A340 Fuel Tank Temp in flight

[SKYTORT]

Hi Guys,

I noted on a flight recently (jump seating in an A340-600) that the fuel tank temperature in the wings varied quite considerably. In other words, the outer tanks were much colder than the inboard tanks. Is there a particular reason for this, or did it just so happen to be?

Thanks

[titi]

On every aircraft the outer portion of the wing is thiner than the wing root, so the effect of temperature are quicker on thiner parts. It is especially the case on Swept wing.

[Joetom]

Volume of fuel is less in the outer tanks as a rule so the temp change will be more.

[hetfield]

Originally Posted by Joetom

Volume of fuel is less in the outer tanks as a rule so the temp change will be more.

It's a little bit ago, but what about eng oil cool/ idg cooling......?

[Joetom]

320 puts warm fuel back in wings, 330/40 not.

[hetfield]

Originally Posted by Joetom

320 puts warm fuel back in wings, 330/40 not.

Are you sure?

A340

FUEL RECIRCULATION SYSTEM

-
The inner fuel tanks supply the fuel to the four engines.

-
Some of this fuel is tapped from the high pressure fuel line of each engine. It goes through the integrated drive generator (IDG) heat exchanger, where it absorbs heat, and continues to the inner fuel tank, via the fuel return valve.

-
Fuel recirculation for IDG cooling moves this heated fuel, from the fuel return valve, back to the inner fuel tank. This operation ensures the IDG cooling during the high temperatures (or at low rates of engine fuel burn).

[Joetom]

Think i'm right, but on Airbus who knows what they do with all those valves in the fuel system, as I remember Airbus 320 went for extra fuel cooling as cheaper than air cooling.

[Joetom]

I may well be wrong, looks like text is for 340-200/300, 600 has an air cooler i think may be?

[titi]

I flew A320 330 and trent engine do not have IDG return valve.
CFM do have it on 320 340 /2 300?
The question is what about Trent 500?

[Thridle Op Des]

The Trent 500 on the 345 uses fan air to cool the IDG

Regards

TOD

[TURIN]

Doesn't the excess servo fuel recirculate back into the tank also?

Again I don't know about the -5/600.

There is also the issue of trim fuel. Fuel being pumped from inner tanks to Stab tanks and back again would possibly create a bit of heat.

There are no boost pumps in the outer cells either. (I think).

[Old Smokey]

I don't fly the A340, but on earlier Airbus that I did fly (A300), the inner tanks were very large, and the outer tanks quite small, in fact, in our operations the outer tank quantity approximated the reserve fuel, and as such, was rarely used.

Normal procedure for most aircraft is to use the outer tank fuel last, a considerable benefit to wing bending relief.

Maybe the A340 is altogether different, but considering my previous ramble, the outer tank fuel will be subject to prolonged and repeated cold soak, with minimal top-up of warm fuel during refuelling, whilst the inner tanks are invariably topped up with significantly large quantities of warm fuel at each refuelling. That would account nicely for a permanent temperature difference between the tanks.

Just my 2 cents worth from someone not rated on the A340.

Regards,

Old Smokey

[TURIN]

It's common practice to drain the o/b cells into the inner tanks before each refuelling (push button in flt deck). Fresh warm fuel is then added to the o/b cells. Helps with de-icing the wing and also ensures no stagnent fuel is 'stored' in the o/b cells.

[Old Smokey]

Thanks TURIN, it seems that Airbus have learned something since their earlier aircraft. The problem that we had on the A300 was not so much the temperature in the outer tanks, but fungus in the fuel as it was rarely used, and did indeed become stagnant

Sorry to all to bring up reference to an earlier Airbus type, thought that it might have shed some light on the original question posed.

Regards,

Old Smokey