ISA

[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?

[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!!!

[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.

[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

[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