3.2 Aircraft Systems and Flight

 3.2 Aircraft Systems and Flight

Sept 24, 2021

                                               Aircraft Systems and Flight: AC/DC Power Generation

When thinking of how an aircraft flies, the first thing that comes to mind is thrust. The engine that propels the aircraft forward and wings to produce lift in order to take off. The second thing is how to control the various aircraft systems that are also essential to flight, this is where power generation comes in play. From starting an engine to turning off the engine, there will always be electrical power involved, the only thing is how to keep the generators running to produce electricity. The AC/DC Power generation for F15s are produced by both the left and right IDGs (one for each engine) and is a . Both these generators power various busses that then power the different systems in the aircraft. If, for example, the left generator stops working for some reason, the GCU (Generator Control Unit), in charge of the power generation, will immediately send power from the right generator to take the load of the other busses that were powered by the left IDG. This backup system is essential during flight to prevent emergency systems from failing and to keep the pilot safe. If both generators stop producing power, the last resort for power generation will come from the emergency generators that are spun up by the use of hydraulic fluid in order to spin the rotor inside the generator. Although since both generators are lost and the aircraft is now powered by one small emergency generator, the only systems that are being powered are the emergency/essential systems that keep the aircraft in the sky. This includes the minimal boost pump, hydraulic pumps, external lighting, etc. to keep the aircraft from falling. This system redundancy allows the pilot able to control the aircraft and prevent a loss of vital electrical power from the busses, keeping the flight safe. 

The IDG is an acronym for Integrated Drive Generators, made of the CSD (Constant speed drive) and the Generator, both mated to make the IDG. The IDG is mechanically linked to the engine, once the engine spins up, the CSD inside the IDG also spins up to maintain the rpm and the generator produces power through the mechanical force it's given by the engine. The IDGs are driven at a constant speed of 12,000 rpm regardless of engine speed. (Code7700, 2021)  There are a couple of situations where the IDG can go bad, this includes a thermal disconnect and the IDG simply falling apart due to over servicing or metal shards in the cooling oil. A thermal disconnect happens when the CSD begins to overheat and cause it to disconnect from the generator, loosing the mechanical power behind the IDG. I have personally witnessed this happen many times throughout my career, seeing the oil pouring out of the IDG panels with the pilot having problems about having a caution light regarding a generator problem. 

Sez, E. S. (2017, July 5). Electrical System. Code7700. https://code7700.com/g450_electrical.htm