Sikorsky S-76: Ask Nick Lappos
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Thanks Nick! Just what I needed. 
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S-76 Tail Pylon Cracking
A UK registered S-76B has allegedly recently suffered a very badly cracked tail pylon structure, above the horizontal stabiliser.
I have heard that it may be a known weak point. Anyone in the know able to comment?
[ 06 December 2001: Message edited by: Skycop ]
I have heard that it may be a known weak point. Anyone in the know able to comment?
[ 06 December 2001: Message edited by: Skycop ]
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Do you know if the Operator is doing the Tail Rotor Pedal/Cyclic Stick Movement Interlock Check During Pre Taxi. This is an old practice that was known to have caused cracking around Station 440 ( Tail Rotor Pylon )
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I checked with the S-76 Chief Pilot, and he told me this:
Recently, one aircraft had difficulty with the stabilizer attachment bolts loostening up (not holding torque). They tightened them up several times before replacing them. In the interim, the lose stab caused high loads in the local area, which caused the cracks. A service bulletin will be out shortly on this.
This is the first such incident in the several million hours for the S-76 fleet.
Recently, one aircraft had difficulty with the stabilizer attachment bolts loostening up (not holding torque). They tightened them up several times before replacing them. In the interim, the lose stab caused high loads in the local area, which caused the cracks. A service bulletin will be out shortly on this.
This is the first such incident in the several million hours for the S-76 fleet.
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As far as I know, the interlock check was not carried out by the operator so that is unlikely to be the cause.
The reason Nick has quoted seems to give the answer.
Is it true that the fitting of the alternative lightweight stabiliser is a possible preventative measure?
The reason Nick has quoted seems to give the answer.
Is it true that the fitting of the alternative lightweight stabiliser is a possible preventative measure?
Cold WX operations for S76A
A general inquiry to accertain the reasoning for the -34.4 degree C limit on the 76. Currently it is -32 outside and we are expection lower with a -55 degree wind chill at one of our potential destinations. . .How was this limit created and what are the ramifications of flight in temps below it? I understand it to be a limitation for the Gearbox. Is it a starting limitation or a general op's limit and is the wind chill factor considered in this equation?. .Brrrrr! 
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My understanding or mis-understanding of the S76 certification limit of -34.4 is as follows:. .They conducted the cold weather testing during the month of March and the coldest temperatures they could find (-34.4) were in Tuktyatuk where the testing was conducted. As you are aware March is the beginning of the end of winter in Canada and in order to get a lower temperature limit they would have had to wait untill the following year, and because of production deadlines ect.ect . that was not acceptable. . .The company I work for has a cold temperature limit of -32, that is because of a limitation in the allison engine manual which to paraphrase goes something like " The Allison 250 C-30 engine will run satisfatory down to a temperature of -32 while using Jet A or Jet A-1 fuel" to "operate below this temperature the aircraft must be fitted with the agro-tech fuel filter" yada yada yada. . .
Have a look at a long ranger with a C30 engine and you will notice that it has an airframe fuel filter on it, for that specific reason.
To operate the 76 down to its airframe limit of -34.4 you must use Jet B.
About the certification stuff above I'm sure Nick . .can fill us in on the exact particulars, I heard the story from one of the test pilots at Sikorsky in 96.. .p.s.. .Wind chill is not taken into account, wind chill was developped for whimpy people who live in the South to make it sound like it is colder than it really is ,they will say something like "with the wind chill it is -40" while Northerners will say its -40 because that is what the actual temperature is.
[ 28 January 2002: Message edited by: IHL ]</p>
Have a look at a long ranger with a C30 engine and you will notice that it has an airframe fuel filter on it, for that specific reason.
To operate the 76 down to its airframe limit of -34.4 you must use Jet B.
About the certification stuff above I'm sure Nick . .can fill us in on the exact particulars, I heard the story from one of the test pilots at Sikorsky in 96.. .p.s.. .Wind chill is not taken into account, wind chill was developped for whimpy people who live in the South to make it sound like it is colder than it really is ,they will say something like "with the wind chill it is -40" while Northerners will say its -40 because that is what the actual temperature is.
[ 28 January 2002: Message edited by: IHL ]</p>
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To: IHL
"Wind chill is not taken into account, wind chill was developped for whimpy people who live in the South to make it sound like it is colder than it really is ,they will say something like "with the wind chill it is -40" while Northerners will say its -40 because that is what the actual temperature is".
In actuality the temperature and the wind chill temperature are different. The actual temperature can be –25 degrees F and depending how fast the wind is blowing the wind chill can measure –45 to –60 degrees F (for example). The wind chill temperature is a perceived temperature and reflects the rate of heat dissipation on the persons body. At least that is what I think it is.
"Wind chill is not taken into account, wind chill was developped for whimpy people who live in the South to make it sound like it is colder than it really is ,they will say something like "with the wind chill it is -40" while Northerners will say its -40 because that is what the actual temperature is".
In actuality the temperature and the wind chill temperature are different. The actual temperature can be –25 degrees F and depending how fast the wind is blowing the wind chill can measure –45 to –60 degrees F (for example). The wind chill temperature is a perceived temperature and reflects the rate of heat dissipation on the persons body. At least that is what I think it is.
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Is the limit on start up temperature or operating ?. Surely once you have started the OAT is not really relevant for the engine and gearboxes . Might have more effect on rotor hub seals and elastomers . If I recall correctly the BK117 had special seals for Low temp ops that were no good at higher temps. We also had to change all the boots as the naugahyde would get brittle at low temps there was a booster fan in the heating ducts as well I think.
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My two cents....
I have also heard that there may be a Hydraulic system concern in extremely cold temperatures. We don't have any TANIS heaters on our hydraulic systems... Any feedback on that.
As far as the BK is concerned, the limit is something like -45, but you reach a limit of -32 using Jet A. Below -25, we used Jet B to be safe, but had an operational limit of -40 (C and F) <img src="smile.gif" border="0"> but who wants to be out there at -40, I think at these temperatures, it becomes a real to life human factors issue: What if you go down with a precautionary, or if you have a heater malfunction? Most of us are civilian operators who really have no business flying at these extremely low temperatures. OAT affects the A/C but wind chill affects the people!
I have also heard that there may be a Hydraulic system concern in extremely cold temperatures. We don't have any TANIS heaters on our hydraulic systems... Any feedback on that.
As far as the BK is concerned, the limit is something like -45, but you reach a limit of -32 using Jet A. Below -25, we used Jet B to be safe, but had an operational limit of -40 (C and F) <img src="smile.gif" border="0"> but who wants to be out there at -40, I think at these temperatures, it becomes a real to life human factors issue: What if you go down with a precautionary, or if you have a heater malfunction? Most of us are civilian operators who really have no business flying at these extremely low temperatures. OAT affects the A/C but wind chill affects the people!
Gidday IHL,. .Hows work? Nice dig at the humans who are blessed enough to be born somewhere WARM and HOSPITABLE <img src="tongue.gif" border="0"> . .Looking foward to hearing Nicks reply..... .Say gidday to those worthless aussies for me..
Steve, as said above windchill is a perceived temperature felt by people (maybe animals as well???). For inanimate objects ie helicopters -32 is -32 regardless of the windchill factor.
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The -34C operating restriction for the Rolls-Royce Model 250-C30 in the S-76 aircraft is due to the fuel specs. Jet A and JP-8 both have a maximum viscosity rating of 8 centistokes where JP-5 has a maximum viscosity of 8.5 centistokes. By referencing fuel spec ASTM-D-1655, you find that at -32C you reach the 8.0 centistoke level for Jet A and JP-8.
This is where the note in the Model 250-C30 Operations and Maintenance Manual comes from, stating "The engine will operate satisfactorily on JP-5, JP-8, Jet A and Jet A-1 at fuel and outside air temperatures down to -32 degrees C (-25 F)." For JP-5, the maximum viscosity is 8.5 centistokes, which translates to -34 C.
Operation of the –C30 / S-76 at lower temperatures is not limited by the engine – most operators simply follow standard cold weather fuel mixture instructions, such as adding Av-Gas to the jet fuel. JP-4 and Jet B do not have maximum viscosity requirements, and are thus also used by some operators operating in extreme cold weather environments.
Steve76 - Email me if you have any additional Qs.
T/shaft
This is where the note in the Model 250-C30 Operations and Maintenance Manual comes from, stating "The engine will operate satisfactorily on JP-5, JP-8, Jet A and Jet A-1 at fuel and outside air temperatures down to -32 degrees C (-25 F)." For JP-5, the maximum viscosity is 8.5 centistokes, which translates to -34 C.
Operation of the –C30 / S-76 at lower temperatures is not limited by the engine – most operators simply follow standard cold weather fuel mixture instructions, such as adding Av-Gas to the jet fuel. JP-4 and Jet B do not have maximum viscosity requirements, and are thus also used by some operators operating in extreme cold weather environments.
Steve76 - Email me if you have any additional Qs.
T/shaft
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I was the Chief S-76 Test Pilot back then and recall the reason for the limit as -34 degrees C. The limit is based on the qualification and demonstration tests done back in the beginning, where we set -34 as a market acceptable number. There is no fundamental difference between the S-76 and other Sikorsky machines regarding cold capability except for that, even though I do see some interesting sidelights in the above posts. The aircraft will not fail to do anything critical if taken to lower temperatures, but you as PIC will not be legal. The fuel reasons for the limit listed in the posts above are not reasons for the original limit, but they quite well could be true, even so. I do know that we took the Jet A down to -34.4, and that the aircraft flight manual limits should override the engine operator's manual, but a quick call to RR customer service should answer the question.. .The limit is both cold soak/start-up and operating, although the start-up is always the worst condition, since most systems warm up as they turn up. Seals are always the issue, transmission, hydraulic and landing gear.
Regarding wind chill, there really is no such thing, be careful not to get caught in "TV weatherman hype." As defined, wind chill is the temperature you have to take still air down to so that you equal the cooling power of the current temperature/wind conditions. It is semi bulls**t, based on exposed flesh, and is of no use for anything else, like if you have clothes on, or if you are out of the full effect of the wind. It is impressive when quoted on the news, however.
If it is -40 degrees, and 50 knots of wind, a thermometer will read -40. If you shelter the thermometer from the wind, it will read -40. If you take the thermometer from a warm house and hang it in the -40 with 50 knots of wind, it will more quickly get to -40 than if there is no wind (that is all wind chill means).
[ 30 January 2002: Message edited by: Nick Lappos ]</p>
Regarding wind chill, there really is no such thing, be careful not to get caught in "TV weatherman hype." As defined, wind chill is the temperature you have to take still air down to so that you equal the cooling power of the current temperature/wind conditions. It is semi bulls**t, based on exposed flesh, and is of no use for anything else, like if you have clothes on, or if you are out of the full effect of the wind. It is impressive when quoted on the news, however.
If it is -40 degrees, and 50 knots of wind, a thermometer will read -40. If you shelter the thermometer from the wind, it will read -40. If you take the thermometer from a warm house and hang it in the -40 with 50 knots of wind, it will more quickly get to -40 than if there is no wind (that is all wind chill means).
[ 30 January 2002: Message edited by: Nick Lappos ]</p>
Thanks for the replies .... .Turboshaft: . .There definately is a fuel temp limitation for the jet B but I cannot see why that is a restriction considering that the Bell 212 can operate to -40 on the same fuel.. .Nick: . .Its a shame that they never got to below -34.4 as this is a definate restriction to our operation and we are only at 51 degrees N latitude. It is (as I assumed...) just a legal issue and it's comforting to know, in your opinion, that temps slightly below that limit should not be cause for serious consternation.. .Another problem is the descepancy between the OAT guage and the AWOS or tower temp. Last night while doing a maintenance run the reported OAT at the AWOS was -33 and the a/c was only reporting -28 !!. Every since I watched your icing video I have paid attention to noting any discrepancy between the two and have tried to apply a correction as necessary. . .Volpe: <img src="tongue.gif" border="0"> <img src="wink.gif" border="0"> <img src="tongue.gif" border="0"> <img src="wink.gif" border="0"> <img src="tongue.gif" border="0"> <img src="wink.gif" border="0">
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Hey Steve76
I agree with Nick on the reasoning for the -34. Don't forget that the Jet A is limited down to -32 using PRIST.
As for the 212 down to -40, don't forget that the 212 has heated fuel via the Fuel/Oil Heat exchange so once your started, your getting nice warm fuel to the fuel control!
Cheers OffshoreIgor <img src="eek.gif" border="0">
PS. How's London?
[ 01 February 2002: Message edited by: offshoreigor ]</p>
I agree with Nick on the reasoning for the -34. Don't forget that the Jet A is limited down to -32 using PRIST.
As for the 212 down to -40, don't forget that the 212 has heated fuel via the Fuel/Oil Heat exchange so once your started, your getting nice warm fuel to the fuel control!
Cheers OffshoreIgor <img src="eek.gif" border="0">
PS. How's London?
[ 01 February 2002: Message edited by: offshoreigor ]</p>
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A few of my colleagues and I had discussions with management in the past about the 365, its data only went up to +40c, when asked to fly the aircraft on +40 c days we refused stating the manufacturer had no performance data for above 40c, ie weight limits, etc.
They stated that as soon as you get airborne you are ascending into cooler temperatures, I said, yes, but you have to land sometime, and if its over 40 c and I mush in, im for a row of outhouses. Dauphins don't like the hot temperatures, and my right boot isn't big enough to hold the pedal all day <img src="wink.gif" border="0">
They stated that as soon as you get airborne you are ascending into cooler temperatures, I said, yes, but you have to land sometime, and if its over 40 c and I mush in, im for a row of outhouses. Dauphins don't like the hot temperatures, and my right boot isn't big enough to hold the pedal all day <img src="wink.gif" border="0">
