Standard pressure and temperature

[RubEric at aol.com]

In a message dated 3/20/01 10:58:34 AM Pacific Standard Time, 
audi at mediaone.net writes:

<<  >  This can make a big difference - at 100 degrees F and 10,000 feet
 > (altitude
 > >  of Leadville, CO, for instance), the density altitude is now equivalent
 > to
 > >  about 15,000 feet, and the outside air pressure is only 15 inches of
 > >  mercury, which means we need THREE bar showing on the boost gauge to get
 > >  sea level air pressure (1 bar) plus .5 bar boost (total 1.5 bar) in the
 > >  manifold and thus sea level performance.

No. You still need TWO bar on the boost guage to equal sea level performance. 
 If the maximum you can get at sea level is 2 bar, you will get 
proportionately less at altitude.

The boost guage is absolute. At 18,000 feet the guage would read .5 bar (or 
15 inches of mercury, or 500 millibars, or ~7psi).  If your turbo/engine 
combination is CAPABLE  of generating  15 lbs of boost (1 bar), your guage 
then would read 1.5 bar at max boost. To get 2 bar on the boost guage, you 
would need a turbo/engine combination capable of generating 22.5 lbs of 
boost. 

(Note: A racing P-51 pulls about 120 inches of manifold pressure in racing 
trim. That is about FORTY FIVE lbs of boost!!!!!  Normal maximum boost for 
the P-51 in wartime trim was about 60 inches for take off.)


 
 <<<can you even *breathe* at 0.5 bar???  Just barely.  In an unpressurized 
aircraft, a pilot must breath supplemental oxygen above 10,000 feet but a 
passenger is nor required to breath supplemental oxygen until 12,000.  People 
do heavy work above 12,000 feet, however.  It does require some acclimation 
to avoid "altitude sickness".  The acclimation is to give the body time to 
generate additional red blood cells in order to extract the necessary oxygen 
from the lower pressure air with lower partial pressure of oxygen. 

Atmospheric pressure is half of sea level pressure at about 18,000 feet.  
There are other considerations of partial pressure of gases that are involved 
with being able to breathe not at issue with a turbocharged engine.


  >>