Pressure Flashcards
The atmosphere is composed of a variety of gases these are….
Nitrogen (78%)
Oxygen (21%)
Carbon Dioxide (0.04%)
Other
What is atmospheric pressure defined as?
Combined weight of gases exerting force in all directions
What is used to measure atmospheric pressure?
A Barometer
What is pressure expressed as?
Inches or Millibars of Mercury
Millibar
Hectopascal
A hectopascal is equal to…
100 newtons per square metre
What is an isobar?
The line on the map to indicate locations of the same pressure
What happens to pressure as you increase altitude?
Reduces
What is the ISA pressure at sea level?
In HPA, Hg and lb/sq.in
- 25 HPA
- 92Hg
- 7lb/sq.in
What is QNE (Question Nil Elevation)?
Setting 1013 on aircraft subscale
QNE is a pressure setting of 29.92 inches or 1013 hPa that will produce a standard atmosphere altitude and provides the basis for flight levels.
With QNE set on the altimeter, the main scale will indicate?
Height above or below 1013 HPA Pressure level
Pressure height or Pressure Altitude
At low level, the pressure reduces at a rate of…
1 HPA / 30ft of altitude increase in the troposphere
=1 Hg / 1000ft
Air density refers to….
Mass of air occupying a given volume
What 3 factors does air density depend on?
- Temperature
- Humidity
- Pressure
Decreased Pressure= …. Density
Decreased Density
Increased Temperature=
Decreased Density
Increased Humidity=
Decreased Density
Does high density give better or worse aircraft performance?
Better
Why do variations in pressure occur?
- The movement of pressure systems
- Changing the intensity of pressure systems
- Semi diurnal Pressure variation
What is semi-diurnal variation?
Rhythmic variation in pressure over 12 hour period
Where is semi-diurnal variation the greatest?
Tropics
Can change up to 5 HPA
What is standard pressure?
1013.25 HPA
What is the actual mean sea level pressure referred to as?
QNH
When QNH is set on altimeter it will read…
Altitude (Height above mean sea level)
What is local QNH?
Actual sea level pressure for a particular location
