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I just spent 61 days driving a complete circle around the United
States in May and June, putting 11,089 miles on the car and using my
MB-2A flight computer to figure ETAs for each day's destinations.



gl

Renee Mattie wrote:

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.


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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