FAA Aviation Mechanic Powerplant (AMP)Turbine EnginesHard
A turbine engine's main shaft is supported by ball bearings at one location and roller bearings at another. What is the primary reason for using these two different bearing types along the same shaft?
- ARoller bearings are used exclusively in accessory gearboxes, never on the main engine shaft
- BBall bearings support radial loads only, while roller bearings support both radial and thrust loads
- CBall bearings are used solely to improve rotor balance and carry no structural load
- DBall bearings support combined radial and thrust (axial) loads, while roller bearings primarily support radial loads and allow for shaft thermal expansion
Show answer & explanationAnswer & explanation
Correct answer: D. Ball bearings support combined radial and thrust (axial) loads, while roller bearings primarily support radial loads and allow for shaft thermal expansion
Ball bearings are well suited to carrying combined radial and axial (thrust) loads and are typically located at a fixed point on the shaft, while roller bearings efficiently carry heavy radial loads and permit the shaft to expand and contract axially with temperature changes without inducing binding stress.
Why the other options are wrong
- A. Roller bearings are commonly used on the main turbine shaft itself, not only in accessory gearboxes.
- B. This reverses the actual load-carrying roles of the two bearing types.
- C. Ball bearings carry real structural radial and thrust loads, not just balance functions.
Turbine Engine Main Bearings
Ball bearings support combined radial and thrust loads at a fixed shaft location, while roller bearings support radial loads and allow axial shaft expansion.
- Ball bearings act as a thrust-locating bearing
- Roller bearings allow shaft to grow with heat without binding
- Bearing sumps with carbon seals retain lubricating oil
Memory trick: 'Ball = Both loads, Roller = Room to grow.'