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Is The Stabilizer Fuel Tank Going To Be A Memory?  
User currently offlineMax Q From United States of America, joined May 2001, 4458 posts, RR: 19
Posted (1 year 5 months 1 week 12 hours ago) and read 9254 times:

Do any of the latest generation (787 / A350) incorporate the stabilizer fuel tank ?


This was a popular way of increasing total fuel capacity and / or actively controlling the CG in flight for improved fuel burn but I haven't read anything about it being included on newer Airliners.


Has this feature had it's day ?

[Edited 2013-03-24 22:46:40]


The best contribution to safety is a competent Pilot.
38 replies: All unread, showing first 25:
 
User currently offlineKELPkid From United States of America, joined Nov 2005, 6372 posts, RR: 3
Reply 1, posted (1 year 5 months 1 week 12 hours ago) and read 9248 times:

The tail tanks used to be one of the reasons for the flight engineer...until the late 1980's or so (with the coming of the 747-400 and the MD11). The computers do the job now. However, the tail tanks in the 747-800 are still not activated due to the unexpected flutter mode that they were found to have caused...and I'm wondering if Boeing will ever activate them.


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlinezeke From Hong Kong, joined Dec 2006, 9029 posts, RR: 75
Reply 2, posted (1 year 5 months 1 week 10 hours ago) and read 9174 times:

Quoting Max Q (Thread starter):
Do any of the latest generation (787 / A350) incorporate the stabilizer fuel tank ?

A350 no.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offline747classic From Netherlands, joined Aug 2009, 2119 posts, RR: 14
Reply 3, posted (1 year 5 months 1 week 10 hours ago) and read 9162 times:

Quoting KELPkid (Reply 1):
The tail tanks used to be one of the reasons for the flight engineer...until the late 1980's or so (with the coming of the 747-400 and the MD11). The computers do the job now

I have no knowledge about flight engineer (F/E) controlled tail tanks or active CG shifting by the FE, except the 3 man operated Concorde.
The sequence of tank usage during (tanking and) flight was controlled by the F/E to keep the CG inside the certified flight envelope.

At the jet aircraft with a basic cockpit crew of 3 , introduced during the 50,60,70 and eighties of the last century (Boeing 707,727,747-100/200/300/SP, Douglas DC8, 10 series and the Lockheed L-1011) no tail tanks were installed. Only auxiliary tanks, installed in the lower cargo holds, were installed at some dedicated aircraft and used at very long stretches.
Airbus also didn't use tail tanks on the early 3 man operated A300 aircraft.

Airbus introduced active CG control only on 2 crew aircraft.( A300-600R, A310-300, A330, A340 and A380 series) and called the tail tank : "trim tank".

Boeing up to now has NO CG control by fuel transfer from or to the installed tail tanks on the 744 series. When the fuel quantity in the CW tank is below a certain treshold, the total amount of tail fuel is drained in that tank.

Some rumours are suggesting that active tail fuel control COULD be introduced at the 747-8I series, however in the original 747-8I design the tail tank operation is identical to the 744 and not used for CG control.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineFoxHunter From United States of America, joined Dec 2001, 65 posts, RR: 0
Reply 4, posted (1 year 5 months 6 days 18 hours ago) and read 8706 times:

The SVC10 had Tail Fuel managed by the FE.

User currently offlineStitch From United States of America, joined Jul 2005, 30901 posts, RR: 87
Reply 5, posted (1 year 5 months 6 days 16 hours ago) and read 8631 times:
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Quoting KELPkid (Reply 1):
I'm wondering if Boeing will ever activate them.

Yes they will. The 747-8 they "bought back" from LH is being used, in part, for this purpose.


User currently onlineferpe From France, joined Nov 2010, 2803 posts, RR: 59
Reply 6, posted (1 year 5 months 6 days 13 hours ago) and read 8538 times:

So the question remains as put by the OP, why no CG control in these days of redusing drag by all means and high fuel prices?

I happen to include the extra induced drag the downward force of the tail adds to the wing and also the tail induced drag in itselves in my frame model so the follwing was easy to do for eg the A358:

Tail down........average fuel burn kg/hour
...2,5%..................... 5289
...1,5% .....................5209

I changed the tail down force from the normal average of 2,5 to 1,5 % and this reduced the fuel burn with 1.5%. IMO this is significant and larger then eg the new laminar flow tail of the 787-9 brings, why does Airbus say no to this? It should help especially on the shorter 358. Is the complexity that large that the invest cost + maintenance does not pay off during the lifetime of the frame?



Non French in France
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 7, posted (1 year 5 months 6 days 11 hours ago) and read 8459 times:

Quoting KELPkid (Reply 1):
However, the tail tanks in the 747-800 are still not activated due to the unexpected flutter mode that they were found to have caused...and I'm wondering if Boeing will ever activate them.

What caused this flutter,which did not occur on the previous models?.



Think of the brighter side!
User currently offlineTristarSteve From Sweden, joined Nov 2005, 4000 posts, RR: 34
Reply 8, posted (1 year 5 months 6 days 10 hours ago) and read 8435 times:

I remember reading in here, or in Flight, that Airbus considered the A330 style C of G trim tank for the A350, but in the end decided that the cost of operating it was more than the savings in fuel.
It is quite complicated, there are many valves and pumps, and seems to me to have defects quite often.
Boeing has never gone down this route, (The B744 is not a trim tank) so perhaps it was always marginal.
Looking at the A330 MEL, there is a penalty of 1pc extra fuel with the trim tank inop. So tiny margins here.


User currently offlinestrfyr51 From United States of America, joined Apr 2012, 1176 posts, RR: 1
Reply 9, posted (1 year 5 months 6 days 5 hours ago) and read 8326 times:
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the trouble with auto fuel Trimming is that were there to be a failure OR a leak in the plumbing you could pump all the fuel over the side and the Pilots couldn't do anything about it. Fuel leveling should be the domain of the flight crew and the management of the fuel should be whatever the flight crew deems it to be with advisories from the airplane.

User currently onlineferpe From France, joined Nov 2010, 2803 posts, RR: 59
Reply 10, posted (1 year 5 months 6 days 2 hours ago) and read 8254 times:

Quoting strfyr51 (Reply 9):
the trouble with auto fuel Trimming is that were there to be a failure OR a leak in the plumbing you could pump all the fuel over the side and the Pilots couldn't do anything about it. Fuel leveling should be the domain of the flight crew and the management of the fuel should be whatever the flight crew deems it to be with advisories from the airplane.

I don't get what would be the difference to any other system on the plane, of course the crew can shut of the pumps, I would also venture they have manual means to correct an automatic system who has sensor faults or such. Automatic trimming does not mean the crew are passengers all of a sudden.



Non French in France
User currently offlineKELPkid From United States of America, joined Nov 2005, 6372 posts, RR: 3
Reply 11, posted (1 year 5 months 6 days ago) and read 8200 times:

Quoting HAWK21M (Reply 7):
What caused this flutter,which did not occur on the previous models?.

I think only a Boeing engineer could enlighten us   And I'm not one of those  



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offline747classic From Netherlands, joined Aug 2009, 2119 posts, RR: 14
Reply 12, posted (1 year 5 months 5 days 21 hours ago) and read 8153 times:

Quoting KELPkid (Reply 11):
What caused this flutter,which did not occur on the previous models?.
I think only a Boeing engineer could enlighten us And I'm not one of those

I am not a Boeing engineer, but I will give it a try :

Boeing first discovered the problem already in the summer of 2011 and AFAIK not during flight testing.

Engineering computer models were run to simulate the failure of a specific wing mounting strut, one of several redundant components that hold the outboard engines on the wings. For safety reasons, such a potential failure must be proved not to threaten flight safety if it occurs.

The computer analysis revealed that if that engine mounting strut were to fail, then extra weight (tail tank more than 15% full) at the rear of the aircraft would cause wing flutter. (the 748 has a heavily modified wing platform and greater length compared to the 744, causing a different flutter behaviour)

Boeing said this specific engine mounting strut has never actually failed on any previous 747 model nor in flight tests of the 747-8.

"This is something we found during analysis, not test,"

See : http://seattletimes.com/html/busines...echnology/2017283893_boeing20.html

Here are the highlights :

- The 747-8I was certified in December 2011 without the additional 3,300-gal. tail tank fuel capacity because Boeing could not show full compliance with FAA requirements that no structural flutter be present in the airframe after any single failure condition.
- The specific case concerned potential flutter in the event of a failure of the R3 under-wing, mid-spar strut-to-wing fitting, which is one of six connecting the outboard engines to the wing.
- The specific load condition assumes also the full weight of the 3,300 gal. in the tail tank as well as a lot of weight forward.
- Boeing became aware of the situation earlier in 2011 and, because there was no likely impact foreseen to any of the initial customers until at least 2013/2014, made the fix part of its longer-term development schedule.
- The tail tank is not currently required for passenger operations by launch customer Lufthansa. In a nominal 467-seat configuration, with the tank full, the 747-8 exceeds weight limits if it is operated at more than a 60% load factor.
- Because the first 747-8I/BBJ (with a relative low payload) is not expected to be active before the end of 2013 the tail tank will not be required before 2014.
- Boeing is at the moment studying several options, ranging from routine checks to minor structural modifications, to reactivate the closed-out tail fuel tank. For this purpose RC021 (former D-ABYE for Lufthansa, but NTU) will be used as a test aircraft.



Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlineMax Q From United States of America, joined May 2001, 4458 posts, RR: 19
Reply 13, posted (1 year 5 months 5 days 9 hours ago) and read 7955 times:

A little off the subject here but the VC10 had a fuel tank in the Fin of all places, I think that's unique, anyone hear of another Aircraft with this arrangement ?


Imagine how much fuel you could put in the Fin on a B747 ?!



The best contribution to safety is a competent Pilot.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17029 posts, RR: 67
Reply 14, posted (1 year 5 months 5 days 8 hours ago) and read 7937 times:

Quoting Max Q (Reply 13):
Imagine how much fuel you could put in the Fin on a B747 ?!

I'm getting a headache thinking of the plumbing. Given the engine location on the VC-10 you'd think it wasn't a long way to go but apparently the fin tank fed into the centre wing tank. I know fueling is done under pressure but getting all that fuel uphill must have been a fun design challenge.


The VC-10 fin tank was comparable in capacity to the outer wing tanks.

"The total usable fuel capacity is 19,340 Imperial gallons contained in the tanks as follows:
Tank Nos. 1A and 4A - 1,433 Imp. gall. each
Tank No. 1 - 1,906 Imp. gall.
Tank No. 2 - 3,375 Imp. gall.
Centre transfer - 4,563 Imp. gall.
Tank No. 3 - 3,370 Imp. gall
Tank No. 4 - 1,900 Imp. gall.
Refuel gallery 10 Imp. gall.
Fin tank 1,350 Imp. gall."
*

While we're at it, why do the main left wing tanks have higher capacities than the right ones? Love classic British jetliners (and jet fighters for that matter) and their oddities. The Trident offset and side retracting nose gear is a fave.


*Source: http://www.vc10.net/Technical/fuel_system.html



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently onlineferpe From France, joined Nov 2010, 2803 posts, RR: 59
Reply 15, posted (1 year 5 months 5 days ago) and read 7848 times:

Quoting Starlionblue (Reply 14):
The Trident offset and side retracting nose gear is a fave.

Lateral thinkers those Brits   



Non French in France
User currently offlinePihero From France, joined Jan 2005, 4407 posts, RR: 76
Reply 16, posted (1 year 5 months 4 days 5 hours ago) and read 7671 times:
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Quoting ferpe (Reply 15):
Lateral thinkers those Brits

     



Contrail designer
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 17, posted (1 year 5 months 4 days 2 hours ago) and read 7637 times:

747classic

...jet aircraft with a basic cockpit crew of 3 , introduced during the 50,60,70 and eighties of the last century...no tail tanks were installed....

Apart from, amongst others, the VC10.


MaxQ

...anyone hear of another Aircraft with this arrangement...

Yes, the Trident 2, which had a fin fuel tank holding 1,231 kg of fuel.

Must be a British thing!  


Best Regards to both

Bellerophon


User currently offlinePihero From France, joined Jan 2005, 4407 posts, RR: 76
Reply 18, posted (1 year 5 months 4 days 2 hours ago) and read 7625 times:
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Quoting Bellerophon (Reply 17):

Yes, the Trident 2, which had a fin fuel tank holding 1,231 kg of fuel.

Can you tell us about the procedure for these airplanes ? When and how they would start transferring ?

Thanks.



Contrail designer
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 19, posted (1 year 5 months 2 days ago) and read 7271 times:

Pihero

As far as I am aware, the fuel tank in the fin of a Trident 2 was only put there because it was the most convenient place in which to install the extra fuel tank required to increase the range of the Trident 2.

Fin tank fuel was not used to control the CG position, and the fin tank never fed the engines directly, it only ever replenished fuel used from the centre and inner tanks.

The fin tank was only used at total fuel loads above 21,809 kg, and if used at all, had to be completely full, 1,231 kg, at take-off.

After FL100 had been passed on the climb, the fin tank cock was opened, and the fin fuel slowly drained, under gravity, into the centre and inner tanks, as soon as sufficient fuel had been used from those tanks to create a space for it. Five minutes after the fin tank showed empty, the fin tank cock was closed.

There was a reduced VMO limit of 300kts whenever the fin tank contained any fuel, but as soon as the fin tank showed Empty, the normal VMO of 365kts could be used.

Joyeux Pâques

Bellerophon


User currently offlinevc10 From United Kingdom, joined Nov 2001, 1408 posts, RR: 16
Reply 20, posted (1 year 5 months 1 day 22 hours ago) and read 7231 times:

On the super VC-10 fuel in the fin was used to get extra fuel on board and also to trim the aircraft during cruise
There was a chart which gave the trim fuel figure required dependant on the loading of the aircraft. Fuel from the fin tank could be transferred to the centre tank or if required directly jettisoned in an emergency



Should the quantity of fuel in the fin tank be greater than that required for trim reasons then during the climb [when there is space in the centre tank ] fuel would be transferred from the fin, by gravity, to the centre tank via a fuel valve with a restrictor until the preselected figure was reached

OR

Should the fin trim figure be greater than the fuel actually in the fin then fuel could be pumped from the centre tank into the fin tank. There was a preselector on both tank gauges so as to achieve the correct figure in the fin tank.

If any of the main fuel feed tanks [1,2,3,4] contents should drop to 1200 kgs or at 45 minutes before landing then the fin tank would be drained into the centre tank and pumped to wing tanks


User currently onlineferpe From France, joined Nov 2010, 2803 posts, RR: 59
Reply 21, posted (1 year 5 months 1 day 19 hours ago) and read 7175 times:

There is a very nice drawing in the latest ACAP for the A380, it is a firefighter info thing but shows among other things the fuel tanks and lines:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/A380tankageetc_zps273d094b.jpg

It is noteworthy that the A380 has a tail trim tank but no fuel in the center wingbox. So A went to the trouble of a trimtank yet they had such ample fuel in those huge thick wings that they didn't even bother to use the center tank (of course this is good for wing bending moment).

Now given all this why doesn't the A350 have a trim tank? Beats me.



Non French in France
User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 22, posted (1 year 5 months 1 day 19 hours ago) and read 7158 times:

Do these tanks require inerting in new designs like the A380? Is that a hassle?

Quoting zeke (Reply 2):
A350 no.

Really? I thought Airbus loved these tanks.

What actually happens in a 744 if fuel is trapped in the stab tank? Do they keep fuel in the centre tank to compensate and divert or something else?


User currently offlinePihero From France, joined Jan 2005, 4407 posts, RR: 76
Reply 23, posted (1 year 5 months 1 day 18 hours ago) and read 7126 times:
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To Bellérophon.
Very nice info. Thanks a lot.

Quoting thegeek (Reply 22):
What actually happens in a 744 if fuel is trapped in the stab tank? Do they keep fuel in the centre tank to compensate and divert or something else?

Good auestion : Actually, it could be a lot more serious as the risk of CoG goingh beyond aft limit is great.
I know of a very switched-on crew who had that failure first, out of Tokyo. When they discover that transfer from the trim tank was impossible, they realised that the situation could be seious as a quick look at the weight and balance sheet showed that the aft CoG limit was going to be reached. The only solution was a return to Tokyo and land overweight as fuel jettisoning was out of the question.
Boeing later issued a procedure and some CoG restrictions to counter the problem.



Contrail designer
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 24, posted (1 year 5 months 1 day 18 hours ago) and read 7125 times:

thegeek

Quote:
...What actually happens in a 744 if fuel is trapped in the stab tank?...

What actually happens is that you have a problem!

On a B744, you will only have stab tank fuel on a long-range flight and the procedure is to transfer this fuel out of the stab tank fairly early in the flight, before most of the centre wing tank fuel or virtually any of the wing tanks fuel has been used.

Somewhere around 90 minutes after take-off, when the CWT fuel has decreased to 36,470 kg, the Fuel Management System Cards will automatically open the appropriate valves and activate the transfer/jettison pumps and transfer all the stab fuel from the stab tank into the CWT, and so all the stab tank fuel should be gone around two and a half to three hours into a 12+ hour flight, leaving us with a (nearly) empty stab tank

The reason for this is that if we left the stab tank fuel to the end of our long flight, when we have no fuel in the centre tank and little fuel in the wing tanks, and only then discovered that both the transfer/jettison pumps had failed leaving fuel trapped in the stab tank, then, with little or no fuel in the centre or wing tanks, the CG would be far too far aft for the aircraft to land safely, and there would be very little we could do about it.

Therefore, to guard against this problem, we use the stab tank fuel early in the flight in order that, if there is a failure of both transfer/jettison pumps, we learn about it whilst we can still manage the situation.

Quote:
...Do they keep fuel in the centre tank to compensate and divert or something else?...

Yes, to both!

We must land whilst we still have sufficient fuel in the centre and wing tanks to keep the CG forward of the aft limit, and very broadly, this means we will have to land within roughly 6-7 hours, not the 12 -15 hours we had planned! This scenario is covered on B744 conversion courses, and new pilots are sometimes surprised at just how awkward a problem it can be.

I'm not aware that it has ever happened for real, but this scenario is a very useful LOFT exercise in the simulator.


Best Regards

Bellerophon


25 thegeek : This is such a tricky problem and you need to know about so soon in the flight because you have to assume that you can't transfer fuel from the wing t
26 Starlionblue : I don't think you'd ever want to transfer from the wing tanks to the centre tank. It would increase wing loading and AFAIK you can't gravity feed fro
27 thegeek : Within allowable limits though, given that the plane would have taken off with a completely full centre tank. I don't think it's an issue that you ca
28 Max Q : Great and informative information but I don't understand how the fin tank could drain under gravity during the climb. Surely the centre and inner tan
29 Starlionblue : Again, I can't think of a reason to transfer from wing to centre tank, unless we're talking CG control, and the difference in CG between these tanks
30 Pihero : In 1994, IIRC, an AF 744. The procedure that you know has been changed after the *return of experience* by Boeing. Simple and superb explanation, for
31 thegeek : That's what we are talking. I expect the difference is not negligible particularly between the centre tank and tanks 1 & 4.
32 Post contains images Bellerophon : thegeek ...you need to know about so soon in the flight because you have to assume that you can't transfer fuel from the wing tanks into the centre ta
33 Max Q : Thank you Bphon for that explanation, love the Trident, I remember travelling on one to Glasgow from Heathrow in the '70s in the backward facing seat
34 thegeek : I got that point. What I was more wondering is why it needs to happen so early in the flight. Let me ask a different question. Is there a facility to
35 Post contains images Bellerophon : thegeek I may not have understood correctly the point you are trying to make, or the question you were asking, so please allow me try again. ...Is the
36 thegeek : Cheers Bellerephon, makes complete sense now. I was more thinking that you could get closer to home. Take a DFW->BNE flight, you might be able to d
37 Post contains images longhauler : The first airliner I commanded was the A310-300, and as we know, it was equipped with a trim tank in the tail. As the aircraft was brand new, I did my
38 ferpe : This is a rather strange attitude and I am surprised EASA went along with it. I agree with your sentiment, a manual valve should have let it trickle
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