Which gear train drives the starter generator and the oil pump?

Which gear train drives the starter generator and the oil pump?

• A. Reduction gear train
• B. Accessory gear train
• C. N1 gear train
• D. N2 gear train

Answer: (C)

The main idea here is how the engine’s accessories get their drive. The starter generator and the oil pump are part of the accessory drive system, which uses a gear train to transfer power from the engine’s rotating shafts to these components and to control the speed they see. In this configuration, the accessory drive is taken from the low‑pressure spool, so the gear train that drives the starter and oil pump is the N1 gear train. Driving from N1 means these accessories begin turning early as the engine starts and can reach the necessary speed to light off and to establish oil pressure as the engine accelerates. The gear ratio within this train reduces the high speed of the N1 shaft down to a suitable, controllable speed for the starter generator and for the oil pump, ensuring reliable starting and lubrication. Why not the others? The N2 gear train would tie accessories to the high‑pressure spool, which isn’t how this particular arrangement is set up. The term reduction gear train describes the purpose of reducing speed within the gear train, but the question asks which shaft drives the accessories, not the general function. The accessory gear train refers to the whole assembly inside the accessory gearbox, but specifying N1 identifies which engine shaft supplies the drive in this design.

The main idea here is how the engine’s accessories get their drive. The starter generator and the oil pump are part of the accessory drive system, which uses a gear train to transfer power from the engine’s rotating shafts to these components and to control the speed they see.

In this configuration, the accessory drive is taken from the low‑pressure spool, so the gear train that drives the starter and oil pump is the N1 gear train. Driving from N1 means these accessories begin turning early as the engine starts and can reach the necessary speed to light off and to establish oil pressure as the engine accelerates. The gear ratio within this train reduces the high speed of the N1 shaft down to a suitable, controllable speed for the starter generator and for the oil pump, ensuring reliable starting and lubrication.

Why not the others? The N2 gear train would tie accessories to the high‑pressure spool, which isn’t how this particular arrangement is set up. The term reduction gear train describes the purpose of reducing speed within the gear train, but the question asks which shaft drives the accessories, not the general function. The accessory gear train refers to the whole assembly inside the accessory gearbox, but specifying N1 identifies which engine shaft supplies the drive in this design.