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Sometimes you find gold in unexpected places. In this case, it’s from a video about the CH-53 helicopter . The CH-53 Sea Stallion first entered service in 1966. It’s a huge helicopter, capable of lifting immense amounts of weight. All that weight hangs from 6 (or 7 on some models) rotor blades. The problem was detecting problems with the blades before they grew into a catastrophic failure.

Much like a fixed-wing aircraft wing, the CH-53 rotor blades are designed with a spar as the main structural member. On early designs, the spar was extruded aluminum. The CH-53D and other variants moved to cold-formed titanium.

All of these blades shared the same problem – detecting tiny cracks in the metal before they grow into blade failure. Detecting cracks turned out to be rather easy. The blades are sealed and pressurized with nitrogen gas. Cracks allow the gas to leak out.…