Brian Whatcott wrote:

On Tue, 21 Jun 2005 04:36:40 GMT, Gord Beaman
wrote:

Well...I also recall hearing crew asking passengers to move on
account of unexpected cargo distribution. That was pre-take-off.

Brian Whatcott

Yes, and that was strictly a CG manipulation thing...this other
isn't, it's a drag reduction thing only. I'm sure most of us know
that lateral stability of an a/c is supplied by the wing's
dihedral and fore/aft stability is a function of having the
aircraft quite nose-heavy which is balanced with quite large
down-force provided by the empennage...if most of that downforce
can be supplied by moving fuel aft then the aerodynamically
supplied downforce can be zeroed out saving considerable
drag...mind you, stability suffers and you need an autopilot to
handle the a/c.


Let me put it this way Gord: in a conventional airplane layout,
loading the aircraft near aft CG limit ALWAYS reduces drag.

Now what do you say? CG aft = drag reduction........

Brian Whatcott Altus OK

Oh yes indeedy...it certainly will, the reason is that now the
horizontal stab doesn't need to be trimmed for so much
'downforce' BUT the a/c tends to be unstable because the
stabilizing effect of having quite a lot of AERODYNAMIC 'tail
down trim' is reduced...this is what I'm querying, is fuel weight
induced tail down trim still used in cruise for economy?...
--


-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"