Gliding unmanned aerial vehicle flight dynamics at low speed and launch altitudes
The authors conduct studies of gliding unmanned flying vehicle (UAV) flight dynamics at low speed and launch altitude. In the case under consideration the UAV flight dynamics significantly depend on initial flight speed and initial flight altitude which determine the total UAV energy and, as consequence, UAVs dynamic capacity while moving along the trajectory. The paper considers the following two problems: 1) Maximum flying range provision under initial UAV motional energy limitations. 2) The UAV stability and maneuverability provision at all flight stages. We assume the UAV is equipped with a certain booster engine with fixed total impulse, which can be realized by various thrust variation functions in the course of UAV movement. Much attention was paid to the study of launching conditions and thrust behavior at the initial trajectory portion impact on the flight range under gross thrust impulse limitation, as well as studying of various possible technological deviations of thrust vector direction from UAV axis of roll impact on movement stability and UAV launching safety. The last problem was considered in the form of the following two problems: · ensuring such UAV angular stability at the initial passive trajectory segment, which would guarantee UAV angular orientation, eliminating the possibility of UAV collision with the carrier by the time of its engine firing; · ensuring the possibility of disturbances parrying, which occur during engine operation at the active trajectory segment and stipulated by technological errors of its mounting on the UAV. The results of the study revealed that the last factor could affect negatively as well on the UAV total flight range. We assume that the UAV is launched in undisturbed air conditions so that at the starting moment it is not subjected to the additional aerodynamic impact, while the carrier is moving at constant altitude with constant speed. The authors developed a mathematical model of UAV spatial motion all over the flight. The control system accounts for pitch angle and angular velocity deviations. Solid fuel accelerator with fixed thrust impulse value, variable thrust value and operating time is considered as a boost engine. A time of engine ignition was computed. Movement parameters at the initial trajectory segment, booster thrust variation functions impact on the flight range and booster thrust misalignment impact on the UAV movement parameters and stabilization were evaluated. Extreme (guaranteed) values of solid fuel booster thrust misalignment caused by technological errors while booster manufacturing and mounting on the UAV ensuring the UAV flight safety at two stages - controlled flight without thrust and controlled flight with operating booster were obtained.