747 weight distribution

Hello, this is an odd question of curiosity from an amateur: Two days
ago I was flying from Dulles to LHR on a United 747-400. The aircraft
taxied to the end of the runway, then the pilot announced there was a
problem with the weight distribution on the aircraft wings, and we
would have to move passengers to compensate. For the next half hour,
cabin crew moved passengers around, apparently from economy to
business, and then we took off. Is this normal? Can passengers body
weight really make a difference on a huge aircraft like a 747?

Yes, it certainly does... nose to tail is where the weight distribution
matters. Sounds like you had too many people at the tail at not enough
toward the nose...

"Robin" wrote in message
om...
Hello, this is an odd question of curiosity from an amateur: Two days
ago I was flying from Dulles to LHR on a United 747-400. The aircraft
taxied to the end of the runway, then the pilot announced there was a
problem with the weight distribution on the aircraft wings, and we
would have to move passengers to compensate. For the next half hour,
cabin crew moved passengers around, apparently from economy to
business, and then we took off. Is this normal? Can passengers body
weight really make a difference on a huge aircraft like a 747?

On 29 Mar 2005 06:11:36 -0800, (Robin)
wrote:

Hello, this is an odd question of curiosity from an amateur: Two days
ago I was flying from Dulles to LHR on a United 747-400. The aircraft
taxied to the end of the runway, then the pilot announced there was a
problem with the weight distribution on the aircraft wings, and we
would have to move passengers to compensate. For the next half hour,
cabin crew moved passengers around, apparently from economy to
business, and then we took off. Is this normal? Can passengers body
weight really make a difference on a huge aircraft like a 747?


loaders like to place the CofG near the aft limit. Fuel and cargo
make huge invisible loads.
Still, when someone gets it wrong, you can still shuffle passengers.

Brian Whatcott Altus, OK

Brian Whatcott wrote:
loaders like to place the CofG near the aft limit. Fuel and cargo
make huge invisible loads.
Still, when someone gets it wrong, you can still shuffle passengers.

I was under the impression that most big jets had a small fuel tank in
the tail, and they could pump fuel back and forth to trim the CG. Am
I mistaken?

(Roy Smith) wrote:

Brian Whatcott wrote:
loaders like to place the CofG near the aft limit. Fuel and cargo
make huge invisible loads.
Still, when someone gets it wrong, you can still shuffle passengers.

I was under the impression that most big jets had a small fuel tank in
the tail, and they could pump fuel back and forth to trim the CG. Am
I mistaken?

No you're not but they use it for economy...most a/c are built to
be quite nose heavy so they need quite a lot of nose up trim in
level flight, this increases the 'fore and aft stability'.

It's done with the moveable horizontal stabilizer and creates a
considerable amount of drag. Long range a/c (used to at least)
pump fuel back to the tail tank to replace the 'down force'
needed thus removing that drag...this removes the fore/aft
stability and mandates the use of autopilot (I think)
--

-Gord.
(use gordon in email)

On Wed, 30 Mar 2005 04:09:15 GMT, Gord Beaman
wrote:

(Roy Smith) wrote:

I was under the impression that most big jets had a small fuel tank in
the tail, and they could pump fuel back and forth to trim the CG. Am
I mistaken?

No you're not but they use it for economy...most a/c are built to
be quite nose heavy so they need quite a lot of nose up trim in
level flight, this increases the 'fore and aft stability'.

Huh? I've not flown a jet with a "small fuel tank in the tail". Am I
missing something?

-Jack Davis
B737

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Jack Davis wrote:

On Wed, 30 Mar 2005 04:09:15 GMT, Gord Beaman
wrote:

(Roy Smith) wrote:

I was under the impression that most big jets had a small fuel tank in
the tail, and they could pump fuel back and forth to trim the CG. Am
I mistaken?

No you're not but they use it for economy...most a/c are built to
be quite nose heavy so they need quite a lot of nose up trim in
level flight, this increases the 'fore and aft stability'.

Huh? I've not flown a jet with a "small fuel tank in the tail". Am I
missing something?

-Jack Davis
B737

Only on larger a/c Jack...747 have them (some at least). What I
find interesting is how few people seem to know much about them,
is it that they aren't used much now?...that they've gone out of
style?...that the risks of using them isn't worth the
savings?...what?. They're called 'Trim Tanks' I believe and the
theory is to replace the aerodynamically derived 'down force' of
the tailplane with fuel weight at some expense of fore/aft
stability which is compensated for by use of very capable
autopilots.

This system is only used in stable cruise. IIRC this system
caused the crash of a large Russian airliner which was handled
roughly while in this mode by the captain's son.
--


-Gord.

"I'm trying to get as old as I can,
and it must be working 'cause I'm
the oldest now that I've ever been"