?
Solved

Another density altitude question

Posted on 2013-06-29
4
Medium Priority
?
451 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 2000 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

A Guide to the PMT, FV, IPMT and PPMT Functions In MS Excel we have the PMT, FV, IPMT and PPMT functions, which do a fantastic job for interest rate calculations.  But what if you don't have Excel ? This article is for programmers looking to re…
We are taking giant steps in technological advances in the field of wireless telephony. At just 10 years since the advent of smartphones, it is crucial to examine the benefits and disadvantages that have been report to us.
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…
I've attached the XLSM Excel spreadsheet I used in the video and also text files containing the macros used below. https://filedb.experts-exchange.com/incoming/2017/03_w12/1151775/Permutations.txt https://filedb.experts-exchange.com/incoming/201…
Suggested Courses

762 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