Re: Flying High ?

Date:         03 Mar 98 03:12:49 
From:         rdd@netcom.nospam.com
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
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In article <airliners.1998.358@ohare.Chicago.COM> cmp086@mail.usask.ca writes:
>Nathan Pusey wrote:
>If you were to measure your weight on an aircraft at FL400 and your
>weight at sea level, you would find that you would weigh less at
>altitude.  For example, I weigh roughly 130 pounds at sea level, yet I
>would only weigh perhaps 110 pounds at 40k feet.  There are formulas to
>determine this which can be derived from the relationship:
>
>	F = G*m1*m2/r^2

So...  If the Earth is F1 and you are F2, then F1/F2 -> R1^2/R2^2.  Given an
earth diameter of 6300 kilometers and the fact that at 40,000' you're at 10.1
kilometers, that gives us what, 6300^2/6300^2 = .9968.  So I would anticipate
that if you weigh 130 pounds at sea level, you'll weigh, oh, 130 pounds at
40,000'.

>	Since it is much easier to move an object through a very low-density
>fluid than it is to move it through a higher density fluid, this means
>that an aircraft will require less power in order for it to overcome
>frictional forces due to wind resistance (ie: drag).

This is a happy cooincidence, given the fact that engine power drops
along with density and pressure (your steroid-ridden CFM-56 at 25K lbs
at sea level is going to be making 2-3K lbs at altitude), however, it is
not a primary factor.

The primary factor for flying at high altitude is the thin air.  The
airplane, being an aerodynamic creature, must have a faster inertial
airspeed in order to remain within safe parameters.  Thus, assuming that
engine costs can be kept in reason, one will simply get to the destination
a whole lot faster.  See g3av8tor@aol.com's article,
<airliners.1998.359@ohare.Chicago.COM>, for details.

--
Robert Dorsett                         Moderator, sci.aeronautics.simulation
rdd@netcom.com                         aero-simulation@cactus.org

           "Bother," said Pooh when his engine quit on take-off.