The choice of aircraft power supply depends on the electrical power requirements of the equipment used in the flight scenario for maximum reliability, safety and low power supply weight. Therefore, load (ie, electrical equipment) analysis is the basis for selecting a power source. The working condition of the load on the aircraft is related to the following factors:① The different flight tasks. From the perspective of power supply, the mission that consumes the most electricity should be selected, such as fighter jets fighting at night, bombers flying in enemy territory at night, and bombing missions. ② The working state of the aircraft is different. According to “Analysis of Aircraft Electrical Load and Power Capacity” GJB-860A-2006, the aircraft flight stage generally includes the following 10 working states: G1, ground maintenance; G2, instrument calibration; G3, loading and preparation; G4, start-up and warm-up; G5, taxi; G6, takeoff and climb; G7, cruise; G8, cruise and combat; G9, landing; G10, emergency . ③The working condition of the power supply. When the power supply is normal, it should be able to meet the load requirements for simultaneous work. In a multi-generator power system, after one or two power sources fail the grid, they should be able to meet the power requirements of key and important electrical equipment. In an emergency state, the emergency power supply should meet the requirements of key electrical equipment, that is, to monitor the load according to the working conditions of the power supply.
When calculating loads by flight stage, the power (active power, reactive power, apparent power), stagger coefficient (the ratio of the number of a certain electrical equipment working at the same time to the total number of the equipment) and working duration of the electrical equipment should be considered. For high-power motors, not only the rated power, but also its starting power must be considered.
After the load statistics, a load diagram should be drawn. There are three types of load diagrams: normal working load diagram, emergency working load diagram and ground power supply load diagram. The normal working load diagram is the basis for selecting the capacity of the main power source, the emergency working load diagram is the basis for selecting the emergency power source, and the ground power supply load diagram is the basis for selecting the ground power source, especially the aircraft auxiliary power source. If you need to start the generator, you must check the starting working state to ensure the smooth start of the engine. For the electric starting of the engine, it is not only a matter of choosing the capacity of the starter generator, but also a starting power source of the corresponding capacity. For aircraft that are required to be self-sufficient, the power supply of the auxiliary power unit on the aircraft should meet the requirements for electric starting of aero-engines.