Electrification of existing fossil fuel systems is actively progressing in the aviation propulsion field as a part of low-carbonization that appears throughout the industry. Recently, as the use of electric air vehicles in various fields such as military, agriculture, logistics, academic, surveillance, and leisure has rapidly increased, technology for long-term use is inevitably required. However, the excessive heat of the propulsion motor is the primary cause restricting the long-term use of electric air vehicles. In addition, the high heat loss that inevitably occurs in pursuing high output and weight reduction requires the development of a cooling structure along with an improved electromagnetic field design. The present study focuses on a severe heat dissipation problem in outer-rotating Brushless DC (BLDC) motors. We perform electromagnetic analysis of the BLDC motor to obtain heat generation in the motor coil and core as well as computation fluid dynamics (CFD) with experimental verification of air-cooled heat dissipation. The base numerical model has been established by comparing and verifying the motor heat saturation test with a deviation of less than 6%. The motor housing's cooling airflow, including centrifugal fan blades and stators, is numerically analyzed to evaluate the cooling performance with the required torque. The blade number and ventilation hole size are vital parameters significantly affecting the cooling performance. It also was found that the cooling performance could be improved by combining the 10 mm ventilation hole with the 18-blade installed cover.