Just sent my questions to Jeppesen for clarification, but thought I would try posting it here as someone else may be able to answer my questions sooner. So here it goes!
(Below is the e-mail I sent to Jeppesen with my question)
I am writing this e-mail in regards to the "Jeppesen CR-3" instruction booklet as downloadable at (
http://www.jeppesen.com/download/mis...structions.pdf). As I was reading through the booklet, I came across the section finding True Air Speed using the CR-3 on page 14 through 16. Please forgive me if I'm the one missing something here, but I am having a real difficult time understanding the context and was hoping I could get someone at Jeppesen to clarify. This may become confusing, therefore I suggest you have a copy of the booklet in question in hand prior to reading any further.
The booklet does an excellent job explaining "temperature rise" and "recovery coefficient" on pages 14 and 15. However, towards the bottom of page 15 it starts to get confusing. The booklet states,
The cursor on the CR is marked with a straight hairline and a curved line to the right of it (see FIG. 11), with recovery coefficients plotted for CT values of .8 and 1.0.
The recovery coefficient of CT = .8 is the straight line. On the CR-2 and CR-3 there are two lines plotted for the CT value of 1.0. The solid line is for the standard stratosphere temperature of -55 degrees Celsius (35,000'), and a dashed line is for the standard sea level temperature of +15 degrees Celsius. (etc. etc.)
Then on page 16 at the top it states, "
In all problems in this book, it is assumed that the recovery coefficient is the more common 1.0, unless otherwise stated."
Following the aforementioned statement, the booklet explains a sample True Air Speed problem. The explanation provided is as follows:
1.
Place CAS (400 kts) opposite PA (15,000').
2.
Move cursor until hairline crosses intersection of long spiral with 30 degree wiggly line.
3.
Read TAS under hairline on scale below.
My confusion with these instructions are:
1. It is my understanding that the "straight hairline" and "curved line" are two different lines, and that the curved line is not labeled as a "hairline".
If my understanding is correct, why is it that in Fig. 12 on page 16, instruction box 2 has an arrow pointing at the curved line when the instructions explicitly states to "Move cursor until hairline crosses ......"?
In extension of the question above, the same instruction box uses terms such as "long spiral" and "30 degree wiggly line".
Which line is the long spiral line? And which one is the wiggly line?
I need to move the cursor until which part of which line intersects with what?
Again, if this example is using the more common recovery coefficient of 1.0, then although contradictory to my initial understanding, I would suppose the instructions are referring to the curved line. It was my understanding that the straight line was referred to as the "hairline" and the curved one was just a "line".
Thanks
