Systematic design methodology for development and flight testing of a variable pitch quadrotor biplane VTOL UAV for payload delivery

Abstract

This paper discusses the conceptual design and proof-of-concept flight demonstration of a novel variable pitch quadrotor biplane Unmanned Aerial Vehicle concept for payload delivery. The proposed design combines vertical take-off and landing (VTOL), precise hover capabilities of a quadrotor helicopter and high range, endurance and high forward cruise speed characteristics of a fixed wing aircraft. The proposed methodology is described by taking an example of a VTOL Unmanned Aerial Vehicle (UAV) for a mission requirement of carrying and delivering 6 kg payload to a destination at 16 km from the point of origin. First, the design of proprotors is carried out using a physics based modified Blade Element Momentum Theory (BEMT) analysis, which is validated using experimental data generated for the purpose. Proprotors have conflicting requirement for optimal hover and forward flight performance and a compromise solution has to be chosen. Next, the biplane wings are designed using simple lifting line theory. The airframe design is followed by power plant selection and transmission design. Finally, weight estimation is carried out to complete the design process. The proprotor design with 24° preset angle and −24∘ twist is found to be suitable for the current mission profile, based on 70% weightage to forward flight and 30% weightage to hovering flight conditions. A reduction in operating RPM of the proprotors from 3200 during hover to 2000 during forward flight results in 27% increase in proprotor efficiency. The VTOL UAV design proposed in this paper is also predicted to consume 64% less power in airplane mode compared to the quadrotor mode, thereby establishing the benefit of this hybrid concept. A proof-of-concept scaled prototype is fabricated using commercial-off-the-shelf parts and a Proportional Integral Derivative (PID) controller is developed and implemented on open source PixHawk autopilot board to enable stable hovering flight and attitude tracking during hover flight tests.