Appendix B: International Standard Atmosphere

Abstract

The International Standardization Organization (ISO) has defined a standard atmosphere based on the model established by the ICAO in their Document 7488/2, Second Edition, 1964. The data in Table B.1 define the state variables at sea level (SL) and the gravitational acceleration at 45 • northern latitude on which the potential altitude is based. The (absolute) temperature varies linearly in the troposphere between SL and 11 km with a gradient of −6.5 • C/km. The stratospheric layer between 11 and 20 km is isothermal. Instead of absolute quantities, atmospheric state variables are often quoted as fractions of their SL values as follows: • relative temperature: θ = T /T sl • relative pressure: δ = p/ p sl • relative density: σ = ρ/ρ sl Table B.1 Basic properties of the International Standard Atmosphere (ISA) Standard values at SL Pressure p = 1.013250 × 10 5 Pa (760 mm Hg) Temperature T = 15 • C (288.15 K) Density ρ = 1.2250 kg/m 3 Speed of sound a = 340.29 m/s Absolute viscosity coefficient μ = 1.7894 × 10 −5 kg/(ms) Gravitational acceleration g = 9.80665 m/s 2 Other standard values Molar weight of ai M = 28.9644 kg/kmol Gas constant of air R = 287.05287 (J/kg)/K Ratio of specific heats γ = c p /c v = 1.4 Tropopause h pot = 11 000 m Troposphere T = −56.5 • C (216.65 K) Advanced Aircraft Design: Conceptual Design, Analysis and Optimization of Subsonic Civil Airplanes, First Edition. Egbert Torenbeek.