## 1 Introduction  
Currently, large-size industrial multicopter platforms with payloads of several tens of kilograms or more are being developed. These large platforms aim to load special heavy payloads, such as large-capacity cargo transport, fire-fighting equipment, first-aid equipment, and military supplies. Such platforms are expected to further expand the scope of the aviation industry, because they can overcome challenges that cannot be overcome by conventional small aircraft or drones. Furthermore, the basic shape of an urban air mobility (UAM), which have attracted attention as next-generation transportation vehicles, is often based on the multicopter platform. The Passenger AAV (Ehang-216) of Ehang, the Volocity of the Volocopter, and the CityAirbus of the Airbus are typical cases of multicopter-type UAMs [1; 2; 3]. Meanwhile, as the size of the platform increases, factors that are to be considered in the design process also increase and become challenging. In terms of the structural strength of the platform, the scale effect of material stiffness, which could have been a benefit in small sizes, is reduced [4]. Thus, more complex structural designs than those of small platforms are required. The high risk of failure and crash, which increases in proportion to the platform weight, is another challenge. For example, in the case of small multicopter unmanned aerial vehicles (UAV), emergency parachutes against falls or propeller guards against collisions are included in the recommendation, but not necessarily used. In contrast, for large-size platforms, these features are strongly demanded as essential design requirements to ensure safety. However, these requirements often result in an increase in weight, which, in turn, leads to reduced power efficiency across the platform. As is well known, a short flight time due to low power efficiency is the main weakness of multicopter platforms. In this regard, research on the optimal design of multicopter platforms is being conducted in various fields. The development of reliable models for performance analysis of electric propulsion systems is one such effort. The propulsion system model forms the basis for reviewing the overall performance of the platform and performing the optimal design; thus, the development of a reliable model is usually a priority for the aircraft design process. For large-size multicopter UAVs, it must be considered that the system will operate under high voltage and heavy current conditions as the size of the electric propulsion system increases. Especially in these high power conditions, the effect of the motor's armature reaction is no longer negligible. The armature reaction is a phenomenon, in which the main field flux is interfered by a magnetic flux that is caused by current flowing through the armature of the motor and it is known to be the main cause of stray losses [5]. In this study, as part of the development of optimal design tools for large-size multicopter UAVs, research on the improvement of a multidisciplinary model of an electric propulsion system was performed. It was focused on improving the reliability of the model for electric propulsion system, and supplementing the dynamics and statistical analysis for each component based on the previous studies [6]. In particular, for motor models, the degradation of rotor performance under high-power conditions can be more accurately predicted by modeling the effect of the armature reaction. A simple thermal effect model was also added to describe the degradation of performance due to overheating of the motor. For statistical analysis, the overall analysis of commercial products dedicated to multicopter UAVs was conducted. Based on this, replaceable models were presented for some factors that were treated as constants or were neglected in previous studies, such as no-load current of motors or power losses in electric speed controllers (ESC).