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.
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:
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.
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.
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.
I don’t have a good intuition for the aerodynamic environment around a helicopter blade in flight. It feels like it ought to be very blustery. Presumably there’s a huge amount of pressure on the underside and a drop in pressure on the top side, maybe even below atmospheric pressure?
The blades are a foot wide and 30’ long, so five of them carrying 25,000lbs is about 1psi of pressure. 3x that for a laden Stallion. I guess I expected it to be a lot more because, from the perspective of the rotor blade, it is in a very windy regime.
The other major open question for me is with the cracks. The system implies there is a non instantaneous progression from unbroken, to having a small crack on the surface, to having a crack large enough for nitrogen to escape, to having a crack so large that the rotor blade fails. I’d love to know what sort of timeframes sit between each of these phases.
Often in software development I encounter code that seems overly complex. It's not always obvious at first glance whether that complexity is because it's solving a really difficult problem, or because the developers made it more complex than it needed to be.
Having no domain knowledge of the problems of detecting cracks in blades, this sounds like either a genius solution to a super hard problem, or unnecessary complexity.
Given the forces involved, the need to avoid wireless communication, the complexity of any bearing with associated electrical contact, and so on this seems like the least complicated solution. You can rely on radioactive elements to emit radioactivity above background, you can build a pretty reliable pressure indicator, and you can fill a cavity in the blades with gas pretty reliably. You sidestep all of the complicated mechanical linkages in favor of a solution that's not in the rotor hub at all.
I though it sounded pretty clever. Now, that can be good or bad depending on context. I mean it in a good way. It seems simple conceptually (I have no idea if it adds a lot of complexity to the manufacturing) and rather foolproof. I guess the radiation shield could jam and not move when it should.
I can just imagine the conversation when they came up with that:
Boss: we need to transmit 1 bit of information indicating pressure loss from a spinning rotor blade to the main body of the helicopter. The blade spins too fast for electronics to work properly.
Engineer: What if we make the blades radioactive when they depressurize, then point a Geiger counter at them to detect if that happens.
Boss: ... where did you say you got your degree from?
What if the helicopter would have to operate in a contaminated area? Wouldn't it cause false positives?
> The CH-53 Sea Stallion first entered service in 1966
1966 is Cold War era, so, I think, an idea that a military helicopter would have to fly in an area that has been recently nuked wasn't totally inconceivable...
Assuming only one rotor cracks, then the radiation is from one rotor IBIS and the detector electronics could detect radiation levels that ripple synchronously with the rotor speed.
The Strontium-90 is a beta radiation emitter.
The external radiation level of the IBIS [is] 75 mR/hr at 12 inches in the failure (extended) mode.
Strontium-90 is a beta emitter, apparently, so you could just measure Alpha, Beta, and Gamma and detect false positives due to elevated background radiation that way. If you're in the air you're probably much closer to your Beta source as well so you could detect it above background due to distance. Gamma is essentially light so it falls off with the square of distance. But Alpha and Beta are probably much worse than Gamma in that respect, so I'm guessing this is fine most of the time and then they rule out false positives by looking at the total background in each type of radiation.
All nuclear things fall off much faster than square of the distance unless you're in vacuum. The atmosphere is nowhere near transparent to any of them. An addition to the inverse square issue the behavior of the various types is complex:
Gamma: Halving distance in the low hundreds of meters.
Alpha: Goes a few centimeters.
Beta: Goes a few meters per million electron volts. Most sources don't go above a few million electron volts.
Neutron: The only one with good penetration, halving distance around a kilometer for high energy neutrons. But note that there are few sources of neutron radiation other than fission.
Thus unless you're flying into fallout it's not much of an issue.
I imagine that if you're flying through an active nuclear war, false positives from the blade crack detector are pretty far down your list of things to worry about.
Exposure to a nuclear blast doesn't necessarily make things radioactive. Hiroshima and Nagasaki are not radioactive wastelands. Even in Chernobyl, the other reactors continued to operate for a time after the accident, and nature is thriving.
But, the radiation detector is on the upper surface of the rear fuselage. Hypothetical Beta particles from the ground will strike the underside of the aircraft and not the detector.
A friend's cousin was a CH-53 pilot out of MCAS Miramar. One day, he was telling us, someone didn't properly secure one of the (chairs? racks? don't know the rotorcraft term...)in the cargo hold. The doors were open, and they were flying above the desert at a few thousand feet when...one of the aluminum & webbing chairs got sucked out the window and hit a rotor.
The number & intensity of the warning lights in the cockpit, and the accompanying alarms when that happens is pretty spectacular. The pilot knows right away.
> The solution is so elegant it’s still being used today. The newest versions of the CH-53 of fiber optics to detect faults in the newest all-composite blades. The older variants? They’re still going with the nuclear option.
Huh? So it's not really in use today as much as hasn't been retrofit out. Those are very different. This also doesn't read well. Maybe rewritten without proofreading
If it hasn't been retrofitted out, then it's still in use today. That sentence would only be incorrect if the new solution was retrofitted on all aircraft.
I think it's the "so elegant" part that's wrong. It's not still being used today because it's so elegant. It's still being used today because the old helicopters haven't replaced it.
JohnU says: "It’s all fun and games until helicopter crashes and what should be a minor incident turns into a nuclear emergency where you have to call very specialized decontamination units to remove radioactive material from the site."
Alan Reid says: "unless they shoot ’em down on your own territory
then you don’t have a helicopter but you have mini-hiroshima to clean up."
How much Strontium-90 do they think these things are carrying?
Do they have smoke detectors at home (I hope so...)?
You must not hang out on there. Those are some pretty standard grade Hackaday comments. I love the site, read every day, but the comments section can be... rough.
Hackaday isn't the end-all, be-all authoritative source for anything. It's a blog that, for the most part, links to neat stuff with a summary write-up. If something interests you then it's on you to follow the links.
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.
There's a good comment:
https://assets.verticalmag.com/wp-content/uploads/2017/01/MH...
And:
From https://public-inspection.federalregister.gov/2019-08531.pdf...
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.
What does “inches” mean here
6 replies →
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.
Wireless arent used because they need power/wires and are less reliable than IBIS. Civilian versions of sikorsky helos use the same system.
carrying a radiation source doesn't sound very opsec either to be honest...
4 replies →
Radioactivity has nothing to do with it.
Was solved in Mi-6/Mi-8/Mi-26 blades without it.
When I read the title I thought it would be about depleted uranium, which other aircraft have used as weight: https://en.wikipedia.org/wiki/Depleted_uranium#Trim_weights_...
I don’t have a good intuition for the aerodynamic environment around a helicopter blade in flight. It feels like it ought to be very blustery. Presumably there’s a huge amount of pressure on the underside and a drop in pressure on the top side, maybe even below atmospheric pressure?
The blades are a foot wide and 30’ long, so five of them carrying 25,000lbs is about 1psi of pressure. 3x that for a laden Stallion. I guess I expected it to be a lot more because, from the perspective of the rotor blade, it is in a very windy regime.
The other major open question for me is with the cracks. The system implies there is a non instantaneous progression from unbroken, to having a small crack on the surface, to having a crack large enough for nitrogen to escape, to having a crack so large that the rotor blade fails. I’d love to know what sort of timeframes sit between each of these phases.
Often in software development I encounter code that seems overly complex. It's not always obvious at first glance whether that complexity is because it's solving a really difficult problem, or because the developers made it more complex than it needed to be.
Having no domain knowledge of the problems of detecting cracks in blades, this sounds like either a genius solution to a super hard problem, or unnecessary complexity.
Given the forces involved, the need to avoid wireless communication, the complexity of any bearing with associated electrical contact, and so on this seems like the least complicated solution. You can rely on radioactive elements to emit radioactivity above background, you can build a pretty reliable pressure indicator, and you can fill a cavity in the blades with gas pretty reliably. You sidestep all of the complicated mechanical linkages in favor of a solution that's not in the rotor hub at all.
I though it sounded pretty clever. Now, that can be good or bad depending on context. I mean it in a good way. It seems simple conceptually (I have no idea if it adds a lot of complexity to the manufacturing) and rather foolproof. I guess the radiation shield could jam and not move when it should.
Chesterton's Fence
I can just imagine the conversation when they came up with that:
Boss: we need to transmit 1 bit of information indicating pressure loss from a spinning rotor blade to the main body of the helicopter. The blade spins too fast for electronics to work properly.
Engineer: What if we make the blades radioactive when they depressurize, then point a Geiger counter at them to detect if that happens.
Boss: ... where did you say you got your degree from?
What if the helicopter would have to operate in a contaminated area? Wouldn't it cause false positives?
> The CH-53 Sea Stallion first entered service in 1966
1966 is Cold War era, so, I think, an idea that a military helicopter would have to fly in an area that has been recently nuked wasn't totally inconceivable...
Assuming only one rotor cracks, then the radiation is from one rotor IBIS and the detector electronics could detect radiation levels that ripple synchronously with the rotor speed.
The Strontium-90 is a beta radiation emitter.
Strontium-90 is a beta emitter, apparently, so you could just measure Alpha, Beta, and Gamma and detect false positives due to elevated background radiation that way. If you're in the air you're probably much closer to your Beta source as well so you could detect it above background due to distance. Gamma is essentially light so it falls off with the square of distance. But Alpha and Beta are probably much worse than Gamma in that respect, so I'm guessing this is fine most of the time and then they rule out false positives by looking at the total background in each type of radiation.
All nuclear things fall off much faster than square of the distance unless you're in vacuum. The atmosphere is nowhere near transparent to any of them. An addition to the inverse square issue the behavior of the various types is complex:
Gamma: Halving distance in the low hundreds of meters.
Alpha: Goes a few centimeters.
Beta: Goes a few meters per million electron volts. Most sources don't go above a few million electron volts.
Neutron: The only one with good penetration, halving distance around a kilometer for high energy neutrons. But note that there are few sources of neutron radiation other than fission.
Thus unless you're flying into fallout it's not much of an issue.
2 replies →
I imagine that if you're flying through an active nuclear war, false positives from the blade crack detector are pretty far down your list of things to worry about.
At that point a blade crack might be the best option
Exposure to a nuclear blast doesn't necessarily make things radioactive. Hiroshima and Nagasaki are not radioactive wastelands. Even in Chernobyl, the other reactors continued to operate for a time after the accident, and nature is thriving.
But, the radiation detector is on the upper surface of the rear fuselage. Hypothetical Beta particles from the ground will strike the underside of the aircraft and not the detector.
> Exposure to a nuclear blast doesn't necessarily make things radioactive
Isn’t this neutron activation?
2 replies →
Strontium-90 is a major component of fallout and strongly in the ‘really not good for you’ category.
5 replies →
Heh...I actually knew about this.
A friend's cousin was a CH-53 pilot out of MCAS Miramar. One day, he was telling us, someone didn't properly secure one of the (chairs? racks? don't know the rotorcraft term...)in the cargo hold. The doors were open, and they were flying above the desert at a few thousand feet when...one of the aluminum & webbing chairs got sucked out the window and hit a rotor.
The number & intensity of the warning lights in the cockpit, and the accompanying alarms when that happens is pretty spectacular. The pilot knows right away.
See too the Porsche 917[0].
[0] https://en.wikipedia.org/wiki/Porsche_917?#Construction
> The solution is so elegant it’s still being used today. The newest versions of the CH-53 of fiber optics to detect faults in the newest all-composite blades. The older variants? They’re still going with the nuclear option.
Huh? So it's not really in use today as much as hasn't been retrofit out. Those are very different. This also doesn't read well. Maybe rewritten without proofreading
If it hasn't been retrofitted out, then it's still in use today. That sentence would only be incorrect if the new solution was retrofitted on all aircraft.
> is so elegant it’s still being used today
I think it's the "so elegant" part that's wrong. It's not still being used today because it's so elegant. It's still being used today because the old helicopters haven't replaced it.
2 replies →
Some really hyperbolic comments on there:
JohnU says: "It’s all fun and games until helicopter crashes and what should be a minor incident turns into a nuclear emergency where you have to call very specialized decontamination units to remove radioactive material from the site."
Alan Reid says: "unless they shoot ’em down on your own territory
then you don’t have a helicopter but you have mini-hiroshima to clean up."
How much Strontium-90 do they think these things are carrying?
Do they have smoke detectors at home (I hope so...)?
You must not hang out on there. Those are some pretty standard grade Hackaday comments. I love the site, read every day, but the comments section can be... rough.
On the bright side, now we can have another comparison scale, for how many banana-copters worth of radiation a given item contains.
Occasionally I browse the comments when something I've worked on is misunderstood on there.
You should never read the comments.
Terrible explanation
Hackaday isn't the end-all, be-all authoritative source for anything. It's a blog that, for the most part, links to neat stuff with a summary write-up. If something interests you then it's on you to follow the links.
This is how the web used to work.
I miss those days.