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violation of Newton's laws
John Denker (talk | contribs) (violation of Newton's laws) |
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The fact is, the altimeter setting is '''not''' the same | The fact is, the altimeter setting is '''not''' the same | ||
thing as the sea | thing as the pressure at sea level (Psl), especially when | ||
airmass has a non-standard temperature profile. | the airmass has a non-standard temperature profile. | ||
The altimeter setting is something | The altimeter setting is something | ||
else; it is properly called the altimeter setting. It | else; it is properly called the altimeter setting. It | ||
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who fly only in the US may be unfamiliar with the QNH | who fly only in the US may be unfamiliar with the QNH | ||
terminology. | terminology. | ||
In the Remarks section of a METAR, you can sometimes | |||
find the ''Reduced'' Sea Level Pressure, which is | |||
unfortunately denoted SLP. This METAR SLP serves | |||
the same function as the altimeter setting. Despite | |||
its name, the METAR SLP is not equal to the honest-to-goodness | |||
pressure at honest-to-goodness sea level (Psl), as | |||
discussed in more detail on | |||
[http://www.av8n.com/physics/altimetry.htm jsd altimetry page]. | |||
There needs to be a facility whereby routines that need | There needs to be a facility whereby routines that need | ||
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needs to be reviewed, to separate proper references | needs to be reviewed, to separate proper references | ||
from misconceived references. | from misconceived references. | ||
==== Newton's laws violated by environment.cxx ==== | |||
Consider the following results of an experiment using fgfs: | |||
alt: 662 mM: 0.0288 P: 99000.8462 T: 286.8563 rho: 1.1975 | |||
alt: 3462 mM: 0.0288 P: 89341.6721 T: 281.3920 rho: 1.1009 | |||
alt: 662 mM: 0.0289 P: 99000.8422 T: 256.9910 rho: 1.3404 | |||
alt: 3462 mM: 0.0289 P: 89341.6740 T: 252.0956 rho: 1.2333 | |||
The first pair of lines represent before and after a simple | |||
flight from one airport to another, with a net gain in altitude of | |||
2800 feet, under standard conditions. So far so good. | |||
The second pair of lines represent exactly the same flight, | |||
except that the ambient temperature was 30 degrees colder | |||
than before. You can see that the density (rho) is greater, | |||
in accordance with the ideal gas law. | |||
The problem is that the delta_P is exactly the same for the two | |||
flights. This is a problem because P is connected to the weight | |||
of the air column. If the air is 12% denser, the laws of physics | |||
require it to have a 12% steeper pressure gradient dP/dh ... but | |||
alas this is not observed. | |||
This incorrect pressure profile P(h) has many consequences affecting | |||
engine performance, airfoil performance, altimetry, et cetera. | |||
==== Z-buffer burn-through. ==== | ==== Z-buffer burn-through. ==== | ||