Computer Simulation of Automatic Control of an Agricultural Small Unmanned Aerial Vehicle with Variable Mass

Introduction. Small unmanned aerial vehicles are effectively used in agriculture for field cultivation. Because of the long flight range, manual control from the ground of the elevator and engine thrust does not allow maintaining the required speed and altitude over the field with the necessary precision to ensure the field uniform processing. The aircraft mass changing in flight and the changing field relief have not yet been taken into account sufficiently in studies on the stabilization of flight altitude and stability. Thus, the study of the automatic control mode of the elevator and engine thrust, ensuring the stabilization of flight altitude under conditions of decreasing aircraft mass and changing field relief, can be considered a relevant and insufficiently studied problem. Aim of the Study. The study is aimed at evaluating the impact of mass changes of a small unmanned aerial vehicle on the flight altitude and of the center-of- mass speed of the vehicle during their stabilization in the automatic elevator and engine thrust control mode. Materials and Methods. The object of the study is a small unmanned aerial vehicle. There were used the methods of differential equations, theoretical mechanics, automatic control, programming in the Lazarus development environment, and numerical methods were used for computer modeling of automatic control of the elevator and engine thrust of an aircraft to stabilize flight altitude. Along with the methods mentioned in the article, there were used visual simulation methods implemented in the Scilab XCOS environment. These methods made it possible to assess the adequacy of the computer model. Results. There have been developed two computer models for automated control of a unmanned aerial vehicles flight at a given altitude and speed. Software control of the elevator and engine thrust, determined based on the solution of differential equations of longitudinal flight of a small unmanned aerial vehicle at a given trajectory angle and a given speed, made it possible to stabilize the altitude and speed. Trajectory management of the elevator and engine thrust based on the readings from altitude, pitch angle, angular velocity and speed sensors made it possible to “track” a given field relief and stabilize the altitude and flight speed with sufficient accuracy. It has been found that in flight sections with a decrease in flight mass, the altitude, flight speed and trajectory angle are stabilized, and the pitch angle decreases along with the mass, and at a high specified flight speed over a field with a negative angle of inclination (on descents) the pitch angle becomes negative (uncomfortable) and loss of control is possible. Discussion and Conclusion. Reducing the flight mass of an unmanned aerial vehicle must be taken into account when using these devices in agriculture for pest control and other work related to the processing of agricultural crops. The conducted study of software and trajectory control for stabilizing flight altitude made it possible to determine the relationship between the change in mass and such controlled parameters as the pitch angle and speed of the mass center of the aircraft. Software control ensures stabilization of flight altitude under any field profile, but its accuracy is caused by the accuracy of the mathematical model and, without taking into account actual flight data, does not allow one to assess the true accuracy of calculations of the current flight altitude and speed of the aircraft. Trajectory control with a proportional-integral controller allows for feedback coupling to be taken into account. The calculations have shown that such control of a flight over a field with a downward slope can lead to a loss of stability and a fall of the aircraft. A field with variable relief has areas where the level decreases and which are the source of uncomfortable flight and loss are of flight stability.