IAS to TAS formula

[Smurfjet]

Greetings all,

I am working on an Excel Flight Log spreadsheet, and was wondering if I had the OAT and the Density Alt I can convert IAS to TAS?

Is there a formula to do that? Or should I rely on my trusty E6B? :)

Jost poking some fun with Excel :)

Cheers

[Tinstaafl]

Jeez, I'd love to see the MS E6B extensions to Visual Basic to allow Excel to interface... :)

I'm sorry, I have the formula but I'm in the UK & it's in my files back in Oz! Damned if I can remember it.

[Smurfjet]

Hmm, where'd I hear this before! :)

Thanks for thought though :)

cheers

[The The]

Try here

http://www.best.com/~williams/avform.html#Mach

[BOING]

If you want a quick mental conversion that works quite well at lower altitudes.

TAS = IAS + (IAS/60 x Ht (in thousands of feet))

IE TAS = 240 + (240/60 x 10)
= 280

Try it and see if the answers are close enough for your use.

------------------

[supermunk]

The formulae at Ed Williams Aviation Formulary (url above in the post by The The)work to 2/3 places of decimals and match up with all the FMS readouts that I have seen. However... can anyone tell me what the value of "k" is for a typical installation?

[TOGA_Party]

Smurfjet,
Not so much a formula as a 'rule of thumb'. Works when conditions are close to ISA and at altitudes not flight levels.

The TAS and IAS will vary by 1.8 kts/1000'.

eg. If we're cruising at 10'000 and indicating 145kts then TAS will be 163kts.
ie 1.8(kts/1000')X 10(lots of 1000')= 18kts

145kts (IAS)
+
18kts = 163kts (TAS)

Also works just as well the other way around!!

[fart]

This will give you a quick answer that comes faily close to the real deal:

Use 2% of IAS per 1000 ft and add to IAS:

Example: IAS is 200 Knots at 25 000 ft
therefore 2% X 25000 divide by 1000 = 25
= 50% of IAS

50% of 200Knots + 200 KNOTS = 100 + 200
= 300 Knots TAS