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The work presented in this paper focuses on the design of a robust nonlinear flight control system for a small fixed-wing UAV against uncertainties and external disturbances. Toward this objective, an integrated UAV waypoints guidance scheme based on Carrot Chasing guidance law (CC) in comparison with the pure pursuit and line of sight-based path following (PLOS) guidance law is analyzed. For path following based on CC, a Virtual Track Point (VTP) is introduced on the path to let the UAV chase the path. For PLOS, the pure pursuit guidance law directs the UAV to the next waypoint, while the LOS guidance law steers the vehicle toward the line of sight (LOS). Nonlinear Dynamic Inversion (NLDI) awards the flight control system researchers a straight forward method of deriving control laws for nonlinear systems. The control inputs are used to eliminate unwanted terms in the equations of motion using negative feedback of these terms. The two-time scale assumption is adopted here to separate the fast dynamics—three angular rates of aircraft—from the slow dynamics—the angle of attack, sideslip, and bank angles. However, precise dynamic models may not be available, therefore a modification of NLDI is presented to compensate the model uncertainties. Simulation results show that the modified NLDI flight control system is robust against wind disturbances and model mismatch. PLOS path-following technique more accurately follows the desired path than CC and also requires the least control effort.

In this paper, the onboard computer software program was developed to predict the full trajectory of the missile in order to improve the accuracy at impact. For system in which time is not critical, the alignment process can be performed prior to launch by utilizing navigation data from the launch platform and calibrating the missile's INS to this reference. However, for systems that require rapid reaction time, significant pre-launch delays for alignment are not tolerable. In addition, due to low quality of the INS and its life cycle is short; hence every aborted mission will bring the INS closer to its mean time between failures (MTBF). These problems can be minimized by in-flight alignment (IFA). While IFA may seem to be less accurate and more complicated than alignment in the rest, it turns out that the ability of the carrier to maneuver during the IFA phase is a blessing in disguise since it enables the excitation of latent modes and thus, enhances their observability of the whole INS. The effects that maneuvers have on the estimability of the INS states during IFA were investigated in the past. But until now, there are many questions such as: what is the degree of observability? What limits the estimability of the system? What are the minimal additional measurements needed to turn the system into a completely observable one? And what are the useful numbers of maneuvers in IFA? , were not completely addressed. These questions are answered through this paper. We introduce the error model, which appropriately describes the INS behavior during IFA. We then substantiate its adequacy for consideration as a piece-wise constant system (PWCS) and then the simpler stripped observability matrix (SOM) can be used in the system observability analysis.

This work is concerned with the study and use of dry friction dampers for : :vibration control. First, the characteristics of the friction damper are 'determined. Then, the friction damper is applied to a hinged-hinged bean, The amplitude-frequency response for a harmonic excitation is determined both theoretically and experimentally. For linearization of the equations. bf motion, the friction force is replaced by an equivalent linear viscous : force dissipating the same energy per cycle. The results obtained from experiments and theory are in good agreement, and it is shown that, by a suitable choice of the ratio of the friction force to applied force' the * friction damper can be an effective damping device.