> >
>

# Cold Temp. Corrections

Tech Log The very best in practical technical discussion on the web

# Cold Temp. Corrections

21st Jan 2002, 08:49

Join Date: Oct 2001
Posts: 30
Likes: 0
Received 0 Likes on 0 Posts
Cold Temp. Corrections

I've been looking for a more accurate way of calculating altitude corrections due to cold temps. I have found a number of formula on the subject but most are not very user freindly. I am looking for a formula that I will be able to calculate quickly during flight. So please no crazy formulas involving gravity and what not. Thanks in advance!

21st Jan 2002, 13:13

Join Date: Sep 2001
Location: Netherlands
Posts: 39
Likes: 0
Received 0 Likes on 0 Posts

4 ft per degree centigrade per 1000 ft altiude.

21st Jan 2002, 13:56

Join Date: Apr 1999
Location: Well, this is cheaper than a Personal Title!
Posts: 135
Likes: 0
Received 0 Likes on 0 Posts

Density Altitude=Pressure Alt +/- 120T, where 'T' is the ISA deviation.

i.e. : if PA is 13000' and SAT is -31 C, ISA deviation is, therefore, -20. DA is 13000-(120 x 20) =11600'. Easy, innit?

Okay, spot the deliberate mistake (please see below) <img src="rolleyes.gif" border="0">

[ 21 January 2002: Message edited by: fokker ]</p>

21st Jan 2002, 15:50

Join Date: Oct 1999
Location: U.A.E.
Posts: 226
Likes: 0
Received 0 Likes on 0 Posts

fokker

Using your Formular and numbers, I make it 10,600' da

21st Jan 2002, 18:09

Join Date: Apr 1999
Location: Well, this is cheaper than a Personal Title!
Posts: 135
Likes: 0
Received 0 Likes on 0 Posts

******, really? Hold on......

At 13000', ISA temp is -11 (15-26 at 2 degrees per 1000'). If the SAT is -31, it is 20 deg C colder than it should be, so 'T' is -20. 120 x -20 is -2400, so the answer should be DA of 10600'. Looks like I had the wrong abacus out earlier! Thanks loc-out. Anyway, I promise the method's right, even if I'm a cabbage! <img src="wink.gif" border="0">

[ 21 January 2002: Message edited by: fokker ]</p>

21st Jan 2002, 18:52

Join Date: Oct 1999
Location: U.A.E.
Posts: 226
Likes: 0
Received 0 Likes on 0 Posts

Take comfort in the thought, that even I make mistakes.

22nd Jan 2002, 20:33

Join Date: Aug 2000
Location: UK
Posts: 3,648
Likes: 0
Received 1 Like on 1 Post

I don't think Amateur Turbines was asking about density altitude, but rather the correction required for true altitude.

The quick and dirty formula for that is that your true altitude (strictly, height above datum) is 0.35% lower/higher than your indicated altitude per degree C that the atmospheric temperature is lower/higher than ISA.

e.g. for ISA -10 degC, an indicated altitude of 10350 ft is actually 10000 ft (if the altimeter setting is correct at sea level).

Another way of putting that is 3.5 ft/degC/1000ft. If the difference between that an static's 4 ft/degC/1000ft makes a difference to your health, you're not doing a very good job of height keeping. <img src="smile.gif" border="0">

23rd Jan 2002, 07:37

Join Date: Aug 1998
Location: Ex-pat Aussie in the UK
Posts: 5,787
Received 110 Likes on 54 Posts

If you are interested, this was discussed pretty extensively in the <a href="http://www.pprune.org/cgibin/ultimatebb.cgi?ubb=get_topic&f=71&t=000003&p=" target="_blank">Altimeter Correction Cold WX OPS</a> thread, located in the <a href="http://www.pprune.org/cgibin/ultimatebb.cgi?ubb=forum&f=71&SUBMIT=Go" target="_blank">Tech Log Archive</a>

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off