Density Altitude Flashcards
Air density is affected by what 3 factors
- Pressure
- Temperature
- Humidity
The main 2 concerns affecting aircraft performance due to air density are;
- Engine power output
- Aerodynamic lift
What are the pressures (hPa) for the following levels
Sea Level
5000
10,000
20,000
30,000
35,000
Sea Level - 1013
5000 - 840
10,000 - 700
20,000 - 466
30,000 - 300
35,000 - 240
Marry up the following pressures (hPa) to the correct level
1013
840
700
466
300
240
Sea Level - 1013
5000 - 840
10,000 - 700
20,000 - 466
30,000 - 300
35,000 - 240
Air density is DIRECTLY or INVERSELY proportional to atmospheric pressure
DIRECTLY
Less pressure = less dense air
Air density is DIRECTLY or INVERSELY proportional to Altitude
INVERSELY
MORE altitude = LESS dense
In the troposphere, what is the standard temperature lapse rate
(minus) -1.98 ℃
Per 1000 ft
Air is MORE or LESS dense with increase in temperature
LESS
Density altitude is impacted more by which affect;
1. Increase in altitude
2. Decrease in temperature
INCREASE IN ALTITUDE
Air with the highest moisture content is typically found at what altitude and what temperature
- LOW altitude
- GREATER temperature
A defined standard atmosphere is required for what 4 reasons
- Performance calculations
- Traffic Separation
- Expected temperatures at altitude
- Baseline (for forecasts)
What is the pressure lapse rate, and up to what altitude
- -1 hPa per 30 ft
- 20,000 ft
POH performance figures are based on what atmospheric conditions
ISA CONDITIONS
Air Density affects
Why does air density have an affect on engine power
LESS oxygen in air to mix with fuel
Less dense air means less oxygen to mix with fuel, meaning less power to engine
Air Density affects
Why does less dense air have an affect on aerodynamic lift
LESS dense air means LESS lift
Less dense air requires more physical speed from the aircraft to produce the same lift than in more dense air. Thus, at higher altitude, TAS is faster than at lower altitude, but IAS would be the same
When calculating for density altitude;
What 2 correction steps need to be carried out
- Differences in ISA atmopsheric pressure at altitude
- Differences in ISA air temperature at altitude
Define the difference between PRESSURE altitude and DENSITY altitude
- PRESSURE altitude is the altitude we would be at under ISA conditions i.e. 1013 hPa
- DENSITY altitude is the altitude level the aircraft will perform as based on temperature and pressure corrections, irrespective of actual altitude
Example, An aircraft in ISA conditions at 10,000 ft will have better performance than an aircraft at 10,000 ft but where the temperature is +10℃ warmer. This is because the air is warmer. Warmer air is less dense, less dense air means less oxygen to mix with the fuel so less performance
Calculate the difference in pressure altitude
Flying at 4,300 ft with 1032 set on the subscale, what is the pressure altitude
Pressure Alt - ISA Alt
1032 - 1013 = 19 hPa
Lapse rate 1 hPa = 30 ft
19 x 30 = 570 ft
4300 - 570 = 3,730 ft
REMEMBER:
Wind off pressure, Wind off altitude
Wind on Pressure, Wind on Altitude