IAS to TAS formula
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 |
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. |
Hmm, where'd I hear this before! :)
Thanks for thought though :) cheers |
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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. ------------------ |
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?
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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!! |
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 |
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