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Usig a CR3 to find TAS
rdarby
Topic Author
rdarby created the topic: Usig a CR3 to find TAS
Hi
I'm trying to work out how to use a Jeppesen CR3 to find the TAS from the Calibrated Airspeed and Pressure Altitude and Temperature.
In the example in the CR3 manual, they give 400kts CAS and 15,000 feet and 30deg.
By lining up the 400 to 15 on the inner window, and following the wavy line down from 30, you get just over 500kts TAS.
Seems easy.
But when I try to line up 100 to 45, for 100kts at 4500 feet, and use 30deg, I get a TAS of 260kts. I know the C172 doesn't go that fast!
I suspect I am not doing something right? Any ideas?
You are using the wrong window by the sounds of it. There is no wavy line in the window you should be using. To configure for altitude against temperature use these windows near the central grommet:
This example has a OAT of 20 degrees at 4500ft which is incidentally a density height of about 6000ft
Once the density height is correctly set, you read off IAS versus TAS on the scale around the outside.
