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Also look at the June 14th posts on the topic "3 star fix-canned
survival problem" for more information about the use of flight
computers

gl

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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