Abstract
This 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.
Highlights
Prompted by progress in the field of electric drive systems, numerous new small aircraft and propulsion system designs have been developed in recent years
Hybrid and electric propulsion systems are opening up design freedoms and enabling new aircraft concepts [5, 7, 33]
The e-boost of 46 kW enables the internal combustion engine (ICE) to operate at a much higher speed of 5590 RPM, where it can deliver 101 kW under initial climb conditions, i.e., 25 kW more than without the e-boost. This is an additional benefit of the e-boost: is electrical power supplied to the fan and converted into thrust, but the increased fan speed enables the ICE to provide substantially more power
Summary
Prompted by progress in the field of electric drive systems, numerous new small aircraft and propulsion system designs have been developed in recent years. Propulsion noise, needs to be considered early on, at the conceptual design stage In this regard, the ducted fan offers potential advantages over the free propeller, typically employed in general aviation (GA) aircraft. Physics-based noise analysis methods have been developed and applied to ducted fans by Jaron [26] and Moreau [34], who in their studies concentrated on turbofan engines for airliners. These methods have been applied to ducted fans for aircraft in the GA domain by Schade et al [37]. The influence of the ducted fan’s main design variables on performance and emitted noise are investigated in trade studies and the essential trade-offs of ducted fan design are discussed
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