Lecture 2 - Introduction to International Standard Atmosphere (ISA) PDF

# Lecture No. 01.2: Introduction to International Standard Atmosphere (ISA) ## Aerospace Vehicles The main categories of aerospace vehicles are: - **Atmospheric vehicles**: Vehicles which fly in the Earth's atmosphere only, such as: - Helicopters - Airplanes - **Space vehicles:** Vehicles...

# Lecture No. 01.2: Introduction to International Standard Atmosphere (ISA) ## Aerospace Vehicles The main categories of aerospace vehicles are: - **Atmospheric vehicles**: Vehicles which fly in the Earth's atmosphere only, such as: - Helicopters - Airplanes - **Space vehicles:** Vehicles which fly in deep space, such as: - Satellites ## Why do we need ISA? - **ISA** (International Standard Atmosphere) is a hypothetical model utilized for: - Design and performance determination for aerospace vehicles - Simulation and Analysis - Relating flight test and wind tunnel results to a common reference for aircraft design and performance - It provides a constant model in lieu of the variable characteristic of the actual Earth's atmosphere. ## What are these different altitudes? - **Geometric altitude**: Measured as vertical distance from mean sea level. It is also known as **true altitude**. - **Absolute altitude**: Measured as vertical distance from the center of the Earth. - **Geopotential altitude**: A variation in gravitational acceleration (g) is considered with respect to altitude. This concept is applied only for space vehicles. - **Pressure altitude**: Measured based on the pressure at a specific altitude. - **Temperature altitude**: Measured based on the temperature at a specific altitude. - **Density altitude**: Measured based on the density at a specific altitude. For the study of atmospheric vehicles, the *geometric altitude* is used for now. The other 5 types of altitudes will be studied in later lectures. ## Indicated Altitude - Indicated altitude is what the pilot sees on the altimeter, as shown in the image of an aircraft cockpit. ## True altitude - True altitude is the geometric altitude, measured as the vertical distance above mean sea level. ## Absolute Altitude - Absolute altitude is the distance from the center of the earth to the specific altitude. This is related to the geometric altitude and radius of the Earth with the formula: $h_a = h_g + r$. - See figure with diagram of a spherical earth. ## Geopotential Altitude - Geopotential altitude takes into account the variation of gravitational acceleration (g) with altitude. - The formula is: $g = g_0 * (r/h_a)² = g_0 *(r/r+h_g)²$. - The formula defines $h$ (geopotential altitude) as: $h = \frac{rh_g}{r+h_g}$ - Geopotential altitude is used for calculation related to space vehicles only. ## Hydrostatic Equation - The hydrostatic equation models the force balance of a fluid element at rest in a gravitational field. - The equation is $p = p + dp + \rho g dh_g$ - The derivative form of the equation is $dp = - \rho g dh_g$ ## LAYOUT - This lecture covers Earth's atmosphere, and related atmospheric standards - It introduces the various types of altitudes - It introduces the two main equations for calculating pressure and density of a fluid element at rest. - It discusses Q code standards used to communicate altitudes in air traffic control communication. - It will be followed by another lecture on the effects of weather. ## Atmosphere - Earth's atmosphere is a blanket of air surrounding the planet. - It is essential to support life on Earth. - The composition of the atmosphere is mainly: - Oxygen ($O_2$): 21% - Nitrogen ($N_2$): 78% - Others: 1% ## Layers of the Atmosphere - The Earth's atmosphere can be divided into several layers, which can be described as the "layers of the atmosphere". - They are: - **Troposphere**: The lowest layer, where most weather phenomena occur. - **Stratosphere**: Contains the ozone layer, which absorbs harmful ultraviolet radiation from the Sun. - **Mesosphere**: The coldest layer of the atmosphere. - **Thermosphere**: The hottest layer, where the temperature increases with altitude due to the absorption of solar radiation. - **Ionosphere**: A region in the upper thermosphere where atoms and molecules are ionized by solar radiation. - **Exosphere**: The outermost layer of the atmosphere, where the atmosphere gradually fades into space. ## AEROSPACE VEHICLES (continued) - This section explores the different types of aerospace vehicles. - The goal is to understand **why we study these vehicles**. - Through this study, we can investigate their design and performance characteristics.