Julesmusician From , joined Dec 1969, posts, RR: Posted (2 years 11 months 3 weeks 9 hours ago) and read 3554 times:
The recent freeze in Moscow saw temperatures dropping to below -30c - are there temperatures below which operating a jet engine becomes hazardous? Also with such low temperatures what, other than having to de-ice, opportunities/problems does it offer to an airline pilot?
DColeMAN From United Kingdom, joined Nov 2004, 274 posts, RR: 10 Reply 1, posted (2 years 11 months 3 weeks 8 hours ago) and read 3545 times:
Obviously jet engines operate at their best in very cold air temperatures but I'm not sure of the limit (if there is one?). Although I believe that when flying over very cold parts of the earth such as the North Pole the fuel can sometimes be at the risk of freezing as temperatures drop down to -60C or below while at very high altitude (FL400, ish).
Arrow From Canada, joined Jun 2002, 1878 posts, RR: 1 Reply 2, posted (2 years 11 months 3 weeks 8 hours ago) and read 3539 times:
I thought extreme cold made getting a jet engine started more of a challenge. I think Twin Otters operating in the Arctic have some sort of maximum shut-down time (for the PT6s) in very cold weather. And I remember many years ago sitting in a DC-9 in Regina one very cold morning when they pumped warm air through the engines before they tried to start them (it had been parked overnight).
Never let the facts get in the way of a good story.
Julesmusician From , joined Dec 1969, posts, RR: Reply 3, posted (2 years 11 months 3 weeks 8 hours ago) and read 3533 times:
Yes i have covered jet fuel freezing in another post recently, it was more of what special things a pilot/engineers need to think about when running engines in such low temps, and anything unusual that can be achieved - such as take off's at much lower power etc - would be interesting to know..
FredT From United Kingdom, joined Feb 2002, 2017 posts, RR: 16 Reply 4, posted (2 years 11 months 3 weeks 8 hours ago) and read 3522 times:
They tend to warm themselves up rather nicely.
One concern is the oil not being fluid enough. Engines I have worked with required a warm-up period before doing much of anything when it was really cold. The oils we have today are good in a wide range of temperatures, but there is a limit to it.
Many pilots flying constant-speed propeller aircraft still cycle the props a few times as part of the run-up. Why? It dates back to the days when rather simple mineral oils was all there was. You wanted the warm lightly flowing oil to replace the cold oil in the propeller hub.
Other interesting practises involved draining the oil from the engines while it was still a fluid, so it could be heated and poured back in prior to starting. Canvas shrounds around the engines heated by burners. You get the picture. I like modern synthetic oils!
I thought I was doing good to avoid those airport hotels... and look at me now.
Sabenapilot From Belgium, joined Feb 2000, 2527 posts, RR: 31 Reply 5, posted (2 years 11 months 3 weeks 8 hours ago) and read 3510 times:
There are indeed limitations to the operating temperatures of modern jet engines, but they are much lower than the temperatures normally experienced in any populated area. Minus 50°C is a golden number, depending on the engine of course.
However, as from minus 25°C (or lower, again, depending on the engine) a pre-heat of the engine should be done by means of hot air blown over the engine with a dedicated heater through a specific port in the engine cowling, this to make the oil more fluid and thus avoid damage to the bearings as well as to avoid chock-heating of the core of the engine.
A342 From Germany, joined Jul 2005, 3560 posts, RR: 1 Reply 6, posted (2 years 11 months 3 weeks 7 hours ago) and read 3456 times:
Quoting Sabenapilot (Reply 5): There are indeed limitations to the operating temperatures of modern jet engines, but they are much lower than the temperatures normally experienced in any populated area. Minus 50°C is a golden number, depending on the engine of course.
I guess you mean -50°C on the ground ? Because in the air, this temperature is registered fairly often.
And most Soviet/Russian engines are capable of operating around these temperatures on the ground.
Matt72033 From United Kingdom (England), joined May 2005, 1617 posts, RR: 4 Reply 7, posted (2 years 11 months 3 weeks 7 hours ago) and read 3452 times:
Quoting DColeMAN (Reply 1): viously jet engines operate at their best in very cold air temperatures but I'm not sure of the limit (if there is one?). Although I believe that when flying over very cold parts of the earth such as the North Pole the fuel can sometimes be at the risk of freezing as temperatures drop down to -60C or below while at very high altitude (FL400, ish).
In the air, and on the ground starting are two very different things, the biggest concern would be the oil, we use mobil jet 2 on our engines which is pretty thin, obviously when its cold it will become more viscous, which isnt really ideal.
Sabenapilot From Belgium, joined Feb 2000, 2527 posts, RR: 31 Reply 8, posted (2 years 11 months 3 weeks 6 hours ago) and read 3423 times:
Quoting A342 (Reply 6): I guess you mean -50°C on the ground? Because in the air, this temperature is registered fairly often.
Obviously yes, since I was talking about engine starting.
In flight a running engine is sufficiently heated to cope with more extreme temperatures; however, for an inflight relight there might be limitations on outside temperature or on the time between relight and throttle up too. If the engine has been shut down for too long, it might even be advisable NOT to try to relight it.
MissedApproach From Canada, joined Oct 2004, 708 posts, RR: 2 Reply 9, posted (2 years 11 months 3 weeks 6 hours ago) and read 3399 times:
Quoting Arrow (Reply 2): I thought extreme cold made getting a jet engine started more of a challenge.
It sure makes them smoke a hell of a lot!
Quoting Arrow (Reply 2): I think Twin Otters operating in the Arctic have some sort of maximum shut-down time (for the PT6s) in very cold weather.
As I understand it the main concern with turboprops & extreme cold relates more to the prop & propeller hub seals than the engine itself. It wouldn't surprise me if there was a time limit beyond which special procedures would be required.
Aogdesk From United States, joined Jun 2004, 786 posts, RR: 2 Reply 10, posted (2 years 11 months 3 weeks 6 hours ago) and read 3368 times:
Quoting Julesmusician (Thread starter): Also with such low temperatures what, other than having to de-ice, opportunities/problems does it offer to an airline pilot?
Not trying to be picky here....BUT.......by the time the flight crew gets to the airplane, in MOST cases, the maintenance guys (deicing crew if they're not the same) have gotten the airplane ready to go. Many times flight crews have no clue what it takes to get that bird ready to go. I've seen crews complain that they had to walk thru 3 inches of glycol to do their walkaround after the mechanics spent two hours in sub zero-windy ass temps warming up everything from batteries to engines.
EMBQA From United States, joined Oct 2003, 7702 posts, RR: 10 Reply 11, posted (2 years 11 months 3 weeks 5 hours ago) and read 3368 times:
Quoting Julesmusician (Thread starter): are there temperatures below which operating a jet engine becomes hazardous? Also with such low temperatures what, other than having to de-ice, opportunities/problems does it offer to an airline pilot?
Well, as said above...engines LOVE cold air. They run better and produce much better power when it gets cold. As far as how cold is too cold, you'd need to refer to the AOM for that. I've started a Saab 340 at -20F and you'll get warning lights in the cockpit for fuel and oil filter by-pass. Once the fuel and oil warms up the lights go out. Also, you might get some in flight restriction. I know on the Saab 340 your not to use the de-ice boots below a certain temprature. I forgot what it is, but I've only seen it once. As far as de-icing.... unless moisture or frost is present, you don't need to do it.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
BuckFifty From Canada, joined Oct 2001, 1264 posts, RR: 18 Reply 13, posted (2 years 11 months 3 weeks 4 hours ago) and read 3181 times:
Saw -70C just recently flying over Siberia at 10600M, even colder than it was over the pole.
We have more of a problem with the fuel jelling up in cruise because of the cold temps than we do with the engines operating. Starting wise, never had a problem, probably because the engineers do such an excellent job prepping a cold soaked aircraft.
Dougloid From France, joined Jul 2005, 7981 posts, RR: 47 Reply 15, posted (2 years 11 months 3 weeks 3 hours ago) and read 3152 times:
I remember one time doing some trim runs on a TPE331 powered Turbo Commander on the ramp in Toledo when the OAT was 20 below zero f (-29C)It was blowing what looked like a lot of blue smoke but as it turned out this was because of the low temps. It started up OK.
A pal of mine used to be a one man band at an FBO at Fort Dodge, Iowa back when ISU had a DC3 that was used to haul the basketball team around. It was parked up there instead of Ames for some funny reason, and the OAT was some frightful number of degrees below zero. So he's sitting there reading the paper and trying to stay warm. Well, the phone rings, the voice says "we need the DC3, you've got eight hours to get it ready to go." He says it took all eight hours to get it going and keep the engines warm enough to restart. After mucho preheat, he got number one running, warmed up, shut off, dragged the heater around to the other side, started preheating number two, got back in, cranked up number one to keep it from freezing up, shut it down, ran out, dragged the preheater away, got in, cranked up number one and then number two, and then alternated them every fifteen minutes the last four hours until the crew and the team bus showed up.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
Greasespot From Canada, joined Apr 2004, 2634 posts, RR: 24 Reply 16, posted (2 years 11 months 3 weeks 1 hour ago) and read 3125 times:
We have "block heaters" installed on all our turbo props in the Arctic..The airplane arrives and we plug it in.....Our JT8's Just have to start...No matter the temp.
GS
In a gunfight even when you do everything right you can still end up dead
DColeMAN From United Kingdom, joined Nov 2004, 274 posts, RR: 10 Reply 17, posted (2 years 11 months 2 weeks 6 days 11 hours ago) and read 2943 times:
Quoting Aogdesk (Reply 10): by the time the flight crew gets to the airplane, in MOST cases, the maintenance guys (deicing crew if they're not the same) have gotten the airplane ready to go.
How do you work that one out? Aircraft need to be de-iced atleast 20 mins before pushback and last time I checked the vast majority of flight crews board the A/C well over an hour before the STD.
Scarebus03 From Ireland, joined Apr 2005, 165 posts, RR: 1 Reply 18, posted (2 years 11 months 2 weeks 6 days 8 hours ago) and read 2859 times:
Quoting DColeMAN (Reply 17): Aircraft need to be de-iced atleast 20 mins before pushback and last time I checked the vast majority of flight crews board the A/C well over an hour before the STD.
Dale,
this is usually not true as depending on Wx conditions aircraft can be de/anti-iced anything from 5hrs to 5mins before departure. In my experience almost nobody uses just de-icing fluid on it's own, these days it's usually an anti-ice fluid thus giving a holdover time as the departure limit. There are a few recent threads on de-icing in techops good to look at for info.
This however has nothing to do with jet engine ops at low temp. Synthetic type II jet engine oils are specified to be viscous enough to operate for start at -54'c. I have never seen an engine started at this temp but thats what the book says.
The reason hot air is pumped through the engine prior to start in low temp ops is not to heat up the engine but to de-ice the back of the fan blades and first(exposed) stages of stators and rotors of the hpc. I have seen the damage caused by hidden ice behind the fan blades and it's not pretty.
Also for inflight engine restart the engine will be windmilling before the start is attempted helping to circulate the oil and keep it viscous,
Arrow From Canada, joined Jun 2002, 1878 posts, RR: 1 Reply 19, posted (2 years 11 months 2 weeks 6 days 7 hours ago) and read 2834 times:
Quoting Greasespot (Reply 16): We have "block heaters" installed on all our turbo props in the Arctic.
At the risk of dating myself, I remember reading about an RCAF procedure for getting the Merlins started on their Lancasters in the winter. After shutdown, they poured some alcohol (or something similar) into the crankcase to keep the oil thin when it got cold. After start-up, engines would warm up and the alcohol would evaporate.
When I lived in a cabin in northern Alberta (with no electricity) I got the car engine crankcase warm in the morning by lighting up a small hibatchi, waiting for the flames to die down, and slid it under the oil pan for about 20 minutes. Worked like a charm, no fires.
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