ISA

This forum has been developed to discuss aviation related topics.

Moderators: lilfssister, North Shore, ahramin, sky's the limit, sepia, Sulako, I WAS Birddog

Post Reply
Edo
Rank 7
Rank 7
Posts: 574
Joined: Wed Feb 18, 2004 8:39 pm

ISA

Post by Edo »

Im having a brain fart (or i just used my last cell up) anyway

How do you calculate ISA

ie: at 10,000 OAT +5 so this is ISA +/_ what?
---------- ADS -----------
 
RB211
Rank 4
Rank 4
Posts: 283
Joined: Sun Feb 15, 2004 10:21 pm

Post by RB211 »

10,000 ft & 5c is ISA + 10.

Using a standard lapse rate of 2c/1000ft (I know 1.98) and 15c at SL gives an ISA temp at 10,000 ft of -5c. (20c temperature decrease for 10,000 ft). At least I hope so!!! :D
---------- ADS -----------
 
Anti-Ice
Rank 3
Rank 3
Posts: 126
Joined: Wed Feb 18, 2004 8:48 pm

maybe?

Post by Anti-Ice »

I believe ISA assumes 15 degrees C @sea level. Average adiabatic lapse rate is about 2 degrees C/1000 feet above sea level. Thus 10000 feet equals 20 degrees. Thus 15 - 20 degrees = -5 degrees celcius (ISA @ 10,000) Therefore your given temp of 5 degrees is ISA +10.

No guarantees but that is what I recall. :?:
---------- ADS -----------
 
ahramin
Rank Moderator
Rank Moderator
Posts: 6032
Joined: Tue Feb 17, 2004 5:21 pm
Location: Vancouver

Post by ahramin »

Adiabatic refers to change in temperature as the air itself moves up or down, not the change in temperature as you move up through the air mass.

ISA Standard lapse rate is 1.98°C per 1000 feet and ISA standard temperature at sea level is 15°C.

And this post is guaranteed (if its wrong you can have a new one).

ahramin
---------- ADS -----------
 
Edo
Rank 7
Rank 7
Posts: 574
Joined: Wed Feb 18, 2004 8:39 pm

Post by Edo »

Thanks.
I was using the same lapse rate and getting 20 degree change. but taking 20-15 and getting +5 instead of using std temp minus the change (15-50) and getting -5 or ISA +10
---------- ADS -----------
 
Post Reply

Return to “General Comments”