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Standard sea-level conditions (SSL), [1] also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations. The term "standard sea level " is used to indicate that values of properties are to be taken to be the same as those standard at sea level, and is done to define values for use in general calculations.
where a 0 is 1,225 km/h (661.45 kn) (the standard speed of sound at 15 °C), M is the Mach number, P is static pressure, and P 0 is standard sea level pressure (1013.25 hPa). Combining the above with the expression for Mach number gives EAS as a function of impact pressure and static pressure (valid for subsonic flow):
Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. To accommodate the lowest points on Earth, the model starts at a base geopotential altitude of 610 meters (2,000 ft) below sea level, with standard temperature set at 19 °C.
Thus, the handling and 'feel' of an aircraft, and the aerodynamic loads upon it, at a given equivalent airspeed, are very nearly constant and equal to those at standard sea level irrespective of the actual flight conditions. At standard sea level pressure, CAS and EAS are equal. Up to about 200 knots CAS and 10,000 ft (3,000 m) the difference ...
The U.S. Standard Atmosphere model starts with many of the same assumptions as the isothermal-barotropic model, including ideal gas behavior, and constant molecular weight, but it differs by defining a more realistic temperature function, consisting of eight data points connected by straight lines; i.e. regions of constant temperature gradient.
For Pilots: At sea level, Altimeter:29.92 in/Hg at 15 °C (59 °F) The "standard day" model of the atmosphere is defined at sea level, with certain present conditions such as temperature and pressure. But other factors, such as humidity, further alter the nature of the atmosphere, and are also defined under standard day conditions:
Aerodynamics – is the study of the motion of air, particularly with respect to its interaction with a solid object, such as an airplane wing. Aerodynamics is a sub-field of gas dynamics, which in turn is a sub-field of fluid dynamics. Many aspects and principles of aerodynamics theory are common to these three fields.
To allow modeling conditions below mean sea level, the troposphere is actually extended to −2,000 feet (−610 m), where the temperature is 66.1 °F (18.9 °C), pressure is 15.79 pounds per square inch (108,900 Pa), and density is 0.08106 pounds per cubic foot (1.2985 kg/m 3).