Comparative analysis of the kinematic schemes of a tiltrotor based on URANS modeling

Abstract

Due to the growth of the unmanned aerial vehicle (UAV) market and the specific tasks they perform, the design of convertible aircraft, such as convertiplanes, is becoming increasingly relevant. These aircraft combine the advantages of helicopters and airplanes: they can take off and land vertically from unprepared surfaces and have higher cruising speeds and ranges than helicopters. The key problem of convertiplane aircraft is transient modes, characterized by complex unsteady aerodynamics and an abrupt change in the dynamic properties of the device. This paper presents a comparative analysis of two kinematic configurations of the aircraft: tilt-wing and tilt-rotor. The primary focus of the study is on the transitional flight modes, during which the aircraft transitions from vertical flight in helicopter mode to horizontal flight in airplane mode. The goal of the study is to quantify the effect of the type of kinematic scheme on the integrated aerodynamic characteristics of an aircraft. To achieve this goal, a 3D model of the aircraft was developed, based on the Bell Eagle Eye prototype. The simulation was carried out in the Ansys Fluent software package based on the solution of nonstationary Reynolds equations (URANS) using the Spalart–Allmaras turbulence model. A number of rotation angles of the power plant were calculated for each kinematic scheme. (0°, 30°, 60°, 90°). The flight speed and rotational speed of the propellers for each design case were selected iteratively to ensure a uniform horizontal flight (equal to zero the sum of the forces acting on the aircraft). The flight speed and rotor speed for each case were iteratively selected to ensure the condition of steady horizontal flight (the sum of forces acting on the aircraft equals zero). The numerical modeling characteristics resulted in obtaining the required power and torque at the rotor shaft, flight speed. It was concluded that the configuration with a fixed wing demonstrates a higher flight speed (22 m/s compared to 10 m/s at a 30° angle) and a more favorable ratio of required power to flight speed compared to the rotary-wing layout.