Design, Fabrication, and Validation of a Blended Wing Body VTOL Unmanned Aerial System for Adverse-Terrain Payload Delivery

Abstract

This senior thesis presents a vertical takeoff and landing (VTOL) blended wing body (BWB) unmanned aerial system designed to transport a 1kg payload of blood products over battlefields to military medical units or perform a secondary intelligence, surveillance, and reconnaissance mission over 24km of range. The final configuration is a tailsitter with blown-wing elevon control to achieve VTOL functionality while maximizing aerodynamic efficiency. The design process began with iterative initial sizing using the battery mass fraction method and finite wing theory. Preliminary planform design was conducted by sweeping design parameters and optimizing for aerodynamic efficiency while maintaining controllability and stability. Linear dynamic analysis was conducted to ensure stability for all longitudinal and lateral eigenmodes. Efficiency and controllability were balanced through airfoil and planform parameter selection, and the final configuration employed Eppler E325 and E327 reflexed airfoils trimmed to the cruise condition. Through control analysis of hover pitching authority using actuator disk theory, elevons were sized to enable a wind disturbance rejection of 5 m/s in vertical hover, which was validated using an LQR control simulation. Propellers and motors were sized and placed for optimal power efficiency and optimal hover pitch authority while maintaining sufficient thrust margin, resulting in the selection of a 13" diameter propeller. Structural components were sized through hand calculations and confirmed with FEA. An aluminum 5052 sheet metal wingbox was designed to sustain extreme aerodynamic loads with a 1.5 safety factor, and tube clamps were designed to fasten the wing spars to the center body for rapid assembly in the field. A detailed mechanical design was produced as structural analysis progressed, incorporating features for a 3D printed outer mold line, carbon fiber spar tubes, and legged retractable landing gear using a four bar over-centering linkage. A Matek F405 flight controller was used to host Ardupilot firmware configured for VTOL functionality, and Simulink simulations of PID control for forward flight confirmed flight stability. Tethered and untethered hover flight tests were conducted to tune PID loop constants, and a maiden forward flight employing a dolly launch system confirmed functionality of the automatically stabilizing fly by wire flight mode. Finally, a transition flight was successfully conducted to validate VTOL to forward flight functionality, where it flew 23km and consumed 49% battery capacity. Hover power consumption during tests was 460-490W, while forward flight consumed an average 74-79W. Using these statistics, the aircraft has a theoretical range of 37.7km without payload and 28.3km with payload, meeting mission requirements. The final empty weight of the airframe was 4.02kg with a 3500mAh 6S battery installed.