AIR Composition Gaseous molecules (oxygen, carbon dioxide, nitrogen...) Particulates ( dust, pollen, water vapor.....) Airplane concerns Molecules ( air molecules) Air molecules are sensitive to heat ( makes them move faster) There are fewer air molecules in a cubic foot of air at 80 degrees than at 50 degrees Air density is determined by molecular motion which is determined by heat (cold air is more dense than hot air) All air movement is caused by heat or a heat differential or mechanical disturbance Air is three dimensional and can move in any direction and at any angle Types of air movement Mechanical ( fan, rotation of earth, solid body moving through air) Heat or heat differential (objects reflecting or absorbing heat energy at different rates) Definitions of air movement Jet Stream- High altitude air movement caused by the rotation of the earth Prevailing winds- General direction of air movement near the surface of the earth and will vary by season Storm winds- Caused by temperature variations within the air in a storm system (rain, hail, sleet, snow and cold air columns falling into warm air near the earths surface) Micro Burst- A small column of cold air falling through warm air at high velocity Wind Shear- The area between two or more air masses that are moving in opposing directions Thermal- A column of warm air that is rising Sea or Ocean Breeze- Caused by the difference in temperature of land and water ( will usually blow toward land by day and will reverse at night) Turbulence- A broad description encompassing many of the above definitions. Turbulent air can be rolling, swirling, rising or falling. Turbulent air masses are usually very small and can appear and disappear very rapidly With the exception of the Jet stream, all of the above affect the performance of a Model Aircraft in one way or another. Air density will affect lift, engine power, and propeller efficiency while air movement will affect flight performance.   Next Page-->