Archives: Theory Courses

12.4.14 State the ISA sea level pressure and temperature conditions.

12.4.14. State the ISA sea level pressure and temperature conditions.

ISA Sealevel pressure = 1013.2hPa
ISA Sealevel temperature = +15deg C

12.4.12 Explain the basis for the International Standard Atmosphere (ISA).Sub Topic Syllabus Item






ISA



12.4.12. Explain the basis for the 
International Standard Atmosphere (ISA) 

- hypothetical set of atmospheric conditions which represents an average of the conditions experience worldwide

Sea level pressure = 1013.2hPa (hectopascals)
Sea level temperature +15 degrees C
Sea level density 1.225kg/m3 

Lapse rates 		






12.4.14. State the ISA sea level pressure 
and temperature conditions.


ISA Sealevel pressure = 1013.2hPa


ISA Sealevel temperature = +15deg C





12.4.16. State the approximate temperature lapse rate

up to the tropopause.		


The ISA temperature lapse rate up to the Troposhere is 1.98degC per 1000ft. 























12.4.12. Explain the basis for the International Standard Atmosphere (ISA).Sub Topic Syllabus Item 



– hypothetical set of atmospheric conditions which represents an average of the conditions experience worldwide


Sea level pressure = 1013.2hPa (hectopascals)
Sea level temperature +15 degrees C
Sea level density 1.225kg/m3 


Lapse rates

12.4.10 Describe how pressure, temperature and density normally vary within the atmosphere.

12.4.10. Describe how pressure, temperature and density normally vary within the atmosphere.

The pressure, temperature and density will normally all decrease with increasing altitude
Pressure decreases rapidly at lower levels and more slowly at higher levels.
Temperature decreases at a constant rate up to the troposphere.
Density decreases rapidly at lower levels and more slowly at higher levels.
(image)

12.4.8 State the relationship between pressure/temperature and the density of an air mass.

12.4.8. State the relationship between pressure/temperature and the density of an air mass.

Pressure and temperature affect the density of any parcel of air.
High temperature and low pressure will result in low density.
Low temperature and high pressure will result in high density.

12.4.6 Explain how air density varies with altitude within the atmosphere.

12.4.6. Explain how air density varies with altitude within the atmosphere.

Density of air is measured by how many molecules are present in any given volume
Near the earths surface the density is higher than at greater altitudes. It reduces rapidly at lower levels and more slowly at higher levels.

Section 12.4 – Flash Cards

[vfr_FlashCards p1=”12.4″]

What is the International Standard Atmosphere (ISA).

What is the
International Standard Atmosphere (ISA).

Hypothetical set of atmospheric conditions which represents an average of the conditions experience worldwide.
We use as a yard stick / measuring stick to work out how our aircraft will performance in varying atmosphere conditions

Yard stick / Measuring sticks are …
Pressure Altitude.
Density Altitude.
By describing Pressure and Density as Altitude, it far more understandable to most pilot than as many hPa’s or kgs/m3. 

At sea level 
Pressure: 1013.2hPa (hectopascals)
Temperature: +15 degrees C
Density: 1.225kg/m3

temperature reduction with
an increase in Altitude
approximate temperature lapse rate up to the tropopause 

is 2C/1000ft (1.98c/1000ft)

Altitude Temperature
S/l 15c  (S/L Temp-(2 x 1000ft))
1,000ft 13c  = (15-(2×1))
 2,000ft  11c  = (15-(2×2))
 5,000ft  5c  =(15-(2×5))
 10,000ft  -5c  = (15-(2×10))

Air Density.

Density
Note Images

Density of air is measured by how many molecules are present in any given volume

High Density, more molecules in a given area. eg. a metre2

The more dense the atmosphere is the better your wings and engine work on  your aircraft

 [vfr_Pic p1=”density_high.png”]

Low Density, less Molecules in a given area.

 [vfr_Pic p1=”density_low.png”]
Now if we put some molecules into a big tube,
you can see that the molecules at the top of the tube
will be pushing down on the molecules below them,

thus the molecules at the bottom of the tube will be pushed together the closest.
thus are more densely packed.

This is the same as our earth’s  Atmosphere.

Density
Checking out the the Grey boxes,
The one that the bottom contains more molecules
 thus has more Density

and then grey box at the top with less molecules
thus has less Density.

So Density Decrease (along with aircraft performance) with an increase in Altitude. 

Temperature and Pressure

To easily work out what the temperature is you need to understand the effect that pressurising or creating a vacuum has on temperature

A bicycle tyre  pump or a tyre compressor they all heat up hence if air in compressed(pressure Increased) the air temperature will increase.


If you create a vacuum like inside your carburettor e.g. carb icing the temperature will decrease. 

So how to work out the pressure difference?

This is really simple just have a look at the distance between the molecules.

If the molecules are close together the pressure is high 

if that further apart the pressure is lower.

So what you notice by studying our column of air,

 is the pressure is higher thus temperature is greater at the lower levels.

 At the top of the column the pressure is lower and also the temperature is the coldest.


So Pressure Decreases with an increase in Altitude
and 
So dose Temperature Decrease with an increase in Altitude

 [vfr_Pic p1=”density_column.png”]

12.4 The Atmosphere

12.4 Atmosphere
Subject Key Points

12.4.2. Name the principal gases

which constitute the atmosphere.

Oxygen – 21%

Nitrogen – 78%
1% – others. neon, argon, CO2 etc 
12.4.4. Define air density. 
Density of air is measured by how many molecules are present in any given volume

Near the earth’s surface the density is higher than at greater altitudes 
12.4.6. Explain how air density varies with altitude within the atmosphere. 
Density of air is measured by how many molecules are present in any given volume

Near the earth’s surface the density is higher than at greater altitudes. It reduces rapidly at lower levels and more slowly at higher levels.
12.4.8. State the relationship between pressure/temperature and the density of an air mass. 
Pressure and temperature affect the density of any parcel of air.

High temperature and low pressure will result in low density.
Low temperature and high pressure will result in high density. 
12.4.10. Describe how pressure, temperature and density normally vary within the atmosphere.

The pressure, temperature and density will normally all decrease with increasing altitude

Pressure decreases rapidly at lower levels and more slowly at higher levels.
Temperature decreases at a constant rate up to the troposphere.
Density
decreases rapidly at lower levels and more slowly at higher levels.
(image) 
12.4.12. Explain the basis for the International Standard Atmosphere (ISA) – hypothetical set of atmospheric conditions which represents an average of the conditions experience worldwide

Sea level pressure = 1013.2hPa (hectopascals)
Sea level temperature +15 degrees C
Sea level density 1.225kg/m3 

Lapse
rates 

12.4.14. State the ISA sea level pressure and temperature conditions. 
ISA Sealevel pressure = 1013.2hPa

ISA Sealevel temperature = +15deg C
12.4.16. State the approximate temperature lapse rate up to the tropopause. 
The ISA temperature lapse rate up to the Troposhere is 1.98degC per 1000ft. 

Section 12.2 – Flash Cards

[vfr_FlashCards p1=”12.2″]