design a controller in order to have a desired performance. As sliding mode is one of the well known robust control technique, it is used to design controller for launch of MAV. The performance of MAV at the time of launch and after that, is analyzed with and without the controller. The controller performs well by reducing transients as well as by avoiding loop formation in the initial period of flight and by controlling the airspeed and pitch angle after the launch.

In this paper we present the design and implementation of autopilot tracking control law for Micro Aerial Vehicle using the second order sliding mode approach. The inner loop attitude tracking control design is carried out using output feedback based second order sliding mode technique, to ensure finite time convergence of the tracking error dynamics. While addressing tracking control of a time varying reference signal, it is important to investigate the stability characteristics of the internal dynamics to ensure perfect tracking. This paper mainly addresses the output tracking control problem for a MAV and investigate the stability characteristics of the longitudinal zero dynamics during tracking. We have proposed a stability proof based on Lyapunov theory to analyze the stability of the MAV longitudinal zero dynamics during tracking. A nonlinear aircraft model obtained using aerodynamic derivatives of The Blackkite 300 mm wingspan fixed MAV is used for both control design and as well as to verify its performance against the classical control methods. Extensive hardware in-loop simulation results of the proposed control algorithm implemented on the commercially available PX4 based Pixhawk autopilot board are also presented here.

This paper carries out a simulation based study on the performance of longitudinal control in an agile fixed-wing UAV with variable pitch propeller (VPP). Transition between cruise level flight at angle of attack (AOA)= 4°, and harrier level flight at AOA = 50° is implemented, on a variable pitch propeller design, in which the pitch of the propeller is actuated to change thrust, at constant rotations per minute (RPM). In a conventional design, the thrust is changed by varying RPM which is actuated by a Brush-less DC (BLDC)motor whereas in a VPP design, the propeller pitch is actuated by a servo motor which has faster response compared to a BLDC motor used in small UAVs. Hence the thrust change is achieved faster using variable pitch actuation. A longitudinal model of an agile fixed-wing UAV which includes propwash, wing downwash, flat plate post-stall aerodynamics and actuator constraints (first order dynamics, saturation and rate limit) is used in the work. The model of a variable pitch propeller is developed from the data of a particular propeller motor combination obtained from a software named QPROP. The longitudinal control used is a backstepping based nonlinear control. The simulation results are compared with that of a conventional design in which the same flight regime with the nonlinear control is implemented. The advantages of VPP based design are observed to be faster settling of velocity, AOA and pitch rate during transitions, very small altitude variation and reduction in maximum pitch rate during cruise to harrier transition. However, an increase in maximum pitch rate during harrier to cruise transition is a disadvantage. But overall, the simulation results shows that VPP design performs better than a conventional design for the above mentioned flight regime and indicates that a VPP based design of fixed-wing agile UAVs would be better for control in agile and high AOA maneuvers like perching, transition to hover and aggressive maneuvers. However, flight testing is essential to conclude this fully.

In this paper, a nonlinear backstepping based longitudinal control is applied to an agile fixed-wing unmanned aerial vehicle (UAV)to achieve transitioning between level flight at low angle of attack (cruise)and level flight at high angle of attack (harrier level)and the performance is compared with a gain scheduled state feedback control. In all flight regimes, the elevator control law is computed using backstepping control strategy designed for error dynamics in pitch and pitch rate. During transition from cruise to harrier flight, the propeller rotations per minute (RPM)is calculated using an additional Lyapunov based nonlinear control which stabilizes the error dynamics in flight path angle to zero. During cruise and harrier level, the respective trim value of RPM is applied and during transition from harrier to cruise the trim value corresponding to cruise is applied. Simulations of the control implemented on a longitudinal model of an agile fixed-wing UAV which includes propwash, wing downwash, flat plate post-stall aerodynamics and actuator constraints (first order dynamics, saturation and rate limit)to achieve the flight objective, are done using Matlab 9.4®. Compared to gain scheduled state feedback control, the advantages of the nonlinear control strategy are: 1)less altitude loss and oscillations in velocity and pitch angle during harrier to cruise transition, 2)reduction of around 60 % in maximum pitch rate during both transitions and 3)less chattering during both transitions. However, significant increase in computational complexity is a disadvantage. Overall, a preliminary assessment can be made that the nonlinear control strategy is better than the gain scheduled state feedback control for achieving the specific flight regime and could be advantageous in high angle of attack (AOA)maneuvers like perching, transition to hover and aggressive maneuvers.

This paper proposes trajectory planning strategies for online reconfiguration of a multi-agent formation on a Lissajous curve. In our earlier work, a multi-agent formation with constant parametric speed was proposed in order to address multiple objectives such as repeated collision-free surveillance and guaranteed sensor coverage of the area with ability for rogue target detection and trapping. This work addresses the issue of formation reconfiguration within this context. In particular, smooth parametric trajectories are designed for the purpose using calculus of variations. These trajectories have been employed in conjunction with a simple local cooperation scheme so as to achieve collision-free reconfiguration between different Lissajous curves. A detailed theoretical analysis of the proposed scheme is provided. These surveillance and reconfiguration strategies have also been validated through simulations in MATLAB\reg for agents performing parametric motion along the curves, and by Software-In-The-Loop simulation for quadrotors. In addition, they are validated experimentally with a team of quadrotors flying in a motion capture environment.

Most classical control design methods are based on mathematical description of plant dynamics. However many physical plants in real world are not only nonlinear and time varying but also highly uncertain. Accurate mathematical description of physical plants are usually not available. Disturbance rejection is another issue in control design. Active Disturbance Rejection Control (ADRC) offers an inherently robust controller which requires very little information of the plant. This control algorithm actively estimates and compensates for the effects of the unknown dynamics and disturbances using extended state observer (ESO). Advantages of ESO and ADRC motivated to implement it on micro-aerial vehicle (MAV), which is highly nonlinear and prone to parametric uncertainties and disturbances while flying. This paper talks about the nonlinear control scheme for longitudinal control of MAV using ADRC. Further the gains of observer and controller are designed using bandwidth parameterization. There are mainly two contributions of this paper: design of observer and controller gains as a function of aerodynamic coefficient and airspeed of MAV and validation of robustness of control algorithm for parametric uncertainties, measurement noise and wind disturbance.

Most of the applications need the Miniature Aerial Vehicles (MAVs) to be capable to navigate in urban environment where many obstacles of different types and sizes like buildings, trees, etc. exist. So the main aim of autonomous MAV is the ability to detect obstacles in its path and avoid them for achieving a robust autonomous flight. Since, an accurate modelling of some critical hardware like actuators is difficult in the numerical simulation, an effective tool named Hardware-In-Loop Simulation (HILS) is used which replaces simulation models of some flight critical hardware like OBC, servos, and communication devices in the loop with actual hardware. The most important feature in the HILS setup is its capability to perform the Real-Time (RT) simulation. In the present work, a PC based Hardware-In-Loop Simulation (HILS) test bed is developed, which consists of Host PC, Target PC, Ground station PC, On-Board Computer (OBC) and RC Servos. A reactive Obstacle Avoidance Controller based on a pair of miniature LRFs is developed for achieving the autonomous flight of the MAV's in urban environment with street canyons and obstacles. The LRFs are forward looking and attached both sides of the MAV body at an angle 30° on both sides of the X-axis and rays aligned parallel to the body XY-axis. Range to obstacle measured by left and right LRFs are fed to two PID controllers which compute the required heading angle command for the MAV to turn. The Obstacle Avoidance (OA) controller is successfully implemented in Hardware-In-Loop Simulation (HILS) testbed, and performance is evaluated for various scenarios in which the MAV is simulated to fly in obstacle rich urban environment.

This paper presents a variant of the cyclic pursuit strategy that can be used for target tracking applications. Cyclic pursuit has been extensively used in multi-agent systems for a variety of applications. In order to monitor a target point or to track a slowly moving vehicle, we propose to use a group of non-holonomic vehicles. At equilibrium, the vehicles form a rigid polygonal around the target while encircling it. Necessary conditions for the existence of equilibrium and the stability of equilibrium formations are analysed considering unicycle model of the vehicles. The strategy is then applied to miniature aerial vehicles (MAV) represented by 6-DOF dynamical model. Finally the results are verified in a hardware in-loop simulator in real time, which included all on-board electronics of the MAVs.

Data on surface heat flux is critical in all hypersonic missions due to the extent of risk and the penalty associated, when it is not properly accounted for. In the present study. an E-type coaxial thermocouple has been designed, fabricated, validated and benchmarked against a more established platinum thin film sensor. The study proves that coaxial thermocouples used in impulse facilities do not require cold junction compensation. The comprehensive study conducted in IIT Bombay Shock Tunnel (IITB-ST) has confirmed the performance, ruggedness and reliability of the coaxial thermocouple, ascertaining it to be an effective, impulse, heat flux sensor. (C) 2014 Elsevier Ltd. All rights reserved.

Vision-based pose estimation is particularly important for small sized mobile robots and aerial vehicles that have limited payload constraints. Accurate localization is of importance for any autonomous vehicle, especially in indoor and GPS-denied (Global Positioning System) environment. The aim of this work is to provide a solution for the pose estimation of an autonomous vehicle using monocular vision alone so that even a small-size vehicle can perform pose estimation without the help of additional sensors. Unlike Visual Odometry which operates on a sequence of images to estimate robot's motion, the proposed method estimates the robot's pose using individual images by constantly tracking four fixed feature points in a rectangular pattern, whose positions are known a priori. Also, unlike Monocular Visual Odometry which suffers from scale ambiguity problem, the proposed algorithm can estimate the pose of the vehicle and can be applied to both planar robots (3-DoF) as well as aerial vehicles (6-DoF). The proposed method has been validated by implementing on a Raspberry Pi2 model B and a RPi camera. Simulation results of controlling a differential drive robot using the proposed pose estimation method are also presented.

Low cost actuators and linkages used in Micro Aerial Vehicles will lead to unmodeled nonlinearities like dead zone and backlash in the actuator. These actuator nonlinearities are often neglected in the design of feedback control system and can detoriate the system performance remarkably. This paper presents the design of robust control laws for Micro Aerial vehicles (MAV) using sliding mode control approach to deal with nonlinear uncertain plant models. The uncertainties can be in the form of parametric variations, external disturbances or uncertain actuator nonlinearities. The uncertainties are assumed to be bounded with known values. Simulation has been carried out using MAV 6 DoF nonlinear model and the results are provided to check the performance of the control laws.

The paper focuses on generating patterns in a plane that can serve several applications like (irregular-boundary) coverage, (differentiated) surveillance, etc. These patterns are centred around a stationary point, termed as target. For practical purposes, a target point can be any landmark, beacon, etc. A control law is proposed as a continuous function of range information (distance between the agent and target) to generate a periodic annular pattern under certain conditions. Also, a switching strategy is presented to switch the agent trajectory periodically among these annular patterns. Simulation and experimental results have been presented to validate the theoretical results.

This paper proposes a trajectory planning strategy to simultaneously address multiple surveillance objectives such as complete area coverage, periodic surveillance, and guaranteed detection of a rogue element attempting to exit the area of interest. For agents with identical sensing capability, the proposed strategy defines a time-varying multi-agent formation on a Lissajous curve, which completes the aforementioned tasks in finite time with collision free paths for all agents in a 2-D rectangular region. This obviates the need for sensing and communication for collision avoidance among agents. A sufficient upper limit on agent dimensions that ensures collision free motion is derived. An algorithm is developed for choosing the number of agents and optimal Lissajous curve for a prescribed rectangle and agents' sensing capability. The optimal Lissajous curve is chosen to minimize the time period for repeated coverage and maximize the upper bound on agent size. The proposed algorithm is validated through computer simulations and experiments using differential drive robots.

Conventional munitions are not guided with sensors and therefore miss the target, particularly if the target is mobile. The miss distance of these munitions can be decreased by incorporating sensors to detect the target and guide the munition during flight. This paper is concerned with a precision guided munition equipped with an infrared (IR) sensor and a millimeter wave radar (MmW). Three-dimensional flight of the munition and its pitch and yaw motion models are developed and simulated. The forward and lateral motion of a target tank on the ground is modeled as two independent second-order Gauss–Markov processes. To estimate the target location on the ground and the line-of-sight (LOS) rate to intercept it, an extended Kalman filter is composed whose state vector consists of cascaded state vectors of missile dynamics and target dynamics. The LOS angle measurement from the IR seeker is by centroiding the target image in 40 Hz. The centroid estimation of the images in the focal plane is at a frequency of 10 Hz. Every 10 Hz, centroids of four consecutive images are averaged, yielding a time-averaged centroid, implying some measurement delay. The miss distance achieved by including image processing delays is 1.45 m., by Sreeja Sulochana, Hari B. Hablani and Hemendra Arya

Nonminimum phase output tracking has been addressed for a fixed-wing micro aerial vehicle. Nonminimum phase characteristics in an aircraft result from the fact that the process of generating upward vertical motion produces an initial downward force, causing the aircraft to lose altitude momentarily, and vice versa. This phenomenon leads to unstable internal dynamics in the plant model. A dynamic sliding-surface-based sliding mode control is chosen to stabilize the internal dynamics and to provide asymptotic output tracking error convergence to zero with desired eigenvalue placement. The control is designed in such a way that the output of the plant model should track a nonlinear time-varying reference trajectory generated at every time instant with a finite number of nonzero time derivatives. Design of second-order sliding-mode-based super twisting controller which ensures finite-time stability of the internal dynamics is proposed in this work. The proposed control methodology is applied in the design of an autolanding controller for a micro aerial vehicle with nonminimum phase behavior. MATLAB-based simulation results and discussions are presented to evaluate the performance of the controller and robustness of the sliding mode with respect to matched and unmatched disturbances. The proposed control algorithm has been successfully implemented in hardware-in-the-loop simulation and results are given.

Global and local (or reactive) obstacle avoidance across unmanned aerial vehicle (UAV) altitudes is a challenging problem. In an UAV autonomous flight when the obstacle threat is determined in-flight from the on-board sensors, techniques to avoid the obstacles autonomously in real-time and continue with the predefined flight path need to be incorporated into the autonomous systems. Hence a requirement in vertical (pitch) plane is to plan vehicle positions different from the obstacle positions. In this paper, a real-time autonomous trajectory generation scheme useful to design these potential vehicle positions incorporating vehicle capability is presented. It is known that vehicle velocity and flight path angle (gamma) uniquely determine vehicle positions. As a result, path planning for obstacle avoidance boils down to gamma tracking and vehicle velocity tracking problems. The trajectory generation scheme as a tracking problem is applied to illustrate avoiding hypothetical static ground obstacle like building in pitch plane using a three degree of freedom fixed wing micro air vehicle model.

Tactical missiles are used against various aerial/ground targets which can be stationary or maneuvering. Tactical missiles should have highly efficient control scheme in order to intercept such targets with acceptable miss distance. It is known that aerodynamic characterization of the missile with high accuracy is very difficult. In addition to this, the inability to model the external disturbances make the autopilot design very difficult. Hence, the need for a robust control arises in the presence of parametric uncertainties and unmodelled external disturbances. Sliding Mode Control (SMC) which has got invariance property against external disturbances and the model inaccuracies has been applied to this plant. This paper concentrates on application of higher order sliding mode control for the roll autopilot design of a tactical missile. Conventionally, the roll autopilot is designed with roll angle and roll rate feedbacks. The addition of roll acceleration feedback helps to obtain a tighter control of roll dynamics especially during high angle of attack requirements. However, the roll acceleration is neither measurable nor estimable by numerical differentiation of roll rate feedback. A differentiator based on Super Twisting Algorithm (STA) is explored to estimate roll acceleration from roll rate measurement. The use of roll acceleration feedback in the autopilot ensures tight control of roll dynamics. The robust sliding mode control gains are designed using Linear Matrix Inequalities (LMI) based technique.

Nature is the best teacher of many scientific research and development. One such nature inspired invention is the flight vehicle system. Among these, Mini Aerial Vehicles (MAVs) are a class of flight vehicles which have size close to birds. The current work is inspired by the fact that MAV with Low Aspect Ratio (LAR) wings (Aspect Ratio < 2) has nonlinear lift curves and it does not stall sharply as compared to high aspect ratio wings. This can be utilized in flying the MAVs at lower speeds and at higher angle of attacks. In LAR wings, the lift is constant or keeps increasing up to large Angle of Attack (AOA) which can help in flying the MAV at slow speed. Main focus of the present work is to estimate the AOA, which can be further used for development of control laws. This paper presents a data fusion algorithm for estimating the aerodynamic angles in a MAV. For simulation, true states of the aircraft motion are generated using a flight simulation program and a zero mean white noise is added to few of these states as required for the measurements. These noisy states are used as sensor measurements for estimating the AOA and Side Slip Angle (SSA). The proposed scheme is a multi-stage in which initially Euler angles are estimated and later stages are used for AOA and SSA estimation. In the first stage, the Euler angles are estimated using the accelerometer outputs and the rate gyro outputs and V in an Extended Kalman Filter (EKF) algorithm. As a first attempt for estimation of AOA and SSA, only acceleration, angular rates and airspeed were used as measurement in six states EKF. It was observed that there is a bias of more than 10° ° ° ° present in the estimated aerodynamic angles. Since, it is not possible to have any additional sensors on-board due to weight restriction, a new modification is proposed in which a pseudo estimation of AOA and SSA was used as measurement. This effectively reduces the estimation bias and the mean error in both AOA and SSA, and are below 1°. Nomenclature Fx = Total force along the body x-axis Fy = Total force along the body y-axis Fz = Total force along the body z-axis L = Total moment along the body x-axis M = Total moment along the body y-axis N = Total moment along the body z-axis p = Roll rate q = Pitch rate r = Yaw rate Cx = Force coefficient in the x direction Cy = Force coefficient in the y direction Cz = Force coefficient in the z direction Cl = Moment coefficient in the x direction Cm = Moment coefficient in the y direction

Investigations on high strain rate behavior of epoxy LY 556 under compressive loading are presented. Compressive Split Hopkinson Pressure Bar (SHPB) apparatus was used for the experimental investigations. The studies are presented in the strain rate range of 683-1890 per second. It was generally observed that the compressive strength is enhanced at high strain rate loading compared with that at quasi-static loading. During SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. Further, an analytical method is presented based on variable rate power law for the prediction of compressive strength at high strain rate loading for epoxy LY 556. Using the analytical method, high strain rate compressive stress-strain behavior is presented up to strain rate of 10,000 per second. (C) 2010 Elsevier B.V. All rights reserved.

Micro Aerial Vehicles (MAVs) are smaller version of UAVs and operate at very small velocities, which makes it very vulnerable to external disturbances. Also, MAV being a small vehicle, obtaining accurate aerodynamic data is difficult. The vulnerability of the vehicle towards external disturbances and the model inaccuracies calls for a robust control. Sliding Mode Control with its invariance property against external disturbances and the model inaccuracies is seen as a potential solution. The Sliding Mode Control algorithm needs all the states, which may not be measurable always. This calls for the design of an observer in order to estimate the unmeasurable states. The application of Sliding Mode Observer is one way to overcome this hurdle. In this paper, the various steps involved in estimating states with a Sliding Mode Observer using Linear Matrix Inequalities (LMI) approach for Longitudinal and Lateral channels of an MAV is discussed. During aggressive maneuvering requirements, it is useful to have a tighter control of Body Accelerations. However, measurement of Angular Acceleration or numerical differentiation of Body Rate measurements is not practical. A Super Twisting Algorithm (STA) based Differentiator to estimate Angular Accelerations from Body Rates is proposed in this paper, which may be useful for tight Body Acceleration control.

Hardware-In-Loop Simulations (HILS) are an integral part in the validation of any system under development, more-so, in case of Aerial Vehicles since flight testing of the vehicles is not always possible. Complex algorithm development for aerial vehicles like swarming and formation control can be tested in HILS during development phase before actual flight test. The focus area of this paper is development and evaluation of different HILS architecture for multiple aerial vehicles for the medium-low fidelity simulations.

Conventional munitions are not guided with sensors and therefore miss the target, particularly if the target is mobile. The miss distance of these munitions can be decreased by incorporating sensors to detect the target and guide the munition during flight. This paper is concerned with a Precision Guided Munition(PGM) equipped with an infrared sensor and a millimeter wave radar [IR and MmW, for short]. Three-dimensional flight of the munition and its pitch and yaw motion models are developed and simulated. The forward and lateral motion of a target tank on the ground is modeled as two independent second-order Gauss-Markov process. To estimate the target location on the ground and the line-of-sight rate to intercept it an Extended Kalman Filter is composed whose state vector consists of cascaded state vectors of missile dynamics and target dynamics. The line-of-sight angle measurement from the infrared seeker is by centroiding the target image in 40 Hz. The centroid estimation of the images in the focal plane is at a frequency of 10 Hz. Every 10 Hz, centroids of four consecutive images are averaged, yielding a time-averaged centroid, implying some measurement delay. The miss distance achieved by including by image processing delays is 1:45m.

First-order shear deformation theories, one proposed by Reissner and another one by Mindlin, are widely in use, even today, because of their simplicity. In this paper, two new displacement based first-order shear deformation theories involving only two unknown functions, as against three functions in case of Reissner’s and Mindlin’s theories, are introduced. For static problems, governing equations of one of the proposed theories are uncoupled. And for dynamic problems, governing equations of one of the theories are only inertially coupled, whereas those of the other theory are only elastically coupled. Both the theories are variationally consistent. The effectiveness of the theories is brought out through illustrative examples. One of the theories has striking similarity with classical plate theory.

A higher order displacement model for laminated composite plates is presented. The displacement model has trigonometric terms in addition to thin plate terms and contains six unknowns. The model satisfies shear stress conditions at top and bottom of the plate. Governing equations and boundary conditions are obtained using virtual work principle. The present displacement model gives simple governing equations. The model has been applied to various simply supported rectangular isotropic, orthotropic and layered plates for static and free vibration analysis. This model yields better results as compared to other higher order displacement models.

Target centric cyclic pursuit is a decentralized strategy developed for monitoring a point of interest with multiple autonomous vehicles. This strategy has been implemented for the vehicles modeled as unicycle. Before implementing such cooperative missions for miniature aerial vehicles they need to be verified considering complete dynamics of the vehicles and practical issues such as communication loss, wind, etc. The work presented in this paper extends the implementation of Target Centric Cyclic Pursuit strategy considering complete 6-DOF aircraft model. Also Hardware Inloop Simulator has been used to verify the effectiveness of strategy considering real time simulation of the 6-DOF model with communication as actual hardware in the loop and Dryden wind model in the flight simulation.

The paper deals with thrust modulation using a variable-pitch propellers for a xedwing MAVs. Those propellers are very e ective when thrust has to be changed rapidly. Such a modulation is very useful while performing aggressive maneuvers. In this paper, several measurements are made and analysed. This analysis is very useful while modelling a variable-pitch propeller and motor combination. Using this analysis a lucid control strategy is proposed to achieve tighter control over RPM.