Atmospheric Pressure (Standard Atmosphere, Pressure and Density Altitude) Flashcards
What is standard atmospheric pressure at sea level? (Temperature & Inches Mercury)
29.92” Hg
59 F or 15 C
What is a standard temperature lapse rate?
3.5 F or 2 C for every 1,000 foot elevation gain up to 36,000 feet.
Above 36k, temperature considered constant until at 80k.
What is a standard pressure lapse rate?
Pressure decreases at 1” Hg per 1,000 foot gain up to 10,000 feet.
What is Pressure Altitude?
A theoretical height where the pressure is equal to 29.92” Hg.
How do you find the Pressure Altitude?
Set your altimeter to 29.92”
Altitude displayed is pressure altitude.
What is Density Altitude?
Pressure altitude corrected for non-standard temperatures.
Vertical distance above sea level in which a given air density is found.
What does Air Density negatively affect?
1) Power - The engine takes in less air.
2) Thrust - The propeller is less efficient in thin air.
3) Lift - Thin air exerts less force on the airfoils.
Low Density Altitude = _____ Indicated Altitude?
High or Low
Low Indicated Altitude
Think LOW and DENSE.
Air is MORE dense at low altitude.
High Density Altitude = _____ Indicated Altitude?
High or Low
High Indicated Altitude
Think HIGH and LESS DENSE.
Air is LESS DENSE at high altitude.
What two parameters do you use to calculate Density Altitude?
Pressure Altitude + Temperature
How do you calculate Density Altitude?
Find Pressure Altitude and then correct it for non-standard temperature variations.
What factors affect Density Altitude?
Altitude
Temperature
Humidity
What effect does temperature have on Density?
At constant pressure:
An increase of temperature = a decrease of density, and vice versa.
What effect does water vapor have on Density?
Water Vapor = Lighter than air.
Moist air is lighter than dry air.
More water content = less density.
How does temperature affect humidity?
Temperature increases allow the air to hold greater amounts of water vapor.
