Sharif Digital Repository

The feasibility of integrating co-flow fluidic thrust-vectoring idea into the dynamics of a small flapless aerial tail-sitter is investigated in this article. The aircraft trimmability in different phases of flight and stability in take-off and level flight, are the main issues of concern for the study presented herein. In this respect, the vehicle's characteristic equations are derived by linearization of the general non-linear equations of motion. Since the vehicle was supposed to be merely controlled by fluidic thrust-vectoring, the concept was novel and some new derivatives are introduced. Margins of the required thrust-vector angle, to obtain a steady-state flight condition, are... 

An analytical procedure for aeroservoplastic stability analysis of guided supersonic flight vehicles is developed by using slender body aerodynamic theory and modal analysis techniques. The roll channel is decoupled from pitch and yaw channels by using the linearized system of equations. Results show that divergence is the only aeroelastic instability that can occur for the nonrolling flight vehicle with no-control loop and is accurately computed using the first bending mode shape. The result of the divergence analysis demonstrates that the vehicle elasticity has a destabilizing effect on the pitch and yaw channels. The inclusion of aeroservoelasticity in the analysis can cause dynamic... 

The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so called 'Quad-tree forms'. The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the 'cost map', lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different... 

This paper presents a method for nonlinear aeroelastic analysis of a Human Powered Aircraft (HPA) wings. In these types of aircrafts there is a long wing with high flexibility. Wing flexibility coupled with the long span leads to the possibility of the large deflections during normal flight operation, so, nonlinear modal analysis technique is used for structural modeling. Unsteady linear aerodynamic theory is used for determination of aerodynamic loading on the wing (linear aerodynamics and nonlinear structure). Combining these two types of formulation yields a nonlinear aeroelastic model. Mode summation techniques along with Galerkin's method are used to determine the governing equations of... 

This paper presents fly-ability, trim-ability, stability, and control ability of a mono-wing aerial vehicle as an under-actuated multi-body system. A nonlinear mathematical model of this vehicle with translational and rotational movements is developed. Based on early simulations, a conceptual prototype of the mono-wing is initially designed and constructed. A comprehensive nonlinear simulation is then performed by modeling aerodynamic forces and moments using the Blade Element Momentum (BEM) theory. Modeling and simulation are validated against experimental data to satisfy research needs. Twenty-three efficient dynamic parameters of the mono-wing are studied in ninety-seven simulation... 

A new methodology has been proposed to enhance inverse dynamics applications in the process of trajectory planning and optimization in terrain following flights (TFFs). The new approach uses a least square scheme to solve a general two-dimensional (2-D) TFF in a vertical plane. In the mathematical process, Chebyshev polynomials are used to model the geographical data of the terrain in a given route in a manner suitable for the aircraft at hand. The aircraft then follows the modeled terrain with sufficient clearance. In this approach the terrain following (TF) problem is effectively converted to an optimal tracking problem. Results show that this method provides a flexible approach to solve... 

The subject of the present paper is the investigation of the sharp edged gust effects on the aeroelastic behavior of a flexible wing. It is important to determine the response of the wing to the atmospheric turbulences during normal flight. So, linear modal analysis technique and linear quasi-steady aerodynamic are used for structural modeling and aerodynamic loading, respectively. Also, Lagrange method is used to obtain the system of equations of motion. Using the normal modes of free vibration, structural and aerodynamic matrices can be constructed. Then the aeroelastic instability of the system is determined using p method. Kussner function is used to model the sharp gust effects on the... 

Traditionally, flying and handling quality evaluation of an aircraft in various flight phases is aimed at pilot workload assessment to guarantee a successful mission. Subsequently, Different levels of acceptability are defined for the aircraft based on the additional work required by the pilot to achieve a desired performance level, feting scales are usually numerical, which pilots utilize as a mean to quantify their subjective opinion about an existing aircraft after hours of flying. Cornell aeronautical laboratory used their own scales in flying qualities research for many years and Cooper of NASA originated a ten-point numerical scale that was used more universally. When Harper of Cornell... 

Purpose - The purpose of this paper is to develop a novel solution for the predicted error and introduces a systematic method to develop optimal and explicit guidance strategies for different missions. Design/methodology/approach - The predicted error is derived from its basic definition through analytic]al dynamics. The relations are developed for two classes of systems. First, for systems in which the acceleration commands are truncated at a specified time. Second, for systems in which the corrective maneuvers are cut off at a specified time. The predicted error differential equation is obtained in a way that allows for derivation of several optimal and explicit guidance schemes. Findings... 

Purpose – This paper aims to focus on mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters. Design/methodology/approach – The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and state-space represented indicial-based unsteady aerodynamics. The model is represented by a set of nonlinear partial differential equations for the main rotor within a state-space representation for all other parts of helicopter dynamics. The coupled rotor and fuselage formulation enforces the use of numerical solution techniques for trim and linearization... 

Extensive wind tunnel tests have been conducted to investigate effects of turbulence intensity variations on the behavior of a section of a wind turbine blade in an oscillatory motion. Special emphasize was applied on the aerodynamic characteristics when oscillating the model in the vicinity of its static stall angle of attack and in the post stall condition. The model had 0.25m chord and was pitched about its quarter-chord. Data were acquired at various Reynolds number, and reduced frequency. Results show that turbulent intensity has strong effect on the unsteady load coefficients, hence aerodynamic performance of this model. Furthermore, free stream turbulence has different effect on the... 

A novel approach in minimum time trajectory planning in Terrain Following/Terrain Avoidance (TF/TA) flight is proposed. In this research, terrain is understood based on fuzzy logic and small changes in terrain are omitted. Another novelty is constructing a relationship between slope of terrain and aircraft height with speed of aircraft by fuzzy approach. Finally after a decision making process and based on governing dynamics and cost function, trajectory is constructed by a polynomial. This method is state of the art in literature  

An expanding flight envelope in the landing phase of a typical jet transport aircraft in presence of strong wind shears using a learning capable control system (LCCS) is investigated. The idea stems from human beings functional architecture that gives them the ability to do more as they age and gain more experience. With the knowledge that classical controllers lack sufficient generality to cope with nonlinear as well as uncertain phenomenon such as turbulent air, the focuse is on different types of intelligent controllers due to their learning and nonlinear generalization capabilities as candidates for the landing flight phase. It is shown that the latter class of controllers could be used... 

The Analytic 6 D.O.F. dynamic model of a helicopter is developed for 3D computer generated imagery simulator. Analytic expressions for the forces and moments on the various helicopter components are derived. By using the forces and moments equilibrium, helicopter trim point is determined using Newton's method of solving the nonlinear set of trim equations. The equations of motion for the fuselage six degree of freedom are assembled by applying Newton's law of motion relating the applied forces and moments to the resulting translational and rotational acceleration. Visual C++ programming software, utilized as a platform will interact to MATLAB Aircraft Instrument ActiveX and 3DSTATE for... 

In this paper, LQG/LTR controller is designed for attitude control of the geostationary satellite at nominal mode. Usage actuator is the reaction wheel and control torque is determined by the LQR regulator. LQR controller signal has good performance, if all states are considered in feedback, but does not include model and sensors noises. Usage sensors are sun and earth sensors and EKF is used for estimation of noisy states. Then, LQG and LQG/LTR controllers are designed based on the estimated states, and are compared with LQR controller. The results show that robustness and performance of LQG/LTR are better than LQG and its control overshoot is smaller than LQR. The term that is provided in... 

To evaluate the propulsion system capabilities of a Flapping Micro Air Vehicle (FMAV), a new aeroelastic model of a typical flexible FMAV is developed, utilizing the Euler-Bernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, flapping amplitude and frequency of the FMAV, as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV, as well as an instrumented test stand for the online measurement of forces, flapping angle and power consumption, has been constructed. The experimental results are... 

In this paper a novel non-rotating space tethered configuration is introduced which its relative positions controlled using electromagnetic forces. The attitude dynamics is controlled by three reaction wheels in the body axes. The nonlinear coupled orbital dynamics of a dumbbell tethered satellite formation flight are derived through a constrained Lagrangian approach. These equations are presented in the leader satellite orbital frame. The tether is assumed to be mass-less and straight, and the J2 perturbation is included to the analysis. The forces and the moments of the electromagnetic coils are modeled based on the far-filed model of the magnetic dipoles. A guidance scheme for generating...