Analytical Model for Ring-Wing Propulsors at Angle of Attack

A simple, accurate, analytical model is developed for predicting the forces and moments on subsonic ring-wing propulsors (aka fan ducts and shrouded propellers) at angle of attack. The method is applicable to drones, aircraft, ships, and more from hover to cruise. The new model is made up from elements of three previously published, closely related models, herein combined and modified for the current purpose: an empty shroud ring-wing force and moment linear aerodynamics model; a ring-wing propulsor axial force model employing linear aerodynamic, axial momentum, and propeller actuator disk theories; and a jet engine normal force model as semi-empirically adapted to ring-wing propulsors. The model’s efficacy is assessed using three independent datasets: two experimental and one Reynolds-averaged Navier–Stokes computational fluid dynamics. It is shown that the model’s algebraic solutions provide good engineering estimates for the lift, drag, normal, and axial forces as well as pitching moments at all operating conditions from hover to cruise and angles of attack up to 85°.