Design of a tilting mechanism for a VTOL flying wing UAV

Abstract

In this paper, the detailed design of a mechanism for the transition from vertical to horizontal flight of a Vertical Take-off and Landing (VTOL) fixed wing Unmanned Aerial Vehicle (UAV) is presented. The UAV, which is being developed in the framework of the MPU research project, under the designation MPU RX-4, is a lightweight, all electric driven UAV with a flying wing layout. The MPU RX-4 is capable of performing both conventional flight, like a regular fixed wing aerial vehicle, as well as vertical hovering, like a multicopter, adapting on different operational demands. To achieve that, the development of a robust transition procedure from one flight phase to the other is required. This procedure is based on mechanisms capable of altering the flying characteristics of the UAV. More specifically, these mechanisms should be designed in order to change the orientation of the thrust vectors from horizontal to vertical and vice versa. MPU RX-4 uses a configuration of three electric motors (two mounted on the canards, and one in the main body) in order to perform both flight phases. For the transition from the hovering phase to the level flight, the two frontal motors have to be tilted from the vertical position to the horizontal, and the rear motor to be nested in its proprietary position, using four external hatches. Two separate mechanisms are designed, one for the canards’ tilting movement and another one for the extension and retraction of the rear motor hatches. Finite Element Analysis is carried out for the structural sizing of the mechanism (i.e. internal loads, linkages cross-section, joints sizing). The aerodynamic loads, acting on the mechanisms, are derived from Computational Fluid Dynamics analysis performed for the various flight phases (hovering, level flight and transition) of the UAV. Finally, the designed mechanisms are presented as integrated parts of the prototype UAV.