Re: Flying High ?

Date:         19 Feb 98 01:34:30 
From:         Paul Hathaway <Paul_Hathaway@ML.Com>
Organization: Merrill Lynch
References:   1
Followups:    1
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Nathan Pusey wrote:
>         Can somebody please explain to me why planes (jet aircraft) fly
> at very high altitudes on long range flights, and how does this conserve
> fuel and get maximum distance ? How does this conserve fuel and save
> time if you can only go half the speed you normally can go at low
> altitude and you have to use twice the amount of power to get too half
> the power you get at lower altitudes ?

Simplest way to think of it is that the time used to attain cruise
altitudes is short in relation to the time spent en route at the fuel
efficient altitudes.  The 'extra fuel" used to get to 35,000 feet is
small compared to the fuel saved by cruising there for 4,5, or 6 hours.
As the air at high altitudes is significantly less dense than air at low
altitudes, the jet encounters less drag as it flies, reducing the amount
of fuel required to "push" the aircraft along.  A jet engine is
essentially an "air pump" which operates just as efficiently at high
altitude (up to a point) as on the ground.  Aircraft also cruise in the
flight levels to avoid much of the weather we experience on the ground,
take advantage of fast moving tailwinds, get improved radio coverage,
and   as a safety margin (ie no terrain to hit, no little planes to
dodge, no birds, sufficient altitude to restart a failed engine etc etc)
Passengers also like the smoother ride.
Hope this helped.