Pressure And Density

Question 1

How to calculate pressure

Answer 1

Force / Area

Question 2

What happens to the weight of air as you go up

Answer 2

It decreases as there are less air particles
As altitude increases, pressure decreases

Question 3

Standard rate of change in pressure

Answer 3

Reduce 1hPa per 30ft

Question 4

What is another unit for a hPa

Answer 4

One milibar
29 inches of mercury

Question 5

How do altimeters work

Answer 5

They sense the change in pressure between the datum point and point we are at

Question 6

What key points could be datum points

Answer 6

QFE
Standard setting
QNH

Question 7

Why are temperature corrections important

Answer 7

If flying in colder air the more compressed air means you could get a reading that is lower than your true altitude

Question 8

What are the lines on an isobar chart

Answer 8

They show the line of equal pressure, between each line is a gap of either 2 or 4 hPa

Question 9

What does it mean if the isobars are close together

Answer 9

It will be very windy
It means there is low pressure created

Question 10

What does QNH use

Answer 10

For every 30ft per hPa
Above mean sea levek

Question 11

What datum start does an isobar chart use

Answer 11

QFF which is the data value used by the MET office

Question 12

How to calculate density

Answer 12

Mass / Volume

Question 13

What happens when temp decreases to density

Answer 13

Volume of air decreases so density increases
Temperature is indirectly proportional to density

Question 14

What is the relationship between density and pressure

Answer 14

Directly proportional as one increases the other does as well

Question 15

Lift / Drag equation

Answer 15

Force = ½ x density x velocity² x surface area x coefficient of drag

Question 16

How to calculate density altitude

Answer 16

120ft per ° ISA deviation (add or minus) from the pressure altitude

Question 17

What I’d the relationship between density and pressure

Answer 17

A nonlinear relationship
Pressure decreases with height

Question 18

How do you measure pressure

Answer 18

Mercury barometer
Aneroid barometer
Barograph

Question 19

What are some key values relating pressure and altitude

Answer 19

10,000ft = 700mb/hPa
18,000ft = 500mb/hPa
30,000ft = 300mb/hPa

Question 20

What is the equation relating temp, pressure and altitude

Answer 20

Height = (96 x Temp in kelvin) / pressure

Question 21

What is QFE

Answer 21

The field elevation pressure at the point you are standing on the airfield

Question 22

What is QNH

Answer 22

The QFE plus the difference in elevation between the airfield height and mean sea level

Question 23

What does if mean if you are at 100ft and your altimeter is set using QFE

Answer 23

Altimeter will indicate 0ft

Question 24

What does it mean if you are at 100ft and the altimeter is set at QNH

Answer 24

Altimeter will indicate 100ft

Question 25

How will a cold atmosphere effect QFF and QNH relationship

Answer 25

It means the airfield will be above mean sea level and QFF is greater than QNH

Question 26

How will a warm atmosphere effect QFF and QNH

Answer 26

It will mean the airfield is below mean sea level and the QFF is smaller than QNH

Question 27

What is a ridge on a weather chart

Answer 27

A line of high pressure

Question 28

What is a trough on a weather chart

Answer 28

A line of low pressure

Question 29

Hat is a col on a weather chart

Answer 29

An area of no pressure change, stays constant

Question 30

What is a secondary depression

Answer 30

A depression that occurs in the same region to a primary depression

Question 32

What is relative density

Answer 32

The prevailing density expressed as a percentage of ISA surface density

Question 33

ISA value for density

Answer 33

1225 g/m³ 1.225 kg/m³

Question 35

What is the relationship between humidity and density

Answer 35

Density is indirectly proportional to humidity

Question 36

What is the effect of altitude on density

Answer 36

Density decreases with altitude even above the tropopause

Question 37

What is the effect of latitude on density

Answer 37

Surface density increases from equator to poles as gets colder However above 26,000ft density will increase from poles to equator

Question 38

What effect does low density have on aircraft operations

Answer 38

Reduced thrust of engines so long take off needed Reduced lift Reduced drag Reduced max take off mass

Question 39

Where would you experience low density

Answer 39

Hot, humid and high airfields