Posted in Aerospace Engineering

### What is The Continuity Equation

Let us intersect the streamtube depicted in Figure 2-2 with three planes, perpendicular to the airflow at stations 1, 2 and 3, with cross-sectional areas of A1, A2, and A3, respectively.  The amount of mass passing any point in the streamtube may be found by multiplying area by velocity to give volume per unit time and then multiplying by density to give mass per unit time. This is called mass flow (or “m dot” for engineering types) and is expressed: [latexpage] $dm/dt =\rho AV= ^\bullet_m$ Because it is a closed system, the amount of mass flowing through A1 must…

Posted in Aerospace Engineering

### Properties Of The Atmosphere

The atmosphere is composed of approximately 78% nitrogen (N2), 21% oxygen (O2), and 1% other gases by volume, which includes argon and carbon dioxide. Air is considered to be a uniform mixture of these gases, so we will examine its characteristics as a whole rather than as separate gases. 1. Static pressure (PS) is the force each air particle exerts on those around it. On a more macroscopic scale, ambient static pressure (14.7 psi at sea level on standard day) is equal to the weight of a column of air over a given area. The force of static pressure acts…