A design procedure for ducted fan propulsion systems is presented in this thesis, which is used to evaluate their operating behavior, noise and drag. Based on an exemplary propulsion system design for a small aircraft with 1000 kg take-off mass and a hybrid electric power train, the design trade-offs of ducted propeller propulsion systems as well as their advantages and disadvantages compared to the free propeller are discussed.A combination of mean line flow analysis and engine performance calculation methods is used to model the ducted fan performance. Losses, noise and drag are accounted for using partly analytical and partly empirical models from literature. The motor operating behavior is evaluated based on performance maps. Design studies show that the fan and nozzle cross-sectional areas are by far the most important parameters influencing performance. Noise emissions also strongly depend on the blade and vane numbers. The influences of pitch, chord length and blade angles on performance and noise emissions are also evaluated; they are significantly lower in most cases. Performance follows steady trends as design parameters or operating points change. Noise emissions, by contrast, often change abruptly and strongly, driven by the complex generation mechanisms of rotor-stator-interaction noise. The exemplary propulsion design deals with a hybrid electric ducted fan propulsion system powered by an internal combustion engine with intermittent support from an electric motor. For ducted fans without variable pitch blades, adding the electric motor partially offsets some operational limitations and makes significantly more thrust available throughout parts of the flight mission, e.g., at take-off. Moreover, ducted fans allow for a much quieter take-off than required by current small aircraft certification standards that have been developed for free propellers. For the exemplary application, the calculated noise is more than 20 dB below the noise limit. Further noise reduction can be achieved with a hybrid electric propulsion system. The additional thrust enables a steeper climb on take-off, which halves the time required to reach cruising altitude and thereby significantly reduces noise on the ground. Overall, ducted fans are promising low-noise propulsion systems and their performance is improved when adding an electric motor, thereby creating a hybrid powertrain. Due to the complex relationship between performance and noise, multidisciplinary methods are required for the predesign of these propulsion systems, such as those presented in this work.
Mantelpropellerantriebe für Kleinflugzeuge
Ducted fan propulsion systemsfor small aircraft
01.01.2025
1 Online-Ressource : Illustrationen pages
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2024; Aachen 1 Online-Ressource : Illustrationen (2025). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2024
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