 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
by0ung(at)brigham.net
Guest
|
 Posted: Sat Jul 05, 2008 9:24 am Post subject: density altitude |
 |
|
Flying from Brigham City at over 4000 ft elevation and hot as blazes out side made me think of a formula to figure Density altitude easily.
years ago I found an article that had a formula to help figure Density Altitude… " DA= E+(66*(T-(59-(E*0.0054))))"
where:
* = Multiply
DA = Density Altitude
E = elevation in feet
T = Temp in deg F
0.0054 = laps rate per ft(or 5.4 Deg / 1000 ft)
A faa article on DA stated 3.6 deg Per 1000 ft. instead of 5.4 DEG F / 1000 I guess I don’t know why the difference in the 2 articles.. unless the laps rate changes with humidity levels. using 5.4 in place of 3.6 would allow for greater safety margins.
anyway I did some math skills on the formula and came out with something that is not as plain to understand, maybe. but is a lot easier to accomplish with a very simple calculator. the results seem to be the same.
DA= E*.0054 - 59 + T * 66 + E
boyd young
Boyd Young
Kolb MkIII C 525+ hours and counting
Brigham City Utah.
[quote][b]
| | - The Matronics Kolb-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kolb-List |
|
|
|
| Back to top |
|
 |
by0ung(at)brigham.net
Guest
|
| Posted: Mon Jul 07, 2008 6:10 am Post subject: density altitude |
|
|
I received this reply back direct from Robert in reference to the formula for density altitude. Included is his text and my reply.
Boyd
| Quote: | >>>>>>>>>>>>>>>>>>>>>>>>>
Boyd --
I could be wrong, but I think the 3.6-degrees is in Centigrade, and
the 5.4-degrees is in Fahrenheit...
I also could be wrong, but, I think the formula -only- works right if
you use the degrees-Centigrade.
-- Robert
>>>>>>>>>>>>>>>>>>>>>>>>>
|
I checked both sources (again) and they both say DEG F.
And I have checked the formula against the automatic weather observation system, awos at the Brigham airport and they are very close.
Also I checked with John Williamson a couple years ago and he uses 2 deg C when figuring the laps rate/ 1000 ft, in changing from deg c to deg f the formula is c * 9 / 5 = f when just talking deg of change. When converting c to f with reference to a thermometer you have to change the formula to c * 9 / 5 + 32 = f using the first formula. 2 deg c change of temp = 3.6 deg F change... and 2 Deg c on the thermometer = 35.6 deg F
if you convert 3.6 ( thinking it was in C) it equals 6.48 deg f...and that does not seem correct.
I did some checking on the internet and looked up laps rate, or adiabatic laps rate, and as I recall there were terms like standard laps rate and variable laps rate, and it seems that the atmospheric conditions Humidity, if the air was ascending or descending, or if there was moisture going into or out of condensation mode made the difference. I know from being in the heating business,,,, there is a term "latent heat of vaporization" it describes a condition where if you can condense the byproducts of water vapor in the combustion process,,, you can gain up to 9% of additional heat in the process, whether you are heating air or water with the appliance. Where the standard laps rate had reference to a stationary mass of air and the temp drop due to a drop in air pressure at higher altitudes.
One last thing I should have mentioned the one article said the 66 in the formula was the density altitude change for each deg F of change from the standard day. and if you were working with deg C. the number in the formula would have to be 118.8 (foot change / deg c)
Boyd Young
Kolb MkIII 912
525 + hours and counting
Brigham City Ut.
[quote][b]
| | - The Matronics Kolb-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kolb-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
