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747 Engine Running For "4" Days?  
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Posted (10 years 1 month 2 weeks 5 days 14 hours ago) and read 6926 times:

Hi guys.

I did a search and found nothing about this photo/topic, so I'm sorry if it's already been discussed.

The photographer of this photo states in his comments ..........

"One engine has run for 4 days for delivering power to the electronics in this plane."


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Photo © Maartenw



I don't know why the APU wasn't used instead of an engine (perhaps it was INOP or something). Or maybe the APU was being used as well as the one engine in order to supply enough electrical power to the electronics - who knows what's inside a USA Air Force Boeing E-4B (747-200). TOP SECRET stuff!

Anyhow, regarding this jet engine (what type?) that was running for 4 days, I have a few questions for you ..........

> At what N1 rpm setting do you think it would have been running at to generate enough electrical power?

> How much fuel do you think would have been burned over the 4 days, in either pounds (lbs) or US gallons?

> Would oil have needed to be added? Can you add oil to a jet engine that's running?


Chris  Smile


"Just a minute while I re-invent myself"
22 replies: All unread, jump to last
 
User currently offlineAuae From United States of America, joined Apr 2004, 296 posts, RR: 3
Reply 1, posted (10 years 1 month 2 weeks 5 days 14 hours ago) and read 6887 times:

N1 speed shouldn't be an issue. Since most generators are powered off a constant speed drive, full generating power should be available at idle.

Someone else will have to chime in on your other questions.

Shawn



Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17079 posts, RR: 66
Reply 2, posted (10 years 1 month 2 weeks 5 days 14 hours ago) and read 6884 times:

The VC-25A can stay in the air about 72 hours at a stretch if it keeps being refueled. After that you run into lubrication issues. However, on the ground maybe you can lubricate while it runs.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMr spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 3, posted (10 years 1 month 2 weeks 5 days 14 hours ago) and read 6866 times:

Hello Auae & Starlionblue.

OK, so full generating power should be available a idle. I suspected that would be the answer, otherwise the engine might start creating enough thrust to try to move the aircraft.

Maybe the 747's engine would be OK regarding lubrication, if it was only running at an idle setting ....... unlike a VC-25A that's flying with engine N1 settings at cruise power.


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineSATL382G From , joined Dec 1969, posts, RR:
Reply 4, posted (10 years 1 month 2 weeks 5 days 12 hours ago) and read 6749 times:

One thing's for sure... Those who KNOW aren't going to say...

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17079 posts, RR: 66
Reply 5, posted (10 years 1 month 2 weeks 5 days 11 hours ago) and read 6700 times:

Maybe the 747's engine would be OK regarding lubrication, if it was only running at an idle setting ....... unlike a VC-25A that's flying with engine N1 settings at cruise power.


Actually running it at idle could create lubrication problems all by itself. I'm not an expert but it's my understanding that these engines aren't really optimized to run on idle for 10+ hours at a stretch. One of the engine dudes will come on soon and tell us hopefully.


One thing's for sure... Those who KNOW aren't going to say...

They're engines, not nuclear bombs. Lighten up  Big grin



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 6, posted (10 years 1 month 2 weeks 5 days 10 hours ago) and read 6647 times:

One engine is kept running at all times when an aircraft with an "immediate response" national defense mission is on the ground. There's a few others besdes the VC-25's but we don't really need to go into that here do we?
It allows for quicker taxi and launch without the possibility of losing a bus due to a potential transfer malfunction. You also have pneumatics from the engine as well as the apu if you need them.
If the running engine needs service the opposite may be started.
I have to admit I never heard of one being kept on line for more than 48 hours, though, and that was during a national defense emergency a few of years ago.
It has been standard operating procedure for well over 45 years.

[Edited 2004-09-13 21:59:54]


One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
User currently offlineSATL382G From , joined Dec 1969, posts, RR:
Reply 7, posted (10 years 1 month 2 weeks 5 days 10 hours ago) and read 6619 times:

Hey STARLION! Lighten up dude! Like everything else here folks are just going to speculate. Probably less than 1% of the traffic here is from folks who KNOW, regardless of the subject....  Smile/happy/getting dizzy

User currently offlineLitz From United States of America, joined Dec 2003, 1767 posts, RR: 0
Reply 8, posted (10 years 1 month 2 weeks 5 days 9 hours ago) and read 6558 times:
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Bear in mind one important thing ...

Keeping one engine running to provide power doesn't necessarily mean the SAME engine was kept running.

There's no reason at all why they can't run #1, then light up #4 and do any MX needed to #1, then light up #2, MX #4, light up #3, MX #2, then back to #1 ...

Or any variation you care to think of ...

My guess, aside from the power generation issue, is that it's FAR faster to light up the other three for a quick departure if one engine is already running ...

- litz


User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 9, posted (10 years 1 month 2 weeks 5 days 8 hours ago) and read 6470 times:

I neglected to mention that they started doing it this way in the 70's because it's a lot cheaper than keeping the plane airborne and because Gen LeMay passed the flag on to some more thrift minded than he.
To those too young to remember or have parents who would remember (man am I starting to feel old) Curtis LeMay kept half of his bomber fleet and direct support aircraft airborne to keep the Soviets at bay at the height of the cold war.



One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
User currently offlineRG828 From Brazil, joined Jan 2004, 582 posts, RR: 2
Reply 10, posted (10 years 1 month 2 weeks 5 days 6 hours ago) and read 6406 times:
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PHOTO SCREENER

Years ago an E-4 visited São Paulo GRU and friends told me one engine was kept running for the 2-day visit I believe. Someone else told me all 4(!) were kept on, but I can't discredit him since I was'nt there.


I dont know the key to success, but the key to failure is trying to please everyone
User currently offlineIFIXCF6 From United States of America, joined Sep 2004, 108 posts, RR: 0
Reply 11, posted (10 years 1 month 2 weeks 5 days 2 hours ago) and read 6335 times:

O.K. So I just joined A.net. Despite having lurked for a long time, this thread spurred me to join. I have overhauled both E4 engines (CF-50E2's) and VC25 (CF6-80C2B1's) engines. The -50 does have an EMP (electro-magnetic pulse) resistant wire harness, but other than that, they are normal, well maintained commercial engines. Service the oil while running it...NO! It would blow hot oil all over you. The wait is 5min minimum after shutdown. As has been stated prior, N1 is not a factor as N2 drives the gearbox (hence the generator). Fuel burn: about 1100-1300 lbs/hr at idle. But I really do not see why you would need to run engines when the 747 has 2 APU generators. The start of the the other engines would not really be quicker either. If you have electrical power, 25 psi of pneumatics, and fuel pressure, (available from the APU) why would an operating engine benefit? Just my opinion.

Regards,
Mike


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 12, posted (10 years 1 month 2 weeks 4 days 17 hours ago) and read 6220 times:

Hi guys.

> SATL382G, you stated ....One thing's for sure... Those who KNOW aren't going to say... I agree! That jet likely has top-notch SECRET stuff onboard (avionics, etc).

> Starlionblue, Thanks for explaining that running a jet engine at idle for more than 10 hours at a stretch could create lubrication problems. We have a brand new engine mechanic (IFIXCF6) as part of this thread, so hopefully he'll let us know for sure about that.

Also, I'm sure that SATL382G's comment was about my comment on SECRET avionics that may be onboard the E-4B ....... not the engines/nuclear bombs Big grin.

> Avioniker, Thanks for explaining why one engine is kept running at all times and that if it needs to be serviced, it can be shut down, and another one can be started. I must admit, because I was born in 1966, I've never heard of Gen LeMay or Curtis LeMay and their involvement with bomber fleets during the Cold War. Very interesting to learn about. I guess you can't read everything!

> Litz, Thanks for your info about switching around what engine is running. I have a feeling though, that member IFIXCF6 doesn't agree with you that having an engine running will make it faster to start the other three .... based on his post.

> RG828, Thanks for your info about the E-4B that visited Sao Paulo GRU. I doubt that all 4 engines were running though IMO. That's a lot of fuel burning.

> IFIXCF6, Welcome Aboard!!!  Big thumbs up.

OK, so now I know that you can't service a jet engine with oil while it's running (I thought it might be possible because they're so technical - unlike a car's engine  Laugh out loud), hey, I was just curious.

You mentioned .......

.........Fuel burn: about 1100-1300 lbs/hr at idle.

Well, 4 complete 24 hour days equals 96 hours. I doubt the E-4B in the photo that landed at Eindhoven (EHEN) arrived at 00:01 hrs on the first day and departed at 23:59 hrs on the fourth day, so, for the sake of an example, if the 747 arrived at 07:00 hrs and departed at 19:00 hrs 4 days later, that would mean the one engine (if it was just one) was running for 84 hours.

So, if we take the middle value between 1100 & 1300 lbs of 1200 lbs and multiply it by 84 hrs, we get ........ 100,800 lbs of fuel burned at idle over the 4 days on the ground.

If a U.S. gallon of fuel weighs 6 lbs (for this example's sake), then 100,800 lbs divided by 6 = 16,800 gallons. Did I do that math correctly? I'm not the greatest at it.  Laugh out loud

A 747-400 has a fuel capacity of +/- 60,495 U.S. gallons depending on how many body tanks it has, so 16,800 gallons seems like a lot of burned fuel (at least to me it does). Then again, who knows how much fuel an E-4B (747-200) can carry? It's cargo hold could be loaded with many auxiliary body fuel tanks.

........But I really do not see why you would need to run engines when the 747 has 2 APU generators.

At first, I honestly thought the photographer was mistaking the sound of the 747's APUs for an engine, but, I wasn't there, and I've learned from this discussion that 747s like the USA's Air Force One, do indeed leave an engine running while on the ground.

Sorry for the long post! Big grin


Chris  Smile




"Just a minute while I re-invent myself"
User currently offlineLogan22L From , joined Dec 1969, posts, RR:
Reply 13, posted (10 years 1 month 2 weeks 4 days 17 hours ago) and read 6196 times:

Mr. Spaceman: Your math is fine, although the density of jet fuel is probably around 6.5 lbs/gal, so this would reduce the fuel burn by 1,300 gallons or so. Still seems like quite a bit to me, but not really over four days.

Logan

[Edited 2004-09-14 15:27:21]

User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 14, posted (10 years 1 month 2 weeks 4 days 17 hours ago) and read 6191 times:

Hello Logan22L.

Thank You, for letting me know my math was on the right track, and that jet fuel weighs closer to 6.5 lbs/gal than 6.0. (it's been over a decade since I've worked on a ramp  Sad so my memory of these things has faded).

I agree with you that the fuel burned doesn't seem like as much when you consider all 4 days.


Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3702 posts, RR: 34
Reply 15, posted (10 years 1 month 2 weeks 4 days 16 hours ago) and read 6152 times:
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Oil consumtion of an idleing engine will be geater than that of an engine running at Crz pwr.

Compressor air is used to seal the various brearing compartments and with age the sealing capabilities deteriorate and oil can leak out of the compartments into the gas flow. Naturally at low pwr settings the air pressure is lower as well.

In addition the oil scavange pumps aren't always as effective at idle power and oil can accumulate in the brg comparments and gearbox and either leak out as mentioned above or disappear through the vent system that balances all the different internal airflows.


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2117 posts, RR: 1
Reply 16, posted (10 years 1 month 2 weeks 4 days 14 hours ago) and read 6108 times:

Welcome aboard IFIXCF6, glad to have you here.


Here Here for Severe Clear!
User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 17, posted (10 years 1 month 2 weeks 4 days 12 hours ago) and read 6052 times:

Hi guys.

> VC-10, Thanks for your excellent info.

I would have never thought that a jet engine would use more oil during an idle power setting then it would while spinning at cruise power.

It's also neat to learn that compressor air is used to seal the various bearing compartments, etc.

I should have gotten/earned my A&P licsense, or licence, or license ....... aahh rating! Big grin

Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineIFIXCF6 From United States of America, joined Sep 2004, 108 posts, RR: 0
Reply 18, posted (10 years 1 month 2 weeks 4 days 3 hours ago) and read 5937 times:

Thanks to all of of you for the welcome!
Mike


User currently offlineIL76TD From United States of America, joined Jul 2004, 289 posts, RR: 0
Reply 19, posted (10 years 1 month 2 weeks 3 days 21 hours ago) and read 5885 times:

did anyone question whether it was actually an engine, for one, i'm sure this photographer wasn't right next to AF1 for security reasons, and two, two apu's running simultaneously could damn easily sound like an engine, i know our apu's are louder than the engines at idle

User currently offlineAvioniker From United States of America, joined Dec 2001, 1109 posts, RR: 11
Reply 20, posted (10 years 1 month 2 weeks 3 days 15 hours ago) and read 5832 times:

Just to clear things up that isn't a VC-25 from the 89th at Andrews. It's an E-4.  Smile/happy/getting dizzy



One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
User currently offlineAPwannabe From Hong Kong, joined Oct 2004, 17 posts, RR: 0
Reply 21, posted (10 years 4 weeks 23 hours ago) and read 5155 times:

questions....for the engine running at Cruising speed is more fuel efficient than the one in idle, is it something to do with both air density and the momentum of the compressor?
thx  Smile



Keep Rollin
User currently offlineSmcmac32msn From United States of America, joined May 2004, 2211 posts, RR: 4
Reply 22, posted (10 years 4 weeks 14 hours ago) and read 5056 times:

Actually just to correct the math to numbers.

(W*H)/F = B

W = Fuel Burn per Hour (1200 for example)
H = Hours (84 in our example)
F = Fuel Weight (6.7 lbs)
B = Fuel Burnt over 4 Days (84 hours) (15,044.7 gallons)



Hey Obama, keep the change! I want my dollar back.
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