Aerodynamic Performance Study on Ducted Propeller System for Propulsion and Control & Stability Applications

Abstract

The Delft University Unconventional Concept (DUUC) is an innovative short take-off medium range aircraft design that utilizes a system of two ducted propellers, mounted on the aft part of the fuselage. The first design of this system consists of two axisymmetric ducts, each containing a propeller mounted to a centerbody that is attached to the duct by a strut. Furthermore each ducted propeller contains two horizontal and two vertical control surfaces and the ducted propellers are mounted to the fuselage by two external struts. Besides the function of propulsion, the ducted propeller system also replaces the horizontal and vertical tail for control and stability. The aerodynamic characteristics of this system are investigated by the construction of an aerodynamic performance model, consisting of a combination of low order analytical and numerical methods. This model aims on predicting the aerodynamic coefficients, which are significant for control and stability over a range of operational conditions, incidence angles and thrust settings. These include lift, side force, drag and control surface effectiveness. The numerical part of the model is first validated against existing experimental data from literature, after which the complete model is held against data from a low speed wind tunnel test on a small scale model of the system. Finally, a sensitivity analysis aims on finding the effect of the most important design parameters on the thrust to power ratio of both the propeller and the total system. The numerical model is succesfully validated in its capability of predicting trends in propeller and total system thrust over a range of operational conditions. The analytical model is capable of predicting the lift and side force performance of the system to a reasonable degree in the unstalled regime. Drag is significantly underestimated by the analytical model, possibly due to unknown flow separation and interference effects, which require higher order methods. Stall angle and maximum lift can not be modeled accurately by the low order performance model. Finally, the sensitivity analysis shows that advance ratio is the most critical operational condition whereas duct shape and duct aspect ratio are most affecting the total system thrust to power ratio.