On 15/02/2012 12:49 AM, Orchid Win7 v1 wrote:
> On 14/02/2012 10:46, Paul Fuller wrote:
>
>> Did you know that in a single trip from Sydney to London a Boeing 747
>> will use approximately as much fuel as one going the other way.
>
> I'm going to contest this one. I was under the impression that the
> various jet streams make it significantly more fuel-efficient in one
> direction than the other...

Contest away.  I expected nothing less.

London to Sydney is normally going to spend a lower proportion of time 
in favourable jet streams than say New York to London where I think they 
can often take great advantage from the North Polar Jet Stream.  The 
great circle path from NY to London is pretty close to the normal jet 
stream position and they are at the right altitude.  London to Sydney on 
the other hand you cross the generally weaker Sub-Tropical Jets more 
obliquely.  They are also at an altitude generally higher than 
commercial flights.

I allowed for some slippage by using 'approximately'.  I'm guessing but 
I think the difference for Sydney-London vs. London-Sydney would be 
negligible or in the low single digit % - all other things being equal. 
  Note that it requires a re-fueling stop either way in current 
commercial airliners.  It is a damned long haul.

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