scanning is undertaken in two directions for the detection of cracks which normally occur on the inner surface but which can start on the outer surface. The two additional diagrams on the sketch show the method scanning.
128. INBOARD AND OUTBOARD NACELLE STRUT FRONT SPAR FITTINGS. Most of the examination of these components is undertaken on the curved sections of the lugs. The angle of the beam is approximately 20° from the tangent of the circle.
To obtain this angle, the probe must have an incident angle of approximately 9°. Inspection is undertaken around the whole of the curved surface which gives more or less complete coverage of the bolt hole by moving a probe in two directions. In order to direct the beam towards any position of the hole in the lug, the probe has to be moved across the lug section from side to side while being rotated around the curved surface. This leaves a PROBES FIGURE 78.-Inboard and Outboard Nacelle Strut Front Spar Fitting small section of the hole at the back of the lug which is not inspected. This is undertaken by a probe having a smaller angle and a slight taper on the lug surface. Both upper and lower parts of the lug have to be inspected by this method so that the entire bolt-hole section is examined. To facilitate examination from the curved surface, the probe surface is also curved. On some aircraft, this radius differs so that two probes would normally be necessary. Practice has indicated that a probe having a larger radius can be used on lugs of the smaller radius. (See Figure 78.)
129. NOSE LANDING GEAR OUTER CYLINDER Figure 79 shows the area of test undertaken using surface-wave probe with a frequency of 2.5 MHz.
The probe is applied to the curved surface of the cylinder and the beam directed towards the lug.
The sound wave follows the surface of the material and penetrates the flat surface of the lug for detection of defects from the corner of the sections into the lug zones marked on the sketch.
TEST AREA PROBE FIGURE 79.-Nose Landing Gear Outer Cylinder 130-135. RESERVED.
43 * U. S. GOVERNMENT PRINTING OFFICE: 1975 O - 569- 931