Bell 206: JetRanger and LongRanger
I wonder if any Bell Engineers (I use the term loosely here) ever in their life saw a BO or BK door? If they did....would they be able to comprehend the noticeable advantages the German's have in commonsense, engineering, and cognative abilities?
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I have never flown in any model helicopter that didn't leak. Not one. 206, 212, 412, S76, ad infinitum, they all leak buckets into the cockpit. The water pouring from the breakers isn't so bad in a 206, but when you're in solid IMC, with weather at minimums at the beach, and barely enough fuel to get there, it's worse. If you have a very good relationship with the maintenance monkeys, and they know their stuff, you can get much of it stopped through the judicious use of proseal and silicone RTV, but you can never get it all stopped. The eyebrow vents above the windshields in the S76 are the worst, because they catch the rain and funnel it to your shoulders or crotch. The only way to stop it is to proseal the vents shut, but then somebody comes along and wants more air, although those vents only allow in a gentle breeze, even if they do allow a tsunami of water, and they break the seals, and you get wet the next time it rains.
You can buy a cheap Yugo that never leaks, but a multimillion dollar aircraft? Leaks every time.
You can buy a cheap Yugo that never leaks, but a multimillion dollar aircraft? Leaks every time.
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Helicopter Doors
Gomer Pylot: "...the maintenance monkeys...and they know their stuff" a slight contradiction of terms there - but I know what you mean. To take up the theme that SASless commented on, yes it does seem that Europeans know how to make helicopter doors watertight. Back in the early '80's when the Republic of Singapore Air Force bought the Super Puma they were assembled from kits at Seletar Air Base. Completed fuselages were pushed under a metal frame contraption that had a multitude of water nozzles spraying from all angles. The fuselage had to be watertight or it wasn't accepted - simple as that. The water rig is still there but looking a bit the worse for wear.
Incidently, and a slight drift here, I've seen C130's with the title 'Republic of Singapore Air Force' and others with 'Republic of Singapore Airforce'. I don't know which is 'correct' or how the 'other one' got there. Nothing really, I'd just thought I'd mention it as it seems very untypical of Singapore's reputed overall efficiency.
Incidently, and a slight drift here, I've seen C130's with the title 'Republic of Singapore Air Force' and others with 'Republic of Singapore Airforce'. I don't know which is 'correct' or how the 'other one' got there. Nothing really, I'd just thought I'd mention it as it seems very untypical of Singapore's reputed overall efficiency.
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Next Question
Touched on briefly earlier in this thread, but I am looking for the reason for the 2 minute cool down period before shutdown on the Allison/RR 250. I understand it's to cool the bearings to prevent coking, but which bearings, and what will eventually happen if the engine is frequently shutdown without the 2 minute cool down?
The main reason for asking is a couple of other pilots flying the same machine I fly almost always shut down early, and then I have to go put my butt in the machine and hope nothing is amiss!
The main reason for asking is a couple of other pilots flying the same machine I fly almost always shut down early, and then I have to go put my butt in the machine and hope nothing is amiss!
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From what I seem to remember from my long and distant days of operating the 206 it will "only" mean higher maintenance bills but I don't think the aircraft will quit on you.
I was once told that Robert Maxwell would not allow his pilot to cool his Allisons on his 355 and this meant higher maintenance bills.
But I stand corrected.
What would irk me is knowing I am flying a machine I know other pilots are not operating within the FLM. Any chance you could point out to them the error in their ways?
I was once told that Robert Maxwell would not allow his pilot to cool his Allisons on his 355 and this meant higher maintenance bills.
But I stand corrected.
What would irk me is knowing I am flying a machine I know other pilots are not operating within the FLM. Any chance you could point out to them the error in their ways?
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Please do your 2 minute cool-downs. If not, coke will form in the turbine rotor lubricating oil passages, and eventually starve the bearings of oil. It's been a while but I think on the 100-hr. inspections we would remove the oil sump at the bottom of the turbine rotor (it looks like a silver box about the size of a cigarette pack), and using a mirror look up inside the oil passage for coke.
We could always tell when the cool-downs were not done. The coke forms easily and the diameter of the oil passage gets smaller and smaller (much like a clogged artery, I suppose).
Will the engine quit? If not caught and cleaned on the 100-hr. inspection, then coke builds and could lead to bearing failure. Chip lights are meant to warn you, but by then it is too late to prevent the expensive repair bill.
We could always tell when the cool-downs were not done. The coke forms easily and the diameter of the oil passage gets smaller and smaller (much like a clogged artery, I suppose).
Will the engine quit? If not caught and cleaned on the 100-hr. inspection, then coke builds and could lead to bearing failure. Chip lights are meant to warn you, but by then it is too late to prevent the expensive repair bill.
And people wonder why engines fail, I am in shock that people play scant disregard for the one thing that keeps them aloft and all for saving 2 mins
Mind you yesterday a chief engineer of a large maintainence company flew a piston engine machine in to where I was and it was shut down within a minute !
Mind you yesterday a chief engineer of a large maintainence company flew a piston engine machine in to where I was and it was shut down within a minute !
bugdriver,
There's a labyrinth seal that can coke up, much as Matari has said, if the 2 minute cool down is not observed. We had this discussion long and often over the years with Bell and with Allison reps, mainly relating to the temperature of the oil as against a set time. Allison have a graph somewhere to prove their requirement that the time (2 minutes) is paramount: I probably have a copy SomeWhere, but don't expect me to find it! Anyway, 2 (two) minutes shut down is mandatory, no more, no less
It can also be worth turning the blades 'backwards' when you tie them down, to break up any carbon starting to build up within the engine bearings. Sounds strange, but a lot of us 'oldies' do it as a matter of course: just a bit of old wisdom to pass on
There's a labyrinth seal that can coke up, much as Matari has said, if the 2 minute cool down is not observed. We had this discussion long and often over the years with Bell and with Allison reps, mainly relating to the temperature of the oil as against a set time. Allison have a graph somewhere to prove their requirement that the time (2 minutes) is paramount: I probably have a copy SomeWhere, but don't expect me to find it! Anyway, 2 (two) minutes shut down is mandatory, no more, no less
It can also be worth turning the blades 'backwards' when you tie them down, to break up any carbon starting to build up within the engine bearings. Sounds strange, but a lot of us 'oldies' do it as a matter of course: just a bit of old wisdom to pass on
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Turning the blades backwards (as if done forward you'd only turn the freewheel unit, not the turbine) after every flight was part of my training for the typerating. Also where i did my CPL afterwards it was normal to do this for at least one full turn after every flight (maybe that was because i learned from people being in the industry for a long time but i think this is just SOP )
The machine i fly recently did build up coke and it was dealt with (read: expensive but as we noticed it in time, not too expensive). This was not due to not taking care of 2 mins cooldown but because of a weak seal, though.
You will notice when coke builds up as you will have difficulties turning your blades backward before the first flight of the day (you do turn the blades by 90 degrees to be sure they are not tied down anymore...? If so, why not turning them backwards - will tell you something if there is something wrong). Here, with N2 being stuck (i.e. you won't be able to turn the turbine wheels by hand through the exhaust pipe) you would need a bit more force to turn the rotor backward after loosening the tie-down. You could also notice that you are probably going to meet a problem when your rotor is hardly turning by 25% N1 in such a case. Still, even it it does, there might be coke built up as with us it started turning at around 20% N1 all the time.
Watch out for these little hints as they will almost always try to tell you something. And the sooner you deal with it, the less expensive it will get.
Beside all this and rule No. 1: Do, what your FM tells you to do and deal with those who don't.
)The machine i fly recently did build up coke and it was dealt with (read: expensive but as we noticed it in time, not too expensive). This was not due to not taking care of 2 mins cooldown but because of a weak seal, though.
You will notice when coke builds up as you will have difficulties turning your blades backward before the first flight of the day (you do turn the blades by 90 degrees to be sure they are not tied down anymore...? If so, why not turning them backwards - will tell you something if there is something wrong). Here, with N2 being stuck (i.e. you won't be able to turn the turbine wheels by hand through the exhaust pipe) you would need a bit more force to turn the rotor backward after loosening the tie-down. You could also notice that you are probably going to meet a problem when your rotor is hardly turning by 25% N1 in such a case. Still, even it it does, there might be coke built up as with us it started turning at around 20% N1 all the time.
Watch out for these little hints as they will almost always try to tell you something. And the sooner you deal with it, the less expensive it will get.
Beside all this and rule No. 1: Do, what your FM tells you to do and deal with those who don't.
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That 2-Minute Dwell Time
There has been a lot of discussion on this subject here and wherever 206 pilots gather, so let me explain in detail how it all originated. John Eacott's post is excellent good but leaves out a few pertinent points.
The first JetRangers were fitted with 250-C18 engines, unfortunately their reliability was not nearly as good as it is today. So in the late 60' or early 70's, the manufacturer, DDA (Detroit Diesel Allison, a Division of General Motors) developed a whole range of modifications to address this reliability issue, DDA called this the 'Blue Ribbon Program'. Subsequently, engines that incorporated all of the modifications were known as 'Blue Ribbon Engines'. This term only applied to C18 engines, the modifications were standard on all subsequent engine models.
Briefly, the modifications relating to the 2-minute dwell time were to prevent coking and seizure of the labyrinth seals, not so much the bearings, and were as follows:
1. A check valve was fitted into the oil pressure tube supplying the No's 6 and 7 bearings in the turbine module. It can be seen on the R/H side of the engine attached to the horizontal firewall and just above the FCU. This check valve closes during the last few seconds following shut-down preventing oil getting into the bearing housing. The oil scavenge pumps continue to run and this minimizes the amount of oil in the bearing housing immediately following shut-down.
2. A small stainless steel sump was fitted to the bottom of the turbine casing to allow any residual oil, again from the No's 6 and 7 bearing, to flow down and collect in there after shut-down rather than remain in the bearing housing and turn to coke under the high residual temperature. This coking would cause the rotating and non-rotating blades of the labyrinth seals to lock preventing subsequent rotation.
3. A procedure was introduced that required pilot, after landing, to observe a 2-minute dwell time between rolling the throttle to flight-idle and shut-off. As John Eacott correctly points out, this results in a significant temperature reduction in turbine module as a whole and the bearings/seals in particular. Yes, there is a DDA-produced graph somewhere showing the temperature reduction and it's quite startling.
4. Another procedure was introduced that required the main rotor to be turned backwards for three revolutions immediately after shut-down (use the main rotor tie-down but be careful not to get it wrapped around the tail rotor blades - those who've done that will know what I mean). By turning the rotor backwards the freewheel unit is engaged and the N2 section of the engine is rotated, also backwards but a lot more than three revolutions. This rotation scrapes any potential coke from the labyrinth seals.
Frankly, I've always thought that there should have been a fifth item here. DDA should have specified which oils were more susceptible to coking, not by mil-spec but by brand name. For example, I believe that anyone who uses Aeroshell 500 oil in a 250 Series engines ought to be flogged. Use this oil and your asking for trouble, use Mobil Jet Oil II instead.
To clear up a couple of misconceptions the some seem to have regarding this issue:
A. Any carbon deposits in the oil will be found in the filter/s, not on the magnetic plugs.
B. Excessive carbon build-up on a labyrinth seal will not cause an in-flight failure, but it may very well prevent a subsequent start.
So now you can see that there are very sound reasons why ALL pilots should observe the 2-minute dwell time after landing and rotate the main rotor backwards three revolutions after it's stopped - that's TWO minutes and THREE revolutions - failure to do these simple tasks WILL eventually cost you a lot of money - now you know.
The first JetRangers were fitted with 250-C18 engines, unfortunately their reliability was not nearly as good as it is today. So in the late 60' or early 70's, the manufacturer, DDA (Detroit Diesel Allison, a Division of General Motors) developed a whole range of modifications to address this reliability issue, DDA called this the 'Blue Ribbon Program'. Subsequently, engines that incorporated all of the modifications were known as 'Blue Ribbon Engines'. This term only applied to C18 engines, the modifications were standard on all subsequent engine models.
Briefly, the modifications relating to the 2-minute dwell time were to prevent coking and seizure of the labyrinth seals, not so much the bearings, and were as follows:
1. A check valve was fitted into the oil pressure tube supplying the No's 6 and 7 bearings in the turbine module. It can be seen on the R/H side of the engine attached to the horizontal firewall and just above the FCU. This check valve closes during the last few seconds following shut-down preventing oil getting into the bearing housing. The oil scavenge pumps continue to run and this minimizes the amount of oil in the bearing housing immediately following shut-down.
2. A small stainless steel sump was fitted to the bottom of the turbine casing to allow any residual oil, again from the No's 6 and 7 bearing, to flow down and collect in there after shut-down rather than remain in the bearing housing and turn to coke under the high residual temperature. This coking would cause the rotating and non-rotating blades of the labyrinth seals to lock preventing subsequent rotation.
3. A procedure was introduced that required pilot, after landing, to observe a 2-minute dwell time between rolling the throttle to flight-idle and shut-off. As John Eacott correctly points out, this results in a significant temperature reduction in turbine module as a whole and the bearings/seals in particular. Yes, there is a DDA-produced graph somewhere showing the temperature reduction and it's quite startling.
4. Another procedure was introduced that required the main rotor to be turned backwards for three revolutions immediately after shut-down (use the main rotor tie-down but be careful not to get it wrapped around the tail rotor blades - those who've done that will know what I mean). By turning the rotor backwards the freewheel unit is engaged and the N2 section of the engine is rotated, also backwards but a lot more than three revolutions. This rotation scrapes any potential coke from the labyrinth seals.
Frankly, I've always thought that there should have been a fifth item here. DDA should have specified which oils were more susceptible to coking, not by mil-spec but by brand name. For example, I believe that anyone who uses Aeroshell 500 oil in a 250 Series engines ought to be flogged. Use this oil and your asking for trouble, use Mobil Jet Oil II instead.
To clear up a couple of misconceptions the some seem to have regarding this issue:
A. Any carbon deposits in the oil will be found in the filter/s, not on the magnetic plugs.
B. Excessive carbon build-up on a labyrinth seal will not cause an in-flight failure, but it may very well prevent a subsequent start.
So now you can see that there are very sound reasons why ALL pilots should observe the 2-minute dwell time after landing and rotate the main rotor backwards three revolutions after it's stopped - that's TWO minutes and THREE revolutions - failure to do these simple tasks WILL eventually cost you a lot of money - now you know.
SJ,
I forgot the oil type issue: thanks for the reminder! Whilst Jet II is the most common used in 206's, I swapped to Shell 560 some years back (in common with my 117) as a '3rd Generation' oil. The anti coking qualities are another stage better than Jet II, certainly quantifiable in the LTS101 as the pressure differential check showed a halving compared to 2nd generation oils used previously.
Googling for the Allison 2 minute temperature chart hasn't borne fruit yet, but I did find this Hughes Service Information letter, with further reference to the practice of turning the blades backwards. It also has an excellent diagram of the areas likely to encounter coking, and the labyrinth seal area, on the last two pages.
I forgot the oil type issue: thanks for the reminder! Whilst Jet II is the most common used in 206's, I swapped to Shell 560 some years back (in common with my 117) as a '3rd Generation' oil. The anti coking qualities are another stage better than Jet II, certainly quantifiable in the LTS101 as the pressure differential check showed a halving compared to 2nd generation oils used previously.
Googling for the Allison 2 minute temperature chart hasn't borne fruit yet, but I did find this Hughes Service Information letter, with further reference to the practice of turning the blades backwards. It also has an excellent diagram of the areas likely to encounter coking, and the labyrinth seal area, on the last two pages.
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Hi,
Personally from my engineering experience I think the relative merit of the 'turning the blades backwards' has reduced on C20B/J if, as John says, 3rd generation 'HTS' oil (Mobil 254) is used, a Facet scavenge oil filter is fitted and strict adherence to the 2 minute cooldown is followed. As a pilot I still do it out of habit but I rarely see any coke build up in the 6/7 strut anymore.
Of far more importance is ensuring engineers actually pull the strut out at the stated interval, regardless of the oil flow figure, and give it a clean.
The graph you all refer to actually shows that it is closer to 1 min 45 secs before the core temperature stabilises, but 2 minutes is take as the figure published in the FM.
Now, C20R's in those stinky 5ooER's are a different story!
TCF
Personally from my engineering experience I think the relative merit of the 'turning the blades backwards' has reduced on C20B/J if, as John says, 3rd generation 'HTS' oil (Mobil 254) is used, a Facet scavenge oil filter is fitted and strict adherence to the 2 minute cooldown is followed. As a pilot I still do it out of habit but I rarely see any coke build up in the 6/7 strut anymore.
Of far more importance is ensuring engineers actually pull the strut out at the stated interval, regardless of the oil flow figure, and give it a clean.
The graph you all refer to actually shows that it is closer to 1 min 45 secs before the core temperature stabilises, but 2 minutes is take as the figure published in the FM.
Now, C20R's in those stinky 5ooER's are a different story!
TCF
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SJ,
interesting read, thx for the background
(btw here it is a C20R in our B206)
Now, if that CSL ist for 250-C20B, does anybody flying a BO-105 do the same? I mean, 2 min cooldown for sure but i never saw anybody turning the rotor of a BO-105 backwards after flight...
interesting read, thx for the background
(btw here it is a C20R in our B206)
Now, if that CSL ist for 250-C20B, does anybody flying a BO-105 do the same? I mean, 2 min cooldown for sure but i never saw anybody turning the rotor of a BO-105 backwards after flight...
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John E. I kind of curious where you can up with the 2 minutes, no more or less. The training material I have from Allison/RR on the C20's and 30's states 2 minutes minimum. However there are a few FAA types here that go with your statement and say we must reheat the engine up and then do a 2 min. coll down if we exceed the 2 minutes.
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Anyway, 2 (two) minutes shut down is mandatory, no more, no less
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Rolls-Royce says that 2 minutes is optimum, but a few seconds more or less is OK. 90 seconds is pretty much the minimum, but more is better, up to 120. If you go much beyond 2 minutes, you're supposed to go to 100%N2 for 2 minutes, then cool down again for 2 minutes. At least that's what our maintenance says, and I've heard this repeatedly. Like John, Google has been unhelpful on this.
Originally Posted by Rick1128
I kind of curious where you can up with the 2 minutes, no more or less.
20+ years ago, not too sure now! It would most likely come from the DDAllison manuals, but I don't have access to one.
There are numerous little gems hidden away like this. Going off the current discussion, where would you look within Bell's manuals for a reference that prohibits having the standard door steps fitted on a 206 if sling loading with high skids? Flight manual: yes, but where? Normal procedures, no: cargo hook supplement, no: high skid supplement: yes!
Where do you find reference in Agusta's A109 manuals to inform a pilot that the last shutdown of the day must not use the rotorbrake since it will then give a false MGB oil level? Flight manual: no. Maintenance manual: yes!
I think the 206 high skid supplement may have been amended, but it was one of those examples that I'm trying to make. Not all these gems are easily referenced, but they are usually there somewhere
that chinese fellow:
We changed to BP 2380 on the 117, when we found that our engineering advice to use Shell 560 was in direct contravention of the Maintenance Manual prohibiting the use of 560 in LTS101's
On the 206, however, 560 is the a 3rd generation oil that is approved for both the engine and the gearbox, which is important if there is a seal leak and oil mixing. Another little point that is sometimes missed
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Oil Mixing - another little 'gem' - hidden away in the depth's of the FM is a section detailing lubricants and Mobil Jet II and 254 are compatible so whilst IMHO not preferrred to constantly mix oils, there are some instances where knowledge of the 'compatabilities' may get you out a 'oil shortage' situation.
Some people swear that Mobil 254 makes gearbox seals leak, I agree that if you change over mid life with the same seals fitted then I have seen that to be true but if, say post overhaul (where new seals are fitted), you start on 254 I have witnessed no more leakage than usual from Bell gearboxes.
FWIW, our 105LS uses 254 in everything - engines, gearboxes and main rotor hub. I have been told that turning the blades backwards on the 105 is bad for the hyd pumps, but have not confirmed it - anyone have any 'offical' advice on this one?
Some people swear that Mobil 254 makes gearbox seals leak, I agree that if you change over mid life with the same seals fitted then I have seen that to be true but if, say post overhaul (where new seals are fitted), you start on 254 I have witnessed no more leakage than usual from Bell gearboxes.
FWIW, our 105LS uses 254 in everything - engines, gearboxes and main rotor hub. I have been told that turning the blades backwards on the 105 is bad for the hyd pumps, but have not confirmed it - anyone have any 'offical' advice on this one?
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Thank you all for your advice on the 2 min cool down.
I have been turning the blades backwards after shutdown for years, good to know it is doing some good.
The engineers have been alerted and will pay close attention!
Another question now:
Is it harmful to let the aircraft run at idle for extended periods? One client requires that the aircraft remain running while the technicians work on Volcano sensing sites, in case we have to depart in a hurry!
Thanks in advance.
Bugdriver
I have been turning the blades backwards after shutdown for years, good to know it is doing some good.
The engineers have been alerted and will pay close attention!
Another question now:
Is it harmful to let the aircraft run at idle for extended periods? One client requires that the aircraft remain running while the technicians work on Volcano sensing sites, in case we have to depart in a hurry!
Thanks in advance.
Bugdriver