formula for Density ltitude

A

Albert B

Guest
Some time ago several shooters asked for a formula to calculate Density Altitude. Searching the net on aviation sites I found several formulas.
The most accurate in metrical system:

Step 1: Calculate Pressure Altitude (Pa) in mbar – the elevation with Standard Atmosphere conditions.
Pa = h + ((1013.25 – p) x 9.0)
h = elevation you are at (above sealevel)
p = local measured airpressure (mbar)

Step 2: Calculate Standaard temperature (Ts) in °K - the temp forr Pa with Standard Atmosphere conditions.
Ts = (15.0 – (0,0065 x h)) + 273.0

Step 3: Calculate Density Altitude.

DA = Pa + [(Ts/Tr) x (1.0 – (Ts/(Th+273.0))^0.234969)]
DA = Density altitude (m)
Pa = Standard Pressure at elevation h (mbar)
Ts = Standard temp at elevation h (°K)
Tr = Decrease of Standard temp per meter height = 0.0065°C/m
Th = measured temp op elevation h (°C)

a more simplefied formula:
DA = h + (36.15 x [(T+273.0)) – (288.15 x 0.0006 x h)]
DA = Density altitude (m)
h = elevation above sealevel (m)
T = local temp (°C)
288.15 x 0.0006 = correctionfactor voor Standard Temperature at elevation h (°K)
-----
I guess you can change this to inches and feet yourself easy.
1m = 3.28ft, 1 degree F = (9/5*degree C)+32

Albert B
(The Netherlands)

Edited:
This part of an article:

The first step in computing density altitude is to determine the pressure altitude by setting 29.92 in the Kollsman window
of the balloonaltimeter, if equipment is anolder type, or bydialing in 29.92 in the digital display of the altimeter of the
Ballor other electronic instrument pack. The indicatedaltitude isthe pressure altitude.
The second step in computing density altitude is to determine the effect ofthe actual air temperature on the airdensity.
The standard temperature of the atmosphere is 15ºC (59ºF) at sea level with a decrease of 2ºC (3.5ºF) per 1,000 feet (This
is the standard temperature lapse rate.). Each degree Celsius variation from the standard temperature changes the density
altitude approximately 120 feet. If the actual temperature is below standard for the pressure altitude, the density altitude
islowered; if the temperature is above standardfor the pressure altitude,the densityaltitude is raised.
Temperature variation is incorporated into a formula for obtaining density altitude from a known pressure altitude:
PA + (120X V)= DA
Where PA is pressure altitude;
120 is the temperature constant;
V isthe variation of the actual temperature from standardatthe pressure altitude; and
DA isthe densityaltitude.
 
Last edited by a moderator:
Back
Top