What is the main purpose of the APU's exhaust system?

The main purpose of the APU's exhaust system is to direct hot gases away from the aircraft. This function is critical for maintaining safety and operational efficiency. The exhaust system ensures that the hot gases produced during operation are expelled away from the aircraft structure and personnel, preventing heat buildup that could affect other components and the surrounding environment.

By effectively directing these gases out into the atmosphere, the exhaust system also helps to minimize potential hazards, such as fire risks and damage to sensitive equipment nearby. Additionally, this design is vital in maintaining the proper function of the APU, ensuring it operates within safe temperature limits.

While cooling APU components, enhancing fuel efficiency, and reducing air resistance may play roles in the overall design and operation of aircraft systems, they are not the primary focus of the exhaust system. The exhaust system's essential role is indeed the safe and effective management of exhaust gases away from the aircraft.