CHAPTER 1 Introduction to Aeronautics What is Aeronautics? Aeronautics Versus Aerospace Before there can be a discussion about aeronautics, it must be defined a bit better. Aeronautics is the science of designing an airplane or other flying machine, There are four basic subjects that aeronautical engineers must understand. Aeronautic 航空 Aerospace 航天 Versus 比较，对抗 Tail 尾翼 Aerodynamic 空气动力学 Spin 旋转 Propeller 螺旋桨 Fall apart 分离，分解，崩溃 Aircraft carrier 航空母舰1.How to shape the airplane and its wing and tail so that it slips easily through the air and can lift itself off the ground. This is called aerodynamics. 2. How to control the airplane so that it will be able to turn but not spin out of control. This is called stability and control. 3. How to build an engine (be it jet or propeller) so that the airplane can push its way through the air. This is called propulsion. How to build the airplane so that it wont fall apart when it hits a gust of wind or slams down on an aircraft carrier. This is called structures. Aeronautical engineering should not be confused with aerospace engineering, which deals with things such as rockets and satellites. While rockets must ascend through the atmosphere, they must also navigate through space where there is no air. Their designs and engines have very different requirements than those of airplanes. How Air Moves-AerodynamicsHow Air and other Gases Move-Aerodynamics Aerodynamics is the study of forces (more pushes and pulls) acting on an object because air or another gas is moving around it. These forces are important for the design of airplanes, sailboats, cars, and other objects moving quickly through the air. Buildings, bridges, and windmills are also affected by the wind moving past them, and they also experience aerodynamic forces. The bulk of the sections in this chapter are devoted to understanding the motions of air around objects. When these motions are defined and measured, they contribute to the calculation of the forces on the object. With the aerodynamic forces known, the flight possibilities of the object can be discussed! MeasurementsIn order to determine if the aerodynamic forces on an object are sufficient to allow flight, the forces must be measured. The different contributions of the air moving around the object must be categorized and defined, and they must be quantified. There are specific qualities that are used to categorize and define these contributions. In addition, these qualities need a guideline to measure them by. The guidelines are called units, and the qualities are mass, time, length, and temperature. Unit Units are used to define measurements so that everyone knows exactly how much. They sound very technical, but they are used all over the world in every day examples. It is important to always include the units when talking about measuring a quality. If a bridge designer develops a bridge across a river that is supposed to be 1000 meters long (a measure of length), and one of the builders tells him or her that the bridge is short by 1, what does that mean? If it is 1 centimeter short (1/100 of a meter), it wont be a problem it cant even be seen. If it is 1 meter short, it may cause a problem years later if the river bank erodes away. If it is short by 1% (10 meters), the bridge may not reach the other side of the river! So units are very important! A measurement should always include 2 things: a number and a unit. Some examples everyone may know include things like: there are 20 minutes until recess; it takes 10 days to drive across the country: a desk top is 20 inches wide and 25 inches long; a recipe uses 2 cups of flour; it is 85 degrees outside today. Each of these measurements includes a number and a unit. Recess 休息，休会，切口，凹口，凹槽， 退刀槽，环槽Recipe 处方，配方，诀窍，秘诀Mass Everything, whether it is a solid, liquid, or gas has mass. It is a measure of how much of the substance is involved-how many molecules. Mass is sometimes used interchangeably with weight (more on that in the properties section), even though they are not the same. In the metric system, the units for mass are grams, kilograms (1000grams) or milligrams (1/1000 grams). In the American units (called the English system), the weight of the substance is used, in pounds or ounces. A pound is 16 ounces. Often, abbreviations are used for the units: a gram is g. a kilogram is kg, a milligram is mg, a pound is lb, and an ounce is oz. substance 物质，物体，实体molecules 分子interchangeably 交替的，可拆卸的，可 交换的metric 度规，度量标准，量度ounce 盎司（1盎司28.349克）abbreviation 缩短，缩写Time The easiest way to think of time is how long it takes something to happen. It may take 10 minutes to drive to school; it may take an hour to eat dinner. The units for time are the same around the world: seconds, hours, days, years. In aerodynamics, a common time measurement is how long it takes an object to go fro