Hi Ryan,

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:

[center][attachment=750]densityAltitude_02.jpg[/attachment]
This example has a OAT of 20 degrees at 4500ft which is incidentally a density height of about 6000ft[/center]

Once the density height is correctly set, you read off IAS versus TAS on the scale around the outside.

Cheers,

Rich

This thread came up while I was running a google search for something totally unrelated. No idea why or how.    Anyway, worth a comment as the underlying question is very common and a reflection of poor training workup due to the average pilot's (including instructors) not having much background understanding of how the computer is constructed ....

I can't readily see what Ryan has done incorrectly, but incorrectly he certainly has done it.   

A bit of background to mull over.  First point is that the CR has two separate and totally unrelated means of calculating TAS -   

(a) the traditional method (seen on most of the Dalton computers and the very early CRs - is how Lahr constructed his device before it was transferred to Jeppesen in the mid-50s) runs incompressible airflow equations as does the ASI which calibration dates back to the 1920s and the ICAN standard atmosphere model of the day.   To use this you set PH against OAT to set density height (actually what you are setting is 1/√σ on the outside CD scale against 10 on the inside scale - the DH scale is there just as a courtesy.   This allows you to run the low Mach number standard multiplication TAS = CAS x 1/√σ).   However, this only works for low Mach numbers.   Once you get above around M0.3 or so, the ASI overreads and tells porkies.   So, to use this at higher speeds, you either have to correct the overreading ASI value (CAS > EAS) or run the sum as is and then multiply the overreading TAS by the F-factor to get the correct TAS.   This is stuff you don't have to worry about until you get to ATPL and faster machinery.

(b) when Jeppesen took over the rights to Lahr's device, he did a deal with the military and co-opted Franz Huber's Supersonic True Airspeed Computer into the CR (which he promptly sold to the military, no doubt for a suitable suitcase full of dollars).   On the CR's calculation side, Huber's scales comprise all the other stuff which is different to the usual Dalton computer's.   Huber, a very bright German engineer who came out to the US of A post WWII via the CIA's Operation Paperclip project and, subsequently, worked at Wright Patterson for the USAF, developed his computer for the early military FJ pilot folk.  Huber's device used the correct compressible flow equations which he had set up to work with indicated temperature, rather than true (outside) temperature, which made it a lot more useful to the single pilot FJ driver.

You can use EITHER set of scales to figure out TAS, but you have to use them correctly.   If you are driving slower Mach aircraft, the incompressible approach is far easier.   For higher performance aircraft, the Huber approach means you don't have the inconvenience of using correction values (for CAS>EAS) or factors (F-factors).

If Ryan reads this and shows us his working, via a graphic, we can sort out the problem in a few seconds.

Either set of scales gives a TAS value around 111 kt.

Postscript:  I can't readily see what Ryan has done incorrectly, but incorrectly he certainly has done it. 

I've just reread this thread and Ryan's mistake is quite obvious, now - not sure just why I missed it, before.   He has set his 100kt CAS against 45000ft, rather than 4500ft.   Set the CAS to 4500ft (which is there just to set the Mach Number) and up comes the answer of about 111kts.  That is to say, he has upped his Mach number from around 0.165 to 0.390 - bit of a difference ?