Solved

Another density altitude question

Posted on 2013-06-29
4
450 Views
Last Modified: 2013-06-29
I asked a similar question to this on experts exchange. I am trying out a few more just to make sure I am doing the calculation correctly. I am close to the answer but not getting the exact answer:

"You are planning your departure from your regular aerodrome at 1032ft elevation. The temperature is quite high at 30 degrees Celsius. The QNH is 1014mb. What is the approximate density altitude"


1. I need to calculate the pressure altitude.
PA= airfield elevation +(30x(1013-1014))
PA=1032 + (30x-1)
=>1002

2. Calculation of density altitude
DA=PA + (120xISA deviation)

When calculating ISA deviation, should I use the calculated pressure altitude or the aerodrome altitude(I think it should be the pressure altitude, just wanted to check).

15 degrees at sea level and -2 for every 1000 feet so isa temperature should be 13 degrees but in fact it's 30 degrees giving a difference of 17 degrees.

DA = 1002 + (120x17)
1002 + 2040
=>3042

I wanted to check that my calculation is correct as the book is 3000 feet giving a difference of 42 feet?

Cheers,

Ross
0
Comment
Question by:ross13
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
4 Comments
 
LVL 24

Expert Comment

by:aadih
ID: 39286764
Use the formula:

DA=1.24 PA + 118.8 OAT - 1782

where DA=density altitude and PA=pressure altitude where PA=Hgt+30(1013-QNH)

Reference:

http://en.wikipedia.org/wiki/Density_altitude >

You do the calculation. ;-)
0
 
LVL 24

Accepted Solution

by:
aadih earned 500 total points
ID: 39286818
Got it yet?

The differences in answers are because of approximations (used in the formulas).

Your answer (3042), my answer (3024), and the book answer (3000) are all correct. :-)

The ~1.5% difference is within the acceptable margin for approximation errors.
0
 

Author Closing Comment

by:ross13
ID: 39286840
I downloaded an app onto my ipad and got a slightly different answer as well:-)

Thanks for the help.

Cheers
0
 
LVL 24

Expert Comment

by:aadih
ID: 39286845
Great.  A good (re)learning experience for me also.  So the pleasure is all mine, i.e., ours.  :-)
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction On a scale of 1 to 10, how would you rate our Product? Many of us have answered that question time and time again. But only a few of us have had the pleasure of receiving a stack of the filled out surveys and being asked to do somethi…
Article by: Nicole
This is a research brief on the potential colonization of humans on Mars.
Although Jacob Bernoulli (1654-1705) has been credited as the creator of "Binomial Distribution Table", Gottfried Leibniz (1646-1716) did his dissertation on the subject in 1666; Leibniz you may recall is the co-inventor of "Calculus" and beat Isaac…
Finds all prime numbers in a range requested and places them in a public primes() array. I've demostrated a template size of 30 (2 * 3 * 5) but larger templates can be built such 210  (2 * 3 * 5 * 7) or 2310  (2 * 3 * 5 * 7 * 11). The larger templa…

705 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question