Robert W. Mellette
All conventional aircraft operate within the ocean of air that surrounds the earth. Aerodynamic forces created by the interaction of the aircraft with the atmosphere makes flight possible. Atmospheric conditions greatly influence aircraft performance. The density of the air, for example is so critical to performance of an aircraft that pilots use air temperature and pressure to compute a figure called the DENSITY ALTITUDE. This is necessary because the density of the air directly affects both LIFT and DRAG on an aircraft.
It is recommended that students have a good working knowledge of the structure of the earth’s atmosphere. This is a prerequisite to an understanding of the basic aerodynamic principles that follow in the next pages. Students should be familiar with the different regions of the atmosphere and the characteristics of each region. It should be explained that although the earth’s atmosphere extends outwards for hundreds of miles, most of the air lies in the two regions closest to the earth’s surface. These two zones or regions are called the TROPOSPHERE and the STRATOSPHERE. The TROPOSPHERE is the region that extends from the surface of the earth out to an altitude of about 10 miles or 16 kilometers. This is the region in which weather occurs and in which we live. The study of this layer is important not only to the study of weather, but also it is the layer in which Lindbergh=s plane flew. His plane, “ The Spirit of St. Louis “ and all other standard single engine aircraft, that have neither pressurized cabin or supercharged engines have a maximum ceiling of about 17,000 feet above sea level.
A transition zone exist between the TROPOSPHERE and the STRATOSPHERE. It is called the TROPOPAUSE. The TROPOPAUSE is an area of relative calm, but because of the temperature change that occurs within this layer, rivers of swiftly moving air are formed. These fast moving rivers of air are called JET STREAMS. These JET STREAMS flow from west to east. Pilots flying commercial jet aircraft often use these JET STREAMS to get a boost from these “tail winds” when they are traveling east in the TROPOPAUSE.
THE ATMOSPHERE
(figure available in print form)