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Robinson Safety Notice SN-25 (carb ice) - additional 1.5 in. HG MAP?

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Robinson Safety Notice SN-25 (carb ice) - additional 1.5 in. HG MAP?

Old 8th Dec 2023, 15:11
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From Robinson's own SN-25, Issued Dec 1986, Updated July 2012:

​​​​​​Pressure drops and fuel evaporation inside the carburetor cause significant cooling. Therefore, carburetor ice can occur at OATs as high as 30C (86F).
@bvgs:
I was hover taxing the other day at just under 25 inches of manifold pressure (almost at full weight) and the gauge was going well into the minus. No big deal .
As the yellow arc is -20 degC to +5 degC or so (from memory), it seems you were operating well beyond normal operating conditions and sudden engine failure initially masked by governor operation was a distinct possibility. Some might disagree with you and call that quite a big deal.
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Old 8th Dec 2023, 15:19
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https://robinsonheli.com/wp-content/uploads/2015/12/rhc_sn25.pdf

https://rotarywingshow.com/93-carb-icing-richardmorningtonsanford-2/









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Old 8th Dec 2023, 21:55
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[QUOTE=pilotmike;11553632]From Robinson's own SN-25, Issued Dec 1986, Updated July 2012:



@bvgs:

As the yellow arc is -20 degC to +5 degC or so (from memory), it seems you were operating well beyond normal operating conditions and sudden engine failure initially masked by governor operation was a distinct possibility. Some might disagree with you and call that quite a big deal.[/QUOTE

As I was hover taxing I was keeping my eye on it and as it started to continue I applied carb heat thus stating I continued to progress using the down draft for the reduced power. So there was never any chance of any significant ice build up never mind engine stoppage. Flying a Raven II normally I had forgotten how much of a thing it was this the post.
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Old 9th Dec 2023, 02:11
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Its called "The latent heat of vaporization" (not to be confused with "The latent heat of fusion" which is why Pluto's surface is dynamic) when the carburetor vaporizes the fuel, if there's moisture in the air, it condenses into ice. Frank actually does a pretty decent job describing it in an old video.

Anyway, carb ice is primarily about temperature and Robinson considers carb icing conditions to be from " -4C to +30C with the temperature/dewpoint spread less than 15C".

With carb heat assist "technically" you're supposed to be able to set it in a hover, then forget it, but,...I never trust memes, lol.
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Old 9th Dec 2023, 09:27
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Originally Posted by ApolloHeli
In order to atomise the fuel and turn it from liquid into gaseous form, energy is required (gaseous state having a higher energy than liquid state). This transfer of energy from the air to the fuel 'sucks' heat out of the air and cools it down slightly. There's far more thermodynamics than I can comprehend going on in reality, but that's one mechanism at work explained in a simple way that can help explain the temperature drop from ambient even at full power.

Its the same principle as how a refrigerator, or aircon works. Anyone running aircon in their car on a hot day in summer may have noticed the puddle of water that drains out underneath, possibly not so much water in colder conditions. Warmer air can absorb more water in the form of vapour. When the air cools down the vapour turns back to liquid. So, the warmer the atmosphere, the more chance of more intake ice.

As a child, I was given a scientific experiment kit, consisting of two simple thermometers. One was kept dry, the other was kept wet with a water container and a piece of gauze bandage wrapped around the bulb. A chart was supplied, which allowed the relative humidity to be calculated from the two temperature readings. It always surprised me how much cooler the wet bulb was on low humidity days.
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Old 9th Dec 2023, 14:35
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I hate you you people move threads. Seriously, this thread is over ten years old! Let it die!
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Old 9th Dec 2023, 15:03
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Originally Posted by Robbiee
I hate you you people move threads. Seriously, this thread is over ten years old! Let it die!
Exactly which people here do you hate?
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Old 9th Dec 2023, 15:12
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Originally Posted by ShyTorque
Exactly which people here do you hate?
Hmm,...that first "you" was supposed to be a "when",...and now I hate myself for not proof reading before posting.
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Old 11th Dec 2023, 17:35
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FAA Lessons Learned on Carb Ice in the R22

https://www.faa.gov/lessonslearned/r...on-r22-beta-ii

This is a pretty thorough and useful article.
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Old 11th Dec 2023, 19:54
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Originally Posted by CertGuy
https://www.faa.gov/lessonslearned/r...on-r22-beta-ii

This is a pretty thorough and useful article.
Hmm, I've got around 350 hours of solo experience in these conditions in an R22 at night over San Francisco. I'd say the cause of this one wasn't really that he didn't use carb heat, but that the reason he didn't even unlatch the carb heat assist, was due to being distracted by it being a photo flight.

Flying solo is easy, but once there's someone next to you, its sooooo easy to get distracted and forget things.
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Old 11th Dec 2023, 21:16
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Originally Posted by Robbiee
Hmm, I've got around 350 hours of solo experience in these conditions in an R22 at night over San Francisco. I'd say the cause of this one wasn't really that he didn't use carb heat, but that the reason he didn't even unlatch the carb heat assist, was due to being distracted by it being a photo flight.

Flying solo is easy, but once there's someone next to you, its sooooo easy to get distracted and forget things.
The way I'm reading that, the carb heat knob was indeed unlocked, but found in the full down (off) position. So it can't be determined with 100% certainty where exactly it was when the aircraft was flying, as it moves up and down in response to the collective. For example, if the pilot raised the collective to max pitch before impact, that would also lower the carburetor heat knob to off, (almost) regardless of where it was before. Of course I can't second guess the conclusion that carb ice was the most likely cause here.

What is a little surprising to me is that there is, after 40+ years, still no bulletproof solution to this carb ice problem that affects especially the R22. How is it possible that the carb air temperature gauge STILL doesnt accurately show what the temperature is inside the critical area of the carb, as it does on the R44. The procedure, paraphrased is still "go by the gauge, but depending on power just add carb heat anyway, because this critical gauge doesn't read correctly at half the time, and if it all goes wrong you got about a second to get the pole down or you are dead. Good luck". Carb ice is far more common than loss of engine oil pressure for example, and it will shut your engine down at least as fast but with fewer warning signs. There's a red light for the oil pressure and a redundant gauge. How is there not also a big yellow warning light that turns on when the cat gauge is in the yellow arc. Or an automatic electric - or engine oil based heater in addition to the mechanical. All this stuff exists and has been in use in other carburetor engines for half a century. And that's before you consider fuel injection.

​​​
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Old 11th Dec 2023, 21:48
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We used to have a poster here, no longer with us, who had a high profile accident in the UK (with his celebrity partner) caused by landing with carb heat left in Hot.
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Old 11th Dec 2023, 22:45
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Originally Posted by lelebebbel
The way I'm reading that, the carb heat knob was indeed unlocked, but found in the full down (off) position. So it can't be determined with 100% certainty where exactly it was when the aircraft was flying, as it moves up and down in response to the collective. For example, if the pilot raised the collective to max pitch before impact, that would also lower the carburetor heat knob to off, (almost) regardless of where it was before. Of course I can't second guess the conclusion that carb ice was the most likely cause here.

What is a little surprising to me is that there is, after 40+ years, still no bulletproof solution to this carb ice problem that affects especially the R22. How is it possible that the carb air temperature gauge STILL doesnt accurately show what the temperature is inside the critical area of the carb, as it does on the R44. The procedure, paraphrased is still "go by the gauge, but depending on power just add carb heat anyway, because this critical gauge doesn't read correctly at half the time, and if it all goes wrong you got about a second to get the pole down or you are dead. Good luck". Carb ice is far more common than loss of engine oil pressure for example, and it will shut your engine down at least as fast but with fewer warning signs. There's a red light for the oil pressure and a redundant gauge. How is there not also a big yellow warning light that turns on when the cat gauge is in the yellow arc. Or an automatic electric - or engine oil based heater in addition to the mechanical. All this stuff exists and has been in use in other carburetor engines for half a century. And that's before you consider fuel injection.

​​​
Hmm, I could of sworn it said the assist was locked, but oh well, my bad.

Anyway, I've never heard that the guage isn't accurate, only that below 18" MAP you need to ignore it and pull full heat, because of where the probe is, it won't detect the temp drop due to that venturi effect thing.

Still,..the problem with carb heat assist, is that you have to remember to set it in a hover. If you set it on the ground, then the assist will lower it back into the yellow when you pick up. Its one reason I prefer the Beta.

,...and you can't just have it full all the time, because you'll foul out the plugs.

In all the years flying 22's (primarily in carb icing conditions) I've never had an issue with ice. That's why I'm still going with this accident being due to pilot distraction as to the underlying cause.
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Old 12th Dec 2023, 01:09
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Originally Posted by Robbiee
Hmm, I could of sworn it said the assist was locked, but oh well, my bad.

Anyway, I've never heard that the guage isn't accurate, only that below 18" MAP you need to ignore it and pull full heat, because of where the probe is, it won't detect the temp drop due to that venturi effect thing.
... In other words, the gauge is inaccurate. It's like an oil pressure gauge that may not indicate if you have low oil pressure. What's the point?

On the carburetor R44 they put the probe in the right spot, why was that not possible on the R22 in all these years?


Still,..the problem with carb heat assist, is that you have to remember to set it in a hover. If you set it on the ground, then the assist will lower it back into the yellow when you pick up. Its one reason I prefer the Beta.

,...and you can't just have it full all the time, because you'll foul out the plugs.
Exactly, the assist does not work very well, and the fully manual heat of the beta is even more likely to be forgotten by someone not used to it. They have in 40 years still not installed a real solution to something that has demonstrably killed dozens of people. Why is there no AD.

In all the years flying 22's (primarily in carb icing conditions) I've never had an issue with ice. That's why I'm still going with this accident being due to pilot distraction as to the underlying cause.
I too have many thousand hours of R22 and R44 time all over the globe, more than I care to admit really. I've never had one stop due to icing, but really - you and I don't know how close we've come. Because the combination of the governor and the non accurate gauges makes it impossible to know for sure when- or if ice could be forming. Maybe I've never had any significant ice (doubt it), maybe I've been 30 seconds away from a stoppage when I happened to decide to add some heat. Twice in my career I was airborne in an R22 when I heard fixed wings declare mayday due to engine failure over the same field I was at. Both of which were later found to be caused by carb icing.

That's why I'm still going with this accident being due to pilot distraction as to the underlying cause.


Well yes there's a 100hr pilot in a relatively high work load scenario over water and (nearly?) at night. My point is that there is a second underlying cause, and that is the very poor design of the machine he was in. I could jump into any of the other types I'm also not current in right now, and provided I'd remember how to start them, there most likely wouldn't be any issues afterwards. The R22 is the only one where I'd really have to be worried about an engine failure due to distraction.


Last edited by lelebebbel; 12th Dec 2023 at 01:25.
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Old 12th Dec 2023, 03:12
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Originally Posted by lelebebbel
... In other words, the gauge is inaccurate. It's like an oil pressure gauge that may not indicate if you have low oil pressure. What's the point?

On the carburetor R44 they put the probe in the right spot, why was that not possible on the R22 in all these years?



Exactly, the assist does not work very well, and the fully manual heat of the beta is even more likely to be forgotten by someone not used to it. They have in 40 years still not installed a real solution to something that has demonstrably killed dozens of people. Why is there no AD.



I too have many thousand hours of R22 and R44 time all over the globe, more than I care to admit really. I've never had one stop due to icing, but really - you and I don't know how close we've come. Because the combination of the governor and the non accurate gauges makes it impossible to know for sure when- or if ice could be forming. Maybe I've never had any significant ice (doubt it), maybe I've been 30 seconds away from a stoppage when I happened to decide to add some heat. Twice in my career I was airborne in an R22 when I heard fixed wings declare mayday due to engine failure over the same field I was at. Both of which were later found to be caused by carb icing.



Well yes there's a 100hr pilot in a relatively high work load scenario over water and (nearly?) at night. My point is that there is a second underlying cause, and that is the very poor design of the machine he was in. I could jump into any of the other types I'm also not current in right now, and provided I'd remember how to start them, there most likely wouldn't be any issues afterwards. The R22 is the only one where I'd really have to be worried about an engine failure due to distraction.
Unless you've heard something I haven't in six trips to the Robinson Safety Course, the 22's carb heat guage is only inaccurate below 18" of MAP, and full heat seems to fix the issue,...and since there isn't an AD to "fix it", it seems the carb ice induced engine failure accident rate and the FAA agree.

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Old 12th Dec 2023, 06:27
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Originally Posted by Robbiee
Unless you've heard something I haven't in six trips to the Robinson Safety Course, the 22's carb heat guage is only inaccurate below 18" of MAP, and full heat seems to fix the issue,...and since there isn't an AD to "fix it", it seems the carb ice induced engine failure accident rate and the FAA agree.
"Only" below 18 inches yes. Like a fuel gauge that is "only" inaccurate below half tank, would you consider that an "accurate" fuel gauge? That's some great engineering. Just pull full heat, you may or may not foul the plugs, and you can always readjust the heater just as you pull into a hover, since you barely got anything else to do at that point, right? Oh, it's ...manageable?
​yeah maybe, with sufficient training.... but is that really where the bar should be here? For a machine predominantly flown by new pilots nonetheless? A little thought experiment, what if you had to press a button every 60 seconds or the engine stops, is that acceptable? If someone failed to press it and had an accident, is that pilot error? Or should someone then step in and say you can't have a helicopter that relies on a system like that. If so, where's the line?

In my opinion, the carb heat system, the little gauge with the sticker that says to ignore it, the lack of a warning light, and the entire fact that carburetor icing is still a thing at all in 2023, is utterly ridiculous beyond all description, and nothing can excuse it in this day and age.

My 30 year old motorcycle is equipped with a fool proof automatic carb heating system, and the worst that ever happened to those (before the heaters were offered for free) if they got carb icing is that you had to pull over for 5 minutes to let the ice melt. Not autorotate into a bay.

Last edited by lelebebbel; 12th Dec 2023 at 06:44.
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Old 12th Dec 2023, 07:53
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Carb heat assist is crap as when you raise the lever it takes carb hear off. so you constantly have to check it.

But yes, the R22 carb heat system is is massive "gotcha" and it really should have been changed by now.
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Old 12th Dec 2023, 15:11
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Originally Posted by lelebebbel
"Only" below 18 inches yes. Like a fuel gauge that is "only" inaccurate below half tank, would you consider that an "accurate" fuel gauge? That's some great engineering. Just pull full heat, you may or may not foul the plugs, and you can always readjust the heater just as you pull into a hover, since you barely got anything else to do at that point, right? Oh, it's ...manageable?
​yeah maybe, with sufficient training.... but is that really where the bar should be here? For a machine predominantly flown by new pilots nonetheless? A little thought experiment, what if you had to press a button every 60 seconds or the engine stops, is that acceptable? If someone failed to press it and had an accident, is that pilot error? Or should someone then step in and say you can't have a helicopter that relies on a system like that. If so, where's the line?

In my opinion, the carb heat system, the little gauge with the sticker that says to ignore it, the lack of a warning light, and the entire fact that carburetor icing is still a thing at all in 2023, is utterly ridiculous beyond all description, and nothing can excuse it in this day and age.

My 30 year old motorcycle is equipped with a fool proof automatic carb heating system, and the worst that ever happened to those (before the heaters were offered for free) if they got carb icing is that you had to pull over for 5 minutes to let the ice melt. Not autorotate into a bay.
The fuel guage on my old Saturn got me four hours on the first half, then two hours on the second, so, its not just Robinson who doesn't make perfect guages.

,...and you must be super light, or something, 'cause I've never spent so much time under 18" that I've had to worry about fouling the plugs,... unless maybe you're still pulling heat even though you're not in carb icing conditions?

Anyway, seems like these days Robinson makes all their decisions based off not wanting to get sued,..and since they haven't fixed the 22 (like they did the Raven) I'm guessing they aren't getting sued over accidents caused by this issue. So, it seems most new pilots aren't struggling with pushing that button "every sixty seconds", lmfao!

Originally Posted by hargreaves99
Carb heat assist is crap as when you raise the lever it takes carb hear off. so you constantly have to check it.

But yes, the R22 carb heat system is is massive "gotcha" and it really should have been changed by now.
Sounds like you're not setting it in a hover. When I do that, it keeps the guage out of the yellow just fine.

,...but yes, I agree, it is crap, and I wish they'd just get rid of it.
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Old 12th Dec 2023, 17:08
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Originally Posted by Robbiee
The fuel guage on my old Saturn got me four hours on the first half, then two hours on the second, so, its not just Robinson who doesn't make perfect guages.
Robinson helicopters: "our critical gauges work about as good as those on an old broken car".
​​​​
No wait I quoted that wrong, it actually says:

"For more than 50 years, Robinson Helicopter has been at the forefront of the helicopter industry by delivering safety enhancing technologies"

​​​​My bad, I wonder how I could have got that confused.


,...and you must be super light, or something, 'cause I've never spent so much time under 18" that I've had to worry about fouling the plugs,...
Certain flight regimes have you well below 18" a lot, yes. Lower speed flight, such as cattle mustering, often has you sitting at 17" all day. Another example is higher altitude flight. At higher altitude, 18" does no longer indicate the same low throttle opening as it does in Torrance CA, however no guidance is given whatsoever how to deal with that, it just says "pull full below 18"."

unless maybe you're still pulling heat even though you're not in carb icing conditions?
Maybe? I don't know since I can't find a relative humidity gauge anywhere on the dash. What is the relative humidity once you're 10 miles and a few thousand feet above the airport? An hour after takeoff? There is no other helicopter type that forces you to make these kind of guesses. A simpler solution would be to just fix the damn carb air temperature gauge, but apparently that challenge is just too difficult for the company at the forefront of the helicopter industry.
​​​​​​
Anyway, seems like these days Robinson makes all their decisions based off not wanting to get sued,..and since they haven't fixed the 22 (like they did the Raven) I'm guessing they aren't getting sued over accidents caused by this issue. So, it seems most new pilots aren't struggling with pushing that button "every sixty seconds", lmfao!
Robinson Helicopters: "barely good enough that we still haven't been sued out of existence"


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Old 12th Dec 2023, 17:33
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Originally Posted by lelebebbel
Robinson helicopters: "our critical gauges work about as good as those on an old broken car".
​​​​
No wait I quoted that wrong, it actually says:

"For more than 50 years, Robinson Helicopter has been at the forefront of the helicopter industry by delivering safety enhancing technologies"

​​​​My bad, I wonder how I could have got that confused.




Certain flight regimes have you well below 18" a lot, yes. Lower speed flight, such as cattle mustering, often has you sitting at 17" all day. Another example is higher altitude flight. At higher altitude, 18" does no longer indicate the same low throttle opening as it does in Torrance CA, however no guidance is given whatsoever how to deal with that, it just says "pull full below 18"."



Maybe? I don't know since I can't find a relative humidity gauge anywhere on the dash. What is the relative humidity once you're 10 miles and a few thousand feet above the airport? An hour after takeoff? There is no other helicopter type that forces you to make these kind of guesses. A simpler solution would be to just fix the damn carb air temperature gauge, but apparently that challenge is just too difficult for the company at the forefront of the helicopter industry.
​​​​​​


Robinson Helicopters: "barely good enough that we still haven't been sued out of existence"
Interesting, I've always been under the impression that slow flight took more power, and that those Cattle Mustering pilots busted MAP limits all the time (at least that's what they mentioned a few times at the Safety Course),..but anyway, are a lot of R22 Cattle Mustering pilots crashing due to carb ice?

Plus, its not just humidity, there's also the outside temp and visible moisture,...but I'm sorry there's no humidity guage in the R22. There's no fog guage either, and I could have used one of those plenty of times, lol.

,...and it was a brand new 2000 Saturn, lol.

Anyway, everyone knows Robbies are budget helicopters. So, either accept them for their flaws, or go fly something else. Plenty of other choices out there you know.

Oh,...and if the throttle is wide open at just 18" at high altitude, you should know that its not going to create that venturi like effect on that side of the butterfly valve, so carb ice shouldn't be a problem. Its probably why they tell you to lower the carb heat on short final at high altitude, but not at sea level.
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