Which gear train drives the main transmission, powering both the main and tail rotor systems?

• A. N2 gear train
• B. Primary gear train
• C. Secondary gear train
• D. Tertiary gear train

Answer: (A)

Power from the engine reaches both rotor systems through the gear path tied to the engine’s high-speed spool. In turbine helicopters, the N2 gear train takes the energy from the N2 shaft, reduces its speed, and feeds the main transmission. Once the main gear train is turning, it drives the main rotor and, through the tail-drive setup, also powers the tail rotor. The other gear train terms aren’t used to describe this main power path in standard rotorcraft design, so they don’t fit the role described.