AER 416: Part 3 Standard Atmosphere

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary purpose of using a standard atmosphere in engineering?

  • To accurately simulate extreme atmospheric conditions.
  • To represent the daily weather conditions.
  • To provide a reference for design and performance assessment. (correct)
  • To measure the precise local temperature.

The standard atmosphere starts at an altitude that is different from sea level.

False (B)

What is the standard sea level temperature in Celsius?

15

The geometrical altitude, denoted as ______, measures the height above sea level.

<p>hG</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Geometrical altitude = Height above sea level Absolute altitude = Height from the center of the earth Standard sea level pressure = 101,325 Pa Standard sea level density = 1.225 kg/m3</p> Signup and view all the answers

What does the term 'pressure altitude' refer to?

<p>The altitude from the standard atmosphere table corresponding to a given pressure. (B)</p> Signup and view all the answers

The pressure altitude and the true altitude are always the same.

<p>False (B)</p> Signup and view all the answers

If a standard atmosphere table indicates that a temperature of 265.4 K corresponds to 3500 m, what is the 'temperature altitude'?

<p>3500 m</p> Signup and view all the answers

The density altitude is the altitude indicated in the standard atmosphere for a given ______ value.

<p>density</p> Signup and view all the answers

Match the following altitude types with their definitions:

<p>Pressure Altitude = The altitude from standard atmosphere corresponding to a given pressure Temperature Altitude = The altitude from standard atmosphere corresponding to a given temperature Density Altitude = The altitude from standard atmosphere corresponding to a given density</p> Signup and view all the answers

What is the value of the acceleration due to gravity at Earth's surface (go)?

<p>9.81 m/s² (D)</p> Signup and view all the answers

The density and pressure of air vary linearly with height, similar to water.

<p>False (B)</p> Signup and view all the answers

The hydrostatic equation applies to both compressible and _____ static fluids.

<p>incompressible</p> Signup and view all the answers

What is the result of using go, a constant, rather than g = f(height) in the hydrostatic equation?

<p>It results in a geopotential altitude.</p> Signup and view all the answers

What does 'dhG' represent in the context of the air cube analysis?

<p>The height of the air cube (D)</p> Signup and view all the answers

The forces on the vertical surfaces of the air cube are not considered in the hydrostatic equation since they are not balanced.

<p>False (B)</p> Signup and view all the answers

The hydrostatic equation is a differential equation that relates pressure to _____.

<p>height</p> Signup and view all the answers

What is the primary reason for the difference between geometric height (hG) and geopotential height (h)?

<p>Differences in the value of 'g' (acceleration due to gravity) (D)</p> Signup and view all the answers

The difference between geopotential and geometric height is significant, particularly at lower altitudes.

<p>False (B)</p> Signup and view all the answers

What is the approximate altitude of the tropopause in kilometers?

<p>10</p> Signup and view all the answers

In regions where temperature varies linearly with height, the rate of change is known as the ______.

<p>lapse rate</p> Signup and view all the answers

Match the atmospheric layers with their approximate height ranges:

<p>Troposphere = 0 - 10 km Stratosphere = 10 - 47 km Mesosphere = 47 - 80 km Thermosphere = 80 - 600 km</p> Signup and view all the answers

Which atmospheric layer is characterized by a constant temperature region between 11km and 25km?

<p>Stratosphere (C)</p> Signup and view all the answers

The temperature in the thermosphere consistently decreases with increasing altitude.

<p>False (B)</p> Signup and view all the answers

What is the temperature in Kelvin at the base of the troposphere?

<p>288.16</p> Signup and view all the answers

For isothermal regions with constant temperature, calculations start with the fixed values at the ______, T1, p1, and 1.

<p>base</p> Signup and view all the answers

Which of these is not a region in the standard atmosphere?

<p>Ionosphere (C)</p> Signup and view all the answers

Flashcards

Standard Atmosphere

A standardized model of the Earth's atmosphere used for aircraft design and performance calculations.

Standard Sea Level Conditions

A reference point for the standard atmosphere that represents average conditions at sea level.

Density (ρ)

A key parameter in the standard atmosphere that represents air density or how much air is packed into a given space.

Pressure (P)

A key parameter in the standard atmosphere that represents the force exerted by the air on a surface.

Signup and view all the flashcards

Temperature (T)

A key parameter in the standard atmosphere that represents the average temperature of the air.

Signup and view all the flashcards

Pressure Altitude

The altitude corresponding to a specific pressure value, as defined by the standard atmosphere. It's not necessarily the actual altitude.

Signup and view all the flashcards

Temperature Altitude

The altitude corresponding to a specific temperature value, as defined by the standard atmosphere. It's not necessarily the actual altitude.

Signup and view all the flashcards

Density Altitude

The altitude corresponding to a specific air density value, as defined by the standard atmosphere. It's not necessarily the actual altitude.

Signup and view all the flashcards

Standard atmosphere conditions

The state of air when both temperature and pressure match their standard atmosphere values at that height.

Signup and view all the flashcards

Acceleration due to gravity at Earth's surface ('go')

The acceleration due to gravity at Earth's surface, denoted by 'go', is calculated using the universal gravitational constant (G), the mass of the Earth (me), and the radius of the Earth (re).

Signup and view all the flashcards

Acceleration due to gravity 'g' at height 'hG'

The acceleration due to gravity (g) at a height 'hG' above the Earth's surface is calculated using the acceleration due to gravity at the Earth's surface ('go') and the ratio of the Earth's radius (re) to the sum of the Earth's radius and the height (hG).

Signup and view all the flashcards

What is the hydrostatic equation?

The hydrostatic equation is used to analyze a column of air, similar to a column of water, and it describes the relationship between pressure, density, and height.

Signup and view all the flashcards

Why doesn't air behave like water?

Air, unlike water, is compressible, meaning its density and pressure can change significantly with height.

Signup and view all the flashcards

What is the model used for hydrostatic equation?

The hydrostatic equation assumes a cube of air with a base of 1 meter by 1 meter and a height of dhG, where dhG is a small change in height.

Signup and view all the flashcards

Explain the forces in the hydrostatic equation.

The hydrostatic equation states that the pressure on the lower surface of the air cube, plus the weight of the air inside the cube, must equal the pressure on the upper surface of the cube, ensuring that the forces are balanced.

Signup and view all the flashcards

What is geopotential altitude?

Geopotential altitude refers to a fictitious altitude calculated assuming a constant acceleration due to gravity ('go'), which is different from the actual acceleration due to gravity (g), which varies with height.

Signup and view all the flashcards

How is the hydrostatic equation used to find pressure and density?

The hydrostatic equation can be solved to determine the relationship between pressure and height, or density and height. However, the equation becomes non-linear due to the dependence of acceleration due to gravity (g) on height. Using a constant 'go' simplifies the calculations and leads to the concept of geopotential altitude.

Signup and view all the flashcards

Geometric Height (h)

The height measured along the Earth's curved surface. It's the height we usually think about.

Signup and view all the flashcards

Geopotential Height (hG)

The height measured along a line perpendicular to the geoid, which is an idealized model of the Earth's mean sea level. It accounts for the Earth's curvature.

Signup and view all the flashcards

Lapse Rate

The rate at which temperature changes with height in the atmosphere. It can be positive (temperature increases with height) or negative (temperature decreases with height).

Signup and view all the flashcards

Troposphere

The layer of the atmosphere closest to the Earth's surface, where weather occurs.

Signup and view all the flashcards

Tropopause

The boundary between the troposphere and the stratosphere.

Signup and view all the flashcards

Stratosphere

The layer of the atmosphere above the troposphere, containing the ozone layer.

Signup and view all the flashcards

Stratopause

The boundary between the stratosphere and the mesosphere.

Signup and view all the flashcards

Mesosphere

The layer of the atmosphere above the stratosphere, where most meteors burn up.

Signup and view all the flashcards

Mesopause

The boundary between the mesosphere and the thermosphere.

Signup and view all the flashcards

Thermosphere

The uppermost layer of the atmosphere, characterized by very high temperatures due to absorption of solar radiation.

Signup and view all the flashcards

Study Notes

AER 416: Part 3 Standard Atmosphere

  • Engineers use a standard atmosphere for design and performance assessment.
  • The standard atmosphere represents the average atmospheric conditions at different heights above Earth's surface.
  • The standard atmosphere starts at sea level (height zero).
  • The standard atmosphere data is typically presented in tabular format.
  • Appendices A (SI units) and B (Imperial units) in the course text contain tables of the standard atmosphere.
  • The course material explores the derivation of the standard atmosphere table and how to apply it.

Standard Sea Level Conditions

  • Pressure: 101,325 Pa or 2116.7 lbf/ft²
  • Density: 1.225 kg/m³ or 0.002378 slug/ft³
  • Temperature: 15°C or 288.16 K or 59°F or 518.69 °R

Height Definitions

  • r: Radius of the Earth (6356 km) from its center to sea level
  • hG: Geometrical altitude (height above sea level)
  • ha: Absolute altitude (height from the center of the Earth)
  • ha = hG + r

Acceleration Due to Gravity

  • The acceleration due to gravity, 'g', varies with height.
  • Acceleration due to gravity at Earth's surface (go) = 9.81 m/s².
  • G = universal gravitational constant (6.67x10⁻¹¹).
  • me = mass of the Earth (5.972x10²⁴ kg).
  • g(ha) = (Gme) / (ha)²

Relating g's

  • The relationship between g at height ha and go (acceleration due to gravity at Earth's surface) is: g = go (r² / (r + hG)²).

Hydrostatic Equation

  • The density and pressure of air do not vary linearly with height, unlike water.
  • This is due to the compressibility of air.
  • The analysis of a column of air begins with the hydrostatic equation, similar to analysis using water.

Deriving the Hydrostatic Equation

  • Forces on a cube of air (1m x 1m) in the atmosphere are balanced.
  • The force on the lower surface is p where p= pressure
  • The force on the upper surface is p + dp where dp = small incremental change in pressure.
  • The weight of the air within the cube acts downwards: density(volume of cube)(gravity force(g)).
  • Sum of forces = 0; dp = (density x gravity x height)

Hydrostatic Equation (continued)

  • This leads to a differential equation: dp = -ρ g dh
  • This equation is based on the assumption of a constant value for g, rather than a value function g(h), for simplicity.
  • The use of a constant value for go simplifies the calculations and analysis of the atmospheric effects and pressure.

Isothermal Regions

  • In isothermal regions, the temperature (T) is constant during any pressure variations.

  • The pressure and density change exponentially with height (in an isothermal region).

Gradient Regions

  • In gradient regions, temperature (T) varies linearly with height.
  • The relationship for temperature at any height is T = T1 + a(h - h1) where a is the lapse rate and h1 and T1 are the reference height and temperature.

Pressure, Temperature, and Density Altitudes

  • The standard atmosphere defines pressure, temperature, and density altitudes.
  • For example, a pressure of 61.6 kPa corresponds to a pressure altitude of 4000 m.
  • The pressure/density/temperature altitude is the standard atmosphere altitude that is given for a particular pressure/density/temperature and is not necessarily a reflection of the actual altitude.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

AER 416: Part 3 Standard Atmosphere PDF

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser