Beijing Forestry University Researchers Develop Precise Tracking System for Drones With Depleting Liquid Payloads

Beijing researchers solve drone flight instability caused by shifting pesticide weight, using new dynamic models for precision agricultural spraying.

By: AXL Media

Published: Apr 30, 2026, 6:22 AM EDT

Source: Information for this report was sourced from EurekAlert!

Engineering Stability Amidst the Fluid Dynamics of Agricultural Spraying

The integration of unmanned aerial vehicles into smart agriculture has long been hampered by the physical volatility of liquid payloads, which alter a craft's center of gravity as they deplete. Dr. Shuting Xu and her colleagues at the Beijing Forestry University School of Technology have addressed this complexity by developing a time-varying multibody dynamic model. Unlike previous iterations that assumed a constant mass, this new framework accounts for the continuous loss of liquid, which traditionally complicates both attitude response and trajectory tracking during vital pest control maneuvers.

Simulating the Shifting Internal Equilibrium of Pesticide Tanks

To refine the accuracy of the drone's flight path, the researchers utilized computational fluid dynamics to map the internal behavior of the pesticide tank. Using ANSYS Fluent software, the team conducted three-dimensional transient simulations of gas-liquid two-phase flow to observe how mass and inertia distribution change in real-time. By applying curve fitting to these simulations, they successfully established time-varying functions that allow the drone's internal computer to predict and compensate for the physical shifts occurring within the chemical reservoir during active spraying.

Advanced Control Laws for Robust Disturbance Rejection

The core of the technological breakthrough lies in a disturbance-rejection trajectory tracking system that employs PD sliding mode control. This architecture is split into an inner loop for attitude management and an outer loop for path navigation. To prevent the mechanical jittering often associated with automated flight corrections, the team replaced standard discontinuous sign functions with continuous hyperbolic tangent functions. According to the research findings, this modification ensures that the system responds rapidly to errors while maintaining the smooth, asymptotic stability required for delicate agricultural work.