Which tool is used to measure the alignment of a rotor shaft?

The tool specifically designed for measuring the alignment of a rotor shaft is the dial indicator. This instrument utilizes a probe that makes contact with the shaft and displays measurements on a dial. It allows for precise readings of any misalignments by showing variations in distance as the rotor shaft is rotated. This precision is crucial in ensuring that the rotor operates smoothly, reducing excessive wear or vibration, which can lead to mechanical failure.

In the context of rotor shaft alignment, the dial indicator provides more accurate and relevant measurements than the other tools listed. For example, while a protractor is useful for measuring angles, it doesn’t provide the detailed linear measurement needed for alignment. A plumb bob can help establish a vertical reference but isn’t suited for precision measurement of mechanical components like a rotor shaft. Similarly, a shift gauge, though it may have its applications, is not the preferred tool for this specific alignment task. Therefore, the dial indicator remains the standard instrument for ensuring rotor shaft alignment in aircraft maintenance and repair.