Aerodynamics part 1.0 Atmosphere

Atmosphere  : The gaseous envelope surrounding earth
aviation takes place around first 60k feet.

Gas composition : Nitrogen 78 % ; Oxigen 21 % ; Other gases 1%
Those proportions do not change with altitude.

Oxigen  : 1. for the sustenance of life
                 2. The combustion of materials.

Water vapour : 1. Responsible for weather around the earth ( turn affects aircraft operations and
                             performance
                         2. May cause icing of the airframe or engine which may impair an aircraft
                             performance

Region Atmosphere : 1. Troposphere : Temp. decreases  with an increase of height
                                                              (all significant weather occurs here)
                                   2. Tropopause : - Upper limit of tropopause    
                                                             - Temp. stops decreasing with an increase of height.
                                   3. Stratosphere : - From tropopause 50 km above sea level,                            
                                                              - Temp steady , increasing in height
                                   4.Thermosphere / Ionosphere : - Temp. increases with height/ altitude increases

Units 
1.Heat is transform of energi,
2.Boiling point of water : 100 C / 212 F / 373 K
3.Melting  point of water : 0 C/ 273 K

Convert temp :

F = (9/5)C + 32
C = (5/9)(F-32)

Temp Variation in the troposphere :
1. At Ground Level, Temp increases with a decrease of latitude
2. With increasing altitude,  temp will usually decrease with height up to the tropopause

Typical values of temp found at the tropopause :
Latitude             Temp (C)
equator               -80
45 N/S                -56
Poles                  -45

Lapse rates
The International Standard Atmosphere (ISA) value : 1,98 C / 1000 feet.

a reduction of density reduces lift.!!

Pressure :1. The force exerted on a unit area
                 2. In the atmosphere, pressure is caused by the mass of gaseous molecules acting under the                      force of gravity on a given area.

Pressure = Force / Area = (Mass x Acceleration) / Area

Units : 1 Newton = 105 dynes

Variation of Pressure in the atmosphere
At Sea Level :  Altitude (ft) = 0
                         Pressure in (mb)  = 1013.25;
                                       in (psi) = 14,7;
                                       in (Hg) = 29.92;
                                       in ( mm Hg)  = 760;

Pressure Altitude : 
The Altitude at which given pressure occurs in the international Standard Atmosphere

The cold air would have greater mass than the warm air due to the density difference. However it caused by the mass of overlying molecules on a unit area.

Density : Mass per unit volume of a substance

Density = Mass / Volume

at sea level : Density (kg/cu m)  = 1.225;

The reduction in pressure results in a lower density.

Humidity : the mass of water vapour in a given volume of air
Condensation : The phase change of a gas to liquid.
Freezing : the phase change of liquid water to ice