Masonaries From United States of America, joined Jun 2000, 93 posts, RR: 0 Posted (10 years 2 months 2 weeks 5 days 18 hours ago) and read 6325 times:
I take several early morning flights a year out of Lansing Capital City (LAN) and I've often had this question. They simply push back, start the engines, make a very short taxi out to the runway and just go. Is there any concern of a turbine engine needing to warm up after sitting all night on the ramp in sub zero temperatures? Just wondering.
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 67
Reply 4, posted (10 years 2 months 2 weeks 5 days 17 hours ago) and read 6278 times:
The only problem I can recall off the top of my head related to extreme cold. I was told that some airliner departing MDW in the dead of winter in a manner like you describe, had both generators trip off line right after liftoff.
I think they reset okay, but it had to have been fun for a moment.
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Speedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 5, posted (10 years 2 months 2 weeks 5 days 10 hours ago) and read 6208 times:
OK, seems like cold weather is good for engine performance, atleast as far as power is concerned; i assume it's a due to the density of cold air, much like a car loves cold air in its combustion chambers to make the most efficient air-fuel burn. However, my imagination suggests to me (perhaps incorrectly) that a jet engine on a heavy airliner needs to run on with warm lubricants to prevent obvoius problems with cold oil, as well as warm critical parts to ensure proper operating tolerances. Greasespot mention earlier that "PW120's have Tanis heaters on the RGB and Compressor section to keep them warm in the Arctic," but I'm wondering if there are any warmup concerns for airliners starting up cold in normally chilly conditions, like a 20 degree F spring morning in the midwest, since this happens hunreds of times per day all over the country. If there is, is it the usual "idle for a while" doctrine that governs most heavy machinery, or are jet engines unique in this respect. Thanks for your replies..
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FredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 6, posted (10 years 2 months 2 weeks 5 days 10 hours ago) and read 6200 times:
Some aircraft do have restrictions on the time from startup to take off in cold conditions, talking -20 deg centigrade here. This was for the exact reason that you wanted the engine oil temp to come up a bit. We're talking a few minutes here though, so not really a concern for airliners.
I thought I was doing good trying to avoid those airport hotels... and look at me now.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 8, posted (10 years 2 months 2 weeks 5 days 7 hours ago) and read 6184 times:
Oil temperature is your limiting parameter. Jet oil has a relatively low viscosity compared to car engine oil. Even so, in cold weather, it can be fairly sluggish. The rule of thumb we've always used is to wait until oil temp is in the green band. It was not uncommon on the JT8 equipped B727's to have the oil pressure light on until the oil warmed up on cold days. The JT9 oil pressure had a tendency to bounce around +/-1 or 2 psi until the oil temp stabilized.
I know the AMM on the B767 & B757 have lower limit where no starts are allowed. I'm not sure of the number, but it's somewhere well below -15c.
XXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Reply 9, posted (10 years 2 months 2 weeks 1 day 5 hours ago) and read 6013 times:
I was on a BA757 departing LHR years ago, before take off we were told by the captain that we would have to wait a few a minutes while the oil temp warms (he said that the plane had been in the mx base all night).
We parked up while the engines were revved and the whole plane shook for a minute or two.
Air2gxs From , joined Dec 1969, posts, RR:
Reply 14, posted (10 years 2 months 1 week 6 days 23 hours ago) and read 5835 times:
"Cold Starts" affect jets the same way they affect recips. Bearings go dry and need to be lubed up. The main difference is that the bearings on jet engines perform better than those on recips. So, a cold start really doesn't cause as much wear, relatively.
The main issue, again, is oil temperature. The oil needs to be warm in order to perform its intended functions efficiently.
Here's a little tidbit of information. The APUs on B757/B767 (and I'm sure most modern APUs) have a de-oiling system. This system purges the oil from the bearing cavities of the APU when shutdown. This prevents any super-cooled oil (from sitting at altitude for several hours) from gumming up the bearings during start. The APU begins its rotation with relatively dry bearings. Of course, that only lasts as long as it takes the APU oil pump to move oil back to the bearings.
And no, airlines do not schedule aircraft around because of temperature. The limiting temperatures in the AMM are well below the average in most major airports.
L-188 From United States of America, joined Jul 1999, 29948 posts, RR: 58
Reply 15, posted (10 years 2 months 1 week 6 days 20 hours ago) and read 5799 times:
Speedracer....Differently engine designs will have different effects.
For example, I used to work with a lot of aircraft with TPE-331 engines. On those engines the gearbox and propeller are driven directly off the shaft in the engine. So when you get very cold oil in the gearbox, it can prevent the engine from turning fast enough to prevent a "Hot Start" or what some have dubbed up here a "Garrett pre-heat"
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Tepidhalibut From Iceland, joined Dec 2004, 211 posts, RR: 6
Reply 16, posted (10 years 2 months 1 week 5 days 12 hours ago) and read 5736 times:
Yes, starting in very cold conditions doesn't do the engines much good. As mentioned, the oil is so thick that it's not great at lubricating the bearings. However, at low speeds, that's not too much of a problem.
Looking at some B757/RB211 paperwork :
Minimum Oil Temp for starting : -40°C
Minimum for opening up : 0°C (ie accelerating above idle.)
Once the engine is warmed up, and it does take time for the big turbine discs etc warm up all the way through, cold air is great for engine performance - Nice dense air, producing tons of thrust. Nice cold air keeping turbine temperature down.
Actually, on the B757, Boeing did do a little test to confirm the cold starting ability. After spending 12 hours at -54ºC in Yakutsk, the test engine started perfectly. Bet it was fun hanging around waiting for the engines to cool...