A Helicopter Detects Rotor Cracks by Exposing a Tiny Radioactive Source
Older CH-53 helicopters use an unusual system to warn crews about cracks in their rotor blades while airborne. Each blade is pressurized with nitrogen; if a crack causes pressure to drop, a mechanical indicator exposes a small amount of strontium-90.
A detector on the helicopter can sense that radiation, providing a warning without putting fragile electronics or complicated wiring on a spinning rotor. Hackaday revisited this decades-old solution.
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Sending a sensor signal from a spinning rotor was difficult, so the solution became: expose a radioactive source and detect that instead. The engineering constraint is ordinary; the answer escalates spectacularly.