Comment by 46Bit

19 hours ago

The article is very vague on how the radioactivity allows detection of leaking gas.

The video at the bottom explains from 7:50 in. Gas pressure pressing on a spring holds a radiation shield in place. If the gas leaks the shield moves and the radiation can be detected.

18 comments

46Bit

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robocat  19 hours ago

There's a good comment:

  MH-53E maintainer here. The system is IBIS (Inflight Blade Inspection System) and the little pods are BIM (blade inspection monitors). The box is pretty obvious sitting just behind the main rotor on the deck above the center engine. I found a random picture on the web:

https://assets.verticalmag.com/wp-content/uploads/2017/01/MH...

And:

  The IBIS devices provide in-flight warning of blade failure on various models of helicopters. One device is located on the root of each blade attached to the rotor. The IBIS detects a decrease in pressure in the blades of a CH-53 model helicopter. Any cracks in the blades will result in a decrease in air pressure in the blade. Such cracks could result in structural failure in the blade, thereby resulting in a potentially dangerous operational situation for the helicopter, such as a hard landing and/or injury to the craft and/or personnel up to, and including, death. Each device contains approximately 500 microcuries (18.5 MBq) of strontium-90 (Sr-90) in the form of a rolled metal foil, encased in a small stainless steel protective cylinder about the size of the press button on a ballpoint pen. The external radiation level of the IBIS is 0.8 mR/hr at 3 inches in the normal (shielded) mode, and 75 mR/hr at 12 inches in the failure (extended) mode.

From https://public-inspection.federalregister.gov/2019-08531.pdf...

  • imglorp  14 hours ago

    The video explains it pretty well. There's a spring loaded plunger in that IBIS sensor that can be seen visually by mechanics on the ground. When the pressure drops, the plunger retracts, showing a visual indication. At the same time, it also removes the rad source from its shielding when it does that, increasing emissions for the in flight sensor to see.

  • laxpri  15 hours ago

    What does “inches” mean here

    • hansvm  12 hours ago

      It's a medieval measurement, still in popular use. Nowadays it means approximately 2.54 centimeters. Historically, it's the height of the ash pile a "witch" would leave behind, and the word has morphed only slightly from "witches" into "inches."

      1 reply →

tomasphan  19 hours ago

The titanium spar is filled with gas. If there was a crack in the spar the gas would escape, therefore tripping the pressure sensitive radiation shield. Releasing radiation that can be detected inside the helicopter.

Wireless systems aren’t used for opsec reasons.

  • sandworm101  17 hours ago

    Wireless arent used because they need power/wires and are less reliable than IBIS. Civilian versions of sikorsky helos use the same system.

  • DoctorOetker  13 hours ago

    carrying a radiation source doesn't sound very opsec either to be honest...

    • Johnny555  12 hours ago

      Since the radiation source is only exposed if it's indicating a potential main rotor crack, and it's not a very strong radiation source in the first place (so it's not like it allows long distance tracking), it seems like a minor risk -- if the radioactive capsule is exposed, the pilot is going to be returning to safe place to land.

      Beta particles typically only travel a few meters in air before they lose most of their energy.

    • kstrauser  7 hours ago

      Wait until you find out about smoke detectors. Or microwave ovens. Or light bulbs. Or anything with nonzero temperature.

lstodd  10 hours ago

Radioactivity has nothing to do with it.

Was solved in Mi-6/Mi-8/Mi-26 blades without it.