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748-I Tailplane Fuel Tanks Excluded From Use  
User currently offlineart From United Kingdom, joined Feb 2005, 3382 posts, RR: 1
Posted (2 years 8 months 2 weeks 20 hours ago) and read 19319 times:

Jon Ostrower report in flightglobal:

"Boeing certified the 747-8 Intercontinental with the tail fuel tanks locked out because during design review of flight test data...it was discovered that, under a certain regulatory-required structural failure scenario, the airplane can experience flutter events when the fuel tanks in the horizontal stabiliser are filled over 15% of their capacity," said Boeing.

Reactivating the tanks and incorporating the fix will be be accomplished during normal maintenance operations as part of a service bulletin expected to be issued by the airframer once a solution is identified, said Boeing.

http://www.flightglobal.com/news/art...-tanks-on-flutter-concerns-367148/

43 replies: All unread, showing first 25:
 
User currently offlineN14AZ From Germany, joined Feb 2007, 2723 posts, RR: 25
Reply 1, posted (2 years 8 months 2 weeks 20 hours ago) and read 19089 times:

Quoting art (Thread starter):
when the fuel tanks in the horizontal stabiliser are filled over 15% of their capacity

Do I understand this correctly - the problem appears only if the tank is overloaded by mistake?

Is this to consider inaccuracies when filling the tank?


User currently offlinenighthawk From UK - Scotland, joined Sep 2001, 5157 posts, RR: 33
Reply 2, posted (2 years 8 months 2 weeks 20 hours ago) and read 19077 times:

Quoting N14AZ (Reply 1):
Do I understand this correctly - the problem appears only if the tank is overloaded by mistake?

Is this to consider inaccuracies when filling the tank?

No, I think they mean that if the fuel tank is filled to a level of 15%, not 115%.



That'll teach you
User currently offlineDaysleeper From UK - England, joined Dec 2009, 845 posts, RR: 1
Reply 3, posted (2 years 8 months 2 weeks 19 hours ago) and read 18820 times:

I wonder if this explains the recent reduction in predicted range despite the increase in payload. And are these tanks used to control the center of gravity, if so how to they compensate for not having that capability?

User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3413 posts, RR: 4
Reply 4, posted (2 years 8 months 2 weeks 19 hours ago) and read 18736 times:

Quoting Daysleeper (Reply 3):

I wonder if this explains the recent reduction in predicted range despite the increase in payload. And are these tanks used to control the center of gravity, if so how to they compensate for not having that capability?

No, the reduction in stated range is due to higher payload at quoted range. Only the passenger version even has tail tanks.

The problem from what I've read is that is there is a flutter issue when there is a failure structural member . The FAA doesn't allow flutter in a single failure case.


User currently offlineQANTAS747-438 From United States of America, joined Jan 2001, 1966 posts, RR: 2
Reply 5, posted (2 years 8 months 2 weeks 19 hours ago) and read 18660 times:

Uh, I don't get what's going on. Can someone explain it in simple terms?

Is Boeing saying that while the tail tank is there, they are never to use it?



My posts/replies are strictly my opinion and not that of any company, organization, or Southwest Airlines.
User currently offlineEagleboy From Niue, joined Dec 2009, 1843 posts, RR: 2
Reply 6, posted (2 years 8 months 2 weeks 19 hours ago) and read 18577 times:
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I think they are saying that IF there is a certain structural failure then having over 15% load in the tail tank will cause flutter. As FAA rules state a single failure cannot cause flutter Boeing have decided to prevent any use of the tail tank until a solution is found. The tank can be reactivated during normal maintenance when instructed by Boeing.

User currently offlinekl911 From Czech Republic, joined Jul 2003, 5147 posts, RR: 15
Reply 7, posted (2 years 8 months 2 weeks 19 hours ago) and read 18552 times:

Quoting QANTAS747-438 (Reply 5):
Is Boeing saying that while the tail tank is there, they are never to use it?

No, it will be fixed:

Quoting art (Thread starter):
Reactivating the tanks and incorporating the fix will be be accomplished during normal maintenance operations as part of a service bulletin expected to be issued by the airframer once a solution is identified, said Boeing.


User currently offlineBurkhard From Germany, joined Nov 2006, 4398 posts, RR: 2
Reply 8, posted (2 years 8 months 2 weeks 17 hours ago) and read 18175 times:

So the first 748I will initially have a slightly lower range. Does LH have any plans to fly the 748 thus far? EZE comes to mind, so it may means EZE sees the 744 a few months longer.

User currently offlineKC135TopBoom From United States of America, joined Jan 2005, 12150 posts, RR: 51
Reply 9, posted (2 years 8 months 2 weeks 17 hours ago) and read 18040 times:

LH said they still will get an 8,000 nm range from the B-747-8I in their 386 seat configueration. LH also said that is still a longer range than the A-380, in their configueration. Once the horizontial tail fuel tanks are activated, LH should get about an 8,400 nm range from their B-747-830Is.

http://www.flightglobal.com/news/art...-tanks-on-flutter-concerns-367148/

"Boeing said the absence of tail fuel tanks will reduce the range of the VIP configured 747-8 by about 550-930km (300-400nm), depending on the aircraft's configuration."

"For our mission profile it's not a problem at the moment," said a Lufthansa spokesman, who said the tail fuel restriction would not restrict the aircraft's deployment on its initial routes, which have not yet been announced.

Boeing indicates the passenger capacity of the 747-8 as up to 467 seats in a three-class configuration. Lufthansa will operate the aircraft in a three-class configuration seating 386.

Lufthansa said it is "still quite positive that there will be a modification" that will restore access to the tail fuel tanks, but "of course you want an airplane that can run as long as possible" in unrestricted operation.

Lufthansa is "waiting to hear from Boeing how they will solve this problem," the airline added.

Despite not having a timeframe for a fix, the airline said it is its expectation that the restriction will not exist on deliveries in 2013."

"Lufthansa launched the 747-8 in December 2006 with an order for 20 of the General Electric GEnx-2B-powered aircraft. The 747-8 will have the longest range of any aircraft in the airline's fleet, it said, exceeding that of the Airbus A380.

The 747-8's range is advertised by Boeing as being around 14,800km (8,000nm) at maximum takeoff weight of 448t (987,000lb), though the airframer is currently updating the figure for its catalog specifications."

I might add LH also has 20 options in addition to the firm order for 20 B-747-830Is.


User currently offlinenighthawk From UK - Scotland, joined Sep 2001, 5157 posts, RR: 33
Reply 10, posted (2 years 8 months 2 weeks 17 hours ago) and read 17808 times:

Quoting QANTAS747-438 (Reply 5):
Is Boeing saying that while the tail tank is there, they are never to use it?

No, Boeing is saying currently they should not use it, until Boeing can come up with a fix for the flutter issue.



That'll teach you
User currently offlineStitch From United States of America, joined Jul 2005, 31058 posts, RR: 87
Reply 11, posted (2 years 8 months 2 weeks 16 hours ago) and read 17512 times:
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Quoting QANTAS747-438 (Reply 5):
Is Boeing saying that while the tail tank is there, they are never to use it?
Quoting nighthawk (Reply 10):
No, Boeing is saying currently they should not use it, until Boeing can come up with a fix for the flutter issue.

Boeing has stated airlines cannot use it until the fix is in place. The FAA is mandating they both pull the breaker in the cockpit that allows fuel to be transferred into the tank and to physically prevent fuel from being transferred by closing off the fittings.

Once Boeing has addressed the issue, then operators will be allowed to use the tank.


User currently offlineN14AZ From Germany, joined Feb 2007, 2723 posts, RR: 25
Reply 12, posted (2 years 8 months 2 weeks 16 hours ago) and read 17503 times:

Quoting nighthawk (Reply 2):
Quoting N14AZ (Reply 1):
Do I understand this correctly - the problem appears only if the tank is overloaded by mistake?

Is this to consider inaccuracies when filling the tank?

No, I think they mean that if the fuel tank is filled to a level of 15%, not 115%.

Oops, quit a difference    . Thanks for the clarification, being a native speaker seems to be very advantageous (now I have a feeling how this CATIA problem started ...  . )


User currently offline777STL From United States of America, joined Dec 2004, 3656 posts, RR: 3
Reply 13, posted (2 years 8 months 2 weeks 16 hours ago) and read 17477 times:

What's LH's longest route? FRA-EZE? I can't imagine it would be too much of an issue for them, it's not as if the aircraft is completely crippled in terms of range.


PHX based
User currently offlineStitch From United States of America, joined Jul 2005, 31058 posts, RR: 87
Reply 14, posted (2 years 8 months 2 weeks 16 hours ago) and read 17446 times:
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Quoting 777STL (Reply 13):
I can't imagine it would be too much of an issue for them, it's not as if the aircraft is completely crippled in terms of range.

LH have stated they do not currently have any planned 747-8 route that would need them to use the auxiliary tanks. They do want the ability to have it for future needs, but for now, it won't affect their planned 747-8 operations.


User currently offlineEPA001 From Netherlands, joined Sep 2006, 4762 posts, RR: 40
Reply 15, posted (2 years 8 months 2 weeks 16 hours ago) and read 17391 times:
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Quoting KC135TopBoom (Reply 9):
LH said they still will get an 8,000 nm range from the B-747-8I in their 386 seat configueration. LH also said that is still a longer range than the A-380, in their configueration.

In their configuration that is correct. In a different configuration the picture would be a little bit different, and slightly favoring the A380.  .

But both 4-holers have a very good combination of passenger capacity, efficiency and range. No other aircraft on the market today offer these capabilities.


User currently offlineJAAlbert From United States of America, joined Jan 2006, 1607 posts, RR: 1
Reply 16, posted (2 years 8 months 2 weeks 15 hours ago) and read 17198 times:

Quoting XT6Wagon (Reply 4):
The problem from what I've read is that is there is a flutter issue when there is a failure structural member

In layperson's terms, what is a "failure structural member?" Can you give some examples so the technologically challenged among us (me) can visualize this?

Quoting Eagleboy (Reply 6):
I think they are saying that IF there is a certain structural failure

"A certain structural failure" sounds kinda scary. What exactly does this mean?


User currently offlineStitch From United States of America, joined Jul 2005, 31058 posts, RR: 87
Reply 17, posted (2 years 8 months 2 weeks 15 hours ago) and read 17004 times:
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Quoting JAAlbert (Reply 16):
In layperson's terms, what is a "failure structural member?" Can you give some examples so the technologically challenged among us (me) can visualize this?

Essentially, the horizontal stabilizer is fine with fuel in it (during normal flight envelopes/loads).

However, if there is a failure in the wing-to-strut join fitting, if the tailplane tank is filled beyond 15%, this creates a flutter situation. FAA regulations do not allow such a scenario, so Boeing cannot currently allow the aft tank to be filled beyond 15%.

Boeing have stated that such a failure has never happened in the operational history of the 747, but the FAA will not grant them a waiver and Boeing must deactivate the system until they have developed and installed a fix.

[Edited 2012-01-20 07:34:36]

User currently offlineOak522 From United States of America, joined Apr 2010, 71 posts, RR: 0
Reply 18, posted (2 years 8 months 2 weeks 14 hours ago) and read 16695 times:

What is "flutter?" Motion in which axis/es?

User currently offlineGulfstream650 From United Kingdom, joined Mar 2008, 539 posts, RR: 0
Reply 19, posted (2 years 8 months 2 weeks 14 hours ago) and read 16400 times:

Here is a good video showing what flutter is:

http://www.youtube.com/watch?v=OhwLojNerMU



I don't proclaim to be the best pilot in the world but I'm safe
User currently offlinerg787 From Brazil, joined Nov 2010, 125 posts, RR: 0
Reply 20, posted (2 years 8 months 2 weeks 13 hours ago) and read 15163 times:

Is this tank exclusive to the 748 or it is normal to be found on other aircrafts? Sorry if it is a dumb question

User currently offlineStitch From United States of America, joined Jul 2005, 31058 posts, RR: 87
Reply 21, posted (2 years 8 months 2 weeks 13 hours ago) and read 15066 times:
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Quoting rg787 (Reply 20):
Is this tank exclusive to the 748 or it is normal to be found on other aircrafts? Sorry if it is a dumb question

On the 747-8 family, it is only found on the Intercontinental.

It is an option on the 747-400, 747-400 Combi and 747-400 Freighter.

If it had been built, the 767-400ERX also would have had a tail tank of 2,145 g / 8,120 l.

[Edited 2012-01-20 09:19:24]

User currently onlineB777LRF From Luxembourg, joined Nov 2008, 1368 posts, RR: 3
Reply 22, posted (2 years 8 months 2 weeks 13 hours ago) and read 15065 times:

Quoting rg787 (Reply 20):
Is this tank exclusive to the 748 or it is normal to be found on other aircrafts? Sorry if it is a dumb question

Quite a few airliners have wet tails, the 747-400 among them (though not the F). First seen (in commercial airline service) on the A310/300-600 I believe, which also used it as a trim tank.



From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
User currently offlineBryanG From United States of America, joined May 1999, 433 posts, RR: 0
Reply 23, posted (2 years 8 months 2 weeks 12 hours ago) and read 14158 times:

Quoting Gulfstream650 (Reply 19):
Here is a good video showing what flutter is:

http://www.youtube.com/watch?v=OhwLo...NerMU

Check out the video at the 1:14 mark in particular. You don't want your 747 to look like that in flight. Obviously the flutter situation on the 747-8I's tailplanes would not be that extreme, but the video gives a good illustration of the concept (as well as some great wind tunnel disaster footage!).


User currently offlineaeropiggot From United States of America, joined May 2005, 284 posts, RR: 0
Reply 24, posted (2 years 8 months 2 weeks 12 hours ago) and read 14158 times:

I wonder if there is an aeroservoelastic solution, this would be the easiest and most cost effective solution, similar to the solution to the flutter problem in the 747-8F.


A scientist discovers that which exists, an engineer creates that which never was.
25 Oak522 : So we're talking about resonance leading to aerodynamic problems leading to disaster?
26 kanban : If I read the background info correctly, the problem would only possibly occur if a wing to strut connection failed. Since the only struts I can think
27 ikramerica : Could this be solved by something as simple as a different setting for trimming all the surfaces in the event of such a failure? I mean, since it's ne
28 Post contains links Gulfstream650 : Here's a video from Discovery's documentary on the A380 flutter tests. The 748 isn't the only mega-plane to have had flutter issues. http://www.youtub
29 Post contains links maxpower1954 : Here's a great article explaining flutter for those unfamiliar with the phenomena. It includes the most famous case of flutter involving a commercial
30 Post contains links BoeingVista : Almost unheard of but not completely, EL AL 1862 was a 747 that did have an engine separation that lead to a crash. http://en.wikipedia.org/wiki/El_A
31 AirbusA370 : Won't this increase the fuel burn, too? Normally the fuel weight in the tail is used to avoid the use of much "nose up" trim in the early part of flig
32 ikramerica : In the article it mentions that the control surfaces could potentially counter flutter, but there are too many modes to cancel all possible sources o
33 Stitch : Based on the article, evidently not since no airline was planning to use the aft tank. And as you could put 15% fuel into it and still not cause flut
34 QANTAS747-438 : Does anybody have a diagram of what a tail fuel tank looks like in the tail?
35 Tristarsteve : The B747 tail tank is not a trim tank. It is a space for extra fuel. It is always empty until the fuel load reaches about 130 tonnes. ( Over 11 hours
36 Post contains links and images Stitch : Here is a diagram of the fuel system for a 744/744M/744F that includes the tail tank: Image courtesy of http://askville.amazon.com/large-fue...erView
37 Post contains images lightsaber : That is impressive. Question: What is the size (by weight) of this fuel tank. What is the unusable fuel portion? (How many lbm of fuel is left over i
38 JoeCanuck : I'm guessing it has something to do with potential harmonics when fuel is sloshing around in the tank. I wonder if baffles might help. Another example
39 ikramerica : Like the Saturn V "Ka-Doing-a-Doing-a-Doing mode". They decided baffles were too heavy, but I doubt they would be too heavy in a 747 considering how
40 Stitch : The usable capacity is 12,490 gallons / 3,300 liters so that would be 2475 kilograms at 0.75kg per liter.
41 prebennorholm : Aeh, rather 3,300 gallons / 12,490 liters so that would be 10,117 kilograms at 0.81kg per liter.
42 Post contains links jetmech : Most "wet wing" type fuel tanks are baffled with the ribs, which are often configured with one way flapper valves along their bottom edges. The flapp
43 JoeCanuck : I agree. My guess is based on the harmonics happening with more fuel in the tank. Since fuel is the difference, I took a stab that it was the fuel mo
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