Talk:Density altitude

Leading Sentence
"Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation"

Is it just me or does that make no sense at all? Where are you measuring it except at the place of observation? Does this mean "the altitude that the ISA table says it must be for the density you just measured". In other words, the ISA converts density to altitude? Nerfer (talk) 03:21, 12 April 2013 (UTC)


 * It makes even less sense to me as it reads now in 2020. "The density altitude is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation." I came here, following a friend's explanation of it, expecting to find a more detail scientific explanation, but the first sentence is already incomprehensible. What does it mean for an altitude to be "relative to" standard atmospheric conditions? An altitude can be relative to another altitude; it seems like this was written by someone who doesn't know what "relative to" means.


 * How about this? "Density altitude is a measure of air density, expressed as the altitude that corresponds to a given air density under standard atmospheric conditions." As with air density, air pressure, temperature, humidity, etc., we can then talk about the density altitude observed at a given place and time, but places and times of observation aren't part of the definition of the term, and only make it confusing. Largoplazo (talk) 20:38, 15 February 2020 (UTC)

Units
What are the units of the density altitude given by the equation in this page?

The units are: hPa for $$P_0$$; K for T; The answer is given in ft; To transform to meters multiply the answer by 0.3048.

I have added better unit specification to this page. "Paploo" 2011-06-30

Units, accuracy etc
I am new to this, so excuse me if I am misunderstanding anything, but I don't understand how this formula can give the density altitude if it does not refer to the actual altitude. Testing it, it only seems to give the correct answer at sea level. For example:

Altitude = 6000 feet Temperature = 25 Deg C (298.15 K) Pressure = 1003.25 mb

Using a "rule of thumb" calculation one gets a density altitude of 8940 Feet, but the formula gives 1497 feet.

Am I doing something wrong?

—Preceding unsigned comment added by User: (talk • contribs)


 * You are not doing anything wrong. However, bear in mind that the pressure in the formula is the actual air pressure at your current altitude. A pressure of 1003.25 hPa at a terrain elevation of 6000 feet would translate to a QNH of about 1225 hPa, which is inconceivably high (remember that pressure drops with around 1 hPa per 27 feet increase in altitude, in ISA conditions in the lower parts of the atmosphere). Presumably, the pressure you mention is a QNH, which would translate to an actual pressure of around 1003 - (6000 / 27) = 781 hPa at 6000 feet.

D3burt (talk) 22:40, 11 June 2008 (UTC)

An easier formula reqd
There exist easier rules of thumb formulae for converting from pressure altitude to density altitude which will be nearly as (in)accurate and of more pratcical use. Looking... Paul Beardsell 03:14, 6 January 2007 (UTC)

I've added an easier formula to calculate Density Altitude, hope this is the one you were looking for. We use this for Aviation Meteorology Calculation. Alex Fossaghi 16:21, 19 April 2007 (UTC)

FFS will someone please clean up the following, - Genericise - Resequence - Explain the terms - Lapse rate, etc. as currently its a heap of utterly meaningless sh*te -

Easy formula to calculate density altitude from pressure altitude

This is an easier formula to calculate (with great approximation) density altitude from pressure altitude ..and International Standard Atmosphere temperature deviation

Density altitude in feet = pressure altitude in feet + 118.8 × (OAT − ISA_temperature)

Where:

OAT = Outside air temperature in °C ISA_temperature = 15 °C − 1.98°C / 1000ft × PA

considering that temperature drops at the rate of 1.98 °C each 1000 ft of altitude until the Tropopause (36000ft), usually rounded to 2°C

Or simply:

DA=PA+118.8([PA/500]+OAT-15)

Or even simpler

DA=1.24 PA + 118.8 OAT − 1782

where DA=density altitude and PA=pressure altitude where PA=Hgt+30(1013-QNH) and QNH = QNauticalHeight = Height above sea level — Preceding unsigned comment added by 31.53.156.35 (talk) 18:38, 23 April 2016 (UTC)

Aircraft Safety, item one
"...reduction in air density reduces the wing's lift" is not lift a function of pressure not density? It would seem this is non sequitur, I suggest: "a corresponding drop in pressure caused through a reduction in air desity, reduces the lift a wing can generate at a given velocity"46.208.62.169 (talk) 17:11, 3 April 2014 (UTC)

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