Density Altitude, Effect of Temperature/Pressure/Humidity on Density (Chapter 4: Principles of Flight)

Density varies directly with pressure and inversely with temperature

Air density is affected by changes in altitude, temperature, and humidity

Effects of Humidity on Density

- Decrease in overall aircraft performance in high humidity conditions (high temperature and high water vapour) - Increases density altitude as air is less dense and lighter due to presence of vapour

Effect of Pressure on Density

- Density is directly proportional to the pressure at a constant temperature - Doubling pressure results in doubling of density - Lowering pressure results in lowering of density - Pressure decreases with increasing altitude, thus density will have the same decreasing effect - Pressure has a dominating effect over temperature as a large drop in pressure results in a large drop in density

Effect of Temperature on Density

- Density is inversely proportional to the temperature at a constant pressure - Increasing temperature, decreases density - Decreasing temperature, increases density

Density of air has significant effects on the aircraft's performance because as air becomes less dense, it reduces:

- Power because the engine takes in less air - Thrust because a propeller is less efficient in thin air - Lift because the thin air exerts less force on the airfoils

Humidity

- The amount of water vapor contained in the atmosphere and is expressed as a percentage of the maximum amount of water vapor the air can hold - Amount varies with temperature - Warm air holds more water vapour whilst cold air holds less

Effect of Moisture on Density

- Water content of air increases, air becomes less dense, increase in density altitude and decrease in performance - Moist air is lighter than dry air, hence less dense

How to find Density Altitude

1) Find pressure Altitude 2) Correcting this altitude with the nonstandard temperature variation

Density of the air increases (lower density altitude), aircraft performance increases;

Air density decreases (higher density altitude), aircraft performance decreases

High-density altitude (thin air, less dense) are high elevations, low atmospheric pressures, high temperatures, high humidity, or some combination of these factors

Low-density altitude (thick air, more dense) are low elevations, high atmospheric pressure, low temperatures, low humidity or some combination of these factors

Density Altitude

The pressure altitude corrected for nonstandard temperature. The vertical distance above sea level in the standard atmosphere at which a given density is to be found.