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777 Parked At Gate-Engines On Idle  
User currently offlineUltrapig From United States of America, joined Dec 2003, 589 posts, RR: 0
Posted (7 years 3 months 8 hours ago) and read 4405 times:
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I was at Logan yesterday-taking an AA MD-80 from B-33. I was there about 1.5 hours before departure time. Next door at Gate B-32 is a T7 which I assumed was eventually going to LHR. I noted that both of the engines were going at about 30 rpm-and continued to do so until I enplanned next door.

Help me-I assume the engines were running to generate electricity to run the airconditioning-but isn't this normally done using ground based service? It was hot-would the grounded service not be sufficient to cool the plane? But would two engines be needed and if my guess is correct why cool the plane at 3:30 for a 7 pm flight?

Even at idle these engines must use a significant amount and chalk up several hours operating time.

I'm sure one of you will tell me what I am missing.

18 replies: All unread, jump to last
 
User currently offlineGraphic From , joined Dec 1969, posts, RR:
Reply 1, posted (7 years 3 months 8 hours ago) and read 4385 times:

30 RPM is effectively 1 rotation every 2 seconds, the rotors were probably just windmilling, as even at idle power, the fans would appear to be a blur.

User currently offlineFriendlySkies From United States of America, joined Aug 2004, 4113 posts, RR: 5
Reply 2, posted (7 years 3 months 8 hours ago) and read 4385 times:

Just for clarification...did you hear them or just see the fans blowing? A gas turbine cannot operate at 30 rpm.

User currently offlineUltrapig From United States of America, joined Dec 2003, 589 posts, RR: 0
Reply 3, posted (7 years 3 months 8 hours ago) and read 4316 times:
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At first I assumed they were spinning down after engine shut off. But they kept spinning at 30 rpm (I timed them using the "squiggles".) It did not occur to me that the wind was spining them- in fact I don't think there was much wind-You gentlemen may know better but I thought it would take a pretty strong win to spin a turbine and the spinning seemed pretty consistent.

User currently offlineUnattendedBag From United States of America, joined Oct 2003, 2329 posts, RR: 1
Reply 4, posted (7 years 3 months 8 hours ago) and read 4275 times:

Quoting Ultrapig (Reply 3):
I thought it would take a pretty strong win to spin a turbine and the spinning seemed pretty consistent.

It takes a good 10-15 knot wind to spin the blades. They are heavy, but they are also free spinning and those fans can easily catch air if the wind is blowing in the right direction. At engine idle, you would never had been able to count the revolutions per minute.



Slower traffic, keep right
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 3 months 8 hours ago) and read 4261 times:

Quoting Ultrapig (Reply 3):
At first I assumed they were spinning down after engine shut off. But they kept spinning at 30 rpm (I timed them using the "squiggles".) It did not occur to me that the wind was spining them- in fact I don't think there was much wind-You gentlemen may know better but I thought it would take a pretty strong win to spin a turbine and the spinning seemed pretty consistent.

Turbofans have extremely good lubrication and bearings. It doesn't take much at all to spin them and this happens fairly commonly.

Yesterday I was at an airport that had winds gusting to 30kts and we were parked directly into the wind. Those fans were spinning very fast just windmilling.... it was showing almost 3% N1!


User currently offlineUnattendedBag From United States of America, joined Oct 2003, 2329 posts, RR: 1
Reply 6, posted (7 years 3 months 8 hours ago) and read 4261 times:

Quoting Ultrapig (Reply 3):
But they kept spinning at 30 rpm (I timed them using the "squiggles".)

I am not familiar with that measuring method.



Slower traffic, keep right
User currently offlineUltrapig From United States of America, joined Dec 2003, 589 posts, RR: 0
Reply 7, posted (7 years 3 months 8 hours ago) and read 4209 times:
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Quoting UnattendedBag (Reply 6):
am not familiar with that measuring method.

It was invented by me yesterday-Counting the number of turns of the squiggles marking on the engine hub per minute.

I'm still confused-I'm not doubting anyoen that the wind can spin the turbines but the wind was pretty slow yesterday.


User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 8, posted (7 years 3 months 8 hours ago) and read 4178 times:

Quoting Ultrapig (Reply 7):
I'm still confused

Just shut your window fan off and watch the blades... they'll start spinning for the reason. It's just the wind passing through the fan case. Very-very-very-very common.....

The blades are also very efficient... I hand spun a CF34-10E once and I could fell the air around me getting sucked in. It doesn't take much to start the blades moving.

[Edited 2007-08-02 21:36:12]


"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineDarkBlue From United States of America, joined Sep 2003, 233 posts, RR: 10
Reply 9, posted (7 years 3 months 7 hours ago) and read 4156 times:

Quoting Ultrapig (Reply 7):
I'm still confused-I'm not doubting anyoen that the wind can spin the turbines but the wind was pretty slow yesterday.

It doesn't take much. I assume it was an AA 777, which means it had Trent800 engines. The 110in diameter fan (66sqft) does a good job of catching any bit wind there is. On top of that, fan blades may be designed to compress the air, but when the fan is unpowered, they make really good wind turbines.

Just for comparison, a Trent800 at idle would have fan speed around 500rpm and would make significant noise.


User currently offlineUltrapig From United States of America, joined Dec 2003, 589 posts, RR: 0
Reply 10, posted (7 years 3 months 7 hours ago) and read 4130 times:
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OK all I think I've got the answer! Thanks

User currently offlineHAWK21M From India, joined Jan 2001, 31692 posts, RR: 56
Reply 11, posted (7 years 2 months 4 weeks 1 day 18 hours ago) and read 3930 times:

Quoting Ultrapig (Reply 3):
I timed them using the "squiggles"

Interesting term.

Quoting UnattendedBag (Reply 4):
It takes a good 10-15 knot wind to spin the blades

Depends on the direction of the wind too.
regds
MEL



Think of the brighter side!
User currently offlineBoeing767mech From United States of America, joined Dec 2000, 1030 posts, RR: 3
Reply 12, posted (7 years 2 months 3 weeks 4 days 8 hours ago) and read 3566 times:

Quoting Ultrapig (Thread starter):
I was at Logan yesterday-taking an AA MD-80 from B-33. I was there about 1.5 hours before departure time. Next door at Gate B-32 is a T7 which I assumed was eventually going to LHR. I noted that both of the engines were going at about 30 rpm-and continued to do so until I enplanned next door.

Gate 32 is at the end of the terminal so you get the wind blowing around causing a high pressure area next to the jetbridge. I has seen B32 almost ripped off the side of the building in a snow storm because of the way the wind blows around the building

David



Never under-estimate the predictably of stupidty
User currently offlineSv2008 From United Kingdom, joined Aug 2006, 622 posts, RR: 0
Reply 13, posted (7 years 2 months 3 weeks 4 days 6 hours ago) and read 3514 times:

Quoting Ultrapig (Reply 3):
spinning seemed pretty consistent.

This (random guess) might be caused by the mass of the blades which smooths out the irregularity of the wind speed (a sort of flywheel affect). For example a car engine is smooth(ish) because it has a flywheel at one end of the crankshaft despite distinct, large irregular forces caused by the combustion process/timing.

Quoting Flyf15 (Reply 5):

Turbofans have extremely good lubrication and bearings.

But are they lubricated without the engine running? Most machines have engine driven oil pumps don't they? I have no idea about this just wondered.........


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (7 years 2 months 3 weeks 4 days 6 hours ago) and read 3503 times:

Quoting Sv2008 (Reply 13):
Quoting Flyf15 (Reply 5):

Turbofans have extremely good lubrication and bearings.

But are they lubricated without the engine running?

Sort of. Most jets run the lube pump off of the accessory gearbox, which is hard-connected to the inner spool (or one of the inner spools in the case of a RR engine). So, if the inner spool turns (for any reason) the lube pump turns too. However, most windmilling will get the fan (outer spool) going but unless the wind is really kicking I doubt it gets the inner spool turning much at all.

So yes, they can be lubricated without the engine running but no, in the case of normal windmilling at the gate, they're not well lubricated.

Tom.


User currently onlineGoldenshield From United States of America, joined Jan 2001, 6085 posts, RR: 14
Reply 15, posted (7 years 2 months 3 weeks 3 days 16 hours ago) and read 3380 times:

Quoting HAWK21M (Reply 11):
Quoting Ultrapig (Reply 3):
I timed them using the "squiggles"

Interesting term.

He's talking about the spiral on the engine spinner which is a visual cue to rampers when an engine is safe to approach.



Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
User currently offlineHAWK21M From India, joined Jan 2001, 31692 posts, RR: 56
Reply 16, posted (7 years 2 months 3 weeks 3 days 13 hours ago) and read 3348 times:

Quoting Goldenshield (Reply 15):
He's talking about the spiral on the engine spinner which is a visual cue to rampers when an engine is safe to approach.


View Large View Medium
Click here for bigger photo!

Photo © Florian Negele


Is that an official term."Squiggles" or just a nickname.
regds
MEL



Think of the brighter side!
User currently offlineFlyf15 From , joined Dec 1969, posts, RR:
Reply 17, posted (7 years 2 months 3 weeks 3 days 12 hours ago) and read 3319 times:

Quoting Sv2008 (Reply 13):
But are they lubricated without the engine running? Most machines have engine driven oil pumps don't they? I have no idea about this just wondered.........

Well, there won't really be any oil pressure when the engine is not running, but there will be residual oil present that is more than adequate to lubricate the engine during windmilling.


User currently offlineAirfoilsguy From , joined Dec 1969, posts, RR:
Reply 18, posted (7 years 2 months 3 weeks 3 days 11 hours ago) and read 3304 times:

Quoting Goldenshield (Reply 15):
He's talking about the spiral on the engine spinner which is a visual cue to rampers when an engine is safe to approach.

It's supposed to keep the birds out too.  duck   spin 


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