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    Re: Dalton E6B Dead Reckoning Computer
    From: Gary LaPook
    Date: 2008 Aug 2, 12:44 -0700

    Also look at the June 14th posts on the topic "3 star fix-canned
    survival problem" for more information about the use of flight
    On Aug 2, 10:12�am, Paul Hirose  wrote:
    > 01 0609
    > Renee Mattie wrote:
    > > I saw an old Weems and Plath Dalton E6B at Bacon's and snapped it up.
    > > Imagine my surprise to see that they are still making these things,
    > > and offering them for sale athttp://www.mypilotstore.com/MyPilotStore/secp/22.
    > > On the slide-rule side, the grommet seems to be off-center. �So if I
    > > set the dial for 60 miles/hour, I'll apparantly go almost 18.1 miles
    > > in 18 minutes, though almost exactly 9 miles in 9 minutes.
    > > Have I got a good one or a bad one?
    > A not so good one, I guess. The centering error on mine is barely
    > detectable, about the width of a line.
    > I also have a Jeppesen CR-2 flight computer. It's much more compact than
    > an E-6B because the effect of wind is calculated by a different
    > principle. With the side of the device that's pictured at the web site,
    > you separate wind into headwind and crosswind components. Crosswind and
    > true airspeed are set on a sine scale (around the outside in the
    > picture) to obtain wind correction angle. Headwind is mentally
    > subtracted from true airspeed to obtain groundspeed.
    > By contrast, on an E-6B you construct the wind triangle and read
    > wind correction angle and groundspeed directly. The solution takes
    > more space, but workload is less.
    > Either computer can solve for drift and set in marine navigation. Just
    > mentally apply a convenient scaling factor of 10, 20, etc. to the values
    > on the wind and airspeed scales. I solved some of the old Silicon Sea
    > problems that way.
    > For time / speed / distance computations both devices have the same
    > facilities. As usual with slide rules, the user is responsible for
    > placing the decimal point, so ship speeds are as easy to handle as
    > airplane speeds. Or car speeds -- I used my E-6B a few days ago to check
    > speedometer error.
    > When compressibility is significant (say, above .4 Mach) the CR
    > computers are superior at converting calibrated airspeed to true
    > airspeed. E-6Bs assume incompressible flow, so they're inaccurate at jet
    > cruise speeds. But airspeed computation is simpler, and the error means
    > nothing at typical light plane speeds.
    > Deluxe E-6Bs are made of sheet aluminum, while CRs are plastic and can
    > warp if left in a hot car.
    > --
    > I block messages that contain attachments or HTML.
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