TABLE OF CONTENTS For computing drag and thrust, it is necessary to know, as functions of altitude, the Earth's atmospheric pressure, density, and speed of sound. These functions follow from the so-called ARDC (Air Research and Development Command, of the U.S. Air Force) model atmosphere, a more accurate model than those used previously (e.g., RAND model). The ARDC model assumes that the air from sea level up to an altitude of roughly 300,000ft (91,440m) is of constant molecular weight and consists of six concentric layers.
In this appendix, the ICAO (International Civil Aviation Organization) standard atmosphere model is used as the flight environment for missiles.
At Sea Level
| T o | = | temperature (288.1667) [kelvin] |
| P o | = | static pressure (101314.628) [ N/m 2] |
At altitude z, an approximation to the standard at mosphere isused. The atmosphere is divided into three zones as follows:
z ? 11,000 m,
1,000 m
z> 25,000 m.
Different formulas are used to find the ambient atmospheric temperature and pressure, T a and P a, in each of the zones.
Zone 1: z ? 11,000 m
Zone 2:11,000 m
Zone 3: z> 25,000 m,
In all three zones, the ambient atmospheric density and the speed of sound are given by
where R is the gas constant (286.99236 [(N-m)/(K p ?K)]. Note that the speed of sound V a, can also...
