TM 1-1520-253-23
2.15.3.8
CRT Display Interpretation. Eddy current interpretation requires an understanding of the material proper-
ties and subsequent manufacturing processes that can effect inspection results. Figures 2.15D, 2.15E, and 2.15F &
G below display hub variations that can be detected while inspecting the main rotor hub.
Figure 2.15D again display the conductivity variation
between cad and non-cad areas on the calibration
standard. Main rotor hub null locations can vary either
side of the null point of the calibration standard
depending on cadmium plating thickness.
Figure 2.15D
Figure 2.15E displays the cad plated and non-cad plated
surfaces when passing over the .040 in. EDM notch.
Impedance values change with cadmium or paint
thickness variations. The center trace is from a section
of the main rotor hub with the paint removed. The flying
dot is off screen to the right due to the change in lift off.
Calibration on the reference standard with the tape
removed will bring these null points closer together.
Figure 2.15E
Figure 2.15F compares the slow wandering dot
movement associated with conductivity/permeability
changes in contrast to the quick rise and fall signature of
the EDM notch.
Figure 2.15G is an actual crack that seldom will be as
cleanly defined as the calibration notches. True cracks
can be readily identified by the rapid rise and fall time of
their eddy current signature.
Figure 2.15F
Figure 2.15G
2.15.4
Marking and Recording of Inspection Results. Mark and record inspection results as required by paragraph
1.3.
2.15.5
If any cracks are found the rotor hub is unserviceable.
2.15.6
Replace the locking beams in accordance with Task 5-40, TM 1-1520-240-23 or Task 5-41, TM
1-1520-252-23.
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