Ducted fans for hybrid electric propulsion of small aircraft

Abstract

AbstractThis paper presents a method for modeling ducted fan propulsion systems for hybrid-electrically driven small aircraft based on mean line flow analysis methods. Studies of the essential design parameters provide the basis for a discussion of potential advantages when compared to free propellers, as well as possible new fields of application for the ducted fan. A two-seater aircraft, equipped with two ducted fans powered by a combustion engine and additionally by a parallel hybrid electric start-boost drive, is used as a reference application case. The fan performance characteristics are described with the aid of aero mean line flow analysis methods and semi-empirical loss correlations. Physics-based methods are applied to assess the nacelle drag and noise emissions. The combustion engine and electric motor performance are described using maps. The ducted fan design variables are investigated to identify the main trade-offs and favorable designs for the target aircraft mission, with special attention to noise. The results show that the performance of fixed pitch fans benefits strongly from hybridization. Ducted fans can also operate considerably more quietly than is required by current certification standards. The physics-based design method presented here can be used for conceptual design and performance prediction of ducted fan propulsion systems, which may be especially interesting if low noise emissions are required.