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    Re: Circular "Navigational Computer"
    From: Gary LaPook
    Date: 2008 Aug 06, 04:08 -0700
    Gary LaPook writes:

    I had never seen this type of flight computer. When you posted your message I looked on Ebay and found three of them for sale, I bid but lost. Another one pooped up about 3 weeks ago and I got it, it arrived yesterday, cost $10.49. There is one for sale right now on ebay:


    even if you do not want to bid look anyway, there are good images of it.

    I have attached two pages of the instruction manual for figuring wind correction angle and ground speed ( the illustration is on the second page.)  I have also attached two pictures showing the solution for a relative wind angle of 50º and 50 knots of wind with a true airspeed of 230 knots which gives a solution of WCA of 10º and ground speed of  196 knots. You first line up the red scale on the top disk with the "zero" line at the (for want of a better name) the "north pole" of the curves on the lower disk and place a wind dot at the intersection of 50º and 50 knots, see 106.jpg. Next you rotate the disk to place the wind dot on your true airspeed and read out the WCA under the wind dot. You look at the red index arrow on the top disk and it points to your ground speed, see 108.jpg.

    Using this type and the CR models as well as the original E-6B requires you to make a pencil mark to represent the wind while the MB-2A and the Felesenthal (links to pictures of these were posted before) solve the problem with trig and so you do not need a pencil. An inconvenience with this type is that you may have to put several wind dots on it, one for each course leg since the dot is placed at the relative wind angle which will change with changes of course. With the E-6B you only need to place one wind dot since you are marking the true wind, not the relative wind angle. It is easy to use and must have been thought well of since American Airlines used them so I am surprised that I had never previously run into one.

    I know how it works but I don't know why it works. The E-6B works by drawing a vector diagram, the CR use a hybrid, a diagram and trig, while the others I mentioned solve the problem with trig only. Although this one is easy to use I don't know the principal behind it, anyone have an idea?


    Mike Burkes wrote:
    Hi dw and others the Jepp CB-1 is at bottom left just above the the plotter. Image was scanned from a 1966 Jeppesen CR Computer Manual/Workbook. Also the afore-mentioned MB series is directly above. Where in the freak did they get those ideas from? When I bought the CR I had no idea how to use the wind side being raised on the good old E6-b. If any of you good folks come up with any CB-1 wind side info it would be greatly appreciated and thanks much!!
    Mike Burkes
    It seems it's NOT a
    Polhemus Celestial Computer Type CPU-41/P
    which gl has mentioned in past posts. (Although, this seems quite an
    interesting device itself!)
    I haven't yet been able to get any info on the "Jeppesen CB-1 computer
    ". Could a scan be posted?
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