Design, Development, and Validation of a High-Performance Tilt-Frame Unmanned Aerial System for Landing in Tree Orchard

Huanglongbing (HLB) is an incurable bacterial disease that kills citrus trees and threatens to decimate California's $2.2 billion citrus industry. A solution for limiting the spread of HLB is to rapidly detect infected trees with a chemical sensor equipped Unmanned Aerial System (UAS), which lands within tree proximity and deploys an extendable boom for air-sample collection. The Agricultural UAS project is a multidisciplinary engineering effort to conduct chemical sample collection and analysis in remote locations, to study a tilt-frame UAS concept performance, and to test a novel Propeller Thrust Governing System (PTGS). Simulated flight metrics show that a tilt-frame UAS concept significantly increases endurance, range, cruising performance, and service envelope over a conventional multi-rotor UAS design. A UAS prototype has been built by integrating the following subsystems: tilt-frame aircraft design, PTGS, and an attitude control system. The PTGS is a novel subsystem designed for regulating thrust of a constant velocity, non-variable pitch propeller through the use of actuated aerodynamic surfaces (flaps) for vehicle attitude control. Experiments conducted on a custom-built force measuring platform show that a standard/inverted flap combination produces a high force-to-flap deflection angle ratio, preserves a linear response, and minimizes coupling between downwards/sideways forces. An attitude controller was designed using a cascade PID scheme with a Mahony filter for rapid attitude estimation. By modeling system dynamics and using airfoil theory, predicted dynamic response and simulated flight metrics are generated and then experimentally validated with a functional prototype vehicle. Collected flight data deviates from predicted performance by less than 5%.