FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesHard
A dual-spool turbofan engine has two independently rotating compressor-turbine assemblies. Which components make up the N1 rotor system?
- AThe fan and high-pressure turbine only, geared to the accessory section
- BThe high-pressure compressor and high-pressure turbine, mechanically independent of N2
- CThe fan, low-pressure compressor, and low-pressure turbine, connected on a shaft independent of N2
- DThe accessory gearbox and starter motor only
Show answer & explanationAnswer & explanation
Correct answer: C. The fan, low-pressure compressor, and low-pressure turbine, connected on a shaft independent of N2
In a dual-spool turbofan, N1 refers to the low-pressure spool, consisting of the fan, low-pressure compressor, and low-pressure turbine, all connected by a shaft running concentrically inside the N2 (high-pressure spool) shaft, allowing each spool to rotate at its own optimum speed.
Why the other options are wrong
- A. The fan is not connected to the high-pressure turbine; they belong to different spools.
- B. This describes the N2 (high-pressure) spool, not N1.
- D. The accessory gearbox is driven off the high-pressure spool, not the N1 system itself.
Dual-Spool N1/N2 System
A turbofan engine design using two independently rotating shafts: N1 (fan, LP compressor, LP turbine) and N2 (HP compressor, HP turbine), each rotating at its own optimum speed.
- N1 = low-pressure spool (fan speed indicator)
- N2 = high-pressure spool (core speed indicator)
- Independent rotation improves efficiency across power settings
Memory trick: 'N1 is the Nice big fan, N2 is the Nimble core' - N1 = fan spool, N2 = core spool