744 horizontal stab fuel
 

How come it is not installed on the freighter aircraft.

Freighters don't fly long enough legs to need the extra fuel. Freight operators would rather carry more payload than more fuel.

The typical 747 freighter missions doesn't even use center tank fuel - wing fuel is all that's needed.

Used CWT fuel yesterday, 9 hour freighter flight. Very close alternate. 6 tons in the CWT. That being said, the payloads are usually pretty heavy and the CWT is so big that I can see why the stab tank would not be used very often as you mentioned. But some flights can be quite long. Thinking of Singapore to the US. I suppose it is cheaper to fuel up enroute with the bigger payload than cut into payload for longer range.

Were stab fuel tanks ever a freighter option or never offered. And it appears that converted freighters have had their stab tanks removed.

There's no such thing as having or not having a stab tank per se, the stab is the tank just like the wings are. During manufacture the basic stab just doesn't get the full treatment to make it qualify as a tank, and a BCF just has as much of the equipment that makes it function as a tank removed.

The classic on the other hand had flight control cables running through the structure of the stab therefore requiring the -400 to have a redesigned flight control system relocating the cables to the outside thereby allowing the stabilizer to be sealed and function as a tank.

Thanks,

I guess then, that it could be described as a wet stab instead of the usually stated wet wing description we hear as a type of fuel tank. Therefore, it is there as a potential fuel tank but the plumbing obviously is not as no vent or dripsticks can be seen on the freighters that I have flown. Have never flown a BCF.

My log book shows one flight ORD-NKG (Chicago to Nanjing) in a 744F with a flight time of 14.1 hours. Admittedly back-loads to China were usually very light, it still demonstrates the Freighter still has considerable 'legs' even without stab-tanks.

It's not only freighters that don't have the stab tank plumbed in. BA have four 747-400 "Lite" aircraft, G-CIVF, G-CIVG. G-CIVH and G-CIVI. They have a higher ZFW and lower fuel capacity.

To the best of my knowledge, stab fuel was never offered on the 747-400F (or the 747-8F). We book-keep a "Typical" freighter mission at about 7 hours, and stab fuel only comes in to play when you're up around 16 hours. BTW, stab fuel had to be deactivated for initial 747-8I deliveries due to a flutter issue (that took quite a bit of work to resolve). New -8I deliveries have stab fuel active, and there is a Service Bulletin to activate it on already delivered airplanes.

While SMOC is technically correct that all -400s (and -8s) have a stab tank, the associated claptrap of pumps, fuel lines, seals, etc. is not insignificant in both cost and weight, so no reason to have it if you're not going to use it. Further, there are MEL implications - if something is INOP, - even optional systems - it needs to be fixed at some point per the MEL. So that provides even more incentive to simply get rid of the stab tank fuel system if you're not going to use it.

And it wasn't designed to be a 'trim tank' as on the A330/340. It was just another place to stuff fuel.

With the freighter, yes the typical mission duration might be 7-8 hours, but remember that is artificially low due to the (in the case of the trans-pac) refuelling stops in Anchorage. If the a/c had the capability to carry the fuel, you'd see longer average sectors. In a perfect world the aircraft could take MZFW, w/ full tanks, but as we know that doesn't happen. You can have the ZFW, or the fuel, but not both. In the freighter version, operators place a higher priority in lifting the weight, and accept tech stops. You could (in theory) install a stab tank on a freighter, but it would only make sense if you know your typical loads were going to bulk out. BTW, fuel starts to go into the stab on a pax a/c at approx 130T of fuel. Broad strokes, 10-12T / hr, so sectors around 11.5-12+ hours you start seeing stab fuel loaded. Above 150T of fuel, you start restricting ZFW.

400 CWT
 

"Freighters don't fly long enough legs to need the extra fuel. Freight operators would rather carry more payload than more fuel."

"The typical 747 freighter missions doesn't even use center tank fuel - wing fuel is all that's needed."


"While SMOC is technically correct that all -400s (and -8s) have a stab tank, the associated claptrap of pumps, fuel lines, seals, etc. is not insignificant in both cost and weight, so no reason to have it if you're not going to use it. Further, there are MEL implications - if something is INOP, - even optional systems - it needs to be fixed at some point per the MEL. So that provides even more incentive to simply get rid of the stab tank fuel system if you're not going to use it."


WHAAAAT?
15 hours KCVG-VHHH.

9.5 hours VHHH-PANC, 910,000 lbs, fully loaded, fuel of fuel all tanks including CWT.
NOT all -400's have horizontal stab tanks. our BCF's don't.

Going from memory, at about a 5 to1 ratio with the CWT tank. Not sure of the reason why but perhaps for balance.

As stated the BCFs still have the tank but it's now full of holes where the plumbing, pumps and access panels were, the vent and dipsticks etc removed and blanked, plus a new fuel panel in the cockpit.

Also the -8 can carry more fuel in its CWT & wings than the -400 can including its stab. It can load an extra 9T in each wing compared to the -400.

Guam

Perhaps I wasn't clear - all 747-400/-8 aircraft structurally have a stab fuel tank. But on Freighters (and some passenger models) it's not functional as a fuel tank - the sealing, pumps, fuel lines, etc. are not installed. Further, when a passenger model is converted to a freighter (e.g BCF), the stab fuel is disabled and most of that equipment comes out to save weight.

A 747-400 with full tanks (but no stab fuel) can carry ~ 180 to 190 tons of fuel (depending on density - about 53,600 US gallons). Stab fuel adds another ~11.5 tons (3300 gallons), or about a 6% increase. I don't know why you'd need stab fuel at ~130 tons unless as JammedStab notes it's for balance.

BTW Guam, why would you need full CWT fuel (again, ~185 tons) for a 9.5 hour flight?

Going from memory, at about a 5 to1 ratio with the CWT tank. Not sure of the reason why but perhaps for balance.

Good memory. The actual ratio is 5.2-1

A 747-400 with full tanks (but no stab fuel) can carry ~ 180 to 190 tons of fuel (depending on density - about 53,600 US gallons). Stab fuel adds another ~11.5 tons (3300 gallons), or about a 6% increase. I don't know why you'd need stab fuel at ~130 tons unless as JammedStab notes it's for balance.

The software in the fuel system determines when the fuel starts to go into the stab tank. It can be between 125-132T of total fuel load, that the stab will start to be used. It will then go in at the ratio of 5.2-1 (CWT-STAB) Total fuel is approx 170 T w/ the stab tank, 160 T w/o. 13.3 in each of Main 1&4, 37.3 in Main 2 &3, 51.0 in CWT, 3.8 in the reserves, plus 10T in the stab (as installed). That using a SG of 0.785.

Max I ever got onto a -400 was 173tons and it came out of the ground cold. usually maxed out about 168tons.

173 tons is the number I am familiar with. I guess that there are versions that can take more. Perhaps an option.

That would be with the stab tank. According to our FCOM, standard 744F carries 163 Tons, and the 744 pax bird with stab tank carries 173. The most I've seen in a 744F is around 161.

For the 744 pax with stab fuel it depends what SG you're using, an SG of 0.80 comes out to 173T if you're using 0.785 it comes out to 169T, so it depends what your company considers a standard SG for their location on the planet. (For us it's 0.785 so 744 = 169T & 744F - 160T).

The only way a -400 could have more gas than standard would be the auxilliary tanks (12,151L) in the forward cargo and only for the 744ER I believe.

http://www.boeing.com/commercial/aer...747ER_fig3.jpg

To be clear, the numbers I posted above are the max fuel weights allowed per the AFM - turns out that's based on a density of .885 which is exceptionally high for jet fuel (but not out of line for gasoline).
Obviously with a more typical .78-.80 density the volume (53,600 gallons, plus another 3,300 gallons for stab fuel) will limit the mass of fuel carried.