julesmusician
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Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 4:22 am

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?

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DColeMAN
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 4:45 am

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).

Correct me if I'm wrong.

Dale
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Arrow
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 4:51 am

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).
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julesmusician
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 4:53 am

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..
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FredT
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 5:04 am

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!  Smile
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sabenapilot
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 5:15 am

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
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 6:03 am

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.
Exceptions confirm the rule.
 
Matt72033
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 6:09 am

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
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 6:41 am

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.

[Edited 2006-01-23 22:44:32]
 
MissedApproach
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 7:03 am

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.
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aogdesk
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 7:23 am

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
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 8:11 am

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.
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Elvisisalive
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 8:31 am

Read this article about Kaiserair doing a rescue mission to recover a Gulfstream
in 35 below zero temps in Russia.

http://www.kaiserair.com/pdf/kaiserair_siberia.pdf
 
buckfifty
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 9:32 am

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.
 
L-188
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 9:58 am

Yes.

There are fluids in airplane engines that can freeze.

This can make it very difficult to get it started.

Once started they can make their own heat to keep the fluids warm.
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Dougloid
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 10:25 am

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.
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greasespot
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Tue Jan 24, 2006 11:57 am

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
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DColeMAN
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 1:43 am

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.

Dale
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scarebus03
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 4:58 am

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,

Hope this helps

Brgds

SB03  cold 
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Arrow
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 6:22 am

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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L-188
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 6:27 am

Quoting Greasespot (Reply 16):
We have "block heaters" installed on all our turbo props in the Arctic..The airplane arrives and we plug it in

Tanis Heaters?...They will keep a warm engine warm under a blanket, but they are worthless for getting a cold engine warm

Quoting Arrow (Reply 19):
After shutdown, they poured some alcohol (or something similar) into the crankcase to keep the oil thin when it got cold.

Avgas....just avgas.

At least that is what I have always heard the old timers doing. Drain a bit from the wing and put it in the crank and turn the prop through to mix.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
greasespot
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 11:30 am

Yes Tanis heaters....On our PW120's that is all we use all night in Yellowknife and Iqaluit.no hangar..Seems to work for starting them in the Canadian Arctic......On the Darts we use the heaters and blankets...Nothing is used on the JT8's and the freighter overnights in the open all the time up there.

GS
Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
 
Mir
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 2:46 pm

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?

It certainly offers some amazing performance. But even if I can get a Warrior off the runway in 500 feet or less in the middle of January in North Dakota, I'd still rather fly in the summer.  cold 

-Mir
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tepidhalibut
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 5:19 pm

Quoting Scarebus03 (Reply 18):
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

I recall a test in around 1995, where a B757 w/RB211s was flown to Yakutsk (Siberia) in winter, and shutdown overnight. One engine covered and protected as normal, the other open to atmosphere. Next day, engine start attempted, with oil temp at -54ºC (Coincidence?). the start procedure called for hot air blower, and following the manual, the engine started - no problem.

I believe that the TC has a min oil stemp for starting of -40º, so no need for heaters until you get below that.
 
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zeke
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 5:32 pm

Quoting BuckFifty (Reply 13):
Saw -70C just recently flying over Siberia at 10600M, even colder than it was over the pole.

Very true, many people incorrectly think the coldest temps at altitude are over the poles, this is incorrect due to the location of the tropopause.
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NWOrientDC10
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Wed Jan 25, 2006 6:25 pm

I read an article about C-130 ops in Antarctica. The engines must be kept running ...

Cheers  Smile

Russell
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Arrow
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 1:16 am

Quoting Zeke (Reply 24):
Very true, many people incorrectly think the coldest temps at altitude are over the poles, this is incorrect due to the location of the tropopause.

I read somewhere (correct me if I'm wrong) that coldest temperatures at high altitude are usually found above the equator, over the Pacific.
Never let the facts get in the way of a good story.
 
A/c train
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 1:24 am

The Aircraft maintenance manual will give procedures for cold weather, start conditions. Use common sense when it comes to these things, if its -55 and ice is forming on your nose, just have a look at the book !! ask the question!! then answer it and everybodys app'y!
This time of year you have too keep switched on, make sure hold over times are good for the night when de-icing airplanes, it may need doing again before it goes in the morning, things like that etc ....
 
Matt72033
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 2:40 am

just remembered, someone told me once that on some ETOPS flights its mandatory to keep the APU running throughout the flight due to difficulties starting it if its been at cruise altitude temperatures for a few hours! not sure how true this is?!!? maybe somebody can expand on this!
 
L-188
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 4:15 am

Quoting A/c train (Reply 27):
The Aircraft maintenance manual will give procedures for cold weather, start conditions

I remember the absolute min temperture to operate the Lears we had at work was -54C.

It wasn't an engine issue that set that limit.....it was the seals in the landing gear.
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NWOrientDC10
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 5:36 am

Here's some relevant info.

http://www.avia.ru/cgi/news/news.cgi?action=geten&id=1137994761

Cheers  Smile

Russell
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Tristarsteve
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 5:46 pm

Quoting Arrow (Reply 19):
After shutdown, they poured some alcohol (or something similar) into the crankcase to keep the oil thin when it got cold.

I have a handbook called Aeronautical Engineering from 1944. It talks about the problems of oil gumming up the pistons at below -5degC. "A device for overcoming this difficulty is now rapidly coming into favour. It is based on the fact that adequate lubrication is provided when cold oil is diluted with petrol, so as to bring about the correct operating viscosity.....The device consists of a small valve which allows petrol to enter the oil supply to the engine in the last four minutes or so before stopping." Brilliant book on how to build your own Lancaster.

Living in ARN we do not have extreme temps. After an 8 hr nightstop the oil temp on the B757 is around -5degC, and they start OK. The A320 does not register below zero!, it shows 0 on the ECAM. The biggest worry is frozen water. If the temp is below about -10 then we leave a heater on the aircraft all night to stop the (emptied) water tank freezing. It is amazing the trouble a couple of drops of ice in a pipe can cause! (usually the air feed pipe to the water tank).

Just a stry from Tristar days. Nordic East had a Tristar that only flew weekends in the winter. So one cold Friday morning ( -20degC) we went out to warm it up. APU started OK, then Nbr 2 eng. It took about 3-4 mins to get to idle. The oil qty read zero, and the oil pressure read max, and loads of fumes out the back. A couple of minutes later all returned to normal. I have seen the fumes completely fill the cul de sac between the terminals, which is why we started all the engines down the hangars first.
 
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Starlionblue
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Thu Jan 26, 2006 11:27 pm

Quoting Matt72033 (Reply 28):
st remembered, someone told me once that on some ETOPS flights its mandatory to keep the APU running throughout the flight due to difficulties starting it if its been at cruise altitude temperatures for a few hours! not sure how true this is?!!? maybe somebody can expand on this!

This was discussed before and I think the consensus was that you don't need to if the APU can be started in flight. Or something like that. My memory about the subject is fuzzy.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
BigJimFX
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RE: Can It Be Too Cold For A Jet Engine To Operate?

Sat Jan 28, 2006 10:19 am

Quoting FredT (Reply 4):
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

Dude... It's in the checklist... If it's in the checklist, You do it.
When I was doing my complex endorsement, I was told by a mechanic that when you cycle the prop to do it 3 times and make sure no oil splashes onto the windshield. Not sure what that was about but seemed like a good idea to me!
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