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Boeing 737NG - Which Tank Gets Filled First?  
User currently offlineMozart From Luxembourg, joined Aug 2003, 2239 posts, RR: 13
Posted (10 years 5 months 3 weeks 5 days 9 hours ago) and read 2507 times:

Which tank gets filled first:

- the center tank, and then remaining fuel in the side tanks
- or first the wing tanks, and then remaining fuel in the center tank?

7 replies: All unread, jump to last
 
User currently offlineOPNLguy From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 5 months 3 weeks 5 days 9 hours ago) and read 2489 times:

On -all- the 737 variants, it's fill the wings first, before you put anything in the center tank. It's an AFM (airplane flight manual) limitation...

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17189 posts, RR: 66
Reply 2, posted (10 years 5 months 3 weeks 5 days 8 hours ago) and read 2476 times:

Heavier wings give less wing bending moment, which is a good thing.

As far as I know, this is pretty much the norm in modern airliners.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineFDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 34
Reply 3, posted (10 years 5 months 3 weeks 5 days 8 hours ago) and read 2465 times:

Are you asking which tanks are refueled first?


You're only as good as your last departure.
User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 25
Reply 4, posted (10 years 5 months 3 weeks 5 days 8 hours ago) and read 2457 times:

Heavier wings give less wing bending moment, which is a good thing.

While that's certainly true, I doubt it comes into play in terms of what get refueled when. Obviously, wing bending is only present when the wings are lifting, so relieving that bending is a mute point while on the ground (refueling).

Cheers,
QantasA332


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17189 posts, RR: 66
Reply 5, posted (10 years 5 months 3 weeks 5 days 1 hour ago) and read 2394 times:

Hmmm, but eventually the plane will be in the air, and in case of a short trip it might dispatch with the center tank empty or partially filled. So that is relevant right? Or I may pf course be wrong  Big grin It's all about learning.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineQantasA332 From Australia, joined Dec 2003, 1500 posts, RR: 25
Reply 6, posted (10 years 5 months 3 weeks 5 days 1 hour ago) and read 2390 times:

You're completely right: in the case of a short trip, yes, wing bending considerations would certainly come into play (assuming you're not just topping up all of the tanks). I was just thinking more along the line of a "normal" (longhaul?) all-tanks-filled flight, for which fuelling order wouldn't matter in terms of wing bending. Sorry, I hadn't be very clear before.

Cheers,
QantasA332


User currently onlineCrosswind From United Kingdom, joined Nov 2000, 2603 posts, RR: 58
Reply 7, posted (10 years 5 months 3 weeks 4 days 19 hours ago) and read 2365 times:
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Even on a long-haul - unless you're really pushing the aircraft's range limits, it's rare for the fuel tanks to be full. You will usually reach your MTOM due to the payload carried before fuel-voulume becomes limiting.

As such, the centre tank will always be filled last, even on short-haul. As OPNL/Starlionblue said, this is a structural requirement to minimise the bending moment of the wings, particularly in the initial stages of flight when the aircraft is haviest. A similar rationale is behind the max ZFM, which I believe is set with reference to the stresses on the wing/body joints, again too much of mass in the fuselage which then has to be supported by the wing/body joints puts additional stess on the aircraft, which is not healthy for them long-term.

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As an example of the use of the centre tank, on the 757, for flights up to around 2-2h30 duration the centre tank will be empty - aside from the unuseable fuel which is mandated by the current ADs.

Regards
CROSSWIND

[Edited 2004-07-07 15:20:33]

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