I have searched on many websites and can not find the answer as to why the aircraft that carry trim tank have the surge tank on the right,. Can someone explain it to me?

For example:

B777 (On Both) (Right and Left)

B747 (Right)

A330 - A340 (Right)

Never heard of a "trim tank" on a 777, nor can I find anything about it in the Boeing manuals. Can you expand on that information. Surge tanks are usually at the end of the wings?

Of course, I send you several image links where the surge tank appears on the wings and trim tank. Ok, B777 haven't trim tank, you're right.
I am asking about on the right side of surge tank. And Why not on the left side on HTP (Stabilizers)

(LINKS FOR BOEING) (THE IMAGES FOR TO UNDERSTAND MY QUESTION)

http://panchromat.org/.misc/B777-docs/t ... system.jpg

http://photobucket.com/gallery/http://s ... f.jpg.html

(LINKS FOR AIRBUS)

http://www.iasa.com.au/folders/images/a ... 02A001.gif (A330 - 340)

THANKS

BravoOne wrote:

Surge tanks are usually at the end of the wings?

I suspect that MMW93 might be talking about the surge tank for the tail-plane fuel tank / trim tank? If so, it indeed appears that the surge tank is located in the right hand horizontal stabiliser only for the B744 and A330 / A340.

Regards, JetMech

jetmech wrote:

BravoOne wrote:

Surge tanks are usually at the end of the wings?

I suspect that MMW93 might be talking about the surge tank for the tail-plane fuel tank / trim tank? If so, it indeed appears that the surge tank is located in the right hand horizontal stabiliser only for the B744 and A330 / A340.

Regards, JetMech

That threw me as he referenced the 777, and the surge tanks are outboard of the main tanks in the wings. The reference to "trim tanks" might be a carry over from the MD11 fuel tanks in the horizontal stab?

BravoOne wrote:

The reference to "trim tanks" might be a carry over from the MD11 fuel tanks in the horizontal stab?

Could be. I think the term "trim tank" is strictly applicable to the A330 / A340 only as the fuel in the stab tank is used to actively trim the aircraft, whereas I seem to recall that the stab tank is for storage only on the B744, and not used to actively trim the aircraft. Do you know if the stab tank was used for trimming on the MD11?

Regards, JetMech

That was as much a part of he system as the extra 13,000 lbs of fuel. Even if you did not need the fuel for the trip, it would pump fuel aft when you climbed through 19,870', or some weird number like that. The purpose was to move the CG aft for less drag. I'm sure some more current MD11 person will chime in with some more accurate data

BravoOne wrote:

That was as much a part of he system as the extra 13,000 lbs of fuel. Even if you did not need the fuel for the trip, it would pump fuel aft when you climbed through 19,870', or some weird number like that. The purpose was to move the CG aft for less drag.

Interesting. Definitely sounds like an active trimming system.

BravoOne wrote:

I'm sure some more current MD11 person will chime in with some more accurate data

In the same vein, perhaps a B744 driver can explain what happens when the stab fuel moves forward to the CWT? Does the stab automatically move to maintain trim?

Regards, JetMech

The stab tank on the 747 is just a 'dumb' fuel tank. It is filled if the total fuel required is in excess of a certain value (according to a fuel distribution logic between the 8 tanks) and is used almost immediately during the cruise (it empties into the center tank if memory serves).

The stab tank on the A330/340, on the other hand, is used by the onboard computers to shift the CG aft during cruise by pumping fuel in and out of it as required.

As to why the tail surge tank is on the right... No particular reason I guess. The tank is not big enough to justify 2 surge tanks, and they had to put it somewhere...

jetmech wrote:

BravoOne wrote:

Surge tanks are usually at the end of the wings?

I suspect that MMW93 might be talking about the surge tank for the tail-plane fuel tank / trim tank? If so, it indeed appears that the surge tank is located in the right hand horizontal stabiliser only for the B744 and A330 / A340.

Regards, JetMech

I've been scratching my head trying to remember the "surge tank is located in the right hand horizontal stabiliser only for the B744", and can't remember one being there. As far as the tail tank, when the CWT opened the transfer valves in the tail tank, it drained into the CWT. That tank was just about over the CG and very little change in trim resulted. I can't remember the numbers and my NNC are packed away, but I seem to remember a 3-4 hour window if the tank failed to transfer until you had to be on the ground due to CG problems.

Francoflier wrote:

The stab tank on the 747 is just a 'dumb' fuel tank. It is filled if the total fuel required is in excess of a certain value (according to a fuel distribution logic between the 8 tanks) and is used almost immediately during the cruise (it empties into the center tank if memory serves).

mmo wrote:

As far as the tail tank, when the CWT opened the transfer valves in the tail tank, it drained into the CWT. That tank was just about over the CG and very little change in trim resulted. I can't remember the numbers and my NNC are packed away, but I seem to remember a 3-4 hour window if the tank failed to transfer until you had to be on the ground due to CG problems.

I'd think there would have to some "smarts" to the B744 stab tank? I understand the CWT is close to the C of G, but the stab tank certainly isn't. A full stab tank represents 10 tonnes of mass at the extremity of the fuselage. I get the feeling the stab would need to move to compensate for that much mass moving from the aft most extreme of the fuselage.

Francoflier wrote:

As to why the tail surge tank is on the right... No particular reason I guess. The tank is not big enough to justify 2 surge tanks, and they had to put it somewhere...

Sounds about right.

mmo wrote:

I've been scratching my head trying to remember the "surge tank is located in the right hand horizontal stabiliser only for the B744", and can't remember one being there

There is definitely a surge tank in the stab according to this diagram.



http://i32.photobucket.com/albums/d7/k4 ... af8c8f.jpg

Regards, JetMech

Yes, the surge tank is in the tail also, not only in the wings when the airplanes have trim tanks. But anybody know why the position is on the right side?

The trim tank is for use the fuel for to balance the C.G. (Center of Gravity). Because you have disequilibrium for the flight, and if you deflect the surfaces (elevators, ailerons) you spend the fuel so, with this system (Trim Tank) you save money for the fuel.

So I read the comments, and the vent (surge tank) is the right side because he fancy the manufacturer, no?

Regards, MMW93

I can think of only one reason for putting it on the right instead of the left. If there is a spill you want to minimise the risk of it splashing on loaders working at the rear main hold and bulk hold doors. I know the doors aren't exactly under the stab, but they're waaaay up there. A little wind goes a long way.

Then again, that seems like a rather weak justification.

MMW93 wrote:

Yes, the surge tank is in the tail also, not only in the wings when the airplanes have trim tanks. But anybody know why the position is on the right side?

The trim tank is for use the fuel for to balance the C.G. (Center of Gravity). Because you have disequilibrium for the flight, and if you deflect the surfaces (elevators, ailerons) you spend the fuel so, with this system (Trim Tank) you save money for the fuel.

So I read the comments, and the vent (surge tank) is the right side because he fancy the manufacturer, no?

Regards, MMW93

I see the English is not your first language, so when pull some name out of the hat and stick it on an object it does not work well. This is not a trim tank, so do yourself a favor along with others, and use the name Boeing uses for the tank. Horizontal Stabilizer Fuel Tank.

It is not a bad answer but there are also the black boxes on the right side inside the non-pressurized area of the plane, I guess, maybe that's why I air it on the right side and do not spill too. It can be used to think about possible reasons.

Ok, Sorry, I didn't know it, but the ventilation occurs in the same side of the others airplanes. But the Horizontal Stabilizers Fuel Tank (HSFT) use the fuel for compensate the C.G., no?
(I am trying compare this information with Airbus). But the origin of the surge tank is in Boeing or american airplanes). My english is not first language yes, but I'm trying to learn more about your experience about this)


regards

MMW93, I think others with experience in the 747-400 have stated that there are no published procedures that enhance CG/versus HFST fuel. I can see nothing in the FCOM that would lead one to believe that the purpose of this tank is anything other that simple additional capacity when all other tanks have been filled. While I agree that there might be some cruise performance enhancements when this fuel configuration is achieved it appears that Boeing, unlike the MD11, does not use them as such. I have access to a couple of Boeing Technical pilots so I'll ask them for comments.

I seem to recall that the HFST was a Boeing option??? If in fact was fuel performance enhancer one might imagine that it would be standard on all 747's.

AFAIk while Airbus 330, 340 and 380 use the stab tank for CofG control in flight, with extra tankage being a secondary function, Boeing 747-400 uses the stab tank purely for extra tankage.

Bravo One Interesting, so MD-11 don't use the HFST like Boeing, thanks for your support.

Stationblue So Boeing don't use the HFTS for compensate CoG (CG), no? (what is AFAlk?)

And the ventilation side of the tail tank is another mystery so Bravo One (if you can get this information also, would be useful to me.) Perhaps it is there for voice recorders and flight data, so if the fuel is spilling, can burn when combined with air and lightning and that can affect the black boxes.

Thanks

Starlionblue wrote:

I can think of only one reason for putting it on the right instead of the left. If there is a spill you want to minimise the risk of it splashing on loaders working at the rear main hold and bulk hold doors. I know the doors aren't exactly under the stab, but they're waaaay up there. A little wind goes a long way.

Then again, that seems like a rather weak justification.

Your answer is contradictory as the main cargo and bulk hold doors are on the right hand side. For the Airbus models I know it for sure and as far as I can see also for the 747 models. Ironically the MD11 had the bulk door and the vent tank both on the left hand side...

But your input gave me another idea. When fueling with passengers on board, we need to provide a clear area at the left aft passenger door in order to have space there for an eventual evacuation. I don't know if this is a general rule to have this area on the left hand side or if it is a company specific rule. However it makes sense to have the primary evacuation side on the opposite side of the vent tank for the case of some malfunction during fueling. And as it makes sense to have this clear area also on the opposite side of all the loading activity, this could indeed be a reason to have the vent tanke on the right hand side.

But as I already said, I don't know if it is a general rule, to have the clear area on the left hand side. I also don't remember, how we handled this on the MD11. With my above idea it would have made sense to have the clear area on the right hand side with the MD11, but I don't know anymore.

And looking at the fact about the MD11 having the vent tank on the left hand side (that's at least what the schematics indicate), I think the 747 and the A330/340 have it both on the right hand side just by pure chance.

MMW93 wrote:

Bravo One Interesting, so MD-11 don't use the HFST like Boeing, thanks for your support.

Stationblue So Boeing don't use the HFTS for compensate CoG (CG), no? (what is AFAlk?)

And the ventilation side of the tail tank is another mystery so Bravo One (if you can get this information also, would be useful to me.) Perhaps it is there for voice recorders and flight data, so if the fuel is spilling, can burn when combined with air and lightning and that can affect the black boxes.

Thanks

I guess I'm starting to wonder why this is important to you? I have known anyone so curious about such an obscure subject.

BravoOne wrote:

That was as much a part of he system as the extra 13,000 lbs of fuel. Even if you did not need the fuel for the trip, it would pump fuel aft when you climbed through 19,870', or some weird number like that. The purpose was to move the CG aft for less drag. I'm sure some more current MD11 person will chime in with some more accurate data

The fuel in the tail is controlled as follows:
The CG is kept to an initially set aft limit. This function is permitted only if the total fuel quantity is more than 60,000 lbs. When the quantity of the fuel is less than 51,000 lbs, no more fuel is moved aft for CG control.
If the No. 2 engine is stopped, the tail fuel level is kept to a maximum of 5,000 lbs.
When it becomes necessary to move fuel to the tail tank, fuel is moved aft from a non-empty forward tank in the following sequence: Lower Aux, Upper Aux tank 2 (when tank 2 quantity is greater than the tank 1 and tank 3 quantities), tanks 1, 2 and 3 (when all main tanks have equal quantities). If any main tanks dump shutoff float indicates down (below approximately 11,500 lbs and the tail tank contains fuel, the FSC will transfer fuel to that main tank from the tail tank.
If fuel remains in the tail tank during aircraft descent below 19,750 feet, that fuel will be moved forward.
Flow through or pressurization of the tail tank manifold during takeoff and landing is prevented.

MMW93 wrote:

Bravo One Interesting, so MD-11 don't use the HFST like Boeing, thanks for your support.

Stationblue So Boeing don't use the HFTS for compensate CoG (CG), no? (what is AFAlk?)

And the ventilation side of the tail tank is another mystery so Bravo One (if you can get this information also, would be useful to me.) Perhaps it is there for voice recorders and flight data, so if the fuel is spilling, can burn when combined with air and lightning and that can affect the black boxes.

Thanks

AFAIK is short for As Far As I Know. So, AFAIK the 747-400 tail tank is not used for CoG correction dynamically like on the 330/340.

glen wrote:

Starlionblue wrote:

I can think of only one reason for putting it on the right instead of the left. If there is a spill you want to minimise the risk of it splashing on loaders working at the rear main hold and bulk hold doors. I know the doors aren't exactly under the stab, but they're waaaay up there. A little wind goes a long way.

Then again, that seems like a rather weak justification.

Your answer is contradictory as the main cargo and bulk hold doors are on the right hand side. For the Airbus models I know it for sure and as far as I can see also for the 747 models. Ironically the MD11 had the bulk door and the vent tank both on the left hand side...

But your input gave me another idea. When fueling with passengers on board, we need to provide a clear area at the left aft passenger door in order to have space there for an eventual evacuation. I don't know if this is a general rule to have this area on the left hand side or if it is a company specific rule. However it makes sense to have the primary evacuation side on the opposite side of the vent tank for the case of some malfunction during fueling. And as it makes sense to have this clear area also on the opposite side of all the loading activity, this could indeed be a reason to have the vent tanke on the right hand side.

But as I already said, I don't know if it is a general rule, to have the clear area on the left hand side. I also don't remember, how we handled this on the MD11. With my above idea it would have made sense to have the clear area on the right hand side with the MD11, but I don't know anymore.

And looking at the fact about the MD11 having the vent tank on the left hand side (that's at least what the schematics indicate), I think the 747 and the A330/340 have it both on the right hand side just by pure chance.

You're completely correct. They're on the right side. That's what happens when you're fatigued and write in haste.

The evacuation idea has merit. However the left wing surge tank is still there.

On the 330/340 all cargo doors are on the right. On the 350 main cargo doors are on the right, bulk on the left.

Bravo One Because I tried to found some reason for understand why don't have vent surge tank in the tail on the left side. Only that

The tail tank on the 744 is only used for range extension. It is not used for CG trimming as other aircraft have. It provides roughly one hour of additional range.

mmo wrote:

The tail tank on the 744 is only used for range extension. It is not used for CG trimming as other aircraft have. It provides roughly one hour of additional range.

And to add to your previous post regarding the rare situation if the stabilizer fuel fails to transfer, then you can't use any fuel in the center tanks, ...and I'll just paste the rest right out of the procedures:

• WARNING: DO NOT JETTISON FUEL
• Usable fuel is all fuel in tanks 1 and 4 plus the fuel in
tanks 2 and 3 down to 35,000 lbs. remaining in each.
Land before tank 2 or 3 reaches 35,000 lbs. to
maintain CG within limits.

I'm too lazy to work out how much time this would give ya, but it would certainly put a damper on your planned NGO layover back in the days.

I asked a couple of 747 Technical pilots and they just shrugged their shoulders and said they no clue. Most of the original design engineers on the -400 are probably long gone and I do not have access to the 747 CSID.

Ok BravoOne I have tried, thank you very much to everyone for giving me new information, especially to you BravoOne for talking to the pilots. Thanks

I would assume it’s usually on the right hand side as this is the service side of the aircraft? In case of overspill out of the tank this might be favourable?